Record-breaking conversion efficiency in a THz nonlinear diode chain using an asymmetric double-layer topology

Record-breaking conversion efficiency in a THz nonlinear diode chain using an asymmetric double-layer topology | 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 Record-breaking conversion efficiency in a THz nonlinear diode chain using an asymmetric double-layer topology yaxin zhang, Hongji Zhou, Hailong Guo, Shixiong Liang, Jun Zhou, and 8 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4467708/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 16 Oct, 2025 Read the published version in Nature Electronics → Version 1 posted You are reading this latest preprint version Abstract The exploitation of radiation in the terahertz (THz) range hinges on the continued development of THz sources. Schottky barrier diode (SBD)--based frequency multiplier devices are one of the most attractive options, as they can produce high power in comparison to direct generation, and can be integrated into all-solid-state systems. Yet, the scaling of the output power of such devices is often limited by the power handling capacity of a single diode. This motivates the idea of forming a connected chain of SBD devices, accompanied by a power combining approach to achieve higher THz output power. While effective, the uneven field distribution among the diodes can pose a significant challenge as it leads to lower efficiency and premature breakdown. This phenomenon is rooted in the similarity between the THz wavelength and the physical dimensions of the diodes themselves. To address this issue, we propose an innovative solution based on an asymmetric double-layer C-type diode chain structure. This arrangement allows for the adjustment of local electromagnetic field distribution, and dramatically enhances the conversion efficiency of the diode chain. Our device achieves the highest frequency doubling efficiency recorded at 38%, with an output exceeding 300 mW at 170 GHz. This design paves the way for a new direction in the development of diode-based THz nonlinear devices. Physical sciences/Engineering/Electrical and electronic engineering Physical sciences/Physics/Optical physics/Terahertz optics Physical sciences/Physics/Techniques and instrumentation/Design, synthesis and processing Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Submillimeter-wave sources have been a key focus of research for many years 1 . The widespread application of such sources can fulfill the requirements of various terahertz (THz) systems 2–4 , including providing local oscillator signals for up- and down-converters in hybrid communication and radar systems, as well as serving as the carrier for directly modulated communication systems 5 . One common approach to the generation of THz signals relies on cascaded nonlinear frequency conversion, starting with a highly stable high-power microwave source as a precursor. This method has advantages over other approaches in factors such as power capacity, energy efficiency, miniaturization, and stability 6–8 . In particular, high-power THz frequency multipliers enable the operation of wireless communication links at distances of several kilometers and speeds of thousands of megabits per second in higher frequency bands 9 . Given the importance of such nonlinear structures, it is important to consider the factors which limit their performance. Previous studies have highlighted that, due to the high THz frequencies and the necessity to maximize the diode cutoff frequency (generally much higher than the actual operating frequency), the size of the diode’s anode column needs to be very small, to minimize capacitive effects 5,10,11 . This results in a corresponding drop in the power handling capacity and an increased susceptibility to breakdown. To address this challenge, one common strategy is to connect multiple Schottky barrier diode (SBD) structures in series. This multi-anode approach 5,7,12–18 together with power combining techniques 7,15,19–23 , has been widely adopted for improved power scaling. Yet, this approach often encounters issues such as chip burn-out or inefficiency during high-power testing. Multiple-anode cascades tend to induce an uneven field distribution, resulting in an imbalanced power distribution on the anodes. As a result, certain diodes may exceed critical power values, making them susceptible to damage. In addition, not all diodes operate at the same optimal power operating point, significantly reducing the overall operating efficiency of the entire system. To address these challenges, researchers have explored a number of options. A series of high-performance frequency doublers and related technologies have emerged to tackle these issues based on the development of multi-anode frequency doubling technology 24–30 . For instance, physical improvements offer a direct approach to increasing conversion efficiency and output power 24,25 . Thin-film diode technology and the use of heterogeneous integrated high-thermal-conductivity substrates (e.g., diamond) are effective solutions. Substrates based on chemical vapor deposition of diamond have achieved output power of 200 mW at 155 GHz and 40 mW at 300 GHz by lowering the junction temperature of the Schottky junction. Techniques such as thinning, skeletonization, or even substrate removal have been employed to minimize dielectric loading and reduce circuit losses. A notable example is the "substrate-less" MMIC topology, which significantly increases output power to the mW range for frequencies above 1 THz 29 . When combined with appropriate power synthesis, these approaches can result in even higher power capacity, although with more complex source architectures 7 , 26 . Despite these achievements, the growth of power capacity, constrained by the number of anodes, gradually approaches saturation. This can be attributed to the fact that the THz wavelength is similar to the size of the diode chain. As a result, the field distribution across the array can be uneven, with some diodes experiencing a larger anode field than others. Consequently, there is a diminished conversion efficiency which ultimately limits the output power. However, this challenge also suggests the exciting possibility that carefully designed microscopic adjustments to the size or arrangement of the SBD array may lead to significant improvements in the electrical properties and performance metrics. In this context, we introduce a novel approach to achieve record-breaking efficiency and output power in a nonlinear THz device. We engineer the microstructure of a multi-anode SBD chain by introducing a nonlinear chain topology and a double-layer near-field coupling effect. This innovative design exhibits a more uniform local electromagnetic distribution, eliminating the constraints of low multiplication efficiency and anode breakdown noted above. The double-layer asymmetric configuration establishes near-field coupling between upper and lower frequency doubling circuits, to further enhance power capacity, output power, and frequency doubling efficiency. As this idea aligns well with the concept of electronic metadevices 31 , we refer to our structure as a meta-asymmetric chip (MAC). Based on these ideas, we have fabricated and tested a 32-anode SBD chain, which can be employed as a THz frequency doubler with a remarkable maximum frequency doubling efficiency of 38% and an impressive output power exceeding 300 mW at 0.17 THz. This work marks the first utilization of artificial microstructures to control the local electromagnetic field distribution in a SBD array, combining the strengths of traditional frequency doubling RF circuit chip integration and the idea of near-field coupling in THz integrated devices 32 . This approach opens up a new direction for the design of THz RF devices. Result and Discussion Structure and Design Fig. 1 shows a schematic of the device. This integrates an artificial microstructure of the multi-anode SBDs, and a double-layer design to promote near-field electromagnetic coupling. Fig. 1a shows the overall device architecture, while Fig. 1b focuses on the two 16-element diode chains, both resembling a C-shaped configuration rather than the conventional linear array. The metal superstructure was fabricated on a thinned (15μm-thick) GaAs substrate using advanced monolithic integration techniques. This array structure comprises 16 diode anode structures, connected at both ends by longitudinally extended center band lines, which are then laterally extended and grounded at the terminals. In contrast to conventional linear frequency multiplier structures, we arrange 12 diode anodes in the xy plane along the x-axis direction (horizontal direction, parallel to the electric field direction), and an additional 4 diode anodes along the y-axis direction (vertical direction, perpendicular to the electric field direction). This structure is then replicated to form a double-layer chip in the z-axis direction, with the two layers placed on the upper and lower surfaces of a split cavity. To ensure that the diodes operate in the nonlinear region, an external feed applies a negative bias voltage. This design satisfies both the mode isolation and harmonic suppression requirements of the circuit [refer to Extended Data 1 for details]. Fig.1c provides an overview of the coupling principle behind this innovative concept. As the input electromagnetic wave propagates along the waveguide in a TE10 mode and interacts with a series array of C-type diodes, it forms a surface resonance mode. By adjusting the geometrical parameters (such as the vertical and horizontal diode spacings (denoted dx and dy in Fig. 1b) and therefore the overall dimensions l and w, it is possible to manipulate the field distribution of this surface mode in order to assure that the field is approximately uniform across all of the diode channels (An air bridge is used to realize the interconnection of the separate anode and cathode ends, forming each small charge channel). —referred to as planar transverse field control. This approach addresses the issue of breakdown in some anodes due to uneven field distribution. Furthermore, introducing asymmetries in the top and bottom structures enhances the electromagnetic coupling between the two layers. Fig. 1b illustrates some of these asymmetries and the optimal coupling spacing, denoted as 'h.' This approach leverages near-field coupling between the top and bottom units, aiming to enhance the diode's frequency doubling efficiency—referred to as spatial transverse field control. Frequency doubling principle Fig. 2 summarizes the numerical simulation results and field distributions of the device performance following the introduction of a diode series array with C-type microstructure. In Fig. 2a-c, the schematic illustrates the coupling mechanism for the formation of microstructured diode tandem arrays. Initially, the conventional multi-anode series diode structure is excited by the input electromagnetic wave, causing electrons to move smoothly in each electronic channel and oscillate in the air bridge of each SBD. This results in less electron accumulation near the center junction of the diode array, concentrating the electric field at the edge of the diode chain. Consequently, this in turn affects the electron transport, forming a composite dipole resonance with an overall resonance frequency at 83.5 GHz, as shown in Fig. 2a. However, this non-uniform resonance state leads to uneven distribution of induced current and electric field, affecting the power capacity handled by the induced input electromagnetic wave. As a result, not all diodes work optimally, leading to performance degradation. With the introduction of the C-shape microstructured SBD array, the composite dipole resonance is suppressed, giving rise to a hybrid resonance state combining the new double LC resonance and the original dipole resonance (Figs. 2b, c). This hybrid resonance state ensures that electron transport is minimally affected by resonance. Consequently, induced current and electric field are smoothly distributed in each diode region, forming a uniform resonant state. By altering the number of horizontally and vertically distributed diodes (i.e., adjusting the horizontal-to-vertical ratio), the percentage of dipole and LC resonance in the hybrid resonant mode can be adjusted, leading to changes in the distribution of electric field intensity. This is illustrated in the numerical simulation plot of normalized electromagnetic wave absorptivity in Fig. 2d. Under guided wave and diode interaction to produce a pure dipole resonance mode, the lowest absorptivity values in the double-layer substrate for a single diode are symmetrically centered, with corresponding highest values at the diode series edges, resulting in a step distribution. With the formation of microstructured C-type diode arrays, the diode regions with the lowest and highest values shift, resulting in a more uniform absorptivity distribution. The diode field and absorbance distributions shown in Fig. 2 demonstrate that the initially non-uniform field and energy distributions became approximately uniform as a result of the microstructure. Consequently, the majority of the anodes efficiently handle more power, preventing breakdown due to localized power overload. However, in a single-cavity frequency-doubling structure, generating THz signals with high efficiency and transmitting them with low loss still poses a significant challenge. To address this challenge and enhance conversion efficiency even further, we introduce a double-layer structure forming the upper and lower boundaries of a waveguide. The upper and lower guiding structures are not identical to each other; this asymmetry enhances the electromagnetic coupling between the two layers (refer to Fig. 1b). The net result is to both improve conversion efficiency and reduce transmission loss. Fig. 3 illustrates the role played by the asymmetry in the guiding structure. Assuming that the two chips are identical and the circuits are matched, the charges excited by the top and bottom chips are symmetrically distributed whether or not an external reverse bias excitation is applied, resulting in a magnetic wall. This idea is illustrated in Fig. 3a, showing that a parallel arrangement of double-layer Meta symmetric chips (MSC) results in the same current distributions on both of them. In this scenario, the field distribution in space is also approximately symmetric (Fig. 3b), forming a mode with a null half-way between the two layers. However, with an asymmetric chip configuration, we can engineer this mode (as shown in Fig. 3c, e, f). One side of the Meta chip is connected to an external low-pass filter (LPF) line and loaded with an external negative bias voltage. This bias voltage influences the degree of semiconductor depletion of the GaAs Schottky diode on the double-layer chip, creating a tunable interaction between the THz wave and the Meta cell. We first consider the case where no external bias excitation is applied, the multi-anode diodes are all in a zero-bias state, and the conduction thus leads to transient currents, which are in the same direction on the cathode and anode of the individual diodes, with differences in intensity (refer to Fig. 1 of Extended Data 1 here, in which the multi-anode diodes are connected in opposite, paralleling to the direction of the quasi-TEM modes). In this case, the guided wave has no resonant interaction with the diode array and the surrounding metallic microstrip, exhibiting only an asymmetry in the electric field distribution. On the other hand, when an external bias excitation is applied, it increases the Schottky barrier, generating opposite charge buildup near the cathode and anode on the multi-anode diode, and opposite reverse currents in the diode arrays of the two chips. This induces the opposite charge on the weak-side chip, and ultimately forms a spatially ring-closed charge distribution (Fig. 3d). In this configuration, these reverse currents induce electromagnetic coupling in the transverse (z-direction) direction. The control of the transverse field is achieved by exciting different external biases. By keeping one bias constant and gradually increasing the bias voltage on the other side, the transverse field modulation from Fig. 3e to Fig. 3c to Fig. 3f can be achieved. Consequently, the maximum resonance interaction result is controlled at different biases (see Extended Data Fig. 2), corresponding to the maximum value of the spatial transverse electric field between the double-layer Meta diodes. To illustrate the operational efficacy of the MAC device in practical scenarios, we documented the total power of fundamental absorption and harmonic output from each diode across varying input/output frequencies [refer to Fig. 4e]. Initially, we utilized electromagnetic simulation software to extract the total absorption and output values from the diode chips on both symmetric and asymmetric chips. Performance disparities were then evaluated by comparing numerical variations in input/output values at resonance frequencies. Subsequently, by controlling one set of chips while modifying the other, we generated two distinct sets of simulated outcomes [Fig. 4e]. When chip 1 and chip 2 are identical, the chips are in a near-field decoupling state (red curve). Then, introducing the asymmetry transitions the chips into a near-field coupling state between them (red dashed line). The output power curve also corresponds to the two states mentioned above. It can be observed that in the near-field decoupling state, the curve is smooth and there is no significant resonance. The power conversion values for chip 1 and chip 2 are almost the same. However, in the near-field coupling state, at a specific resonance frequency, near-field coupling occurs between chip 1 and chip 2. Energy is transferred between the chips, resulting in an increase of 100mW in the power handled by the base and a 47mW increase in the output power. This leads to a 34% improvement in conversion performance. In Fig. 4a, b, we conducted numerical calculations of the energy conversion efficiency for each diode. Consistent with previous simulation results, when the inter-chip is in the near-field decoupling state, the conversion efficiency of each diode remains consistent, equivalent to power synthesis. This continuation is attributed to planar transverse field control, where the distribution of the diode's efficiency strength closely follows the trend of the field strength distribution. However, when the inter-chip is in the near-field coupling, the conversion efficiency of the diodes undergoes significant alterations, revealing several distinctly split resonance regions. The conversion efficiency is improved (darker color) to a maximum value of 50%. We identified several prominent splitting regions (resonance frequencies @150, 167, and 176 GHz) in Fig. 4c. Here, it is evident that there is an energy transition between the diodes of the two layers of the chip due to the spatial transverse field. The pink and red dotted lines represent the near-field decoupling state, while the blue and black lines represent the near-field coupling state. This transition is not only related to the microstructural dimensions and structure but also to the frequency. The optimized regulation compensates for the efficiency degradation caused by the edge power weakening brought by planar transverse field control, achieving an overall efficiency improvement. This further demonstrates that the chips operate independently during the inter-chip near-field decoupling state. Thus, the three-dimensional electric field distribution depends on the spatial transverse coupling between the multi-anode Meta diodes of the double-layer chip, which is determined by the transverse coupling distance between the diodes (H) and the operating bias control characteristic (V). A prerequisite for this coupling to occur is that the inter-chip field is in near-field coupling state, i.e., the asymmetric chip is mounted at a specific scale [e.g., Fig. 4d]. Using these simulations as a guide, we can adjust the geometry to obtain optimal coupling efficiency at the selected operating frequency. This process can be illustrated by the port scattering parameters simulated in Extended Data 3. We further observed that controlling any arbitrary asymmetric behavior at the optimal transverse coupling distance also leads to the phenomenon of optimal coupling parameters. Our comprehensive design, which includes asymmetric design and tuning of the transverse coupling distance, effectively controls the transverse field coupling. With this approach, we are able to integrate dual or even more layers of chips in a single cavity while achieving superior performance. Processing and Assembly Based on the previous analysis and simulation results, we fabricated the MAC device. Fig. 5a and 5e present micrographs of the manufactured chip. Fig. 5b and c show optical microscope images of the element chip of a THz frequency multiplier with two multi-anode GaAs Schottky diodes. These images display the microscopic structure and details of the device. The diode preparation process is shown in Extended Data 2. To protect and optimize the performance of the chip, we encapsulated the device in a metallic cavity. This metallic cavity consists of input/output hollow metallic rectangular waveguides, chip-loading area, and control circuits, as illustrated in Fig. 5d. This encapsulation design helps ensure the stability and reliability of the device and provides appropriate interfaces and connections. Experimental Results To assess the performance of the dual Meta chip frequency multiplier, a power test rig was constructed (refer to Extended Fig.4). The setup involved placing a directional coupler (20 dB coupling) at the input of the sample under test, enabling calibration of input power (a bidirectional coupler could also be employed for calibrating input power while testing reflected power). Output power levels were measured using a VDI PM5 waveguide power meter. The test trials covered input frequencies ranging from 77 to 88.5 GHz. Results showed that, for a two-layer asymmetric Meta chip structure with different bias voltages, an average power output of 23.24 dBm was achieved at an input power of 28 dBm, with a conversion loss of about 4.8 dB@33% (refer to Fig. 6a). Furthermore, a comparison between Figs. 6a and 6b revealed that the conversion loss was optimized for the dual-layer asymmetric Meta chip structure compared to the single-layer Meta chip under the same bias voltage. Importantly, the experimental and simulation results demonstrated good agreement. This further confirms that the dual-chip frequency doubler structure enhances the device's performance by optimizing near-field coupling. The dual Meta frequency doubler chip, incorporating 32 anodes, allows for power capacity to reach the watt scale. As depicted in Fig. 6d, output power increases with the rise in input power. With a feed power of 28dBm, the lowest frequency conversion loss is achieved. As the feed power reaches 30dBm (1W), the output power surpasses 25dBm (316mW), exceeding international leading levels, as indicated in Extended Data Table 1. Conclusion In summary, we present a double-layer asymmetric C-shaped array diode frequency doubler, achieving remarkable results by utilizing the electromagnetic resonance property of the Meta-unit structure in an array of nonlinear semiconductor devices. The introduction of a dual-chip MAC structure enhances the near-field coupling between the chips, thereby improving the nonlinear characteristics of the device. Experimental results demonstrate a maximum conversion loss of 4.2 dB (38%) and an output power exceeding 300 mW at 170 GHz, aligning well with the numerical simulation results of the device's performance. In addition, we have also designed meta-chips at higher frequencies (e.g., 220 and 340 GHz) using this structure, again with performance gains. The core concept of this device revolves around the essence of a multi-anode frequency multiplier, aiming to increase the number of cores to enhance power capacity. The highly integrated dual-chip Meta diodes design with 32 anodes addresses issues such as uneven field distribution in traditional THz frequency multipliers, leading to improved absorption rates for the fundamental wave and higher harmonic conversion rates. This breakthrough opens up new avenues for developing high-performance integrated multilayer THz chips. While initially designed for THz frequency multiplication, the device's applicability extends to the multilayer integration of system chips, offering broad prospects for diverse applications. Declarations Acknowledgements This work was supported by the National Key Research and Development Program of China (2018YFB1801503 and 2021YFA1401000); National Natural Science Foundation of China(61931006, 62131007, U20A20212, 61901093, 61871419, 62101111, 61921002, U1930127);the Fundamental Research Funds for the Central Universities (ZYGX2020ZB011, ZYGX2019J013, ZYGX2021-YGLH205, ZYGX2021YGLH205, ZYGX2021YGLH216); the China Postdoctoral Science Foundation (2020M683285,2021M700706). References Wiltse, J. C. History of Millimeter and Submillimeter Waves. IEEE Trans. Microw. Theory Tech. 32 , 1118–1127 (1984). Wang, H. et al. 280 GHz frequency multiplied source for meteorological Doppler radar applications. in 2015 8th UK, Europe, China Millimeter Waves and THz Techn. Workshop (UCMMT) 1–4 (IEEE, Cardiff, United Kingdom, 2015). Treuttel, J. et al. A 2 THz Schottky solid-state heterodyne receiver for atmospheric studies. 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Supplementary Files ExtendedData.docx Cite Share Download PDF Status: Published Journal Publication published 16 Oct, 2025 Read the published version in Nature Electronics → Version 1 posted 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. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-4467708","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":316990206,"identity":"41f0cc80-1bb7-4ce8-9538-124c966b7e2f","order_by":0,"name":"yaxin zhang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA/UlEQVRIiWNgGAWjYDACCSjNxsB8ACZmQKwWtgSYaiK1MDDwGBCnRX5287OHX9vsEvuke75JfPjzR56BvXmbBEPNHZxaGOccMzeWbUs2ZpM5u01yZpuBYQPPsTIJhmPPcGphlkgwk5ZsY5Zjk8jdJs3bYJDAIJFjJsHYcBinFjaJ9G9ALfU8bBI5z6T//AFqkX+DXwsP0EzJj22HgbbksEkzsIFs4cGvRUIip0ya4dxxYzaJNGPL3jZjwzaetGKLhGO4tcjPSN8m+aOsOnH+jOSHN378kZPnZz+88caHGtxawEHAy4bsOxCRgFcDMKB//CGgYhSMglEwCkY2AABTbkjwXoHYMAAAAABJRU5ErkJggg==","orcid":"","institution":"University of Electronic Science and Technology of China","correspondingAuthor":true,"prefix":"","firstName":"yaxin","middleName":"","lastName":"zhang","suffix":""},{"id":316990207,"identity":"5e844733-91f9-4ae5-99de-fc67470973b7","order_by":1,"name":"Hongji Zhou","email":"","orcid":"","institution":"University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Hongji","middleName":"","lastName":"Zhou","suffix":""},{"id":316990208,"identity":"445a3a03-ca89-40a5-b7a6-567c02c064c0","order_by":2,"name":"Hailong Guo","email":"","orcid":"","institution":"Engineering Center of Integrated Optoelectronic \u0026 Radio Meta-chips, University of Electronic Science and Technology, Chengdu, China.","correspondingAuthor":false,"prefix":"","firstName":"Hailong","middleName":"","lastName":"Guo","suffix":""},{"id":316990209,"identity":"118059b2-fbb8-4f11-9302-ee12f676d672","order_by":3,"name":"Shixiong Liang","email":"","orcid":"","institution":"Hebei Semiconductor Research Institute","correspondingAuthor":false,"prefix":"","firstName":"Shixiong","middleName":"","lastName":"Liang","suffix":""},{"id":316990210,"identity":"e1fdafd2-7587-40ee-bbf0-e5d2fc1054f6","order_by":4,"name":"Jun Zhou","email":"","orcid":"","institution":"Engineering Center of Integrated Optoelectronic \u0026 Radio Meta-chips, University of Electronic Science and Technology, Chengdu, China.","correspondingAuthor":false,"prefix":"","firstName":"Jun","middleName":"","lastName":"Zhou","suffix":""},{"id":316990211,"identity":"028aa4fd-3e05-445f-abdc-c19e567fd2f0","order_by":5,"name":"Tianchi Zhou","email":"","orcid":"","institution":"University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Tianchi","middleName":"","lastName":"Zhou","suffix":""},{"id":316990212,"identity":"f9e288e6-919e-436f-ad97-ef50f74424ad","order_by":6,"name":"Hongxin Zeng","email":"","orcid":"","institution":"UESTC","correspondingAuthor":false,"prefix":"","firstName":"Hongxin","middleName":"","lastName":"Zeng","suffix":""},{"id":316990213,"identity":"5a6c5c2e-be0f-4da2-8cde-60cbcb7411b6","order_by":7,"name":"Lin Huang","email":"","orcid":"","institution":"Engineering Center of Integrated Optoelectronic \u0026 Radio Meta-chips, University of Electronic Science and Technology, Chengdu, China.","correspondingAuthor":false,"prefix":"","firstName":"Lin","middleName":"","lastName":"Huang","suffix":""},{"id":316990214,"identity":"1b4665cf-27bd-4aa0-910d-424ab64f869d","order_by":8,"name":"Yazhou Dong","email":"","orcid":"","institution":"Engineering Center of Integrated Optoelectronic \u0026 Radio Meta-chips, University of Electronic Science and Technology, Chengdu, China.","correspondingAuthor":false,"prefix":"","firstName":"Yazhou","middleName":"","lastName":"Dong","suffix":""},{"id":316990215,"identity":"4913dc13-26d9-43d5-9709-b93be9901510","order_by":9,"name":"Jingrui Liang","email":"","orcid":"","institution":"Engineering Center of Integrated Optoelectronic \u0026 Radio Meta-chips, University of Electronic Science and Technology, Chengdu, China.","correspondingAuthor":false,"prefix":"","firstName":"Jingrui","middleName":"","lastName":"Liang","suffix":""},{"id":316990216,"identity":"756e039f-06a2-4b9b-91c5-2046d4c0f150","order_by":10,"name":"Sen Gong","email":"","orcid":"","institution":"Engineering Center of Integrated Optoelectronic \u0026 Radio Meta-chips, University of Electronic Science and Technology, Chengdu, China.","correspondingAuthor":false,"prefix":"","firstName":"Sen","middleName":"","lastName":"Gong","suffix":""},{"id":316990217,"identity":"08fd56cf-9bbc-4f40-8811-666e6b910691","order_by":11,"name":"ziqiang yang","email":"","orcid":"","institution":"University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"ziqiang","middleName":"","lastName":"yang","suffix":""},{"id":316990218,"identity":"21a82abe-630f-4ae6-abaf-9eb82df28a22","order_by":12,"name":"Daniel Mittleman","email":"","orcid":"https://orcid.org/0000-0003-4277-7419","institution":"Brown University","correspondingAuthor":false,"prefix":"","firstName":"Daniel","middleName":"","lastName":"Mittleman","suffix":""}],"badges":[],"createdAt":"2024-05-23 15:01:47","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4467708/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4467708/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41928-025-01460-9","type":"published","date":"2025-10-16T04:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":58788360,"identity":"5ffe1217-76c7-491c-b618-58893b893417","added_by":"auto","created_at":"2024-06-21 06:43:59","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":343171,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea,\u003c/strong\u003e Schematic diagram summarizing the device structure.\u003cstrong\u003e b, \u003c/strong\u003eSchematic diagram illustrating the double-layer Meta asymmetric chip (MAC) and SBD nanostructures with geometrical parameters (dx=46μm, dy=46μm, w=514μm, l=134μm, and h=51.3μm). \u003cstrong\u003ec, \u003c/strong\u003eSchematic diagram depicting the artificial microstructured diode array for field distribution regulation. Free electron transport is impeded to one side of the series structure by the electric field force, leading to charge accumulation on both sides and eventual formation of electron transport. Schematic diagram illustrating the artificial microstructured diode array for field distribution regulation. As the mode propagates along the waveguide and interacts with the conventional diode series structure, free electrons are directed to one side by the electric field force, resulting in charge buildup on both sides and hindering free electron transport. This forms a dipole resonance-like mode. When combined with the C-type diode array series structure, the internal carrier transport becomes more uniform, creating a composite resonance mode with dipole and LC resonance modes. When placed inside the waveguide with non-equal two chips, the chip transport modes couple in the output mode, and carriers excited by the chips move in opposite directions, forming near-field coupling.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4467708/v1/b9b28d5e60477be057ce9efd.png"},{"id":58788952,"identity":"7ffdc09b-c638-4d36-969e-cd10a7f1025d","added_by":"auto","created_at":"2024-06-21 06:51:59","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1547360,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElectronic properties and electric field distributions of Meta diodes are detailed as follows:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ea, \u003c/strong\u003eSimulated surface current and electric field distributions on the anode of a conventional diode series structure at 83.5 GHz.\u003cstrong\u003eb, c \u003c/strong\u003eSimulated surface current and electric field distributions on the anode of a C-type diode array structure at an input electromagnetic wave frequency of 83.5 GHz. This illustrates the impact of the number of horizontally and vertically distributed cores on the electric field distribution. \u003cstrong\u003ed, \u003c/strong\u003eObserved normalized absorption rates for N=24, N=28, and N=32 anodes at 90 GHz, demonstrating the effect of the number of anodes on absorptivity at a fixed frequency. \u003cstrong\u003ee, \u003c/strong\u003eSimulations are conducted to compare the conversion capabilities of conventional and novel Meta diode structures at the input and output of the anodes.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4467708/v1/1a49d276da7c2c6779dfe5d7.png"},{"id":58788363,"identity":"9555713d-01dd-4ae9-9095-f449f7dac70b","added_by":"auto","created_at":"2024-06-21 06:43:59","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":181652,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe electromagnetic simulation results were calculated using the commercial simulation software CST Studio Suite for the simulated double-layer Meta chip at 0.17 THz.\u003c/strong\u003e \u003cstrong\u003ea, d\u003c/strong\u003e show different distribution characteristics of surface currents under the near-field decoupling state \u003cstrong\u003e(a)\u003c/strong\u003e and the near-field coupling state \u003cstrong\u003e(d)\u003c/strong\u003ebetween the chips. The introduction of asymmetric chips combined with different external electric fields results in diverse three-dimensional electric field distributions. Under the same chip and external electric field conditions, the z-directional electric field exhibits a specific distribution pattern. \u003cstrong\u003eb, \u003c/strong\u003eUnder the same chip and external electric field conditions, the z-directional electric field exhibits a specific distribution pattern. \u003cstrong\u003ec, \u003c/strong\u003eDifferent chip structures result in different z-directional electric field distributions under the same external electric field. \u003cstrong\u003ee, f,\u003c/strong\u003e By simulating different chip structures and external electric field parameters, we obtained different z-directional electric field distribution results.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4467708/v1/554d8835e9fee8e2c68e8566.png"},{"id":58788364,"identity":"6b2b3a2f-a039-4266-85fc-f22bd5e27c15","added_by":"auto","created_at":"2024-06-21 06:43:59","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":205641,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eOptimization simulation of channel conversion efficiency.\u003c/strong\u003e \u003cstrong\u003ea, b,\u003c/strong\u003eOptimization of the conversion efficiency of the dual-layer Meta chip. Heat maps of the conversion efficiency of individual anodes corresponding to the top and bottom layers of the MSC (a) and the MAC (b) in the dual-layer chip. \u003cstrong\u003ec,\u003c/strong\u003eSimulated conversion efficiencies of individual anodes when the output frequencies are 150 GHz, 167 GHz, and 176 GHz, in accordance with the sequential +x -\u0026gt; -x axes. \u003cstrong\u003ed,\u003c/strong\u003e Simulated input-output matching of MSC and MAC for different inter-board distances. \u003cstrong\u003ee,\u003c/strong\u003e Total energy feed-in (75~90GHz) and output (150~180GHz) for symmetric and asymmetric chips at each substrate.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4467708/v1/beb66946e8cd67082b82adfe.png"},{"id":58788367,"identity":"1db18ded-140e-4ef4-83a3-419204857d73","added_by":"auto","created_at":"2024-06-21 06:43:59","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":483962,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePhotographs of a typical dual-layer Meta frequency multiplier chip and the assembled testing cavity.\u003c/strong\u003e \u003cstrong\u003ea, e,\u003c/strong\u003e Optical microscope images of the top and bottom layers of the Meta frequency multiplier chip. \u003cstrong\u003eb, c，\u003c/strong\u003eLocal optical microscope images of a series array of diodes based on C-shaped microstructures. \u003cstrong\u003ed，\u003c/strong\u003ePhotographic image of the testing cavity containing the dual-layer Meta frequency multiplier chip that has been fabricated.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4467708/v1/7f86de8c68c4debf17ee5bbd.png"},{"id":58788951,"identity":"2faa7f86-cde3-4197-927c-5e394442e366","added_by":"auto","created_at":"2024-06-21 06:51:59","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":200704,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eExperimental measurement results of prototype device.\u003c/strong\u003e \u003cstrong\u003ea,\u003c/strong\u003eDifferent bias voltages were applied to feed the double-layer MAC, and the input and output power curves were plotted. \u003cstrong\u003eb,\u003c/strong\u003e The single-layer Meta chip was tested, and the input and output power curves were plotted. \u003cstrong\u003ec,\u003c/strong\u003eExperimental and simulation results of the double-layer MAC were compared. Simultaneously, the performance improvement of the double-layer MAC was compared with the single-layer Meta chip. \u003cstrong\u003ed,\u003c/strong\u003e Test curves of the feed-in and output power of the dual-layer asymmetric Meta chip were plotted, with the maximum input power approaching 1 W (30 dBm).\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4467708/v1/1391e837a5555a115a151895.png"},{"id":93748258,"identity":"14f2275e-8a01-478d-943e-5bbed5c5e318","added_by":"auto","created_at":"2025-10-17 07:10:27","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4701761,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4467708/v1/910d26fb-248e-4a86-9b3b-eab190651627.pdf"},{"id":58788362,"identity":"ce13543c-c87f-4d7b-b903-7947f206588a","added_by":"auto","created_at":"2024-06-21 06:43:59","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":4253117,"visible":true,"origin":"","legend":"","description":"","filename":"ExtendedData.docx","url":"https://assets-eu.researchsquare.com/files/rs-4467708/v1/ced9d441c303998b11c7414c.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Record-breaking conversion efficiency in a THz nonlinear diode chain using an asymmetric double-layer topology","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSubmillimeter-wave sources have been a key focus of research for many years\u003csup\u003e1\u003c/sup\u003e. The widespread application of such sources can fulfill the requirements of various terahertz (THz) systems\u003csup\u003e2\u0026ndash;4\u003c/sup\u003e, including providing local oscillator signals for up- and down-converters in hybrid communication and radar systems, as well as serving as the carrier for directly modulated communication systems\u003csup\u003e5\u003c/sup\u003e. One common approach to the generation of THz signals relies on cascaded nonlinear frequency conversion, starting with a highly stable high-power microwave source as a precursor. This method has advantages over other approaches in factors such as power capacity, energy efficiency, miniaturization, and stability\u003csup\u003e6\u0026ndash;8\u003c/sup\u003e. In particular, high-power THz frequency multipliers enable the operation of wireless communication links at distances of several kilometers and speeds of thousands of megabits per second in higher frequency bands\u003csup\u003e9\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eGiven the importance of such nonlinear structures, it is important to consider the factors which limit their performance. Previous studies have highlighted that, due to the high THz frequencies and the necessity to maximize the diode cutoff frequency (generally much higher than the actual operating frequency), the size of the diode\u0026rsquo;s anode column needs to be very small, to minimize capacitive effects\u003csup\u003e5,10,11\u003c/sup\u003e. This results in a corresponding drop in the power handling capacity and an increased susceptibility to breakdown. To address this challenge, one common strategy is to connect multiple Schottky barrier diode (SBD) structures in series. This multi-anode approach\u003csup\u003e5,7,12\u0026ndash;18\u003c/sup\u003e together with power combining techniques\u003csup\u003e7,15,19\u0026ndash;23\u003c/sup\u003e, has been widely adopted for improved power scaling. Yet, this approach often encounters issues such as chip burn-out or inefficiency during high-power testing. Multiple-anode cascades tend to induce an uneven field distribution, resulting in an imbalanced power distribution on the anodes. As a result, certain diodes may exceed critical power values, making them susceptible to damage. In addition, not all diodes operate at the same optimal power operating point, significantly reducing the overall operating efficiency of the entire system.\u003c/p\u003e\n\u003cp\u003eTo address these challenges, researchers have explored a number of options. A series of high-performance frequency doublers and related technologies have emerged to tackle these issues based on the development of multi-anode frequency doubling technology\u003csup\u003e24\u0026ndash;30\u003c/sup\u003e. For instance, physical improvements offer a direct approach to increasing conversion efficiency and output power\u003csup\u003e24,25\u003c/sup\u003e. Thin-film diode technology and the use of heterogeneous integrated high-thermal-conductivity substrates (e.g., diamond) are effective solutions. Substrates based on chemical vapor deposition of diamond have achieved output power of 200 mW at 155 GHz and 40 mW at 300 GHz by lowering the junction temperature of the Schottky junction. Techniques such as thinning, skeletonization, or even substrate removal have been employed to minimize dielectric loading and reduce circuit losses. A notable example is the \u0026quot;substrate-less\u0026quot; MMIC topology, which significantly increases output power to the mW range for frequencies above 1 THz\u003csup\u003e29\u003c/sup\u003e. When combined with appropriate power synthesis, these approaches can result in even higher power capacity, although with more complex source architectures\u003csup\u003e7\u003c/sup\u003e\u003csup\u003e,\u003c/sup\u003e\u003csup\u003e26\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDespite these achievements, the growth of power capacity, constrained by the number of anodes, gradually approaches saturation. This can be attributed to the fact that the THz wavelength is similar to the size of the diode chain. As a result, the field distribution across the array can be uneven, with some diodes experiencing a larger anode field than others. Consequently, there is a diminished conversion efficiency which ultimately limits the output power. However, this challenge also suggests the exciting possibility that carefully designed microscopic adjustments to the size or arrangement of the SBD array may lead to significant improvements in the electrical properties and performance metrics.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn this context, we introduce a novel approach to achieve record-breaking efficiency and output power in a nonlinear THz device. We engineer the microstructure of a multi-anode SBD chain by introducing a nonlinear chain topology and a double-layer near-field coupling effect. This innovative design exhibits a more uniform local electromagnetic distribution, eliminating the constraints of low multiplication efficiency and anode breakdown noted above. The double-layer asymmetric configuration establishes near-field coupling between upper and lower frequency doubling circuits, to further enhance power capacity, output power, and frequency doubling efficiency. As this idea aligns well with the concept of electronic metadevices\u003csup\u003e31\u003c/sup\u003e, we refer to our structure as a meta-asymmetric chip (MAC).\u003c/p\u003e\n\u003cp\u003eBased on these ideas, we have fabricated and tested a 32-anode SBD chain, which can be employed as a THz frequency doubler with a remarkable maximum frequency doubling efficiency of 38% and an impressive output power exceeding 300 mW at 0.17 THz. This work marks the first utilization of artificial microstructures to control the local electromagnetic field distribution in a SBD array, combining the strengths of traditional frequency doubling RF circuit chip integration and the idea of near-field coupling in THz integrated devices\u003csup\u003e32\u003c/sup\u003e. This approach opens up a new direction for the design of THz RF devices.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"Result and Discussion","content":"\u003ch3\u003eStructure and Design\u003c/h3\u003e\n\u003cp\u003eFig. 1\u0026nbsp;shows a schematic of the device. This integrates an artificial microstructure of the multi-anode SBDs, and a double-layer design to promote near-field electromagnetic coupling. Fig. 1a shows the overall device architecture, while Fig. 1b focuses on the two 16-element diode chains, both resembling a C-shaped configuration rather than the conventional linear array. The metal superstructure was fabricated on a thinned (15\u0026mu;m-thick) GaAs substrate using advanced monolithic integration techniques. This array structure comprises 16 diode anode structures, connected at both ends by longitudinally extended center band lines, which are then laterally extended and grounded at the terminals. In contrast to conventional linear frequency multiplier structures, we arrange 12 diode anodes in the xy plane along the x-axis direction (horizontal direction, parallel to the electric field direction), and an additional 4 diode anodes along the y-axis direction (vertical direction, perpendicular to the electric field direction). This structure is then replicated to form a double-layer chip in the z-axis direction, with the two layers placed on the upper and lower surfaces of a split cavity. To ensure that the diodes operate in the nonlinear region, an external feed applies a negative bias voltage. This design satisfies both the mode isolation and harmonic suppression requirements of the circuit [refer to Extended Data 1 for details].\u003c/p\u003e\n\u003cp\u003eFig.1c provides an overview of the coupling principle behind this innovative concept. As the input electromagnetic wave propagates along the waveguide in a TE10 mode and interacts with a series array of C-type diodes, it forms a surface resonance mode. By adjusting the geometrical parameters (such as the vertical and horizontal diode spacings (denoted dx and dy in Fig. 1b) and therefore the overall dimensions l and w, it is possible to manipulate the field distribution of this surface mode in order to assure that the field is approximately uniform across all of the diode channels (An air bridge is used to realize the interconnection of the separate anode and cathode ends, forming each small charge channel). \u0026mdash;referred to as planar transverse field control. This approach addresses the issue of breakdown in some anodes due to uneven field distribution. Furthermore, introducing asymmetries in the top and bottom structures enhances the electromagnetic coupling between the two layers. Fig. 1b illustrates some of these asymmetries and the optimal coupling spacing, denoted as \u0026apos;h.\u0026apos; This approach leverages near-field coupling between the top and bottom units, aiming to enhance the diode\u0026apos;s frequency doubling efficiency\u0026mdash;referred to as spatial transverse field control.\u003c/p\u003e\n\u003ch3\u003eFrequency doubling principle\u003c/h3\u003e\n\u003cp\u003eFig. 2\u0026nbsp;summarizes the numerical simulation results and field distributions of the device performance following the introduction of a diode series array with C-type microstructure. In Fig. 2a-c, the schematic illustrates the coupling mechanism for the formation of microstructured diode tandem arrays.\u003c/p\u003e\n\u003cp\u003eInitially, the conventional multi-anode series diode structure is excited by the input electromagnetic wave, causing electrons to move smoothly in each electronic channel and oscillate in the air bridge of each SBD. This results in less electron accumulation near the center junction of the diode array, concentrating the electric field at the edge of the diode chain. Consequently, this in turn affects the electron transport, forming a composite dipole resonance with an overall resonance frequency at 83.5 GHz, as shown in Fig. 2a. However, this non-uniform resonance state leads to uneven distribution of induced current and electric field, affecting the power capacity handled by the induced input electromagnetic wave. As a result, not all diodes work optimally, leading to performance degradation.\u003c/p\u003e\n\u003cp\u003eWith the introduction of the C-shape microstructured SBD array, the composite dipole resonance is suppressed, giving rise to a hybrid resonance state combining the new double LC resonance and the original dipole resonance (Figs. 2b, c). This hybrid resonance state ensures that electron transport is minimally affected by resonance. Consequently, induced current and electric field are smoothly distributed in each diode region, forming a uniform resonant state.\u003c/p\u003e\n\u003cp\u003eBy altering the number of horizontally and vertically distributed diodes (i.e., adjusting the horizontal-to-vertical ratio), the percentage of dipole and LC resonance in the hybrid resonant mode can be adjusted, leading to changes in the distribution of electric field intensity. This is illustrated in the numerical simulation plot of normalized electromagnetic wave absorptivity in Fig. 2d. Under guided wave and diode interaction to produce a pure dipole resonance mode, the lowest absorptivity values in the double-layer substrate for a single diode are symmetrically centered, with corresponding highest values at the diode series edges, resulting in a step distribution. With the formation of microstructured C-type diode arrays, the diode regions with the lowest and highest values shift, resulting in a more uniform absorptivity distribution.\u003c/p\u003e\n\u003cp\u003eThe diode field and absorbance distributions shown in\u0026nbsp;Fig. 2 demonstrate that the initially non-uniform field and energy distributions became approximately uniform as a result of the microstructure. Consequently, the majority of the anodes efficiently handle more power, preventing breakdown due to localized power overload.\u003c/p\u003e\n\u003cp\u003eHowever, in a single-cavity frequency-doubling structure, generating THz signals with high efficiency and transmitting them with low loss still poses a significant challenge.\u003c/p\u003e\n\u003cp\u003eTo address this challenge and enhance conversion efficiency even further, we introduce a double-layer structure forming the upper and lower boundaries of a waveguide. The upper and lower guiding structures are not identical to each other; this asymmetry enhances the electromagnetic coupling between the two layers (refer to Fig. 1b). The net result is to both improve conversion efficiency and reduce transmission loss.\u003c/p\u003e\n\u003cp\u003eFig. 3\u0026nbsp;illustrates the role played by the asymmetry in the guiding structure. Assuming that the two chips are identical and the circuits are matched, the charges excited by the top and bottom chips are symmetrically distributed whether or not an external reverse bias excitation is applied, resulting in a magnetic wall. This idea is illustrated in Fig. 3a, showing that a parallel arrangement of double-layer Meta symmetric chips (MSC) results in the same current distributions on both of them. In this scenario, the field distribution in space is also approximately symmetric (Fig. 3b), forming a mode with a null half-way between the two layers. However, with an asymmetric chip configuration, we can engineer this mode (as shown\u0026nbsp;in Fig. 3c, e, f). One side of the Meta chip is connected to an external low-pass filter (LPF) line and loaded with an external negative bias voltage. This bias voltage influences the degree of semiconductor depletion of the GaAs Schottky diode on the double-layer chip, creating a tunable interaction between the THz wave and the Meta cell. We first consider the case where no external bias excitation is applied, the multi-anode diodes are all in a zero-bias state, and the conduction thus leads to transient currents, which are in the same direction on the cathode and anode of the individual diodes, with differences in intensity (refer to Fig. 1 of Extended Data 1 here, in which the multi-anode diodes are connected in opposite, paralleling to the direction of the quasi-TEM modes). In this case, the guided wave has no resonant interaction with the diode array and the surrounding metallic microstrip, exhibiting only an asymmetry in the electric field distribution.\u003c/p\u003e\n\u003cp\u003eOn the other hand, when an external bias excitation is applied, it increases the Schottky barrier, generating opposite charge buildup near the cathode and anode on the multi-anode diode, and opposite reverse currents in the diode arrays of the two chips. This induces the opposite charge on the weak-side chip, and ultimately forms a spatially ring-closed charge distribution (Fig. 3d). In this configuration, these reverse currents induce electromagnetic coupling in the transverse (z-direction) direction. The control of the transverse field is achieved by exciting different external biases. By keeping one bias constant and gradually increasing the bias voltage on the other side, the transverse field modulation from Fig. 3e to Fig. 3c to Fig. 3f can be achieved. Consequently, the maximum resonance interaction result is controlled at different biases (see Extended Data Fig. 2), corresponding to the maximum value of the spatial transverse electric field between the double-layer Meta diodes.\u003c/p\u003e\n\u003cp\u003eTo illustrate the operational efficacy of the MAC device in practical scenarios, we documented the total power of fundamental absorption and harmonic output from each diode across varying input/output frequencies [refer to Fig. 4e]. Initially, we utilized electromagnetic simulation software to extract the total absorption and output values from the diode chips on both symmetric and asymmetric chips. Performance disparities were then evaluated by comparing numerical variations in input/output values at resonance frequencies.\u0026nbsp;Subsequently, by controlling one set of chips while modifying the other, we generated two distinct sets of simulated outcomes [Fig. 4e].\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eWhen chip 1 and chip 2 are identical, the chips are in a near-field decoupling state (red curve).\u003c/li\u003e\n \u003cli\u003eThen, introducing the asymmetry transitions the chips into a near-field coupling state between them (red dashed line).\u003c/li\u003e\n \u003cli\u003eThe output power curve also corresponds to the two states mentioned above.\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eIt can be observed that in the near-field decoupling state, the curve is smooth and there is no significant resonance. The power conversion values for chip 1 and chip 2 are almost the same. However, in the near-field coupling state, at a specific resonance frequency, near-field coupling occurs between chip 1 and chip 2. Energy is transferred between the chips, resulting in an increase of 100mW in the power handled by the base and a 47mW increase in the output power. This leads to a 34% improvement in conversion performance.\u003c/p\u003e\n\u003cp\u003eIn Fig. 4a, b, we conducted numerical calculations of the energy conversion efficiency for each diode. Consistent with previous simulation results, when the inter-chip is in the near-field decoupling state, the conversion efficiency of each diode remains consistent, equivalent to power synthesis. This continuation is attributed to planar transverse field control, where the distribution of the diode\u0026apos;s efficiency strength closely follows the trend of the field strength distribution.\u003c/p\u003e\n\u003cp\u003eHowever, when the inter-chip is in the near-field coupling, the conversion efficiency of the diodes undergoes significant alterations, revealing several distinctly split resonance regions. The conversion efficiency is improved (darker color) to a maximum value of 50%. We identified several prominent splitting regions (resonance frequencies @150, 167, and 176 GHz) in Fig. 4c. Here, it is evident that there is an energy transition between the diodes of the two layers of the chip due to the spatial transverse field. The pink and red dotted lines represent the near-field decoupling state, while the blue and black lines represent the near-field coupling state. This transition is not only related to the microstructural dimensions and structure but also to the frequency. The optimized regulation compensates for the efficiency degradation caused by the edge power weakening brought by planar transverse field control, achieving an overall efficiency improvement.\u003c/p\u003e\n\u003cp\u003eThis further demonstrates that the chips operate independently during the inter-chip near-field decoupling state. Thus, the three-dimensional electric field distribution depends on the spatial transverse coupling between the multi-anode Meta diodes of the double-layer chip, which is determined by the transverse coupling distance between the diodes (H) and the operating bias control characteristic (V). A prerequisite for this coupling to occur is that the inter-chip field is in near-field coupling state, i.e., the asymmetric chip is mounted at a specific scale [e.g., Fig. 4d]. Using these simulations as a guide, we can adjust the geometry to obtain optimal coupling efficiency at the selected operating frequency. This process can be illustrated by the port scattering parameters simulated in Extended Data 3.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eWe further observed that controlling any arbitrary asymmetric behavior at the optimal transverse coupling distance also leads to the phenomenon of optimal coupling parameters. Our comprehensive design, which includes asymmetric design and tuning of the transverse coupling distance, effectively controls the transverse field coupling. \u0026nbsp;With this approach, we are able to integrate dual or even more layers of chips in a single cavity while achieving superior performance.\u003c/p\u003e\n\u003ch3\u003eProcessing and Assembly\u003c/h3\u003e\n\u003cp\u003eBased on the previous analysis and simulation results, we fabricated the MAC device. Fig. 5a and 5e present micrographs of the manufactured chip. Fig. 5b and c show optical microscope images of the element chip of a THz frequency multiplier with two multi-anode GaAs Schottky diodes. These images display the microscopic structure and details of the device. The diode preparation process is shown in Extended Data 2. To protect and optimize the performance of the chip, we encapsulated the device in a metallic cavity. This metallic cavity consists of input/output hollow metallic rectangular waveguides, chip-loading area, and control circuits, as illustrated in Fig. 5d. This encapsulation design helps ensure the stability and reliability of the device and provides appropriate interfaces and connections.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003eExperimental Results\u003c/h3\u003e\n\u003cp\u003eTo assess the performance of the dual Meta chip frequency multiplier, a power test rig was constructed (refer to\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eExtended Fig.4). The setup involved placing a directional coupler (20 dB coupling) at the input of the sample under test, enabling calibration of input power (a bidirectional coupler could also be employed for calibrating input power while testing reflected power). Output power levels were measured using a VDI PM5 waveguide power meter. The test trials covered input frequencies ranging from 77 to 88.5 GHz.\u003c/p\u003e\n\u003cp\u003eResults showed that, for a two-layer asymmetric Meta chip structure with different bias voltages, an average power output of 23.24 dBm was achieved at an input power of 28 dBm, with a conversion loss of about 4.8 dB@33% (refer to Fig. 6a). Furthermore, a comparison between Figs. 6a and 6b revealed that the conversion loss was optimized for the dual-layer asymmetric Meta chip structure compared to the single-layer Meta chip under the same bias voltage. Importantly, the experimental and simulation results demonstrated good agreement.\u003c/p\u003e\n\u003cp\u003eThis further confirms that the dual-chip frequency doubler structure enhances the device\u0026apos;s performance by optimizing near-field coupling. The dual Meta frequency doubler chip, incorporating 32 anodes, allows for power capacity to reach the watt scale. As depicted in Fig. 6d, output power increases with the rise in input power. With a feed power of 28dBm, the lowest frequency conversion loss is achieved. As the feed power reaches 30dBm (1W), the output power surpasses 25dBm (316mW), exceeding international leading levels, as indicated in Extended Data Table 1.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn summary, we present a double-layer asymmetric C-shaped array diode frequency doubler, achieving remarkable results by utilizing the electromagnetic resonance property of the Meta-unit structure in an array of nonlinear semiconductor devices. The introduction of a dual-chip MAC structure enhances the near-field coupling between the chips, thereby improving the nonlinear characteristics of the device. Experimental results demonstrate a maximum conversion loss of 4.2 dB (38%) and an output power exceeding 300 mW at 170 GHz, aligning well with the numerical simulation results of the device's performance. In addition, we have also designed meta-chips at higher frequencies (e.g., 220 and 340 GHz) using this structure, again with performance gains.\u003c/p\u003e \u003cp\u003eThe core concept of this device revolves around the essence of a multi-anode frequency multiplier, aiming to increase the number of cores to enhance power capacity. The highly integrated dual-chip Meta diodes design with 32 anodes addresses issues such as uneven field distribution in traditional THz frequency multipliers, leading to improved absorption rates for the fundamental wave and higher harmonic conversion rates. This breakthrough opens up new avenues for developing high-performance integrated multilayer THz chips. While initially designed for THz frequency multiplication, the device's applicability extends to the multilayer integration of system chips, offering broad prospects for diverse applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e\n\u003cp\u003eThis work was supported by the National Key Research and Development Program of China (2018YFB1801503 and 2021YFA1401000); National Natural Science Foundation of China(61931006, 62131007, U20A20212, 61901093, 61871419, 62101111, 61921002, U1930127);the Fundamental Research Funds for the Central Universities (ZYGX2020ZB011, ZYGX2019J013, ZYGX2021-YGLH205, ZYGX2021YGLH205, ZYGX2021YGLH216); the China Postdoctoral Science Foundation (2020M683285,2021M700706).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWiltse, J. C. 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Accessed: Mar. 2024. [Online]. Available: https://acst.de/product/frequency-doublers/\u003c/li\u003e\n\u003cli\u003eFeng, Z. H.\u003cem\u003e, et al.\u003c/em\u003e High-frequency multiplier based on GaN planar Schottky barrier diodes. \u003cem\u003e2016 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP).\u003c/em\u003e IEEE, 2016.\u003c/li\u003e\n\u003cli\u003eErickson, Neal. High efficiency submillimeter frequency multipliers. \u003cem\u003eIEEE MTT-S Int. Microwave Symp.\u003c/em\u003e \u003cem\u003eDig.\u003c/em\u003e Vol. 3. 1990.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-4467708/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4467708/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe exploitation of radiation in the terahertz (THz) range hinges on the continued development of THz sources. Schottky barrier diode (SBD)--based frequency multiplier devices are one of the most attractive options, as they can produce high power in comparison to direct generation, and can be integrated into all-solid-state systems. Yet, the scaling of the output power of such devices is often limited by the power handling capacity of a single diode. This motivates the idea of forming a connected chain of SBD devices, accompanied by a power combining approach to achieve higher THz output power. While effective, the uneven field distribution among the diodes can pose a significant challenge as it leads to lower efficiency and premature breakdown. This phenomenon is rooted in the similarity between the THz wavelength and the physical dimensions of the diodes themselves. To address this issue, we propose an innovative solution based on an asymmetric double-layer C-type diode chain structure. This arrangement allows for the adjustment of local electromagnetic field distribution, and dramatically enhances the conversion efficiency of the diode chain. Our device achieves the highest frequency doubling efficiency recorded at 38%, with an output exceeding 300 mW at 170 GHz. This design paves the way for a new direction in the development of diode-based THz nonlinear devices.\u003c/p\u003e","manuscriptTitle":"Record-breaking conversion efficiency in a THz nonlinear diode chain using an asymmetric double-layer topology","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-21 06:43:54","doi":"10.21203/rs.3.rs-4467708/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-electronics","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"natelectron","sideBox":"Learn more about [Nature Electronics](http://www.nature.com/natelectron/)","snPcode":"","submissionUrl":"","title":"Nature Electronics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"be278320-df0b-41c6-8531-1d7535c30fa9","owner":[],"postedDate":"June 21st, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":33520876,"name":"Physical sciences/Engineering/Electrical and electronic engineering"},{"id":33520877,"name":"Physical sciences/Physics/Optical physics/Terahertz optics"},{"id":33520878,"name":"Physical sciences/Physics/Techniques and instrumentation/Design, synthesis and processing"}],"tags":[],"updatedAt":"2025-10-17T07:10:20+00:00","versionOfRecord":{"articleIdentity":"rs-4467708","link":"https://doi.org/10.1038/s41928-025-01460-9","journal":{"identity":"nature-electronics","isVorOnly":false,"title":"Nature Electronics"},"publishedOn":"2025-10-16 04:00:00","publishedOnDateReadable":"October 16th, 2025"},"versionCreatedAt":"2024-06-21 06:43:54","video":"","vorDoi":"10.1038/s41928-025-01460-9","vorDoiUrl":"https://doi.org/10.1038/s41928-025-01460-9","workflowStages":[]},"version":"v1","identity":"rs-4467708","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4467708","identity":"rs-4467708","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}