New Tunneling Source Follower with Low 1/f Noise and High Voltage Gain

New Tunneling Source Follower with Low 1/f Noise and High Voltage Gain | 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 New Tunneling Source Follower with Low 1/f Noise and High Voltage Gain Ki Yeong Kim, Hyangwoo Kim, Hyeongseok Yoo, Minkeun Choi, Yijoon Kim, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4175618/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 09 Oct, 2024 Read the published version in Scientific Reports → Version 1 posted 10 You are reading this latest preprint version Abstract We have designed a tunneling source follower (TSF) for image sensors that achieves high voltage gain (Av) and low 1/f noise simultaneously. The TSF is composed of N-P-N-N, especially the p-doped grounded area, which serves to amplify the insufficient tunneling current, allowing the source follower (SF) to utilize band-to-band tunneling (BTBT). Compared to thermionic emission, tunneling based structures contribute to increasing Av through lower channel length modulation and lower body effect. As a result, TSF achieves a higher Av (~1.0 V/V) than conventional SF (~0.9 V/V). Moreover, the n-doped channel makes the buried conductive channel farther from the interface, lowering the noise. The current noise spectral density (SI) is approximately 10 times lower in TSF than that of in conventional SF. Therefore, our TSF can be a possible candidate for High Av and low 1/f noise image sensors. Physical sciences/Engineering/Electrical and electronic engineering Physical sciences/Nanoscience and technology/Nanoscale devices/Electronic devices Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction A CMOS Image Sensors (CIS) is a sensor that measures the amount of light using a transistor. It has dominated industrial vision applications with their excellent performance in mass production, power efficiency and parallel data transmission 1–3 . In order to obtain a clear image, it is important to control in-pixel noise by ensuring a distinct separation between the signal and noise. However, research on CIS has focused on downsizing for high resolution, and recently, the pixel pitch has reached the level of 0.56 μm 4 . As the sensing area decreases, the light signal also becomes smaller, leading to problems with dynamic range (DR) and pixel dark noise generated by amplifying small signals. Low signal is especially problematic in low illumination. This is because read noise is constant regardless of the input photons, which is fatal to signal-to-ratio (SNR). Therefore, the need for research to reduce read noise has emerged. Read noise consists of reset noise, thermal noise, 1/ f noise, etc 5,6 . The reset noise is mostly removed using correlated double sampling (CDS) technology, which takes the difference between the sampled signal and reset level as the signal value. Thermal noise is relatively small compared to other noises at the low frequencies where SF operates. As a result, 1/ f noise became the main source of read noise 5,6 . The 1/ f noise stands for the output fluctuations that occurs when electrons repeat trapping and detrapping on the dangling bond at the silicon/gate-oxide interface of source follower (SF). A common way to reduce 1/ f noise is to move the current flow away from the interface traps. This is said to form buried channel (BC), and research has been conducted to apply it to NMOS, FinFET, multi-gate structure, and junction FET 7–12 . In the NMOS, the channel area is doped n-type to form BC, which is called buried channel SF (BCSF) 7–9 . The BC effect can be amplified by using fin sidewalls as potential barriers in FinFET structure 10 . Furthermore, BCSFs with multi-gate can be designed to achieve low 1/ f noise while maintaining small gate areas 11 . These structures generally have a trade-off that gate control becomes more difficult as the current path moves away from the surface. This reduces transconductance ( g m ), leading to a reduction in voltage gain ( A v ). Consequently, these structures have decreased fixed pattern noise and output voltage 7,8,13 . Alternatively, BC can be applied to the junction FET structure 12 . The buried channel junction FET uses a floating diffusion node as the gate. Since the gate is located underneath the channel, the interface traps have less impact on the conduction carriers, resulting in lower 1/ f noise. However, A v is low because holes with lower mobility are used as carriers. In this study, we have proposed a tunneling source follower (TSF) that achieves improved SF characteristics of both A v and 1/ f noise without degrading the output voltage. It is particularly characterized by tunneling mechanism and BC. Additionally, the output voltage is improved by adding a grounded area between the source and channel areas. The operation mechanism was thoroughly investigated in comparison with a typical tunneling field-effect transistor (TFET). The noise reduction was analyzed based on BC shape, and electric field. It was also quantitatively compared with conventional SF (CSF) and BCSF. Then, the A v is subdivided into several conductances and analyzed by comparing the weights assigned to each element to provide a detailed and substantiated explanation. Device structure and Mechanism Figure 1 depicts our proposed TSF. It has an N-P-N-N configuration, unlike typical P-I-N TFET. Also, there is a 50 nm oxide gap between the gate and ground contact to avoid interconnections interference 11 . Device parameters were appropriately adjusted to ensure reasonable comparison with CSF and BCSF under the set operating range and bias conditions. The detailed design parameters are listed in Table 1. When TSF operates as SF, high and linear gain can be achieved. These properties are obtained in devices based on tunneling mechanisms due to reduced channel length modulation and body effects 14 . However, the typical TFET requires sufficient gate-source voltage ( V GS ), which lowers the output voltage of the SF. The energy band diagram of TFET and TSF are represented in Fig. 2. For a TFET with the source voltage = 0 V (black line), carriers in the valence band of the source area are directly transferred to the conduction band of the channel area by band-to-band tunneling (BTBT), resulting in tunneling current. On the other hand, when the source potential follows the gate voltage ( V G ) (green line), the tunneling width becomes wider and the BTBT rarely occurs. If a constant current source is set, sufficient current can be obtained to operate as SF, but the output voltage ( V S ) decreases. A lower V S requires a higher supply voltage or more signal amplification that increases noise. This problem can be solved by applying the grounded area. Even under the same operating conditions, applying a grounded area forms an abrupt energy band between the grounded area and the channel area (blue line), which generates enough tunneling current to operate as SF. Figure 3 shows the SF behavior of TSF at V G = 1.6 V, 2.0 V, 2.4 V. The shaded area represents the tunneling probability, which depends on the electric field and tunneling distance at the tunneling junction. This should be the same throughout the operating range for ensuring constant current. TSF satisfies this condition because the source potential increases at the same rate as the V G increases. That is, the V S follows the V G linearly. As a result, TSF provides superior SF operation in terms of linearity and improved output voltage compared to TFET. The n-channel is adopted for noise reduction. This reduces the interface trap noise by depleting the subsurface area. Despite the BTBT generates close to the surface, this study indicates that n-channel can be effectively used in conjunction with tunneling mechanism. Furthermore, the n-channel makes BCSF junctionless and causes a negative threshold voltage, whereas in TSF, the grounded area suppresses the thermionic emission and maintains the operating range. The technology computer aided design (TCAD) simulations were performed using a dynamic nonlocal BTBT model. Here, G ( F ) is the BTBT generation rate, which can be extracted by Kane’s model 15 : where F is the electric field and the tunable parameter P is 2.5 for indirect BTBT 16,17 . The Kane’s parameters A and B were calibrated using the fabricated planar TFET, and set to 4´10 14 cm -3 s -1 and 3´10 6 Vcm -1 , respectively. The measured and simulated data in Fig. 4 show good agreement indicating that the model was well calibrated for the fabricated TFET and BCSF 8,18 . Also, referring to Ref. 19,20 , a trap model considering the interface trap is applied for 1/ f noise analysis. Based on the calibrated TCAD, the electrical and 1/ f noise characteristics were analyzed under the following conditions: the bias current ( I D ) is 0.1 μA, the drain voltage ( V D ) is 3.0 V, and the operating range for V G is 1.6-2.6 V 21 . Results and Discussion Noise Characteristics. Figure 5a represents the electron current density and the electric field of TSF as a function of V G at 1.6 V, 2.0 V, and 2.4 V. This shows that the TSF is operating in depletion mode and forming a BC throughout the operating range. However, TSF forms L-shaped BC that is different from BCSF in that BTBT occurs at the surface closest to the gate. In the BTBT generation region, despite the current path being close to the surface, the high electric field rapidly accelerates electrons and allows them to be transmitted with less influence of traps. This effect could be confirmed by simulating a current noise spectral density ( S I ) over frequency. Within the operating range, the TSF and BCSF form the same BC depth of 20-30 nm, allowing insight into the shape of the BC. Figure 5b plots the S I of CSF, BCSF, and TSF under the condition of V G = 2.0 V. It clearly shows the 1/ f noise characteristic that is inversely proportional to frequency. TSF and BCSF have one order of magnitude lower S I than CSF, which is expected to be the effect of BC 8 . As a result, S I is influenced by the depth of BC regardless of shape. That is, n-channel can be effectively applied and reduces 1/ f noise even in tunneling mechanism-based devices. Electrical Characteristics. According to Fig. 6, the TFET outputs only 60 % of the CSF to ensure sufficient tunneling current. On the other hand, TSF has 90 % of the CSF, which is 1.5 times larger than TFET. The A v is derived from differentiating the V S with the V G (line data). Tunneling devices achieve high A v (~ 1.0 V/V) over the operating range, exceeding that of BCSF (~0.8 V/V) and CSF (~0.9 V/V). Another approach to calculate A v is to use Eq. (2): where R S is the source resistance, g m is the transconductance, g mb is the body effect transconductance, and g ds is the output conductance. R S is approximated to infinity by using a constant current source. The calculated A v with Eq. (2) (symbol data) has good agreement with the A v obtained by differentiation. To analyze the high A v of tunneling devices, g ds , g mb , and g m are compared in detail. First, tunneling devices have very low g ds . This is because short-channel effects are suppressed and gate controllability is high. Tunneling devices typically have a drain induced barrier thinning that is generally lower than a drain induced barrier lowering (DIBL) of the thermionic device 22 . Conversely, BCSF has higher DIBL than CSF as BC reduces gate controllability, resulting in higher g ds 23 . Although the TSF also forms a BC, it is attached to the surface where gate control occurs for BTBT generation. This L-shaped BC enables TSF to maintain the low g ds of the tunneling device. Second, the g mb of the tunneling device converges to 0. g mb is mainly caused by the body effect, where the depletion layer changes. However, tunneling device has p-type region that suppresses the depletion layer. Therefore, there is no body effect, leading to the low and linear g mb 13 . Third, both tunneling devices have g m of 20 % compared to the CSF. This is because the tunneling mechanism is more difficult to generate current changes than thermionic emission 22,24 . However, ( g ds + g mb ) / g m is the lowest due to g ds and g mb being low enough to compensate for the low g m . Interestingly, TSF has similar g m to TFET. As in the case of BCSF and CSF, the g m of TSF could be expected to decrease significantly due to BC 7,8 , but this is not the case. The reason comes from L-shaped BC and grounded area. As mentioned in g ds , the L-shaped BC of TSF does not reduce gate controllability. Therefore, unlike the case of BCSF and CSF, TSF has a g m similar to TFET. The g m of TSF is slightly higher than that of TFET, because the grounded area amplifies the tunneling current by reducing the tunneling width. As a result, tunneling devices have a high and linear A v , and in particular, TSF can output a 1.5 times higher voltage than TFET. Conclusion We have designed and simulated the TSF for CIS. First, TSF with n-channel forms the BC, and achieves the S I that is 10 times lower than CSF. Although BTBT generates current from the surface, the high electric field can accelerate electrons, mitigating the effects of traps. Next, TSF achieves a higher A v , close to 1 V/V, compared to BCSF (~0.8 V/V) and CSF (~0.9 V/V). The reduced body effect and channel length modulation contribute to high A v . This is caused by the p-doped region and the BTBT generation region far from the drain. Furthermore, the grounded area compensates for insufficient tunneling current by narrowing the tunneling width to maintain low V GS (= 0.4 V). In other words, TSF outputs 1.5 times larger voltage than TFET. Consequently, TSF can be a potential alternative to SF in CIS that simultaneously achieves excellent 1/ f noise characteristic, A v , and V S simultaneously. Declarations Data availability The data that support the findings of this study are available from the corresponding authors upon reasonable request. Acknowledgements This research was supported by the Samsung Co., Ltd (IO230303-05245-01), in part by the MSIT (Ministry of Science and ICT), Korea, under the ICAN (ICT Challenge and Advanced Network of HRD) program (IITP-2023-2020-0-01822) supervised by the IITP (Institute of Information & Communications Technology Planning & Evaluation). The EDA tool was supported by the IC Design Education Center (IDEC), South Korea. Author contributions K. Y. Kim and H. Kim presented the conceptualization and methodology for the idea and wrote the manuscript with assistance from J.-K. Lee and C.-K. Baek. M. Choi and Y. Kim conceived the noise characterizations with assistance from Y. Sol and S. Park. K. Y. Kim, H. Yoo and K. Oh conducted simulations and analyzed the results. Competing interests The authors declare no competing interests. References El Gamal, A. & Eltoukhy, H. CMOS image sensors. IEEE Circuits and Devices Magazine 21 , 6–20 (2005). Fossum, E. R. CMOS image sensors: Electronic camera-on-a-chip. IEEE Trans Electron Devices 44 , 1689–1698 (1997). Bigas, M., Cabruja, E., Forest, J. & Salvi, J. Review of CMOS image sensors. Microelectronics J 37 , 433–451 (2006). Park, S. et al. A 64Mpixel CMOS Image Sensor with 0.56 μm Unit Pixels Separated by Front Deep-Trench Isolation. in 2022 IEEE International Solid-State Circuits Conference (ISSCC) vol. 65 1–3 (IEEE, 2022). Enz, C. C. & Temes, G. C. Circuit techniques for reducing the effects of op-amp imperfections: autozeroing, correlated double sampling, and chopper stabilization. Proceedings of the IEEE 84 , 1584–1614 (1996). Findlater, K. M. et al. 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Transient Analysis of Tunnel Field-Effect Transistor with Raised Drain. J Nanosci Nanotechnol 19 , 6212–6216 (2019). Esqueda, I. S. & Barnaby, H. J. Modeling the non-uniform distribution of radiation-induced interface traps. IEEE Trans Nucl Sci 59 , 723–727 (2012). Esqueda, I. S., Barnaby, H. J. & King, M. P. Compact modeling of total ionizing dose and aging effects in MOS technologies. IEEE Trans Nucl Sci 62 , 1501–1515 (2015). Sakakibara, M. et al. A 6.9- μ m Pixel-Pitch Back-Illuminated Global Shutter CMOS Image Sensor With Pixel-Parallel 14-Bit Subthreshold ADC. IEEE J Solid-State Circuits 53 , 3017–3025 (2018). Trivedi, A. R., Carlo, S. & Mukhopadhyay, S. Exploring tunnel-FET for ultra low power analog applications: A case study on operational transconductance amplifier. in Proceedings of the 50th annual design automation conference 1–6 (2013). Enda, T. & Shigyo, N. Alleviation of subthreshold swing and short‐channel effect in buried‐channel MOSFETs: The counter‐doped surface‐channel MOSFET structure. Electronics and Communications in Japan (Part II: Electronics) 79 , 43–50 (1996). Lu, H. & Seabaugh, A. Tunnel field-effect transistors: State-of-the-art. IEEE Journal of the Electron Devices Society 2 , 44–49 (2014). Table Table 1 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Table1.tif Table 1. Default values of CSF, BCSF, and TSF parameters. Cite Share Download PDF Status: Published Journal Publication published 09 Oct, 2024 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 14 May, 2024 Reviews received at journal 30 Apr, 2024 Reviews received at journal 25 Apr, 2024 Reviewers agreed at journal 16 Apr, 2024 Reviewers agreed at journal 16 Apr, 2024 Reviewers invited by journal 16 Apr, 2024 Editor assigned by journal 08 Apr, 2024 Editor invited by journal 03 Apr, 2024 Submission checks completed at journal 03 Apr, 2024 First submitted to journal 27 Mar, 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-4175618","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":288217716,"identity":"eecd5b07-d247-48c1-9c00-4052735ff3db","order_by":0,"name":"Ki Yeong Kim","email":"","orcid":"","institution":"Pohang University of Science and Technology (POSTECH)","correspondingAuthor":false,"prefix":"","firstName":"Ki","middleName":"Yeong","lastName":"Kim","suffix":""},{"id":288217717,"identity":"1c00ad8d-c4a0-49de-a37c-fd442928bb95","order_by":1,"name":"Hyangwoo 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1","display":"","copyAsset":false,"role":"figure","size":218503,"visible":true,"origin":"","legend":"\u003cp\u003eThe schematic and parameters of the TSF.\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4175618/v1/086f34c89c8eab0857001b92.jpg"},{"id":54322340,"identity":"224066b0-3ac4-4e0b-a305-b0720df8f322","added_by":"auto","created_at":"2024-04-08 19:49:14","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":384777,"visible":true,"origin":"","legend":"\u003cp\u003eThe energy band diagram of TFET and TSF. The grounded area in the TSF keeps the potential low, allowing sufficient tunneling even at low \u003cem\u003eV\u003c/em\u003e\u003csub\u003eGS\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4175618/v1/18f6e1999678e4a950ea9e89.jpg"},{"id":54323110,"identity":"54268d8c-d5ff-4e60-aefe-2825911566d3","added_by":"auto","created_at":"2024-04-08 19:57:14","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":407091,"visible":true,"origin":"","legend":"\u003cp\u003eThe energy band diagrams of TSF according to the \u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e and shaded areas represent tunneling probability.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4175618/v1/f3ff3d437ca8e5a1ff97cd49.jpg"},{"id":54322344,"identity":"ec873e5d-773e-404e-a7e0-adf66e5d4787","added_by":"auto","created_at":"2024-04-08 19:49:15","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":478707,"visible":true,"origin":"","legend":"\u003cp\u003eThe electrical characteristics of (a) BCSF and (b) TFET were simulated and calibrated with experimental data from the fabricated device.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4175618/v1/2a71ec356322a73483993bd3.jpg"},{"id":54322345,"identity":"473bc4e7-5c7f-47f2-b964-4e4f64d223a1","added_by":"auto","created_at":"2024-04-08 19:49:15","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":550820,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The electron current density and electric field at \u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e = 1.6 V, 2.0 V, and 2.4 V. (b) The 1/\u003cem\u003ef\u003c/em\u003e noise characteristics comparison.\u003c/p\u003e","description":"","filename":"Figure5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4175618/v1/f3aedeb78182d728f35765c7.jpg"},{"id":54323112,"identity":"2344f7b3-a2b8-4c79-9ac8-97da866d61e8","added_by":"auto","created_at":"2024-04-08 19:57:15","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":513696,"visible":true,"origin":"","legend":"\u003cp\u003eSF characteristics are compared within the operation range. The comparison includes \u003cem\u003eV\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e, \u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003ev\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e, \u003cem\u003eg\u003c/em\u003e\u003csub\u003emb\u003c/sub\u003e, \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e, and (\u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e+\u003cem\u003eg\u003c/em\u003e\u003csub\u003emb\u003c/sub\u003e)/\u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e curves among TSF, TFET, BCSF, and CSF.\u003c/p\u003e","description":"","filename":"Figure6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4175618/v1/844721089213d1a6039ba32c.jpg"},{"id":66597494,"identity":"3811864c-7255-4ac5-acf6-da3fd7a230e2","added_by":"auto","created_at":"2024-10-14 16:10:52","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2961387,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4175618/v1/baabd742-8c47-46dd-89ed-145330648303.pdf"},{"id":54323111,"identity":"691e109a-20a4-419e-bce1-c06f759aeee6","added_by":"auto","created_at":"2024-04-08 19:57:14","extension":"tif","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":189858,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTable 1.\u003c/strong\u003e Default values of CSF, BCSF, and TSF parameters.\u003c/p\u003e","description":"","filename":"Table1.tif","url":"https://assets-eu.researchsquare.com/files/rs-4175618/v1/6842757e4dff16b57beebb74.tif"}],"financialInterests":"No competing interests reported.","formattedTitle":"New Tunneling Source Follower with Low 1/f Noise and High Voltage Gain","fulltext":[{"header":"Introduction","content":"\u003cp\u003eA CMOS Image Sensors (CIS) is a sensor that measures the amount of light using a transistor. It has dominated industrial vision applications with their excellent performance in mass production, power efficiency and parallel data transmission\u003csup\u003e1\u0026ndash;3\u003c/sup\u003e. In order to obtain a clear image, it is important to control in-pixel noise by ensuring a distinct separation between the signal and noise. However, research on CIS has focused on downsizing for high resolution, and recently, the pixel pitch has reached the level of 0.56 \u0026mu;m\u003csup\u003e4\u003c/sup\u003e. As the sensing area decreases, the light signal also becomes smaller, leading to problems with dynamic range (DR) and pixel dark noise generated by amplifying small signals. Low signal is especially problematic in low illumination. This is because read noise is constant regardless of the input photons, which is fatal to signal-to-ratio (SNR). Therefore, the need for research to reduce read noise has emerged. Read noise consists of reset noise, thermal noise, 1/\u003cem\u003ef\u003c/em\u003e noise, etc\u003csup\u003e5,6\u003c/sup\u003e. The reset noise is mostly removed using correlated double sampling (CDS) technology, which takes the difference between the sampled signal and reset level as the signal value. Thermal noise is relatively small compared to other noises at the low frequencies where SF operates. As a result, 1/\u003cem\u003ef\u003c/em\u003e noise became the main source of read noise \u003csup\u003e5,6\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe\u0026nbsp;1/\u003cem\u003ef\u003c/em\u003e noise stands for the output fluctuations that occurs when electrons repeat trapping and detrapping on the dangling bond at the silicon/gate-oxide interface of source follower (SF).\u0026nbsp;A common way to reduce 1/\u003cem\u003ef\u003c/em\u003e noise is to move the current flow away from the interface traps. This is said to form buried channel (BC), and research has been conducted to apply it to NMOS, FinFET, multi-gate structure, and junction FET\u003csup\u003e7\u0026ndash;12\u003c/sup\u003e. In the NMOS, the channel\u0026nbsp;area\u0026nbsp;is doped n-type to form BC, which is called\u0026nbsp;buried\u0026nbsp;channel SF (BCSF)\u003csup\u003e7\u0026ndash;9\u003c/sup\u003e. The BC effect can be amplified by using fin sidewalls as potential barriers in FinFET structure\u003csup\u003e10\u003c/sup\u003e. Furthermore, BCSFs with multi-gate can be designed to achieve low 1/\u003cem\u003ef\u003c/em\u003e noise while maintaining small gate areas\u003csup\u003e11\u003c/sup\u003e. These structures generally have a trade-off that gate control becomes more difficult as the current path moves away from the surface.\u0026nbsp;This reduces transconductance (\u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e), leading to a reduction in voltage gain (\u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e). Consequently, these structures have decreased fixed pattern noise and output voltage\u003csup\u003e7,8,13\u003c/sup\u003e. Alternatively, BC can be applied to the junction FET structure\u003csup\u003e12\u003c/sup\u003e. The buried channel junction FET uses a floating diffusion node as the gate. Since the gate is located underneath the channel, the interface traps have less impact on the conduction carriers, resulting in lower 1/\u003cem\u003ef\u003c/em\u003e noise.\u0026nbsp; However, \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e is low because holes with lower mobility are used as carriers.\u003c/p\u003e\n\u003cp\u003eIn this study, we have proposed a tunneling source follower (TSF) that achieves improved SF characteristics of both \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e and 1/\u003cem\u003ef\u003c/em\u003e noise without degrading the output voltage. It is particularly characterized by tunneling mechanism and BC. \u0026nbsp;Additionally, the output voltage is improved by adding a grounded area between the source and channel areas. The operation mechanism was thoroughly investigated in comparison with a typical tunneling field-effect transistor (TFET). The noise reduction was analyzed based on BC shape, and electric field. It was also quantitatively compared with conventional SF (CSF) and BCSF. Then, the \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e is subdivided into several conductances and analyzed by comparing the weights assigned to each element to provide a detailed and substantiated explanation.\u003c/p\u003e"},{"header":"Device structure and Mechanism","content":"\u003cp\u003eFigure 1 depicts our proposed TSF. It has an N-P-N-N configuration, unlike typical P-I-N TFET. Also, there is a 50 nm oxide gap between the gate and ground contact to avoid interconnections interference\u003csup\u003e11\u003c/sup\u003e.\u0026nbsp;Device parameters were appropriately adjusted to ensure reasonable comparison with CSF and BCSF under the set operating range and bias conditions.\u0026nbsp;The\u0026nbsp;detailed\u0026nbsp;design parameters are listed in Table 1.\u003c/p\u003e\n\u003cp\u003eWhen TSF operates as SF, high and linear gain can be achieved. These properties are obtained in devices based on tunneling mechanisms due to reduced channel length modulation and body effects\u003csup\u003e14\u003c/sup\u003e. However, the typical TFET requires sufficient gate-source voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003eGS\u003c/sub\u003e), which lowers the output voltage of the SF. The energy band diagram of TFET and TSF are represented in Fig. 2. For a TFET with the source voltage = 0 V (black line), carriers in the valence band of the source area are directly transferred to the conduction band of the channel area by band-to-band tunneling (BTBT), resulting in tunneling current. On the other hand, when the source potential follows the gate voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e) (green line), the tunneling width becomes wider and the BTBT rarely occurs. If a constant current source is set, sufficient current can be obtained to operate as SF, but the output voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e) decreases. A lower \u003cem\u003eV\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e requires a higher supply voltage or more signal amplification that increases noise. This problem can be solved by applying the grounded area. Even under the same operating conditions, applying a grounded area forms an abrupt energy band between the grounded area and the channel area (blue line), which generates enough tunneling current to operate as SF.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 3 shows the SF behavior of TSF at \u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e = 1.6 V, 2.0 V, 2.4 V. The shaded area represents the tunneling probability, which depends on the electric field and tunneling distance at the tunneling junction. This should be the same throughout the operating range for ensuring constant current. TSF satisfies this condition because the source potential increases at the same rate as the \u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e increases. That is, the \u003cem\u003eV\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e follows the \u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e linearly. As a result, TSF provides superior SF operation in terms of linearity and improved output voltage compared to TFET.\u003c/p\u003e\n\u003cp\u003eThe n-channel is adopted for noise reduction. This reduces the interface trap noise by depleting the subsurface area. Despite the BTBT generates close to the surface, this study indicates that n-channel can be effectively used in conjunction with tunneling mechanism. Furthermore, the n-channel makes BCSF junctionless and causes a negative threshold voltage, whereas in TSF, the grounded area suppresses the thermionic emission and maintains the operating range.\u003c/p\u003e\n\u003cp\u003eThe technology computer aided design (TCAD) simulations were performed using a dynamic nonlocal BTBT model. Here, \u003cem\u003eG\u003c/em\u003e(\u003cem\u003eF\u003c/em\u003e) is the BTBT generation rate, which can be extracted by Kane\u0026rsquo;s model\u003csup\u003e15\u003c/sup\u003e:\u003c/p\u003e\n\u003cp\u003e\u003cimg 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oBtOnz5tbd3SNr0WOwAIrdP8o2s5R5q0ocepZ0jhVE9RO0W9SeptK1rRUpb+GtFzq5dn0FSJQTeoV0//fvYvOcVBE1zLGOTYAUDMouxZQ3Xr1q2z9sCBA9a28vXXX1t77bXXWiuqjafetk73v9yzZ49NcL/99tvTM4OjSgxCU2+eevU0987/klNPmeJadsePQY4dAMSMZK1PaDWghjW98GsrWv0oa9asmd7PVMOAnQ6LqligEgZV++/H4eZ2qsQgNN+IXgm3x3TJkiU2rFlmWHTQYwcAMSNZ6yM7duywm/Phw4fTM/l0U1YPylSmtIPmW3WyAlR8H81We532u7IxCM3n3qlEh8fUS3mU2buU2AFAvEjW+ohuyurZUcJQxLfTaJ5Ert4ULz/hNIymLcLUSzM0NGRbZBVRT5L20dy0aVPf7XVaRZkYdINvRL9s2TJrRaU8lIS3Q+wAIG4ka31GSYKGwrJ7X2Z50dYVK1ZY6w4dOpSsXr06/ezfG7gec++991ovjVa1bN26tTBh27t3r7X0zLSPQTdoI3r1lmbnHCpxPHHiRPpZMWIHAHEjWeszXthPCUPevCnvgWkuhttMw2IazvNifprLpF6aN9980z7P8p4ZVWmmZ6Z9DELz3tK8YrjtEDsAiB/JWh/avHmz9bIMDw+nZy44fvy4tUooWtm/f/9FCw7Uy6Yeo2aPPPKIJQr9tjNEJ1rFILTx8XFr68w5JHYAED+StT6k+Wcqw6AVntmhOBXrU2+ZaPVfXdmtODQsqgRu37596RlIUQxCU8/Yzp077eOqW10ROwDoDSRrfUpzl1SBWZvTytjYWLJx40b7WFSPq+4Q3ezZs63V92tYVfPdKPdwseYYdMOqVaumezuVGJatuE3sAKB3zJrS7HGgiZIA3dCzE9TVE6NFBrxlAACYOfSsIZcmmzfvc6memDKlIAAAQDgka8j1wAMPWPvMM89YqxWHKg/x7LPP2ucAAGBmkKwhl1aLqgK+tqZSUdy1a9cmo6Oj/6nFBgAAuo85awAAABGjZw0AACBiJGsAAAARI1kDAACIGMkaAABAxEjWAAAAIkayBgAAEDGSNQAAgIiRrAEAAESMZA0AACBiJGsAAADRSpL/A4CXJhZtD3ZCAAAAAElFTkSuQmCC\" style=\"width: 478px; height: 61.0048px;\" width=\"478\" height=\"61.0048\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003eF\u003c/em\u003e is the electric field and the tunable parameter \u003cem\u003eP\u003c/em\u003e is 2.5 for indirect BTBT\u003csup\u003e16,17\u003c/sup\u003e. The Kane\u0026rsquo;s parameters \u003cem\u003eA\u003c/em\u003e and \u003cem\u003eB\u003c/em\u003e were calibrated using the fabricated planar TFET, and set to 4\u0026acute;10\u003csup\u003e14\u003c/sup\u003e cm\u003csup\u003e-3\u003c/sup\u003es\u003csup\u003e-1\u003c/sup\u003e and 3\u0026acute;10\u003csup\u003e6\u003c/sup\u003e Vcm\u003csup\u003e-1\u003c/sup\u003e, respectively. The measured and simulated data in Fig. 4 show good agreement indicating that the model was well calibrated for the fabricated TFET and BCSF\u003csup\u003e8,18\u003c/sup\u003e. Also, referring to Ref.\u003csup\u003e19,20\u003c/sup\u003e, a trap model\u0026nbsp;considering the interface trap is applied for 1/\u003cem\u003ef\u003c/em\u003e noise analysis. Based on the calibrated TCAD, the electrical and 1/\u003cem\u003ef\u003c/em\u003e noise characteristics were analyzed under the following conditions: the bias current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003eD\u003c/sub\u003e) is 0.1 \u0026mu;A, the drain voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003eD\u003c/sub\u003e) is 3.0 V, and the operating range for \u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e is 1.6-2.6 V\u003csup\u003e21\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003eNoise Characteristics.\u003c/strong\u003e Figure 5a represents the electron current density and the electric field of TSF as a function of \u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e at 1.6 V, 2.0 V, and 2.4 V. This shows that the TSF is operating in depletion mode and forming a BC throughout the operating range. However, TSF forms L-shaped BC that is different from BCSF in that BTBT occurs at the surface closest to the gate. In the BTBT generation region, despite the current path being close to the surface, the high electric field rapidly accelerates electrons and allows them to be transmitted with less influence of traps. This effect could be confirmed by simulating a current noise spectral density (\u003cem\u003eS\u003csub\u003eI\u003c/sub\u003e\u003c/em\u003e) over frequency. Within the operating range, the TSF and BCSF form the same BC depth of 20-30 nm, allowing insight into the shape of the BC. Figure 5b plots the \u003cem\u003eS\u003csub\u003eI\u003c/sub\u003e\u003c/em\u003e of CSF, BCSF, and TSF under the condition of \u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e = 2.0 V. It clearly shows the 1/\u003cem\u003ef\u003c/em\u003e noise characteristic that is inversely proportional to frequency. TSF and BCSF have one order of magnitude lower\u003cem\u003e\u0026nbsp;S\u003csub\u003eI\u003c/sub\u003e\u003c/em\u003e than CSF, which is expected to be the effect of BC\u003csup\u003e8\u003c/sup\u003e. As a result, \u003cem\u003eS\u003csub\u003eI\u003c/sub\u003e\u003c/em\u003e is influenced by the depth of BC regardless of shape. That is, n-channel can be effectively applied and reduces 1/\u003cem\u003ef\u003c/em\u003e noise even in tunneling mechanism-based devices.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eElectrical Characteristics.\u003c/strong\u003e According to Fig. 6, the TFET outputs only 60 % of the CSF to ensure sufficient tunneling current. On the other hand, TSF has 90 % of the CSF, which is 1.5 times larger than TFET. The \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e is derived from differentiating the \u003cem\u003eV\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e with the \u003cem\u003eV\u003c/em\u003e\u003csub\u003eG\u003c/sub\u003e (line data). Tunneling devices achieve high \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e (~ 1.0 V/V) over the operating range, exceeding that of BCSF (~0.8 V/V) and CSF (~0.9 V/V). Another approach to calculate \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e is to use Eq. (2):\u003c/p\u003e\n\u003cp\u003e\u003cimg 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\" style=\"width: 638px; height: 91.0202px;\" width=\"638\" height=\"91.0202\"\u003e\u003c/p\u003e\n\u003cp\u003ewhere \u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e is the source resistance, \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e is the transconductance, \u003cem\u003eg\u003c/em\u003e\u003csub\u003emb\u003c/sub\u003e is the body effect transconductance, and \u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e is the output conductance. \u003cem\u003eR\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e is approximated to infinity by using a constant current source. The calculated \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e with Eq. (2) (symbol data) has good agreement with the \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e obtained by differentiation. To analyze the high \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e of tunneling devices, \u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e, \u003cem\u003eg\u003c/em\u003e\u003csub\u003emb\u003c/sub\u003e, and \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e are compared in detail. First, tunneling devices have very low \u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e. This is because short-channel effects are suppressed and gate controllability is high. Tunneling devices typically have a drain induced barrier thinning that is generally lower than a drain induced barrier lowering (DIBL) of the thermionic device\u003csup\u003e22\u003c/sup\u003e. Conversely, BCSF has higher DIBL than CSF as BC reduces gate controllability, resulting in higher \u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e\u003csup\u003e23\u003c/sup\u003e. Although the TSF also forms a BC, it is attached to the surface where gate control occurs for BTBT generation. This L-shaped BC enables TSF to maintain the low \u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e of the tunneling device. Second, the \u003cem\u003eg\u003c/em\u003e\u003csub\u003emb\u003c/sub\u003e of the tunneling device converges to 0. \u003cem\u003eg\u003c/em\u003e\u003csub\u003emb\u003c/sub\u003e is mainly caused by the body effect, where the depletion layer changes. However, tunneling device has p-type region that suppresses the depletion layer. Therefore, there is no body effect, leading to the low and linear \u003cem\u003eg\u003c/em\u003e\u003csub\u003emb\u003c/sub\u003e\u003csup\u003e13\u003c/sup\u003e. Third, both tunneling devices have \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e of 20 % compared to the CSF. This is because the tunneling mechanism is more difficult to generate current changes than thermionic emission\u003csup\u003e22,24\u003c/sup\u003e. However, (\u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e + \u003cem\u003eg\u003c/em\u003e\u003csub\u003emb\u003c/sub\u003e) / \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e is the lowest due to \u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e and \u003cem\u003eg\u003c/em\u003e\u003csub\u003emb\u003c/sub\u003e being low enough to compensate for the low \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e. Interestingly, TSF has similar \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e to TFET. As in the case of BCSF and CSF, the \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e of TSF could be expected to decrease significantly due to BC\u003csup\u003e7,8\u003c/sup\u003e, but this is not the case. The reason comes from L-shaped BC and grounded area. As mentioned in \u003cem\u003eg\u003c/em\u003e\u003csub\u003eds\u003c/sub\u003e, the L-shaped BC of TSF does not reduce gate controllability. Therefore, unlike the case of BCSF and CSF, TSF has a \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e similar to TFET. The \u003cem\u003eg\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e of TSF is slightly higher than that of TFET,\u0026nbsp;because the grounded area amplifies the tunneling current by reducing the tunneling width. As a result, tunneling devices have a high and linear \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e, and in particular, TSF can output a 1.5 times higher voltage than TFET.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eWe have designed and simulated the TSF for CIS. First, TSF with n-channel forms the BC, and achieves the \u003cem\u003eS\u003csub\u003eI\u003c/sub\u003e\u003c/em\u003e that is 10 times lower than CSF. Although BTBT generates current from the surface, the high electric field can accelerate electrons, mitigating the effects of traps. Next, TSF achieves a higher \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e, close to 1 V/V, compared to BCSF (~0.8 V/V) and CSF (~0.9 V/V). The reduced body effect and channel length modulation contribute to high \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e. This is caused by the p-doped region and the BTBT generation region far from the drain. Furthermore, the grounded area compensates for insufficient tunneling current by narrowing the tunneling width to maintain low \u003cem\u003eV\u003c/em\u003e\u003csub\u003eGS\u003c/sub\u003e (= 0.4 V). In other words, TSF outputs 1.5 times larger voltage than TFET. Consequently, TSF can be a potential alternative to SF in CIS that simultaneously achieves excellent 1/\u003cem\u003ef\u003c/em\u003e noise characteristic, \u003cem\u003eA\u003csub\u003ev\u003c/sub\u003e\u003c/em\u003e, and\u0026nbsp;\u003cem\u003eV\u003c/em\u003e\u003csub\u003eS\u003c/sub\u003e simultaneously.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding authors upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Samsung Co., Ltd (IO230303-05245-01), in part by the MSIT (Ministry of Science and ICT), Korea, under the ICAN (ICT Challenge and Advanced Network of HRD) program (IITP-2023-2020-0-01822) supervised by the IITP (Institute of Information \u0026amp; Communications Technology Planning \u0026amp; Evaluation).\u0026nbsp;The EDA tool was supported by the IC Design Education Center (IDEC), South Korea.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eK.\u0026nbsp;Y.\u0026nbsp;Kim and H. Kim presented the conceptualization and methodology for the idea\u0026nbsp;and wrote the manuscript with assistance from\u0026nbsp;J.-K.\u0026nbsp;Lee\u0026nbsp;and\u0026nbsp;C.-K. Baek. M. Choi and Y. Kim conceived the noise characterizations\u0026nbsp;with\u0026nbsp;assistance\u0026nbsp;from\u0026nbsp;Y. Sol and S. Park.\u0026nbsp;K.\u0026nbsp;Y. Kim,\u0026nbsp;H.\u0026nbsp;Yoo\u0026nbsp;and\u0026nbsp;K.\u0026nbsp;Oh\u0026nbsp;conducted simulations\u0026nbsp;and\u0026nbsp;analyzed the results.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eEl Gamal, A. \u0026amp; Eltoukhy, H. CMOS image sensors. \u003cem\u003eIEEE Circuits and Devices Magazine\u003c/em\u003e \u003cstrong\u003e21\u003c/strong\u003e, 6\u0026ndash;20 (2005).\u003c/li\u003e\n\u003cli\u003eFossum, E. R. 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Tunnel field-effect transistors: State-of-the-art. \u003cem\u003eIEEE Journal of the Electron Devices Society\u003c/em\u003e \u003cstrong\u003e2\u003c/strong\u003e, 44\u0026ndash;49 (2014).\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Table","content":"\u003cp\u003eTable 1 is available in the Supplementary Files section.\u003c/p\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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4175618/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4175618/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"We have designed a tunneling source follower (TSF) for image sensors that achieves high voltage gain (Av) and low 1/f noise simultaneously. The TSF is composed of N-P-N-N, especially the p-doped grounded area, which serves to amplify the insufficient tunneling current, allowing the source follower (SF) to utilize band-to-band tunneling (BTBT). Compared to thermionic emission, tunneling based structures contribute to increasing Av through lower channel length modulation and lower body effect. As a result, TSF achieves a higher Av (~1.0 V/V) than conventional SF (~0.9 V/V). Moreover, the n-doped channel makes the buried conductive channel farther from the interface, lowering the noise. The current noise spectral density (SI) is approximately 10 times lower in TSF than that of in conventional SF. Therefore, our TSF can be a possible candidate for High Av and low 1/f noise image sensors.","manuscriptTitle":"New Tunneling Source Follower with Low 1/f Noise and High Voltage Gain","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-04-08 19:49:09","doi":"10.21203/rs.3.rs-4175618/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-05-14T07:09:55+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-04-30T14:49:46+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-04-25T09:09:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"b3c5cbc7-6fbe-45f1-a560-793cbb74c8a1","date":"2024-04-16T12:51:03+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"366ee61b-465d-408a-ab5d-4ada51db32d5","date":"2024-04-16T11:53:43+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-04-16T11:38:42+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-08T07:44:53+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-04-03T12:07:00+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-04-03T12:04:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-03-27T11:15:11+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"48382857-31c8-468e-bdfe-bb61cb3cd4f6","owner":[],"postedDate":"April 8th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":30346212,"name":"Physical sciences/Engineering/Electrical and electronic engineering"},{"id":30346213,"name":"Physical sciences/Nanoscience and technology/Nanoscale devices/Electronic devices"}],"tags":[],"updatedAt":"2024-10-14T16:06:36+00:00","versionOfRecord":{"articleIdentity":"rs-4175618","link":"https://doi.org/10.1038/s41598-024-73501-w","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2024-10-09 15:58:02","publishedOnDateReadable":"October 9th, 2024"},"versionCreatedAt":"2024-04-08 19:49:09","video":"","vorDoi":"10.1038/s41598-024-73501-w","vorDoiUrl":"https://doi.org/10.1038/s41598-024-73501-w","workflowStages":[]},"version":"v1","identity":"rs-4175618","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4175618","identity":"rs-4175618","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}