All-Inorganic Ultrathin High Sensitivity Transparent Temperature Sensor Based on Mn-Co-Ni-O Nanofilms

All-Inorganic Ultrathin High Sensitivity Transparent Temperature Sensor Based on Mn-Co-Ni-O Nanofilms | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article All-Inorganic Ultrathin High Sensitivity Transparent Temperature Sensor Based on Mn-Co-Ni-O Nanofilms Changbo Liu, Yuanyuan Cui, Mengwei Sun, Yuan Deng This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3890600/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 27 May, 2024 Read the published version in Microsystems & Nanoengineering → Version 1 posted 12 You are reading this latest preprint version Abstract The demand for optically transparent temperature sensors in intelligent devices is escalating. However, the performances of these sensors, particularly their sensitivity and resolution, require further enhancement. This study introduces a novel transparent and highly sensitive temperature sensor, characterized by its ultra-thin, freestanding design, and based on Mn-Co-Ni-O nanofilms. The Mn-Co-Ni-O-based sensor exhibits remarkable sensitivity, with a temperature coefficient of resistance of -4%℃ -1 , and is capable of detecting minuscule temperature fluctuations as small as 0.03 ℃. Additionally, the freestanding sensor can be transferred to any substrate for versatile application while maintaining robust structural stability and excellent resistance to interference, indicating its suitability for operation in challenging environments. The vertical integration of the sensor and a micro light-emitting diode on a polyimide substrate demonstrates its practical utility in monitoring the surface temperature of optical devices. Moreover, the implantation experiment of the sensor in rats confirms its favorable biocompatibility, highlighting the sensor's promising applications in the biomedical domain. Physical sciences/Engineering/Electrical and electronic engineering Physical sciences/Materials science/Nanoscale materials transparent temperature sensor NTC nanofilms biocompatible optogenetics probes Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Transparent temperature sensors are gaining prominence due to their unique advantages in optically sensitive applications, including light-emitting devices such as touch screens 1 , displays 2 , light-emitting diode (LED) devices 3 , and invisible devices such as smart windows 4 , electronic skins 5 , and invisible robots. Furthermore, certain biological applications require temperature sensors to possess a degree of optical transmittance. For example, optogenetics, which is an emerging neuromodulation technique that combines genetic and optical methods to activate or inhibit specific neurons by light 6 , faces a thorny issue that overheating of the region stimulated by light pulses can cause cell damage or abnormal biological reactions 7 . Therefore, it is imperative to precisely monitor the temperature elevation in tissues adjacent to the light source while simultaneously providing an adequate light energy density. This ensures both the safety of biological experiments and the validity of the experimental findings. In diverse application contexts, transparent temperature sensors must exhibit high sensitivity and reliability. Additionally, the evolving application environments dictate that these sensors be lightweight, thin, and flexible 8 . This flexibility is especially crucial in biological applications, where it aids in minimizing rejection reactions and improving the biocompatibility of functional devices. Existing pathways for improving the transparency of temperature sensors incorporate thermal sensitive materials with high transparency, such as ionogels 8 – 11 , liquid crystals 12 , ion doped transparent ceramics 4 , 13 , 14 , polymer matrix composites 15 , 16 , metal mesh 17 and transparent thermoelectric materials 18 . Supplementary Table S1 presents comparisons of various parameters such as transparency, sensitivity, resolution, and response time across transparent temperature sensors fabricated from these distinct materials. Transparent temperature sensors made of these materials demonstrate high transmittance, especially those made of polymer materials, which also possess advantages in flexibility. However, these transparent materials are usually limited in temperature sensing performances, such as insufficient sensitivity, long response time and low resolution. To surmount these limitations and further improve the temperature sensing performances of transparent temperature sensors, more sensitive transparent thermal sensitive materials need to be developed and utilized. Mn–Co–Ni–O (MCN) spinel oxides, exhibiting excellent negative temperature coefficient (NTC) characters, have been widely used in temperature sensing with high sensitivity, good stability, excellent aging resistance performance and wide operating temperature range 19 – 21 . Compared with bulk and thick film MCN materials, thin film MCN materials have higher sensitivity and faster response 22 . More importantly, MCN films with nanoscale thickness may exhibit certain optical transparency characteristics 23 , making them a potential highly sensitive material in transparent temperature sensors. In this study, we fabricated an ultra-thin, all-inorganic, highly sensitive, microscale and freestanding transparent temperature sensor based on MCN nanofilms. The temperature sensor is characterized by a sandwich structure of "encapsulation layer - sensitive layer - encapsulation layer". Encapsulation layers provides mechanical support and improves anti-interference ability, allowing the sensor to operate in adverse environments while maintaining stability in electrical performance. An inorganic water-soluble sacrificial layer is used for releasing sensors from donor substrate. The freestanding MCN transparent temperature sensor has excellent sensitivity and resolution, and ultra short response time (Table S1 ). The freestanding MCN temperature sensor developed in this study can be transferred to any receiving substrate while maintaining good stability. Its microscale dimensions allow for flexible position selection, making it widely applicable. When integrated with flexible substrates, MCN temperature sensors can stably measure temperature under bending conditions and have strong anti-interference performance. We briefly demonstrate the application of the freestanding MCN transparent temperature sensor in optogenetics neural probes. The sensor can monitor the surface temperature of the micro-LED with minimal obstruction on LED luminous performance. The immunohistochemical staining experiment demonstrates its good biocompatibility and great potential for application in the field of biomedicine. 2. Results and discussion 2.1 Fabrication of sensors. Figure 1 a schematically demonstrates the fabrication process of the freestanding MCN transparent temperature sensor. The preparation starts with depositing a sacrificial layer composed of water-soluble germanium oxide (GeO x ) onto single crystalline silicon (Si) wafers. This specific selection of GeO x for the sacrificial layer is predicated on its capacity to withstand the high annealing temperature which is crucial to ensure the crystallinity and achieve temperature sensitive characteristics of MCN thermistors. At the same time, acid and alkali etchant are avoided throughout the process design, making the process safer and more economical 24 . Then the bottom encapsulation layer composed of SiO 2 is deposited on the sacrificial layer. SiO 2 is chosen for its high transparency and thermal conductivity, and it has been widely used for encapsulation materials in implantable devices with high electrical insulation, good biocompatibility, and low permeability 25 , 26 . Subsequently, by spin coating MCN acetate precursor solution under controlled humidity on the bottom encapsulation layer and annealing, the MCN thermistor layer which has a thickness of about 100 nm is obtained with high density and crystal quality. After patterning the MCN thermistor through photolithography and ion beam etching, patterned indium tin oxide (ITO) electrodes are prepared on it. ITO conductive thin film is a commonly used transparent electrode with high optical transmittance and low resistivity 27 (Figure S1 ). Then the patterned SiO 2 top encapsulation layer encapsulates the MCN thermistor and exposes the solder pads of ITO electrodes. Finally, the GeO x sacrificial layer is dissolved in water to obtain the freestanding sensor. Through advanced micro/nano processing technologies, hundreds of devices can be efficiently prepared at once. 2.2 Structure and morphology. Figure 1 b are optical images of sensors on Si substrate. The microscale sensor has a size of approximately 210 µm*180 µm and can measure temperature in precise locations, providing high spatial resolution. Figure 1 c shows the multi-layer structure of the prepared sensor. The total thickness of the sensor is about 4.1 µm. From bottom to top, there are a SiO 2 bottom encapsulation layer with a thickness of 2 µm, a MCN sensitive layer with a thickness of 100 nm, and a SiO 2 top encapsulation layer with a thickness of 2 µm. Thin films are tightly bonded and there are clear boundaries between layers. It can be seen from the X-ray diffraction pattern (Fig. 1 d) that the MCN nanofilm exhibited a typical cubic spinel structure with the strongest peak detected at (311) according to the PDF card No. 01-088-0241, demonstrating that the films are highly crystallized and orientated 20 . Figure 1 e depicts the morphology of the MCN nanofilm through scanning electron microscope (SEM) observation. It can be observed that the film is dense polycrystalline film, and devoid of cracks or defects. The optical transmittance spectra of the MCN nanofilm on quartz glass are depicted in Fig. 1 f. The transmittance of the MCN nanofilm on glass is between 50% and 60% in the visible light wavelengths range. It can also be observed from the optical image (inset in Fig. 1 f) that the MCN nanofilm has good optical transmission performance. In a freestanding MCN temperature sensor, the area of the MCN nanofilm only accounts for 15% of the total sensor size, with most of the area being optically transparent SiO 2 and ITO. Therefore, the overall sensor has better transparency. 2.3 Electrical properties. Figure 2 a shows the relationship between electrical resistance (R) and temperature (T) of the MCN nanofilm in the temperature range of 30–120°C. The MCN nanofilm exhibits typical Arrhenius plots of a NTC thermistor. The reproducibility of thermal response is recorded during heating and cooling processes, where both of R-T curves are overlap and the hysteresis is negligible (Fig. 2 a and 2 b). In Fig. 2 b, the \(lnR\) - \(\frac{1}{T}\) plot shows a good linear relation at 300 − 390 K, and the resultant B-value is calculated as 3640 K for the overall measuring range. Temperature coefficient of the resistance (TCR) refers to the relative rate of change of the resistance value when the temperature is changed by 1°C. The TCR of the MCN nanofilm is calculated as − 4.0% °C − 1 at 30°C, which means the high sensitivity of the sensor. MCN transparent temperature sensors are transferred to glass substrates for electrical property testing (Fig. 2 c). The electrical resistance of NTC thermistors usually has a drift over time, which is known as aging and effects the stability of NTC thermistors in long-time use 28 . In order to achieve stable performance of the MCN transparent temperature sensor in long-term use, we explore the influence of aging annealing time on the resistance drift of the freestanding MCN transparent temperature sensor with the annealing temperature of 120 ℃ (Fig. 2 d). It can be seen that the resistance drift of sensors without annealing treatment increases continuously over time, and still exhibits 0.25%·d − 1 after 21 days of storage. The resistance drift of sensors which are annealed for 30, 60, and 100 hours gradually decrease over time. After being placed for 21 days, the resistance drift increased slowly and exhibits less than 0.04%·d − 1 , indicating an improvement in stability. The resistance of sensors which are annealed for 300 hours, although has a lager drift in the first 7 days of storage, is basically stable after 21 days of storage and the resistance drift is less than 0.01%·d − 1 . The results show that 120 ℃ annealing treatment can significantly decrease the resistance drift, and the stability improves as the annealing treatment time increases. Therefore, MCN transparent temperature sensors are annealed at 120 ℃ for 300 hours to improve the stability of their performance. After annealing treatment, the MCN transparent temperature sensor exhibits high level of reliability under three repetitions of full range scanning (Figure S2 and Note S2). More interestingly, the tiny temperature variations (0.03°C) can be accurately discriminated (Fig. 2 e), suggesting that the freestanding MCN transparent temperature sensor possesses unprecedentedly high temperature resolution and guarantees the accurate temperature detection. The instantaneous temperature response of the freestanding MCN transparent temperature sensor is investigated (Fig. 2 f). According to the temperature change curve recorded by the sensor, the response time of the sensor is 224 ms in the case of elevating detection temperature from 25 to 70°C, suggesting a very rapid, sharp response, which mainly benefits from the use of ultra-thin and high thermal conductivity SiO 2 encapsulation layers and is desirable for temperature sensors. The freestanding MCN transparent temperature sensor retains the high sensitivity, stability, resolution, and fast response characteristics of MCN thermistors while obtaining transparent characteristics. 2.4 Structure stability and anti-interference ability. The freestanding MCN transparent temperature sensor can be integrated with various substrates by utilizing transfer printing technology. To obtain a flexible transparent temperature sensor, the freestanding MCN sensor is transferred to a polyimide (PI) substrate (Fig. 3 a). Electrical signals are drawn from ITO electrodes of the sensor utilizing photolithography and magnetron sputtering metal electrode. Figure 3 b shows the bending test for the sensor. Sensors are bent into bending radius of 15 mm, 10 mm, and 5 mm, respectively, to test the performance of sensors with different bending amplitudes. The resistance (R)–temperature (T) curves are measured to examine the structure stability of the flexible sensor (Fig. 3 b). It can be seen that sensors with different bending amplitudes exhibit excellent negative temperature coefficient thermistors characters in the temperature range of 25 to 100°C, same as sensors in flat state. The resistance of the sensor at various temperatures is almost unaffected by bending, indicating that the temperature sensor has good structural stability and strain insensitivity. The resistance change of the sensor during bending is also tested (Fig. 3 c). The sensor undergoes a cycle from a flat state to a bending state with a bending radius of 5 mm and then returns to a flat state. During this process, the resistance change is less than 0.5%. The bending cycle tests for the flexible MCN sensors are also carried out. The frequency of the alternating bending was 1 Hz. After bending for 1k, 5k, and 10k cycles with a bending radius of 5mm, R-T curves of sensors are measured. As is shown in Fig. 3 d, R-T curves of sensors after multiple cycles of bending almost coincide with the curve of the initial state sensor. The electrical parameters of the sensor are barely affected by the bending effect, which validates the potential of the freestanding MCN transparent temperature sensor in flexible electronics application. The conductivity of oxides is usually sensitive to gas composition in the surrounding atmosphere. NTC thermistors often operate in an atmosphere of constant or known oxygen partial pressure to avoid possible influence from the probing atmosphere 29 . However, there is an increasing need for sensors capable of operating in harsh working environments for measurement in industrial processes where various potentially hazardous gases may exist, such as strong acids, strong alkalis, organic solvents, etc. In addition, some special application scenarios of temperature sensors, such as temperature compensation for gas sensors 30 , 31 , require temperature sensors to have good anti-interference ability and selectivity, that is, no response to other stimuli. To verify the reliability for working in harsh environments of the MCN transparent temperature sensor, four representative interfering gases are used to test the impact of the environment on the sensor, in which ethanol and acetone are common volatile polar organic solvents, hydrogen chloride is a strongly acidic gas, and ammonia is an alkaline gas (Note S3). According to the acquired results (Fig. 3 e- 3 h), it can be seen that as the concentration of interfering gases increases, the resistance of the sensor changes within 0.5%, indicating that the temperature sensor has high reliability and good anti-interference performance, and this mainly benefits from the low permeability of the SiO 2 encapsulation layer. 2.5 Application in optogenetics neural probes. Optogenetics is an emerging neuromodulation technique that combines genetic and optical methods to activate to activate or inhibit specific neurons by light 6 . In recent years, with the development of optogenetics technology, implantable light sources have become increasingly popular among researchers, where LED probes stand out by overcoming coupling light losses and maximizing delivered light power due to the proximity to target cells 32 . A thorny issue faced by optogenetics technology is that overheating of the region stimulated by light pulses can cause cell damage or abnormal biological reactions 7 . Therefore, it is crucial to evaluate the thermal characteristics of optical points during operations. At the same time, the implantation of probes is always accompanied by inflammatory reactions related to temperature rise. Continuous monitoring of tissue temperature can provide relevant inflammatory information and evaluate the biocompatibility of implants 33 . Temperature sensors are often integrated on LED probes to detect changes in tissue temperature 7 , 34 , 35 . However, commonly used temperature sensors such as Pt thermistors have poor light transmittance. To prevent obstruction of LED light, they can only be integrated below or next to the LED and are not located near the biological tissue stimulated by the light on the front of the LED, thus cannot reflect the true temperature rise of the target tissue. The freestanding MCN transparent temperature sensor is integrated onto the LED optogenetic probe to verify its potential applications in the field of optogenetics (Figure S3). The preparation process of the LED optogenetic probe can be found in previous work 36 , 37 . The thin film LED on the probe maintains good electrical and optical properties (Figure S4 and Note S4). Figure 4 a is a schematic illustration of the optogenetics neural probe integrated with temperature sensor. Due to its good transparency, it can be integrated directly above the LED, with almost no obstruction to the LED. The electrodes of LED and temperature sensor are distributed vertically separated by insulated SU-8 photoresist, reducing crosstalk during operation. As shown in Fig. 4 b, the sensor is integrated directly above the LED with LED off on the left and LED open (input current is 1 mA) on the right. It can be seen that LED blue light can penetrate the temperature sensor with only a slight decrease in light intensity. The temperature sensor will directly contact the biological tissue stimulated by the light of the LED when the probe is implanted in an organism, achieving accurate measurement of temperature changes in the target tissue. To demonstrate the minimal obstruction on LED luminous performance by the MCN transparent temperature sensor, the light intensity distribution of the system is measured and the multi angle luminescence spectrum is plotted (Fig. 4 c and Note S5). It can be seen that the LED integrated with a MCN transparent temperature sensor exhibits symmetrical distribution of light intensity in its multi angle emission spectrum, which conforms to the typical Lambert radiation characteristics. This indicates that the vertically integrated MCN transparent temperature sensor does not change the LED emission angle. In addition, after the integration of the MCN transparent temperature sensor, the LED still maintains about 80% of the luminous power, which is because the MCN sensitive layer has a certain degree of transparency, and high transparent SiO 2 and ITO account for 85% of the total sensor area. The luminous power of LEDs is also measured under different input currents before and after the integration of thin film temperature sensors (Fig. 4 d). It can be seen that the luminous power of LEDs increases as the input current increases. After the integration of the temperature sensor, the light output power slightly decreases, but remained above 80%, indicating that the thin film temperature sensor has good transparency. It can be inferred that the integration of MCN transparent temperature sensors will not hinder the optogenetics operation of implanted LED probes. To verify the temperature measurement functions of the probe, the temperature rise of the LED surface under different injection currents is measured by the integrated MCN transparent temperature sensor, and the calibrated infrared measurement is used as a control experiment. As is shown in Fig. 4 e, the temperature rise of the LED surface increases as the input current increases and exhibits a good linear relationship. The measurement curves of the integrated MCN transparent temperature sensor and the calibrated infrared measurement are highly coincident with an error of less than 1%. This indicates that the integrated MCN transparent temperature sensor can accurately measure the surface temperature rise of LED. In addition, the anti light interference ability of the MCN transparent temperature sensor is tested using different wavelengths of light (Figure S5 and Note S6), and the results show that the sensor is almost unaffected by light, and can accurately measure temperature when integrated with the optical system. A finite element thermal simulation model of the optogenetics system is established and simulates the surface temperature rise of LED (Note S7). As is shown in Fig. 4 f, the simulation curve highly coincides with the measurement curve of the integrated MCN transparent temperature sensor, indicating that the calculated results are basically consistent with the experimental results, with an error of less than 2%, and the simulation model can predict the surface temperature rise of LED under different input currents (Figure S6). The simulation result at an input current of 3 mA on the surface of the probe model is compared with the measurement results of an infrared thermal imager (Fig. 4 g). The maximum temperature difference is 0.5 ℃. Therefore, the thermal simulation model of optogenetics system can truly reflect the temperature rise of LED surface, which has important reference significance for predicting and studying the thermal impact of probes on biological tissues. To verify the biocompatibility of the MCN transparent temperature sensor, sensors are implanted into the back of rats, and the surrounding tissues are stained and sliced for observation at 7 days, 14 days, and 21 days, respectively (Note S8 and Note S9). Histological images show minimal damage to the tissue and negligible immune response caused by the implantation (Fig. 4 h), indicating that the MCN transparent temperature sensor has good biocompatibility and potential for application in the biomedical field. 3. Conclusion We developed an ultra-thin, all-inorganic, transparent, highly sensitive and freestanding temperature sensor based on Mn-Co-Ni-O nanofilms. The sensor obtains transparent characteristics through the prepared MCN thin film with a thickness of 100 nm, while retaining the high sensitivity, stability, resolution, and fast response characteristics of MCN thermistors through the high crystallization quality of MCN nanofilms. The freestanding MCN temperature sensor can be transferred to any receiving substrate and maintain good stability. The resistance of the sensor remains almost constant in harsh environments, indicating its anti-interference ability and potential in extreme applications. The sensor can accurately monitor the temperature rise on the LED optogenetics probe with minimal obstruction to LED luminescence and have good biocompatibility, indicating the application prospects of the MCN temperature transparent sensor in the field of implantable optogenetics. With good biocompatibility and microscale dimensions, the transparent MCN temperature transparent sensor has broad application prospects in the field of biomedicine. In addition, the sensor can be used for various stealth devices and may improve the spatial resolution of temperature measurement through array integration. 4. Materials and methods 4.1 Fabrication process. The germanium oxide (GeO x ) sacrificial layer with a thickness of 40 nm is grown on single crystalline silicon (Si) wafers with dimensions of 3cm*3cm by magnetron sputtering. Then the SiO 2 bottom encapsulation layer with a thickness of 2 µm is deposited onto the sacrificial layer using electron beam physical vapor deposition. Subsequently, the sample is heated at 250 ℃ for 10 minutes to diminish the water solubility of GeO x , thus desensitizing it. After cooling, the sample is subjected to oxygen plasma treatment with the aim of improving the binding ability of SiO 2 and MCN. The next step involves spin-casting the MCN acetate precursor solution (0.2 mol/L Mn 1.56 Co 0.96 Ni 0.48 O 4 in mixed solution of acetic acid and water) onto the SiO 2 bottom encapsulation layer under controlled humidity, followed by drying at 250°C for 5 min. The assembly, now comprising Si/GeO x /SiO 2 /MCN layers, is annealed in an air atmosphere at 750 ℃ for 90 min, resulting in the formation of a MCN thermistor layer with high density, high crystal quality and a thickness of about 100 nm. This layer is subsequently patterned through photolithography and ion beam etching, and patterned indium tin oxide (ITO) electrodes are then prepared on it through photolithography and magnetron sputtering. Then the patterned SiO 2 top encapsulation layer is prepared on through photolithography and electron beam physical vapor deposition, and the SiO 2 bottom encapsulation layer is patterned through photolithography and ion beam etching. Finally, samples are placed in water at 80 ℃ to dissolve the GeO x sacrificial layer and release freestanding sensors from Si wafers. Suction filtration is used to transfer freestanding sensors onto filter paper. 4.2 Transfer process of sensors to PI substrate. A thin layer of diluted SU-8 photoresist (1:1 with cyclopentanone) is spin-cast onto the PI substrate as an adhesive. Before the SU-8 photoresist solidifies, the freestanding sensor is adsorbed from the filter paper by the electrostatic adsorption of a needle tip and is gently placed on the PI substrate coated with SU-8 photoresist. Then the sample is exposed to ultraviolet light and heat for curing the photoresist. Ni/Cu electrodes are subsequently fabricated through photolithography and magnetron sputtering to establish electrical connectivity with ITO electrodes intrinsic to the sensor and draw electrical signals from the sensor. 4.3 Integration process of sensors with optogenetics neural probes. A thin layer of SU-8 photoresist is spin-cast onto the LED optogenetic probe as an adhesive. Before the SU-8 photoresist solidifies, the freestanding sensor is gently placed directly above the emitting site of the LED probe. Then the probe is exposed to ultraviolet light and heat for curing the photoresist. Ni/Cu electrodes are subsequently fabricated through photolithography and magnetron sputtering to draw electrical signals from ITO electrodes of the sensor. 4.4 Measurements and characterization. Optical images are captured by a microscope VMX40M. Scanning electron microscopic (SEM) images are taken with a ZEISS Sigma 300 System. The crystalline structures of the thin films are identified with an XRD (Malvern Panalytical Empyrean). MCN film is ground into powder for XRD testing to avoid interference from substrate materials. To characterize the light transmittance performance of the sensor, the MCN/SiO 2 thin film (5 × 5 mm) is prepared using thin film deposition technology and is transferred to a quartz substrate. The UV-Vis-IR absorption spectra of the MCN nanofilm is characterized by using a spectrophotometer (PerkinElmer Lambda 750S). The relationship between resistance and testing temperature is measured using an automatic data acquisition system, which included a vacuum films probe system (Lake Shore) with temperature control unit and a semiconductor parameter analyzer (Keithley 4200A-SCS). In order to maintain the quasi-thermal equilibrium state between the temperature sensor and the temperature control stage, every measurement is conducted for every 5°C interval with at least 5 minutes of stabilization period. Measurement details of other sensor performances can be found in the supplementary materials. Declarations Acknowledgements This work is supported by the National Natural Science Foundation of China (NSFC) (62004009 for C. L.), the National Key Research and Development Program of China (Grant No. 2018YFA0702100), the Zhejiang Provincial Key Research and Development Program of China (Grant Nos. 2021C01026 and 2021C05002), the Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang (2020R01007) and the Beijing Nova Program (20230484412). Author details 1 Research Institute for Frontier Science, Beihang University, Beijing 100191, China. 2 School of Materials Science and Engineering, Beihang University, Beijing 100191, China. 3 Key Laboratory of Intelligent Sensing Materials and Chip Integration Technology of Zhejiang Province, Hangzhou Innovation Institute of Beihang University, Hangzhou 310051, China. Author contributions Y.C. and M.S. contributed equally to this work. M.S. and C.L. developed the methods and designed the structures. Y.C. and M.S. fabricated the devices, conducted the experiment, and performed the characterization. C.L. and Y.D. provided tools and supervised the research. Y.C. and C.L. wrote the paper in consultation with other authors. Conflict of interest The authors declare no competing interests. Ethics statements All animal work was approved by Wuhan Servicebio Technology Co., Ltd., China, and the ethical approval protocol number was Servicebio Animal Welfare NO. 2022158. All study methods were carried out in accordance with relevant guidelines and regulations. All animals are socially housed in a 12 h/12 h (lights on at 8 am) light/dark cycle, with access to food pellets and water ad libitum. The owner of animals is informed and consents to this study. Supplementary information The online version contains supplementary material available at References Jung, H. & Lee, H. Semi-transparent reduced graphene oxide temperature sensor on organic light-emitting diodes for fingerprint liveness detection of smartphone authentication. Sens. Actuators, A 331 (2021). https://doi.org:10.1016/j.sna.2021.112876 An, B. W., Heo, S., Ji, S., Bien, F. & Park, J. U. Transparent and flexible fingerprint sensor array with multiplexed detection of tactile pressure and skin temperature. Nat. Commun. 9, 2458 (2018). https://doi.org:10.1038/s41467-018-04906-1 Lee, C. Y., Su, A., Liu, Y. C., Fan, W. Y. & Hsieh, W. J. In situ measurement of the junction temperature of light emitting diodes using a flexible micro temperature sensor. Sensors (Basel) 9, 5068–5075 (2009). https://doi.org:10.3390/s90705068 Ye, Y., Lu, K. & Qi, J. Developing Smart Temperature Sensing Window Based on Highly Transparent Rare-Earth Doped Yttrium Zirconate Ceramics. ACS Appl. Mater. Interfaces 14, 39072–39080 (2022). https://doi.org:10.1021/acsami.2c11404 Chen, X., Ren, Z., Guo, H., Cheng, X. & Zhang, H. Self-powered flexible and transparent smart patch for temperature sensing. Appl. Phys. Lett. 116 (2020). https://doi.org:10.1063/1.5134526 Zhao, H. Recent Progress of Development of Optogenetic Implantable Neural Probes. Int. J. Mol. Sci. 18 (2017). https://doi.org:10.3390/ijms18081751 Goncalves, S. B. et al. LED Optrode with Integrated Temperature Sensing for Optogenetics. Micromachines (Basel) 9 (2018). https://doi.org:10.3390/mi9090473 Jiang, N. et al. Flexible, transparent, and antibacterial ionogels toward highly sensitive strain and temperature sensors. Chem. Eng. J. 424 (2021). https://doi.org:10.1016/j.cej.2021.130418 Xu, Y., Chen, L., Chen, J., Chang, X. & Zhu, Y. Flexible and Transparent Pressure/Temperature Sensors Based on Ionogels with Bioinspired Interlocked Microstructures. ACS Appl. Mater. Interfaces 14, 2122–2131 (2022). https://doi.org:10.1021/acsami.1c22428 Jiang, N. et al. Ionic liquid enabled flexible transparent polydimethylsiloxane sensors for both strain and temperature sensing. Adv. Compos. Hybrid Mater. 4, 574–583 (2021). https://doi.org:10.1007/s42114-021-00262-9 Tie, J. et al. Highly transparent, self-healing and adhesive wearable ionogel as strain and temperature sensor. Polym. Chem. 13, 4064–4075 (2022). https://doi.org:10.1039/d2py00594h Wu, K. et al. Highly sensitive and transparent flexible temperature sensor based on nematic liquid crystals. Liq. Cryst. 49, 372–379 (2021). https://doi.org:10.1080/02678292.2021.1970834 Hu, S., Lu, C., Liu, X. & Xu, Z. Optical temperature sensing based on the luminescence from YAG:Pr transparent ceramics. Opt. Mater. 60, 394–397 (2016). https://doi.org:10.1016/j.optmat.2016.08.026 Chen, D., Wan, Z., Zhou, Y. & Ji, Z. Cr3+-doped gallium-based transparent bulk glass ceramics for optical temperature sensing. J. Eur. Ceram. Soc. 35, 4211–4216 (2015). https://doi.org:10.1016/j.jeurceramsoc.2015.08.005 Cai, T. et al. Phosphorescence-Based Flexible and Transparent Optical Temperature-Sensing Skin Capable of Operating in Extreme Environments. ACS Appl. Polym. Mater. 3, 2461–2469 (2021). https://doi.org:10.1021/acsapm.1c00062 Trung, T. Q., Ramasundaram, S., Hwang, B. U. & Lee, N. E. An All-Elastomeric Transparent and Stretchable Temperature Sensor for Body-Attachable Wearable Electronics. Adv. Mater. 28, 502–509 (2016). https://doi.org:10.1002/adma.201504441 Walia, S., Mondal, I. & Kulkarni, G. U. Patterned Cu-Mesh-Based Transparent and Wearable Touch Panel for Tactile, Proximity, Pressure, and Temperature Sensing. ACS Appl. Electron. Mater. 1, 1597–1604 (2019). https://doi.org:10.1021/acsaelm.9b00330 Bianchi, C. et al. V2O5Thin Films for Flexible and High Sensitivity Transparent Temperature Sensor. Adv. Mater. Technol. 1 (2016). https://doi.org:10.1002/admt.201600077 Muralidharan, M. N., Rohini, P. R., Sunny, E. K., Dayas, K. R. & Seema, A. Effect of Cu and Fe addition on electrical properties of Ni–Mn–Co–O NTC thermistor compositions. Ceram. Int. 38, 6481–6486 (2012). https://doi.org:10.1016/j.ceramint.2012.05.025 Kong, W., Wei, W., Gao, B. & Chang, A. A study on the electrical properties of Mn-Co-Ni-O thin films grown by radio frequency magnetron sputtering with different thicknesses. Appl. Surf. Sci. 423, 1012–1018 (2017). https://doi.org:10.1016/j.apsusc.2017.06.290 Feteira, A. Negative Temperature Coefficient Resistance (NTCR) Ceramic Thermistors: An Industrial Perspective. J. Am. Ceram. Soc. 92, 967–983 (2009). https://doi.org:10.1111/j.1551-2916.2009.02990.x Li, R. et al. Mn-Co-Ni-O thin films prepared by sputtering with alloy target. J. Adv. Ceram. 9, 64–71 (2020). https://doi.org:10.1007/s40145-019-0348-y Zhou, W. et al. Micro structural, electrical and optical properties of highly (220) oriented spinel Mn–Co–Ni–O film grown by radio frequency magnetron sputtering. Appl. Surf. Sci. 311, 443–447 (2014). https://doi.org:10.1016/j.apsusc.2014.05.088 Nam, J. et al. Transfer Printed Flexible and Stretchable Thin Film Solar Cells Using a Water-Soluble Sacrificial Layer. Adv. Energy Mater. 6 (2016). https://doi.org:10.1002/aenm.201601269 Fang, H. et al. Ultrathin, transferred layers of thermally grown silicon dioxide as biofluid barriers for biointegrated flexible electronic systems. Proc Natl Acad Sci U S A 113, 11682–11687 (2016). https://doi.org:10.1073/pnas.1605269113 Song, E. et al. Thin, Transferred Layers of Silicon Dioxide and Silicon Nitride as Water and Ion Barriers for Implantable Flexible Electronic Systems. Adv. Electron. Mater. 3 (2017). https://doi.org:10.1002/aelm.201700077 Aydın, E. B. & Sezgintürk, M. K. Indium tin oxide (ITO): A promising material in biosensing technology. TrAC, Trends Anal. Chem. 97, 309–315 (2017). https://doi.org:10.1016/j.trac.2017.09.021 Zhao, M., Chen, W., Wu, W., Zhang, M. & Li, Z. Aging characteristic of Cu-doped nickel manganite NTC ceramics. J. Mater. Sci.: Mater. Electron. 31, 11784–11790 (2020). https://doi.org:10.1007/s10854-020-03730-y Wang, C. C., Akbar, S. A. & Madou, M. J. Ceramic Based Resistive Sensors. J. Electroceram. 2, 273–282 (1998). https://doi.org:10.1023/A:1009978607621 Algamili, A. S. et al. Fabrication and Characterization of the Micro-Heater and Temperature Sensor for PolyMUMPs-Based MEMS Gas Sensor. Micromachines (Basel) 13 (2022). https://doi.org:10.3390/mi13040525 Kang, J.-g. et al. Temperature control of micro heater using Pt thin film temperature sensor embedded in micro gas sensor. Micro Nano Syst. Lett. 5 (2017). https://doi.org:10.1186/s40486-017-0060-z Goncalves, S. B., Ribeiro, J. F., Silva, A. F., Costa, R. M. & Correia, J. H. Design and manufacturing challenges of optogenetic neural interfaces: a review. J. Neural Eng. 14, 041001 (2017). https://doi.org:10.1088/1741-2552/aa7004 Fekete, Z. et al. Simultaneous in vivo recording of local brain temperature and electrophysiological signals with a novel neural probe. J. Neural Eng. 14, 034001 (2017). https://doi.org:10.1088/1741-2552/aa60b1 Zgierski-Johnston, C. M. et al. Cardiac pacing using transmural multi-LED probes in channelrhodopsin-expressing mouse hearts. Prog. Biophys. Mol. Biol. 154, 51–61 (2020). https://doi.org:10.1016/j.pbiomolbio.2019.11.004 Ayub, S. et al. Compact Optical Neural Probes With Up to 20 Integrated Thin-Film muLEDs Applied in Acute Optogenetic Studies. IEEE Trans. Biomed. Eng. 67, 2603–2615 (2020). https://doi.org:10.1109/TBME.2020.2966293 Li, L. et al. Heterogeneous Integration of Microscale GaN Light-Emitting Diodes and Their Electrical, Optical, and Thermal Characteristics on Flexible Substrates. Adv. Mater. Technol. 3 (2017). https://doi.org:10.1002/admt.201700239 Liu, C. et al. A wireless, implantable optoelectrochemical probe for optogenetic stimulation and dopamine detection. Microsyst. Nanoeng. 6, 64 (2020). https://doi.org:10.1038/s41378-020-0176-9 Additional Declarations (Not answered) Supplementary Files SupplementaryInformation20240130Micronano.docx Supplementary Information for All-Inorganic Ultrathin High Sensitivity Transparent Temperature Sensor Based on Mn-Co-Ni-O Nanofilms Cite Share Download PDF Status: Published Journal Publication published 27 May, 2024 Read the published version in Microsystems & Nanoengineering → Version 1 posted Editorial decision: revise 25 Feb, 2024 Review # 3 received at journal 22 Feb, 2024 Review # 2 received at journal 11 Feb, 2024 Review # 1 received at journal 06 Feb, 2024 Reviewer # 3 agreed at journal 05 Feb, 2024 Reviewer # 2 agreed at journal 04 Feb, 2024 Reviewer # 1 agreed at journal 02 Feb, 2024 Reviewers invited by journal 02 Feb, 2024 Submission checks completed at journal 31 Jan, 2024 First submitted to journal 30 Jan, 2024 Unknown event 26 Jan, 2024 Editor assigned by journal 23 Jan, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3890600","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":270669519,"identity":"ff36846e-4b90-4f34-8444-a9296ef70dbc","order_by":0,"name":"Changbo Liu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwElEQVRIiWNgGAWjYBACPmYGBmbGBpsECJeNCC1sEC1ppGhhAGs5TIoWdh7Dz4U7zucZHD/8gOFD2WEG/tkNhBzGYyw988ztYoMzaQaMM84dZpC4c4CgFjNm3rbbiRsOJBgAGYcZDCQSiNJyLnHD+ecfmP+SoOVA4oYbOQbMjMRpYSuW5j2TXCx5403BwZ5z6TwSNwho4ec/vPEz7w67PL7z6Rsf/CizluOfQUALCjgAxDwkqB8Fo2AUjIJRgAsAAAeIPcYhx67aAAAAAElFTkSuQmCC","orcid":"","institution":"Beihang University","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Changbo","middleName":"","lastName":"Liu","suffix":""},{"id":270669520,"identity":"a20bfe56-add4-4489-89a2-946703f7f14f","order_by":1,"name":"Yuanyuan Cui","email":"","orcid":"","institution":"Beihang University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuanyuan","middleName":"","lastName":"Cui","suffix":""},{"id":270669521,"identity":"d124d53e-0424-4399-92a5-30f4906b7d4f","order_by":2,"name":"Mengwei Sun","email":"","orcid":"","institution":"Beihang University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Mengwei","middleName":"","lastName":"Sun","suffix":""},{"id":270669522,"identity":"41eae341-a571-4322-a747-a67eddef5c88","order_by":3,"name":"Yuan Deng","email":"","orcid":"","institution":"[email protected]","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yuan","middleName":"","lastName":"Deng","suffix":""}],"badges":[],"createdAt":"2024-01-23 09:21:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3890600/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3890600/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41378-024-00706-4","type":"published","date":"2024-05-27T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":50655570,"identity":"cd6a6cef-2908-46ad-a833-4e00e560a1d1","added_by":"auto","created_at":"2024-02-05 10:11:57","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":790268,"visible":true,"origin":"","legend":"\u003cp\u003ea) Schematic illustrations of the process flow to fabricate the free-standing MCN thermistor temperature sensor. b) Optical image of temperature sensors on Si substrates. c) Scanning electron microscopic (SEM) image of sandwich-structured thin film temperature sensors on Si substrate. d) XRD patterns of the MCN nanofilm. e) Scanning electron microscopic (SEM) image of the surface of the MCN nanofilm. f) Optical transmission performance of the MCN nanofilm.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3890600/v1/2bbd25243b33b2b8d9a402fe.jpg"},{"id":50655566,"identity":"9e49a33f-f41d-4c46-bc47-c4c9b5d8fa91","added_by":"auto","created_at":"2024-02-05 10:11:56","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":444099,"visible":true,"origin":"","legend":"\u003cp\u003eElectrical Properties. a-b) Temperature variation of electrical resistance. c) Optical image of the freestanding MCN transparent temperature sensor on transparent substrate. d) The variation of resistance drift of temperature sensors with aging time. e) Resolution test for the freestanding MCN transparent temperature sensor. f) Response time test of the freestanding MCN transparent temperature sensor.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3890600/v1/cd942c9440f2413f55ad68bb.jpg"},{"id":50655565,"identity":"a22b8da1-aef7-4ed6-a918-de2f1aff4d50","added_by":"auto","created_at":"2024-02-05 10:11:55","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1110580,"visible":true,"origin":"","legend":"\u003cp\u003eStructure stability and anti-interference ability of the freestanding MCN transparent temperature sensor. a) Optical image of the freestanding MCN transparent temperature sensor on flexible substrates. b) Temperature variation of electrical resistance for sensors on flexible substrates at 25–100℃ with a bending radius of 15 mm, 10 mm, 5 mm. c) Resistance changes during sensor bending. d) Cyclic bending test of sensors. The resistance of thin film temperature sensors varies with the concentration of interfering gases e) Ethanol vapor, f) Acetone vapor, g) NH3 and h) HCl.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3890600/v1/c5dee95c406c52f767cd53c4.jpg"},{"id":50656340,"identity":"e4fff5ee-5aca-43ec-bfe3-fff05e0a1914","added_by":"auto","created_at":"2024-02-05 10:19:56","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1003186,"visible":true,"origin":"","legend":"\u003cp\u003eIntegration with optogenetics neural probes. a) Schematic illustrations of the optogenetics neural probe integrated with the MCN transparent temperature sensor. b) Optical image of the optogenetics neural probe integrated with the MCN transparent temperature sensor. c) Angular emission profiles for LED with and without integrated temperature sensors. d) The luminous power of LED with and without integrated temperature sensors as a function of input current. e) Measurement of LED surface temperature rise with different injection currents by the MCN transparent temperature sensor and infrared. f) Sensor testing and finite element simulation results of LED surface temperature rise with different injection currents. g) Infrared testing and finite element simulation results of LED surface temperature rise with injection currents of 3 mA. h) Hematoxylin and eosin (H\u0026amp;E) stained histological sections of the tissue surrounding the implanted sensor in the back of rats for days 7, 14, and 21. The image for the control sample is from a rat without implants.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-3890600/v1/36bb45809242563b0704c798.jpg"},{"id":57190182,"identity":"40a00ef0-7d41-41c7-a230-bbaae3a4fefc","added_by":"auto","created_at":"2024-05-27 07:05:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3806305,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3890600/v1/d1fb8b67-dce4-4014-9e93-9e9a20f6b39c.pdf"},{"id":50655567,"identity":"d4524f0f-92cc-42d1-bfa6-a651efcf1e36","added_by":"auto","created_at":"2024-02-05 10:11:56","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":1604418,"visible":true,"origin":"","legend":"Supplementary Information for All-Inorganic Ultrathin High Sensitivity Transparent Temperature Sensor Based on Mn-Co-Ni-O Nanofilms","description":"","filename":"SupplementaryInformation20240130Micronano.docx","url":"https://assets-eu.researchsquare.com/files/rs-3890600/v1/62d8c5fb8faed5a927807b17.docx"}],"financialInterests":"(Not answered)","formattedTitle":"All-Inorganic Ultrathin High Sensitivity Transparent Temperature Sensor Based on Mn-Co-Ni-O Nanofilms","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eTransparent temperature sensors are gaining prominence due to their unique advantages in optically sensitive applications, including light-emitting devices such as touch screens\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e, displays\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, light-emitting diode (LED) devices\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e, and invisible devices such as smart windows\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e, electronic skins\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e, and invisible robots. Furthermore, certain biological applications require temperature sensors to possess a degree of optical transmittance. For example, optogenetics, which is an emerging neuromodulation technique that combines genetic and optical methods to activate or inhibit specific neurons by light\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e, faces a thorny issue that overheating of the region stimulated by light pulses can cause cell damage or abnormal biological reactions\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Therefore, it is imperative to precisely monitor the temperature elevation in tissues adjacent to the light source while simultaneously providing an adequate light energy density. This ensures both the safety of biological experiments and the validity of the experimental findings. In diverse application contexts, transparent temperature sensors must exhibit high sensitivity and reliability. Additionally, the evolving application environments dictate that these sensors be lightweight, thin, and flexible\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. This flexibility is especially crucial in biological applications, where it aids in minimizing rejection reactions and improving the biocompatibility of functional devices.\u003c/p\u003e \u003cp\u003eExisting pathways for improving the transparency of temperature sensors incorporate thermal sensitive materials with high transparency, such as ionogels\u003csup\u003e\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e, liquid crystals\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, ion doped transparent ceramics\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e,\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e, polymer matrix composites\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e, metal mesh\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e and transparent thermoelectric materials\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. Supplementary Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e presents comparisons of various parameters such as transparency, sensitivity, resolution, and response time across transparent temperature sensors fabricated from these distinct materials. Transparent temperature sensors made of these materials demonstrate high transmittance, especially those made of polymer materials, which also possess advantages in flexibility. However, these transparent materials are usually limited in temperature sensing performances, such as insufficient sensitivity, long response time and low resolution. To surmount these limitations and further improve the temperature sensing performances of transparent temperature sensors, more sensitive transparent thermal sensitive materials need to be developed and utilized.\u003c/p\u003e \u003cp\u003eMn\u0026ndash;Co\u0026ndash;Ni\u0026ndash;O (MCN) spinel oxides, exhibiting excellent negative temperature coefficient (NTC) characters, have been widely used in temperature sensing with high sensitivity, good stability, excellent aging resistance performance and wide operating temperature range\u003csup\u003e\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. Compared with bulk and thick film MCN materials, thin film MCN materials have higher sensitivity and faster response\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. More importantly, MCN films with nanoscale thickness may exhibit certain optical transparency characteristics\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, making them a potential highly sensitive material in transparent temperature sensors.\u003c/p\u003e \u003cp\u003eIn this study, we fabricated an ultra-thin, all-inorganic, highly sensitive, microscale and freestanding transparent temperature sensor based on MCN nanofilms. The temperature sensor is characterized by a sandwich structure of \"encapsulation layer - sensitive layer - encapsulation layer\". Encapsulation layers provides mechanical support and improves anti-interference ability, allowing the sensor to operate in adverse environments while maintaining stability in electrical performance. An inorganic water-soluble sacrificial layer is used for releasing sensors from donor substrate. The freestanding MCN transparent temperature sensor has excellent sensitivity and resolution, and ultra short response time (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe freestanding MCN temperature sensor developed in this study can be transferred to any receiving substrate while maintaining good stability. Its microscale dimensions allow for flexible position selection, making it widely applicable. When integrated with flexible substrates, MCN temperature sensors can stably measure temperature under bending conditions and have strong anti-interference performance. We briefly demonstrate the application of the freestanding MCN transparent temperature sensor in optogenetics neural probes. The sensor can monitor the surface temperature of the micro-LED with minimal obstruction on LED luminous performance. The immunohistochemical staining experiment demonstrates its good biocompatibility and great potential for application in the field of biomedicine.\u003c/p\u003e"},{"header":"2. Results and discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Fabrication of sensors.\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea schematically demonstrates the fabrication process of the freestanding MCN transparent temperature sensor. The preparation starts with depositing a sacrificial layer composed of water-soluble germanium oxide (GeO\u003csub\u003ex\u003c/sub\u003e) onto single crystalline silicon (Si) wafers. This specific selection of GeO\u003csub\u003ex\u003c/sub\u003e for the sacrificial layer is predicated on its capacity to withstand the high annealing temperature which is crucial to ensure the crystallinity and achieve temperature sensitive characteristics of MCN thermistors. At the same time, acid and alkali etchant are avoided throughout the process design, making the process safer and more economical\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Then the bottom encapsulation layer composed of SiO\u003csub\u003e2\u003c/sub\u003e is deposited on the sacrificial layer. SiO\u003csub\u003e2\u003c/sub\u003e is chosen for its high transparency and thermal conductivity, and it has been widely used for encapsulation materials in implantable devices with high electrical insulation, good biocompatibility, and low permeability\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. Subsequently, by spin coating MCN acetate precursor solution under controlled humidity on the bottom encapsulation layer and annealing, the MCN thermistor layer which has a thickness of about 100 nm is obtained with high density and crystal quality. After patterning the MCN thermistor through photolithography and ion beam etching, patterned indium tin oxide (ITO) electrodes are prepared on it. ITO conductive thin film is a commonly used transparent electrode with high optical transmittance and low resistivity\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e). Then the patterned SiO\u003csub\u003e2\u003c/sub\u003e top encapsulation layer encapsulates the MCN thermistor and exposes the solder pads of ITO electrodes. Finally, the GeO\u003csub\u003ex\u003c/sub\u003e sacrificial layer is dissolved in water to obtain the freestanding sensor. Through advanced micro/nano processing technologies, hundreds of devices can be efficiently prepared at once.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Structure and morphology.\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb are optical images of sensors on Si substrate. The microscale sensor has a size of approximately 210 \u0026micro;m*180 \u0026micro;m and can measure temperature in precise locations, providing high spatial resolution. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec shows the multi-layer structure of the prepared sensor. The total thickness of the sensor is about 4.1 \u0026micro;m. From bottom to top, there are a SiO\u003csub\u003e2\u003c/sub\u003e bottom encapsulation layer with a thickness of 2 \u0026micro;m, a MCN sensitive layer with a thickness of 100 nm, and a SiO\u003csub\u003e2\u003c/sub\u003e top encapsulation layer with a thickness of 2 \u0026micro;m. Thin films are tightly bonded and there are clear boundaries between layers.\u003c/p\u003e \u003cp\u003eIt can be seen from the X-ray diffraction pattern (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed) that the MCN nanofilm exhibited a typical cubic spinel structure with the strongest peak detected at (311) according to the PDF card No. 01-088-0241, demonstrating that the films are highly crystallized and orientated\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee depicts the morphology of the MCN nanofilm through scanning electron microscope (SEM) observation. It can be observed that the film is dense polycrystalline film, and devoid of cracks or defects. The optical transmittance spectra of the MCN nanofilm on quartz glass are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef. The transmittance of the MCN nanofilm on glass is between 50% and 60% in the visible light wavelengths range. It can also be observed from the optical image (inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ef) that the MCN nanofilm has good optical transmission performance. In a freestanding MCN temperature sensor, the area of the MCN nanofilm only accounts for 15% of the total sensor size, with most of the area being optically transparent SiO\u003csub\u003e2\u003c/sub\u003e and ITO. Therefore, the overall sensor has better transparency.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Electrical properties.\u003c/h2\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea shows the relationship between electrical resistance (R) and temperature (T) of the MCN nanofilm in the temperature range of 30\u0026ndash;120\u0026deg;C. The MCN nanofilm exhibits typical Arrhenius plots of a NTC thermistor. The reproducibility of thermal response is recorded during heating and cooling processes, where both of R-T curves are overlap and the hysteresis is negligible (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, the \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(lnR\\)\u003c/span\u003e\u003c/span\u003e - \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\frac{1}{T}\\)\u003c/span\u003e\u003c/span\u003e plot shows a good linear relation at 300\u0026thinsp;\u0026minus;\u0026thinsp;390 K, and the resultant B-value is calculated as 3640 K for the overall measuring range. Temperature coefficient of the resistance (TCR) refers to the relative rate of change of the resistance value when the temperature is changed by 1\u0026deg;C. The TCR of the MCN nanofilm is calculated as \u0026minus;\u0026thinsp;4.0% \u0026deg;C\u003csup\u003e\u0026minus;\u0026thinsp;\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e at 30\u0026deg;C, which means the high sensitivity of the sensor.\u003c/p\u003e \u003cp\u003eMCN transparent temperature sensors are transferred to glass substrates for electrical property testing (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec). The electrical resistance of NTC thermistors usually has a drift over time, which is known as aging and effects the stability of NTC thermistors in long-time use\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. In order to achieve stable performance of the MCN transparent temperature sensor in long-term use, we explore the influence of aging annealing time on the resistance drift of the freestanding MCN transparent temperature sensor with the annealing temperature of 120 ℃ (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed). It can be seen that the resistance drift of sensors without annealing treatment increases continuously over time, and still exhibits 0.25%\u0026middot;d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e after 21 days of storage. The resistance drift of sensors which are annealed for 30, 60, and 100 hours gradually decrease over time. After being placed for 21 days, the resistance drift increased slowly and exhibits less than 0.04%\u0026middot;d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indicating an improvement in stability. The resistance of sensors which are annealed for 300 hours, although has a lager drift in the first 7 days of storage, is basically stable after 21 days of storage and the resistance drift is less than 0.01%\u0026middot;d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The results show that 120 ℃ annealing treatment can significantly decrease the resistance drift, and the stability improves as the annealing treatment time increases. Therefore, MCN transparent temperature sensors are annealed at 120 ℃ for 300 hours to improve the stability of their performance. After annealing treatment, the MCN transparent temperature sensor exhibits high level of reliability under three repetitions of full range scanning (Figure S2 and Note S2).\u003c/p\u003e \u003cp\u003eMore interestingly, the tiny temperature variations (0.03\u0026deg;C) can be accurately discriminated (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee), suggesting that the freestanding MCN transparent temperature sensor possesses unprecedentedly high temperature resolution and guarantees the accurate temperature detection. The instantaneous temperature response of the freestanding MCN transparent temperature sensor is investigated (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ef). According to the temperature change curve recorded by the sensor, the response time of the sensor is 224 ms in the case of elevating detection temperature from 25 to 70\u0026deg;C, suggesting a very rapid, sharp response, which mainly benefits from the use of ultra-thin and high thermal conductivity SiO\u003csub\u003e2\u003c/sub\u003e encapsulation layers and is desirable for temperature sensors.\u003c/p\u003e \u003cp\u003eThe freestanding MCN transparent temperature sensor retains the high sensitivity, stability, resolution, and fast response characteristics of MCN thermistors while obtaining transparent characteristics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Structure stability and anti-interference ability.\u003c/h2\u003e \u003cp\u003eThe freestanding MCN transparent temperature sensor can be integrated with various substrates by utilizing transfer printing technology. To obtain a flexible transparent temperature sensor, the freestanding MCN sensor is transferred to a polyimide (PI) substrate (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea). Electrical signals are drawn from ITO electrodes of the sensor utilizing photolithography and magnetron sputtering metal electrode. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb shows the bending test for the sensor. Sensors are bent into bending radius of 15 mm, 10 mm, and 5 mm, respectively, to test the performance of sensors with different bending amplitudes. The resistance (R)\u0026ndash;temperature (T) curves are measured to examine the structure stability of the flexible sensor (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). It can be seen that sensors with different bending amplitudes exhibit excellent negative temperature coefficient thermistors characters in the temperature range of 25 to 100\u0026deg;C, same as sensors in flat state. The resistance of the sensor at various temperatures is almost unaffected by bending, indicating that the temperature sensor has good structural stability and strain insensitivity. The resistance change of the sensor during bending is also tested (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec). The sensor undergoes a cycle from a flat state to a bending state with a bending radius of 5 mm and then returns to a flat state. During this process, the resistance change is less than 0.5%. The bending cycle tests for the flexible MCN sensors are also carried out. The frequency of the alternating bending was 1 Hz. After bending for 1k, 5k, and 10k cycles with a bending radius of 5mm, R-T curves of sensors are measured. As is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed, R-T curves of sensors after multiple cycles of bending almost coincide with the curve of the initial state sensor. The electrical parameters of the sensor are barely affected by the bending effect, which validates the potential of the freestanding MCN transparent temperature sensor in flexible electronics application.\u003c/p\u003e \u003cp\u003eThe conductivity of oxides is usually sensitive to gas composition in the surrounding atmosphere. NTC thermistors often operate in an atmosphere of constant or known oxygen partial pressure to avoid possible influence from the probing atmosphere\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. However, there is an increasing need for sensors capable of operating in harsh working environments for measurement in industrial processes where various potentially hazardous gases may exist, such as strong acids, strong alkalis, organic solvents, etc. In addition, some special application scenarios of temperature sensors, such as temperature compensation for gas sensors\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e, require temperature sensors to have good anti-interference ability and selectivity, that is, no response to other stimuli. To verify the reliability for working in harsh environments of the MCN transparent temperature sensor, four representative interfering gases are used to test the impact of the environment on the sensor, in which ethanol and acetone are common volatile polar organic solvents, hydrogen chloride is a strongly acidic gas, and ammonia is an alkaline gas (Note S3). According to the acquired results (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee-\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eh), it can be seen that as the concentration of interfering gases increases, the resistance of the sensor changes within 0.5%, indicating that the temperature sensor has high reliability and good anti-interference performance, and this mainly benefits from the low permeability of the SiO\u003csub\u003e2\u003c/sub\u003e encapsulation layer.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Application in optogenetics neural probes.\u003c/h2\u003e \u003cp\u003eOptogenetics is an emerging neuromodulation technique that combines genetic and optical methods to activate to activate or inhibit specific neurons by light\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. In recent years, with the development of optogenetics technology, implantable light sources have become increasingly popular among researchers, where LED probes stand out by overcoming coupling light losses and maximizing delivered light power due to the proximity to target cells\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. A thorny issue faced by optogenetics technology is that overheating of the region stimulated by light pulses can cause cell damage or abnormal biological reactions\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Therefore, it is crucial to evaluate the thermal characteristics of optical points during operations. At the same time, the implantation of probes is always accompanied by inflammatory reactions related to temperature rise. Continuous monitoring of tissue temperature can provide relevant inflammatory information and evaluate the biocompatibility of implants\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. Temperature sensors are often integrated on LED probes to detect changes in tissue temperature\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e,\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. However, commonly used temperature sensors such as Pt thermistors have poor light transmittance. To prevent obstruction of LED light, they can only be integrated below or next to the LED and are not located near the biological tissue stimulated by the light on the front of the LED, thus cannot reflect the true temperature rise of the target tissue.\u003c/p\u003e \u003cp\u003eThe freestanding MCN transparent temperature sensor is integrated onto the LED optogenetic probe to verify its potential applications in the field of optogenetics (Figure S3). The preparation process of the LED optogenetic probe can be found in previous work\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e,\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e. The thin film LED on the probe maintains good electrical and optical properties (Figure S4 and Note S4). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea is a schematic illustration of the optogenetics neural probe integrated with temperature sensor. Due to its good transparency, it can be integrated directly above the LED, with almost no obstruction to the LED. The electrodes of LED and temperature sensor are distributed vertically separated by insulated SU-8 photoresist, reducing crosstalk during operation. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, the sensor is integrated directly above the LED with LED off on the left and LED open (input current is 1 mA) on the right. It can be seen that LED blue light can penetrate the temperature sensor with only a slight decrease in light intensity. The temperature sensor will directly contact the biological tissue stimulated by the light of the LED when the probe is implanted in an organism, achieving accurate measurement of temperature changes in the target tissue.\u003c/p\u003e \u003cp\u003eTo demonstrate the minimal obstruction on LED luminous performance by the MCN transparent temperature sensor, the light intensity distribution of the system is measured and the multi angle luminescence spectrum is plotted (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec and Note S5). It can be seen that the LED integrated with a MCN transparent temperature sensor exhibits symmetrical distribution of light intensity in its multi angle emission spectrum, which conforms to the typical Lambert radiation characteristics. This indicates that the vertically integrated MCN transparent temperature sensor does not change the LED emission angle. In addition, after the integration of the MCN transparent temperature sensor, the LED still maintains about 80% of the luminous power, which is because the MCN sensitive layer has a certain degree of transparency, and high transparent SiO\u003csub\u003e2\u003c/sub\u003e and ITO account for 85% of the total sensor area.\u003c/p\u003e \u003cp\u003eThe luminous power of LEDs is also measured under different input currents before and after the integration of thin film temperature sensors (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed). It can be seen that the luminous power of LEDs increases as the input current increases. After the integration of the temperature sensor, the light output power slightly decreases, but remained above 80%, indicating that the thin film temperature sensor has good transparency. It can be inferred that the integration of MCN transparent temperature sensors will not hinder the optogenetics operation of implanted LED probes.\u003c/p\u003e \u003cp\u003eTo verify the temperature measurement functions of the probe, the temperature rise of the LED surface under different injection currents is measured by the integrated MCN transparent temperature sensor, and the calibrated infrared measurement is used as a control experiment. As is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee, the temperature rise of the LED surface increases as the input current increases and exhibits a good linear relationship. The measurement curves of the integrated MCN transparent temperature sensor and the calibrated infrared measurement are highly coincident with an error of less than 1%. This indicates that the integrated MCN transparent temperature sensor can accurately measure the surface temperature rise of LED. In addition, the anti light interference ability of the MCN transparent temperature sensor is tested using different wavelengths of light (Figure S5 and Note S6), and the results show that the sensor is almost unaffected by light, and can accurately measure temperature when integrated with the optical system.\u003c/p\u003e \u003cp\u003eA finite element thermal simulation model of the optogenetics system is established and simulates the surface temperature rise of LED (Note S7). As is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef, the simulation curve highly coincides with the measurement curve of the integrated MCN transparent temperature sensor, indicating that the calculated results are basically consistent with the experimental results, with an error of less than 2%, and the simulation model can predict the surface temperature rise of LED under different input currents (Figure S6). The simulation result at an input current of 3 mA on the surface of the probe model is compared with the measurement results of an infrared thermal imager (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eg). The maximum temperature difference is 0.5 ℃. Therefore, the thermal simulation model of optogenetics system can truly reflect the temperature rise of LED surface, which has important reference significance for predicting and studying the thermal impact of probes on biological tissues.\u003c/p\u003e \u003cp\u003eTo verify the biocompatibility of the MCN transparent temperature sensor, sensors are implanted into the back of rats, and the surrounding tissues are stained and sliced for observation at 7 days, 14 days, and 21 days, respectively (Note S8 and Note S9). Histological images show minimal damage to the tissue and negligible immune response caused by the implantation (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eh), indicating that the MCN transparent temperature sensor has good biocompatibility and potential for application in the biomedical field.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Conclusion","content":"\u003cp\u003eWe developed an ultra-thin, all-inorganic, transparent, highly sensitive and freestanding temperature sensor based on Mn-Co-Ni-O nanofilms. The sensor obtains transparent characteristics through the prepared MCN thin film with a thickness of 100 nm, while retaining the high sensitivity, stability, resolution, and fast response characteristics of MCN thermistors through the high crystallization quality of MCN nanofilms. The freestanding MCN temperature sensor can be transferred to any receiving substrate and maintain good stability. The resistance of the sensor remains almost constant in harsh environments, indicating its anti-interference ability and potential in extreme applications. The sensor can accurately monitor the temperature rise on the LED optogenetics probe with minimal obstruction to LED luminescence and have good biocompatibility, indicating the application prospects of the MCN temperature transparent sensor in the field of implantable optogenetics. With good biocompatibility and microscale dimensions, the transparent MCN temperature transparent sensor has broad application prospects in the field of biomedicine. In addition, the sensor can be used for various stealth devices and may improve the spatial resolution of temperature measurement through array integration.\u003c/p\u003e"},{"header":"4. Materials and methods","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e4.1 Fabrication process.\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eThe germanium oxide (GeO\u003csub\u003ex\u003c/sub\u003e) sacrificial layer with a thickness of 40 nm is grown on single crystalline silicon (Si) wafers with dimensions of 3cm*3cm by magnetron sputtering. Then the SiO\u003csub\u003e2\u003c/sub\u003e bottom encapsulation layer with a thickness of 2 \u0026micro;m is deposited onto the sacrificial layer using electron beam physical vapor deposition. Subsequently, the sample is heated at 250 ℃ for 10 minutes to diminish the water solubility of GeO\u003csub\u003ex\u003c/sub\u003e, thus desensitizing it. After cooling, the sample is subjected to oxygen plasma treatment with the aim of improving the binding ability of SiO\u003csub\u003e2\u003c/sub\u003e and MCN. The next step involves spin-casting the MCN acetate precursor solution (0.2 mol/L Mn\u003csub\u003e1.56\u003c/sub\u003eCo\u003csub\u003e0.96\u003c/sub\u003eNi\u003csub\u003e0.48\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e in mixed solution of acetic acid and water) onto the SiO\u003csub\u003e2\u003c/sub\u003e bottom encapsulation layer under controlled humidity, followed by drying at 250\u0026deg;C for 5 min. The assembly, now comprising Si/GeO\u003csub\u003ex\u003c/sub\u003e/SiO\u003csub\u003e2\u003c/sub\u003e/MCN layers, is annealed in an air atmosphere at 750 ℃ for 90 min, resulting in the formation of a MCN thermistor layer with high density, high crystal quality and a thickness of about 100 nm. This layer is subsequently patterned through photolithography and ion beam etching, and patterned indium tin oxide (ITO) electrodes are then prepared on it through photolithography and magnetron sputtering. Then the patterned SiO\u003csub\u003e2\u003c/sub\u003e top encapsulation layer is prepared on through photolithography and electron beam physical vapor deposition, and the SiO\u003csub\u003e2\u003c/sub\u003e bottom encapsulation layer is patterned through photolithography and ion beam etching. Finally, samples are placed in water at 80 ℃ to dissolve the GeO\u003csub\u003ex\u003c/sub\u003e sacrificial layer and release freestanding sensors from Si wafers. Suction filtration is used to transfer freestanding sensors onto filter paper.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e4.2 Transfer process of sensors to PI substrate.\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eA thin layer of diluted SU-8 photoresist (1:1 with cyclopentanone) is spin-cast onto the PI substrate as an adhesive. Before the SU-8 photoresist solidifies, the freestanding sensor is adsorbed from the filter paper by the electrostatic adsorption of a needle tip and is gently placed on the PI substrate coated with SU-8 photoresist. Then the sample is exposed to ultraviolet light and heat for curing the photoresist. Ni/Cu electrodes are subsequently fabricated through photolithography and magnetron sputtering to establish electrical connectivity with ITO electrodes intrinsic to the sensor and draw electrical signals from the sensor.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e4.3 Integration process of sensors with optogenetics neural probes.\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eA thin layer of SU-8 photoresist is spin-cast onto the LED optogenetic probe as an adhesive. Before the SU-8 photoresist solidifies, the freestanding sensor is gently placed directly above the emitting site of the LED probe. Then the probe is exposed to ultraviolet light and heat for curing the photoresist. Ni/Cu electrodes are subsequently fabricated through photolithography and magnetron sputtering to draw electrical signals from ITO electrodes of the sensor.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Measurements and characterization.\u003c/h2\u003e \u003cp\u003eOptical images are captured by a microscope VMX40M. Scanning electron microscopic (SEM) images are taken with a ZEISS Sigma 300 System. The crystalline structures of the thin films are identified with an XRD (Malvern Panalytical Empyrean). MCN film is ground into powder for XRD testing to avoid interference from substrate materials. To characterize the light transmittance performance of the sensor, the MCN/SiO\u003csub\u003e2\u003c/sub\u003e thin film (5 \u0026times; 5 mm) is prepared using thin film deposition technology and is transferred to a quartz substrate. The UV-Vis-IR absorption spectra of the MCN nanofilm is characterized by using a spectrophotometer (PerkinElmer Lambda 750S).\u003c/p\u003e \u003cp\u003eThe relationship between resistance and testing temperature is measured using an automatic data acquisition system, which included a vacuum films probe system (Lake Shore) with temperature control unit and a semiconductor parameter analyzer (Keithley 4200A-SCS). In order to maintain the quasi-thermal equilibrium state between the temperature sensor and the temperature control stage, every measurement is conducted for every 5\u0026deg;C interval with at least 5 minutes of stabilization period. Measurement details of other sensor performances can be found in the supplementary materials.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eThis work is supported by the National Natural Science Foundation of China (NSFC) (62004009 for C. L.), the National Key Research and Development Program of China (Grant No. 2018YFA0702100), the Zhejiang Provincial Key Research and Development Program of China (Grant Nos. 2021C01026 and 2021C05002), the Leading Innovative and Entrepreneur Team Introduction Program of Zhejiang (2020R01007) and the Beijing Nova Program (20230484412).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor details\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e1\u003c/sup\u003e Research Institute for Frontier Science, Beihang University, Beijing 100191, China. \u003csup\u003e2\u003c/sup\u003eSchool of Materials Science and Engineering, Beihang University, Beijing 100191, China. \u003csup\u003e3\u003c/sup\u003eKey Laboratory of Intelligent Sensing Materials and Chip Integration Technology of Zhejiang Province, Hangzhou Innovation Institute of Beihang University, Hangzhou 310051, China.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eY.C. and M.S. contributed equally to this work. M.S. and C.L. developed the methods and designed the structures. Y.C. and M.S. fabricated the devices, conducted the experiment, and performed the characterization. C.L. and Y.D. provided tools and supervised the research. Y.C. and C.L. wrote the paper in consultation with other authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics\u003c/strong\u003e \u003cstrong\u003estatements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll animal work was approved by Wuhan Servicebio Technology Co., Ltd., China, and the ethical approval protocol number was Servicebio Animal Welfare NO. 2022158. All study methods were carried out in accordance with relevant guidelines and regulations. All animals are socially housed in a 12 h/12 h (lights on at 8 am) light/dark cycle, with access to food pellets and water ad libitum. The owner of animals is informed and consents to this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe online version contains supplementary material available at\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eJung, H. \u0026amp; Lee, H. Semi-transparent reduced graphene oxide temperature sensor on organic light-emitting diodes for fingerprint liveness detection of smartphone authentication. \u003cem\u003eSens. Actuators, A\u003c/em\u003e 331 (2021). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1016/j.sna.2021.112876\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1016/j.sna.2021.112876\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAn, B. W., Heo, S., Ji, S., Bien, F. \u0026amp; Park, J. U. Transparent and flexible fingerprint sensor array with multiplexed detection of tactile pressure and skin temperature. Nat. Commun. 9, 2458 (2018). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1038/s41467-018-04906-1\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1038/s41467-018-04906-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee, C. Y., Su, A., Liu, Y. C., Fan, W. Y. \u0026amp; Hsieh, W. J. In situ measurement of the junction temperature of light emitting diodes using a flexible micro temperature sensor. Sensors (Basel) 9, 5068\u0026ndash;5075 (2009). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.3390/s90705068\u003c/span\u003e\u003cspan address=\"https://doi.org:10.3390/s90705068\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYe, Y., Lu, K. \u0026amp; Qi, J. Developing Smart Temperature Sensing Window Based on Highly Transparent Rare-Earth Doped Yttrium Zirconate Ceramics. ACS Appl. Mater. Interfaces 14, 39072\u0026ndash;39080 (2022). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1021/acsami.2c11404\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1021/acsami.2c11404\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, X., Ren, Z., Guo, H., Cheng, X. \u0026amp; Zhang, H. Self-powered flexible and transparent smart patch for temperature sensing. Appl. Phys. Lett. 116 (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1063/1.5134526\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1063/1.5134526\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhao, H. Recent Progress of Development of Optogenetic Implantable Neural Probes. Int. J. Mol. Sci. 18 (2017). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.3390/ijms18081751\u003c/span\u003e\u003cspan address=\"https://doi.org:10.3390/ijms18081751\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoncalves, S. B. \u003cem\u003eet al.\u003c/em\u003e LED Optrode with Integrated Temperature Sensing for Optogenetics. Micromachines (Basel) 9 (2018). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.3390/mi9090473\u003c/span\u003e\u003cspan address=\"https://doi.org:10.3390/mi9090473\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJiang, N. \u003cem\u003eet al.\u003c/em\u003e Flexible, transparent, and antibacterial ionogels toward highly sensitive strain and temperature sensors. Chem. Eng. J. 424 (2021). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1016/j.cej.2021.130418\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1016/j.cej.2021.130418\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXu, Y., Chen, L., Chen, J., Chang, X. \u0026amp; Zhu, Y. Flexible and Transparent Pressure/Temperature Sensors Based on Ionogels with Bioinspired Interlocked Microstructures. ACS Appl. Mater. Interfaces 14, 2122\u0026ndash;2131 (2022). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1021/acsami.1c22428\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1021/acsami.1c22428\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJiang, N. \u003cem\u003eet al.\u003c/em\u003e Ionic liquid enabled flexible transparent polydimethylsiloxane sensors for both strain and temperature sensing. Adv. Compos. Hybrid Mater. 4, 574\u0026ndash;583 (2021). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1007/s42114-021-00262-9\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1007/s42114-021-00262-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTie, J. \u003cem\u003eet al.\u003c/em\u003e Highly transparent, self-healing and adhesive wearable ionogel as strain and temperature sensor. Polym. Chem. 13, 4064\u0026ndash;4075 (2022). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1039/d2py00594h\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1039/d2py00594h\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu, K. \u003cem\u003eet al.\u003c/em\u003e Highly sensitive and transparent flexible temperature sensor based on nematic liquid crystals. Liq. Cryst. 49, 372\u0026ndash;379 (2021). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1080/02678292.2021.1970834\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1080/02678292.2021.1970834\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHu, S., Lu, C., Liu, X. \u0026amp; Xu, Z. Optical temperature sensing based on the luminescence from YAG:Pr transparent ceramics. Opt. Mater. 60, 394\u0026ndash;397 (2016). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1016/j.optmat.2016.08.026\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1016/j.optmat.2016.08.026\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen, D., Wan, Z., Zhou, Y. \u0026amp; Ji, Z. Cr3+-doped gallium-based transparent bulk glass ceramics for optical temperature sensing. J. Eur. Ceram. Soc. 35, 4211\u0026ndash;4216 (2015). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1016/j.jeurceramsoc.2015.08.005\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1016/j.jeurceramsoc.2015.08.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCai, T. \u003cem\u003eet al.\u003c/em\u003e Phosphorescence-Based Flexible and Transparent Optical Temperature-Sensing Skin Capable of Operating in Extreme Environments. ACS Appl. Polym. Mater. 3, 2461\u0026ndash;2469 (2021). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1021/acsapm.1c00062\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1021/acsapm.1c00062\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTrung, T. Q., Ramasundaram, S., Hwang, B. U. \u0026amp; Lee, N. E. An All-Elastomeric Transparent and Stretchable Temperature Sensor for Body-Attachable Wearable Electronics. Adv. Mater. 28, 502\u0026ndash;509 (2016). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1002/adma.201504441\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1002/adma.201504441\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWalia, S., Mondal, I. \u0026amp; Kulkarni, G. U. Patterned Cu-Mesh-Based Transparent and Wearable Touch Panel for Tactile, Proximity, Pressure, and Temperature Sensing. ACS Appl. Electron. Mater. 1, 1597\u0026ndash;1604 (2019). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1021/acsaelm.9b00330\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1021/acsaelm.9b00330\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBianchi, C. \u003cem\u003eet al.\u003c/em\u003e V2O5Thin Films for Flexible and High Sensitivity Transparent Temperature Sensor. Adv. Mater. Technol. 1 (2016). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1002/admt.201600077\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1002/admt.201600077\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMuralidharan, M. N., Rohini, P. R., Sunny, E. K., Dayas, K. R. \u0026amp; Seema, A. Effect of Cu and Fe addition on electrical properties of Ni\u0026ndash;Mn\u0026ndash;Co\u0026ndash;O NTC thermistor compositions. Ceram. Int. 38, 6481\u0026ndash;6486 (2012). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1016/j.ceramint.2012.05.025\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1016/j.ceramint.2012.05.025\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKong, W., Wei, W., Gao, B. \u0026amp; Chang, A. A study on the electrical properties of Mn-Co-Ni-O thin films grown by radio frequency magnetron sputtering with different thicknesses. Appl. Surf. Sci. 423, 1012\u0026ndash;1018 (2017). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1016/j.apsusc.2017.06.290\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1016/j.apsusc.2017.06.290\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFeteira, A. Negative Temperature Coefficient Resistance (NTCR) Ceramic Thermistors: An Industrial Perspective. J. Am. Ceram. Soc. 92, 967\u0026ndash;983 (2009). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1111/j.1551-2916.2009.02990.x\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1111/j.1551-2916.2009.02990.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, R. \u003cem\u003eet al.\u003c/em\u003e Mn-Co-Ni-O thin films prepared by sputtering with alloy target. J. Adv. Ceram. 9, 64\u0026ndash;71 (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1007/s40145-019-0348-y\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1007/s40145-019-0348-y\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou, W. \u003cem\u003eet al.\u003c/em\u003e Micro structural, electrical and optical properties of highly (220) oriented spinel Mn\u0026ndash;Co\u0026ndash;Ni\u0026ndash;O film grown by radio frequency magnetron sputtering. Appl. Surf. Sci. 311, 443\u0026ndash;447 (2014). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1016/j.apsusc.2014.05.088\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1016/j.apsusc.2014.05.088\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNam, J. \u003cem\u003eet al.\u003c/em\u003e Transfer Printed Flexible and Stretchable Thin Film Solar Cells Using a Water-Soluble Sacrificial Layer. Adv. Energy Mater. 6 (2016). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1002/aenm.201601269\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1002/aenm.201601269\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFang, H. \u003cem\u003eet al.\u003c/em\u003e Ultrathin, transferred layers of thermally grown silicon dioxide as biofluid barriers for biointegrated flexible electronic systems. Proc Natl Acad Sci U S A 113, 11682\u0026ndash;11687 (2016). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1073/pnas.1605269113\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1073/pnas.1605269113\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSong, E. \u003cem\u003eet al.\u003c/em\u003e Thin, Transferred Layers of Silicon Dioxide and Silicon Nitride as Water and Ion Barriers for Implantable Flexible Electronic Systems. Adv. Electron. Mater. 3 (2017). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1002/aelm.201700077\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1002/aelm.201700077\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAydın, E. B. \u0026amp; Sezgint\u0026uuml;rk, M. K. Indium tin oxide (ITO): A promising material in biosensing technology. TrAC, Trends Anal. Chem. 97, 309\u0026ndash;315 (2017). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1016/j.trac.2017.09.021\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1016/j.trac.2017.09.021\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhao, M., Chen, W., Wu, W., Zhang, M. \u0026amp; Li, Z. Aging characteristic of Cu-doped nickel manganite NTC ceramics. J. Mater. Sci.: Mater. Electron. 31, 11784\u0026ndash;11790 (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1007/s10854-020-03730-y\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1007/s10854-020-03730-y\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang, C. C., Akbar, S. A. \u0026amp; Madou, M. J. Ceramic Based Resistive Sensors. J. Electroceram. 2, 273\u0026ndash;282 (1998). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1023/A:1009978607621\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1023/A:1009978607621\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlgamili, A. S. \u003cem\u003eet al.\u003c/em\u003e Fabrication and Characterization of the Micro-Heater and Temperature Sensor for PolyMUMPs-Based MEMS Gas Sensor. Micromachines (Basel) 13 (2022). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.3390/mi13040525\u003c/span\u003e\u003cspan address=\"https://doi.org:10.3390/mi13040525\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKang, J.-g. \u003cem\u003eet al.\u003c/em\u003e Temperature control of micro heater using Pt thin film temperature sensor embedded in micro gas sensor. Micro Nano Syst. Lett. 5 (2017). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1186/s40486-017-0060-z\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1186/s40486-017-0060-z\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoncalves, S. B., Ribeiro, J. F., Silva, A. F., Costa, R. M. \u0026amp; Correia, J. H. Design and manufacturing challenges of optogenetic neural interfaces: a review. J. Neural Eng. 14, 041001 (2017). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1088/1741-2552/aa7004\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1088/1741-2552/aa7004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFekete, Z. \u003cem\u003eet al.\u003c/em\u003e Simultaneous in vivo recording of local brain temperature and electrophysiological signals with a novel neural probe. J. Neural Eng. 14, 034001 (2017). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1088/1741-2552/aa60b1\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1088/1741-2552/aa60b1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZgierski-Johnston, C. M. \u003cem\u003eet al.\u003c/em\u003e Cardiac pacing using transmural multi-LED probes in channelrhodopsin-expressing mouse hearts. Prog. Biophys. Mol. Biol. 154, 51\u0026ndash;61 (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1016/j.pbiomolbio.2019.11.004\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1016/j.pbiomolbio.2019.11.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAyub, S. \u003cem\u003eet al.\u003c/em\u003e Compact Optical Neural Probes With Up to 20 Integrated Thin-Film muLEDs Applied in Acute Optogenetic Studies. IEEE Trans. Biomed. Eng. 67, 2603\u0026ndash;2615 (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1109/TBME.2020.2966293\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1109/TBME.2020.2966293\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi, L. \u003cem\u003eet al.\u003c/em\u003e Heterogeneous Integration of Microscale GaN Light-Emitting Diodes and Their Electrical, Optical, and Thermal Characteristics on Flexible Substrates. Adv. Mater. Technol. 3 (2017). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1002/admt.201700239\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1002/admt.201700239\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu, C. \u003cem\u003eet al.\u003c/em\u003e A wireless, implantable optoelectrochemical probe for optogenetic stimulation and dopamine detection. Microsyst. Nanoeng. 6, 64 (2020). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org:10.1038/s41378-020-0176-9\u003c/span\u003e\u003cspan address=\"https://doi.org:10.1038/s41378-020-0176-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"microsystems-and-nanoengineering","isNatureJournal":false,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"micronano","sideBox":"Learn more about [Microsystems \u0026 Nanoengineering](http://www.nature.com/micronano/)","snPcode":"41378","submissionUrl":"https://mts-micronano.nature.com/","title":"Microsystems \u0026 Nanoengineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"transparent temperature sensor, NTC nanofilms, biocompatible, optogenetics probes","lastPublishedDoi":"10.21203/rs.3.rs-3890600/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3890600/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe demand for optically transparent temperature sensors in intelligent devices is escalating. However, the performances of these sensors, particularly their sensitivity and resolution, require further enhancement. This study introduces a novel transparent and highly sensitive temperature sensor, characterized by its ultra-thin, freestanding design, and based on Mn-Co-Ni-O nanofilms. The Mn-Co-Ni-O-based sensor exhibits remarkable sensitivity, with a temperature coefficient of resistance of -4%℃\u003csup\u003e-1\u003c/sup\u003e, and is capable of detecting minuscule temperature fluctuations as small as 0.03 ℃. Additionally, the freestanding sensor can be transferred to any substrate for versatile application while maintaining robust structural stability and excellent resistance to interference, indicating its suitability for operation in challenging environments. The vertical integration of the sensor and a micro light-emitting diode on a polyimide substrate demonstrates its practical utility in monitoring the surface temperature of optical devices. Moreover, the implantation experiment of the sensor in rats confirms its favorable biocompatibility, highlighting the sensor's promising applications in the biomedical domain.\u003c/p\u003e","manuscriptTitle":"All-Inorganic Ultrathin High Sensitivity Transparent Temperature Sensor Based on Mn-Co-Ni-O Nanofilms","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-05 10:11:51","doi":"10.21203/rs.3.rs-3890600/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"revise","date":"2024-02-26T02:01:40+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"This content is not available.","date":"2024-02-22T16:12:24+00:00","index":3,"fulltext":"This content is not available."},{"type":"editorInvitedReview","content":"This content is not available.","date":"2024-02-12T03:08:55+00:00","index":2,"fulltext":"This content is not available."},{"type":"editorInvitedReview","content":"This content is not available.","date":"2024-02-06T05:25:50+00:00","index":1,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2024-02-05T08:09:36+00:00","index":3,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2024-02-04T09:14:35+00:00","index":2,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2024-02-02T16:23:30+00:00","index":1,"fulltext":"This content is not available."},{"type":"reviewersInvited","content":"","date":"2024-02-02T14:18:40+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-01-31T06:34:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"Microsystems \u0026 Nanoengineering","date":"2024-01-30T16:22:16+00:00","index":"","fulltext":""},{"type":"checksFailed","content":"","date":"2024-01-26T05:41:36+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-01-23T09:17:15+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"microsystems-and-nanoengineering","isNatureJournal":false,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"micronano","sideBox":"Learn more about [Microsystems \u0026 Nanoengineering](http://www.nature.com/micronano/)","snPcode":"41378","submissionUrl":"https://mts-micronano.nature.com/","title":"Microsystems \u0026 Nanoengineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"67a391d3-9385-469d-80e0-ac95fb37c75b","owner":[],"postedDate":"February 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":28535890,"name":"Physical sciences/Engineering/Electrical and electronic engineering"},{"id":28535891,"name":"Physical sciences/Materials science/Nanoscale materials"}],"tags":[],"updatedAt":"2024-05-27T07:05:35+00:00","versionOfRecord":{"articleIdentity":"rs-3890600","link":"https://doi.org/10.1038/s41378-024-00706-4","journal":{"identity":"microsystems-and-nanoengineering","isVorOnly":false,"title":"Microsystems \u0026 Nanoengineering"},"publishedOn":"2024-05-27 04:00:00","publishedOnDateReadable":"May 27th, 2024"},"versionCreatedAt":"2024-02-05 10:11:51","video":"","vorDoi":"10.1038/s41378-024-00706-4","vorDoiUrl":"https://doi.org/10.1038/s41378-024-00706-4","workflowStages":[]},"version":"v1","identity":"rs-3890600","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3890600","identity":"rs-3890600","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}