A heterostructure optoelectronic synapse device and a preparation method thereof

Abstract

This invention relates to the field of electronic device technology, and more particularly to a heterostructured photoelectric synaptic device and its fabrication method. In the MXene / ZnO / patterned Se three-layer heterostructure constructed in this invention, MXene possesses excellent conductivity and a layered structure, providing a fast transport channel for charge carriers; ZnO has good ultraviolet light absorption; and Se has a narrow bandgap and strong visible light absorption. The combination of these three components significantly broadens the spectral response range of the device and improves its ability to recognize different wavelengths of light signals. This invention employs a patterned Se thin film design, which, compared to a continuous Se capping layer, enables localized light absorption modulation and spatial distribution optimization, enhancing the device's localized light field effect and non-uniform light response characteristics, thereby improving the device's wavelength selectivity and bifacial asymmetric response capability.

Description

Technical Field

[0001] This invention relates to the field of electronic device technology, and in particular to a heterogeneous structure photoelectric synapse device and its fabrication method. Background Technology

[0002] With the rapid development of technologies such as artificial intelligence, machine vision, intelligent sensing, and neuromorphic computing, the traditional von Neumann architecture, which separates perception, storage, and processing, is increasingly revealing problems such as large data transfer delays, high energy consumption, and insufficient real-time performance when faced with massive amounts of unstructured visual data. Inspired by the biological visual nervous system, optoelectronic synaptic devices, which can combine optical signal sensing, information storage, and synaptic weight control functions, have become an important research direction in neuromorphic electronics and novel intelligent optoelectronic devices because they can achieve integrated sensing, storage, and computing processing.

[0003] Currently, optoelectronic synaptic devices are mostly constructed based on systems such as oxide semiconductors, transition metal chalcogenides, perovskites, organic semiconductors, and two-dimensional materials. Among them, ZnO, as a typical wide-bandgap semiconductor, has advantages such as relatively mature fabrication processes, significant ultraviolet response, and good stability, and has attracted widespread attention in the fields of photoelectric detection and photoelectric storage. Se materials have good visible light absorption characteristics and photoelectric conversion capabilities, and can be used to extend the response band of devices. MXene, as a class of emerging two-dimensional transition metal carbide / nitride materials, has excellent conductivity, abundant surface functional groups, and good interface modulation capabilities, showing great potential in constructing low-resistivity transport channels, improving carrier extraction efficiency, and enhancing interface coupling. Therefore, constructing heterostructures based on the complementary advantages of different materials has become an important research approach to improve the overall performance of optoelectronic synaptic devices.

[0004] Existing research indicates that constructing heterojunctions can, to some extent, improve the problems of narrow light absorption range, low photogenerated carrier separation efficiency, and limited response functionality in single-material devices. For example, using ZnO in combination with other narrow-bandgap semiconductors can extend the device's response range from ultraviolet to visible wavelengths; introducing two-dimensional conductive materials as charge transport layers can reduce interface transport impedance and improve response speed; and through defect state modulation, surface modification, or interface engineering, the photogenerated charge trapping and release behavior of the device can be enhanced, thereby achieving a certain degree of synaptic plasticity simulation. However, existing optoelectronic synaptic devices still have the following shortcomings: First, the response band of the devices is relatively narrow, usually only showing a strong response to a single band of ultraviolet or visible light, which is difficult to meet the requirements of broadband sensing; second, most devices mainly rely on unilateral incident light or have no significant difference in response to different incident directions, making it difficult to achieve directionally selective bilateral asymmetric sensing; third, the interface coupling between the functional layers in the device is insufficient, which leads to limited separation and transmission efficiency of photogenerated carriers, thus affecting the synaptic response strength, stability and repeatability; fourth, although some devices can achieve photocurrent modulation, they are still insufficient in wavelength resolution, spectral selective recognition and multidimensional stimulus information processing, which is not conducive to brain-like sensing applications in complex visual scenarios.

[0005] To address the aforementioned issues, researchers have proposed several improvement schemes. First, by introducing narrow-bandgap semiconductors, quantum dots, or organic photosensitive layers in combination with wide-bandgap materials such as ZnO, visible light response can be improved. However, this approach often suffers from insufficient material stability, weak interfacial bonding, or complex fabrication processes, and is prone to performance degradation during long-term operation. Second, composite heterojunctions can be constructed using two-dimensional materials such as graphene and transition metal chalcogenides to enhance carrier migration and interfacial separation efficiency. However, some two-dimensional materials inherently have small band gaps or high dark currents, which can easily affect the device's signal-to-noise ratio, and large-area uniform fabrication of certain materials is challenging. Third, the capture and release processes of photogenerated charges can be improved through surface defect engineering, doping control, and interfacial modification to enhance synaptic-like behavior. However, these methods are typically sensitive to process windows, and repeatability and consistency still need improvement. Furthermore, it is difficult to simultaneously achieve broad-spectrum response, directional selectivity, and stable synaptic plasticity output. Fourth, some studies have achieved multifunctional integration by constructing multi-layer heterostructures, but most existing structures focus more on improving a single performance, such as responsivity, retention time or single-band recognition capability. There is still insufficient research on the asymmetric light response mechanism under double-sided incident conditions, wavelength selective recognition capability and device structure designability.

[0006] Furthermore, in existing multilayer optoelectronic heterostructures, the photosensitive layer is typically deposited using a continuous overlay method. While this facilitates the formation of a complete thin film, it can lead to a limited range of light field utilization methods, insufficient local interface modulation capabilities, and relatively fixed device response modes. This hinders further improvements in the device's performance in spatially selective absorption, local carrier modulation, and multidimensional information sensing. Especially for applications in intelligent vision and neuromorphic perception, devices not only need to be sensitive to different wavelengths of light but also need to exhibit differentiated output characteristics under different incident surface conditions to simulate more complex biological visual information processing. Current technologies still lack effective solutions that balance material synergy, structural asymmetry, and functional integration. Therefore, there is an urgent need to develop novel optoelectronic synaptic devices with a rational structural design, feasible fabrication, broad-spectrum light response capabilities, bifacial asymmetric sensing characteristics, and stable synaptic plasticity behavior. This would address the limitations of existing technologies, such as restricted response bands, insufficient directional selectivity, low interface transmission efficiency, and limited multifunctional integration capabilities. Summary of the Invention

[0007] Therefore, the technical problem to be solved by the present invention is to overcome the problems of narrow response band, insufficient asymmetric sensing ability under double-sided incident light, low efficiency of interface carrier separation and transmission, limited wavelength selective recognition ability, and insufficient integration of sensing-storage-processing in the existing photoelectric synaptic devices. Thus, the present invention provides a photoelectric synaptic device based on a three-layer heterostructure of MXene / ZnO / patterned Se, its preparation method and application.

[0008] To address the aforementioned technical problems, this invention provides a method for fabricating a heterogeneous opto-synaptic device, comprising the following steps: S11: Coat the substrate surface with an MXene aqueous dispersion and heat-treat at 80-120℃ for 30-60 s to form an MXene layer; S12: Coat the surface of the MXene layer with a ZnO alcohol dispersion and heat-treat at 80-120℃ for 60-90 s to form a ZnO layer; S13: Se layer and metal electrode are sequentially deposited on the surface of the ZnO layer to obtain the heterostructure photoelectric synapse device; both the Se layer and the metal electrode are patterned.

[0009] This invention aims to address the difficulty in simultaneously achieving broadband optical response, bifacial asymmetric optical sensing, and stable synaptic plasticity control in existing single-material or conventional heterostructure devices. Furthermore, it addresses the shortcomings of existing continuous thin-film structures in terms of insufficient local light absorption control, limited interface coupling capability, and weak multidimensional visual information processing capability.

[0010] Preferably, the MXene aqueous dispersion is prepared as follows: S21: Add the metal carbide to an aqueous solution containing hydrochloric acid and lithium fluoride, and etch at 35-45℃ for 40-56 h to obtain an etching mixture; S22: Separate the solid and liquid components of the etching mixture, and disperse the obtained solid in water for 0.5-1.5 h to obtain a mixed dispersion; the dispersion conditions are a protective atmosphere and an ice-water bath. S23: Separate the solid and liquid components of the mixed dispersion and collect the liquid to obtain the MXene aqueous dispersion.

[0011] For existing single-layer or ordinary double-layer optoelectronic devices, the limited absorption band of the materials, the weak built-in electric field at the interface, and the short separation path of photogenerated carriers easily lead to severe recombination of photogenerated electron-hole pairs, thus affecting the photocurrent output, wavelength recognition capability, and synaptic response stability of the device. This invention employs a three-layer heterostructure of MXene / ZnO / patterned Se, where the MXene layer serves as a highly conductive carrier transport layer, the ZnO layer as a wide-bandgap inorganic photoresponse layer, and the patterned Se layer as a visible light enhancement absorption layer. By increasing the built-in potential through multi-interface coupling and optimizing the carrier separation and transport process, the device's photoresponse intensity, double-sided asymmetric sensing capability, and photosynaptic performance are effectively improved.

[0012] Furthermore, the metal carbide is Ti3AlC2 powder.

[0013] Furthermore, in step S21, the mass ratio of metal carbide to lithium fluoride is 1:0.4-1.2.

[0014] Furthermore, in step S22, the solid-liquid mixture is washed with hydrochloric acid before solid-liquid separation. Hydrochloric acid can wash away residual lithium fluoride, unreacted impurities, and byproducts from the etching process, preventing fluoride residue from affecting material performance. The acid wash within the same system has good compatibility, will not damage the etched metal carbide structure, can inhibit product hydrolysis, and gently removes loose surface deposits, improving product purity.

[0015] Furthermore, the protective atmosphere is argon, and the ice-water bath temperature is 0-4℃.

[0016] Furthermore, the dispersion method is ultrasound.

[0017] Furthermore, in steps S22 and S23, the solid-liquid separation method is to perform centrifugation at a speed of 3000-5000 rpm for 150-210 s.

[0018] Preferably, the substrate is a composite substrate composed of silicon, silicon dioxide and a metal electrode; wherein the silicon and silicon dioxide are N100 type SiO2 / Si substrates from Lijing Electronics Co., Ltd., and the metal electrode is obtained by magnetron sputtering.

[0019] Preferably, the coating method in steps S11 and S12 is spraying, and the distance between the spray gun and the substrate is 15-25 cm during spraying.

[0020] Preferably, the ZnO alcohol dispersion is obtained by grinding ZnO and then adding it to ethanol.

[0021] Furthermore, anhydrous ethanol was used as a dispersant, and the ultrasonic dispersion time for ZnO was 30-60 min.

[0022] Preferably, in step S13, the patterning process is as follows: S31: Photolithographic patterning after coating the surface with photoresist; S32: Deposit Se or a metal electrode on the pattern; S32: Remove the photoresist to complete the patterning process.

[0023] The window formed by photolithography is created by exposing the photoresist to ultraviolet light in a photolithography machine, which denatures the exposed portion and allows it to be removed by acetone cleaning. The final photolithography-formed Se thin film grooves are the patterns retained from the photoresist deformed by the photolithography machine. In the final device form, the patterned Se thin film sits on top of the ZnO material.

[0024] The above method enables the fabrication of fine micro- and nano-scale patterns, meeting the miniaturization requirements of devices. The process is simple, mature, and compatible with Se and various metal electrode deposition. Pattern edges are regular, electrode morphology is controllable, and yield and repeatability are good. The overall process has strong compatibility, suitable for mass production of optoelectronic synaptic devices, and is less likely to damage the underlying functional film.

[0025] Preferably, the metal electrode is gold, silver, aluminum, or magnesium. These metals have high conductivity, which can reduce device power consumption and improve signal transmission efficiency. Their chemical activity is tunable: gold is stable and adaptable to inert interfaces, while silver / aluminum / magnesium have moderate activity, easily forming Schottky junctions or participating in redox reactions, facilitating conductivity regulation and synaptic plasticity. They offer good optical compatibility: silver has high visible light reflectivity, while aluminum / magnesium can be thinned for light transmission, adapting to optical signal input. They are easy to process into films, suitable for large-scale fabrication, balancing performance and process compatibility.

[0026] Preferably, the metal electrode is deposited by magnetron sputtering in an inert gas atmosphere, more preferably an argon atmosphere; the working pressure of the magnetron sputtering is 0.1-2 Pa, the sputtering power is 30-150 W, and the deposition time is 5-30 min. Magnetron sputtering deposits metal electrodes to form uniform, dense films with strong adhesion, making them less prone to detachment. The deposition rate is stable, the film thickness is controllable, and the repeatability is excellent, enabling the mass production of adapter devices. The low-temperature process does not damage the functional layer of the photosynapse or the photosensitive material. It offers strong process compatibility and high film purity, ensuring excellent electrode conductivity.

[0027] Preferably, the pattern is a square, rectangle, circle, or array pattern.

[0028] Preferably, the Se is deposited via thermal evaporation, specifically: under vacuum conditions, Se particles or Se powder are used as the evaporation source to perform thermal evaporation deposition within a preset patterned window on the surface of the ZnO layer. After deposition, the photoresist is removed to form a patterned Se layer. The cavity vacuum degree of the thermal evaporation process is 1×10⁻⁶. -3 Up to 1×10 -5 Pa, with a deposition rate of 0.1-2 nm / s. The above method can yield patterned Se films with clear boundary lines, uniform coverage, and minimal risk of damaging the underlying functional layers.

[0029] Specifically, the fabrication method of the heterostructure photoelectric synapse device includes the following steps: (1) Pretreatment of the substrate: Silicon and silicon dioxide were cleaned with acetone, ethanol and deionized water in sequence, and then dried and subjected to plasma treatment for 10 min to improve the cleanliness and hydrophilicity of the substrate surface. Then, Ag electrode composite substrate with a thickness of 40-100 nm was sputtered by magnetron sputtering.

[0030] (2) Preparation of MXene dispersion: The Al layer in Ti3AlC2 MAX phase powder was selectively etched using a lithium fluoride / hydrochloric acid etching system. 2 g of lithium fluoride was dissolved in 20 mL of 9 mol / L hydrochloric acid and stirred for 15 min. Then, 3 g of Ti3AlC2 powder was slowly added and stirred at 40 °C for 48 h. After etching, 2 mol / L hydrochloric acid was added for washing, and then deionized water was used for repeated washing until the pH of the supernatant was about 6. Subsequently, the supernatant was sonicated for 1 h under argon atmosphere and ice-water bath conditions. The supernatant was collected to obtain the MXene dispersion. The washing endpoint was that the supernatant was dark green and the pH was 5-7.

[0031] (3) Preparation of MXene film: The SiO2 substrate treated in step (1) is placed on a heating table at 100°C. The spray gun is fixed at a distance of 20 cm from the substrate. The MXene dispersion obtained in step (2) is sprayed onto the substrate surface to form a uniform MXene film.

[0032] (4) Preparation of ZnO film: ZnO powder was ground for 1 h and then added to pure ethanol and sonicated for 30 min to obtain a uniform ZnO dispersion; then the dispersion was sprayed onto the surface of the MXene film obtained in step (3) to form a ZnO film and obtain an MXene / ZnO bilayer structure.

[0033] (5) Preparation of patterned Se film: Photoresist is spin-coated on the surface of the MXene / ZnO bilayer film obtained in step (4). First, spin-coat at 600 rpm for 10 s, then spin-coat at 3000 rpm for 60 s to make the photoresist uniformly cover the sample surface. Then, the photoresist is pre-baked and exposed using a TuoTuo maskless lithography machine with a preset square pattern. After development, a uniformly distributed square pattern window is formed in the photoresist layer. Then, the sample is placed in a thermal evaporation device and Se material is deposited under vacuum conditions so that Se is deposited in the pattern window. After deposition, acetone is used to remove the photoresist and the Se material on the photoresist, leaving only the Se film in the pattern window area, thereby obtaining a uniformly distributed square patterned Se film.

[0034] (6) Electrode fabrication: Electrode patterns are formed on the device surface using photolithography, followed by Ag electrode deposition by magnetron sputtering and removal of photoresist to obtain MXene / ZnO / heterogeneous structure opto-synaptic device.

[0035] The present invention also provides a heterostructure photoelectric synapse device prepared by the above preparation method.

[0036] Preferably, the heterostructure photoelectric synaptic device includes a substrate, an MXene layer, a ZnO layer, a patterned Se layer, and a metal electrode; wherein the thickness of the substrate is 50 μm-2 mm; the thickness of the MXene layer is 200-500 nm; the thickness of the ZnO layer is 400-800 nm; the thickness of the patterned Se layer is 50-200 nm; and the thickness of the metal electrode is 40-100 nm.

[0037] The heterostructured opto-synaptic device of the present invention can be applied in broadband optical detection, two-sided asymmetric sensing, and brain-like visual information processing.

[0038] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: This invention uses a combination of spraying, photolithography, thermal evaporation and magnetron sputtering to fabricate heterostructure devices. The process is simple, the equipment requirements are relatively low, it is easy to repeat, and it is suitable for large-area fabrication.

[0039] Compared with complex high-vacuum epitaxial growth or multiple transfer processes, this invention has better process feasibility and application promotion value. In the MXene / ZnO / patterned Se three-layer heterostructure constructed by this invention, MXene has excellent conductivity and layered structure, which can provide a fast transport channel for charge carriers; ZnO has good ultraviolet light absorption capability; and Se has a narrow bandgap and strong visible light absorption capability. The combination of these three elements significantly broadens the spectral response range of the device and improves its ability to recognize light signals of different wavelengths. This invention, through multi-layer heterogeneous interface coupling, forms a more favorable bandgap matching relationship and a built-in electric field, effectively promoting the separation of photogenerated electron-hole pairs and reducing the probability of carrier recombination, thereby improving the photocurrent output and response sensitivity of the device. The patterned Se thin film design, compared to continuous Se capping layers, enables local light absorption modulation and spatial distribution optimization, enhancing the device's local light field effect and non-uniform light response characteristics, thus improving the device's wavelength selectivity and bifacial asymmetric response capability. The device prepared by this invention exhibits differentiated responses under different incident directions and different wavelength illumination conditions, which is beneficial for simulating the directional sensitivity and multi-wavelength recognition behavior in biological visual systems, and is suitable for constructing neuromorphic visual devices with integrated sensing, storage, and processing characteristics.

[0040] Furthermore, the device of this invention utilizes the carrier trapping, release, and migration behavior in heterogeneous interfaces, exhibiting excellent synaptic plasticity characteristics, including excitatory postsynaptic current response, short-term memory behavior, and a certain degree of long-term modulation capability, showing promising application prospects in fields such as brain-like computing, intelligent sensing, and artificial vision systems. Attached Figure Description

[0041] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0042] Figure 1 This is a structural diagram of the photoelectric synapse device in Embodiment 1 of the present invention; Figure 2 This is the pulse response diagram of the photoelectric synaptic device in Embodiment 1 of the present invention; Figure 3 This is a plasticity test curve of the photoelectric synaptic device in Embodiment 1 of the present invention.

[0043] Explanation of reference numerals in the accompanying drawings: 101-Si substrate, 102-SiO2 layer, 103-Ag electrode, 104-MXene layer, 105-ZnO layer, 106-patterned Se layer. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0045] The testing method of this invention: The photoelectric and photosynaptic properties of the device are characterized using a Keithley 2636B semiconductor testing system equipped with a multi-band laser. During testing, probes are placed in contact with the electrodes at both ends of the device, and all tests are performed under normal temperature and pressure conditions. Depending on the testing requirements, continuous or pulsed light of the corresponding wavelength is provided by the multi-band laser, and the current response of the device is recorded under set bias conditions to characterize the device's photocurrent response characteristics, excitatory postsynaptic current characteristics, and short-term synaptic plasticity behavior.

[0046] Example 1: Fabrication of MXene / ZnO / heterogeneous optosynaptic devices SiO2 / Si wafers with an N100 oxide layer thickness of 285 nm and an overall thickness of 500 μm from Lijing Electronics Co., Ltd. were sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 10 min each. After being dried with nitrogen, they were subjected to plasma treatment for 5 min to improve the hydrophilicity of the substrate surface, and then an 80 nm Ag electrode was sputtered by magnetron sputtering.

[0047] 2 g of LiF was dissolved in 20 mL of 9 mol / L HCl and magnetically stirred for 15 min. Then, 3 g of Ti3AlC2 powder was slowly added, and etching was performed by continuous stirring at 400 rpm for 48 h at 40 °C. After etching, 5 mL of 2 mol / L HCl was added to the resulting suspension for washing once. After centrifugation at 3000 rpm for 30 s, the supernatant was discarded. The precipitate obtained after centrifugation was then resuspended and washed with deionized water. The steps of centrifugation and discarding the supernatant were repeated until the supernatant obtained after centrifugation was dark green and the pH was approximately 6.

[0048] The resulting dispersion was then sonicated for 1 h under an argon atmosphere and an ice-water bath. The supernatant was collected by centrifugation to obtain a Ti3AlC2 MXene dispersion. The treated substrate was placed on a heating stage heated to 100°C, and the spray gun was fixed 20 cm away from the substrate. The MXene dispersion was sprayed onto the substrate surface to form a uniform MXene film with a thickness of 300 nm. Subsequently, commercial ZnO powder was ground for 1 h and dispersed in anhydrous ethanol. After sonication for 30 min, a ZnO dispersion was obtained. The ZnO dispersion was then sprayed onto the surface of the MXene layer at 100°C to form a ZnO film with a thickness of 800 nm, resulting in an MXene / ZnO bilayer structure.

[0049] The AZ5214E ​​photoresist from Suzhou Ruicai Semiconductor Co., Ltd. was spin-coated onto the surface of the prepared MXene / ZnO bilayer film. First, the photoresist was spin-coated at 600 rpm for 10 s, and then at 3000 rpm for 60 s to ensure uniform coverage of the sample surface. The photoresist was then pre-baked for 1 min and exposed to ultraviolet light using either a mask with a preset square pattern or a maskless exposure method to create a difference in solubility between the exposed and unexposed areas. Afterward, the photoresist was developed by immersion in a developer for 60 s to remove the photoresist in the corresponding areas, thereby forming a uniformly distributed square pattern window on the sample surface.

[0050] The sample with the patterned window was placed in a thermal evaporation apparatus, and a Se thin film was deposited under vacuum conditions using Se as the evaporation source; the thermal evaporation vacuum degree was 2 × 10⁻⁶. −4 The photoresist was removed at a rate of 1 nm / s and a thickness of 100 nm. The deposition process was carried out at room temperature. After evaporation, the sample was immersed in acetone to remove the photoresist, and the Se material on the photoresist was removed along with the photoresist, resulting in a uniformly distributed square patterned Se film. Electrode pattern windows were then formed on the device surface using the same photolithography process. The sample was then placed in a magnetron sputtering apparatus with an Ag target as the sputtering source, and magnetron sputtering deposition was performed in an Ar atmosphere. The base vacuum of the magnetron sputtering was 7 × 10⁻⁶. −4 The working pressure was 0.6 Pa, the sputtering power was 30 W, the substrate temperature was room temperature, and the thickness of the deposited Ag electrode was 80 nm. After deposition, the photoresist and the Ag material covering it were removed to form a patterned Ag electrode, and finally the MXene / ZnO / heterogeneous structure optosynaptic device was obtained.

[0051] like Figure 1 As shown, the MXene / ZnO / patterned Se heterostructure device includes a Si substrate 101, a SiO2 layer 102 disposed on the surface of the Si substrate 101, an Ag electrode 103 disposed on the surface of the SiO2 layer 102, an MXene layer 104 disposed on the surface of the Ag electrode 103, a ZnO layer 105 disposed on the surface of the MXene layer 104, a patterned Se layer 106 disposed on the surface of the ZnO layer 105, and an Ag electrode 103 disposed on the surface of the patterned Se layer 106.

[0052] The Ag electrode 103 includes a lower Ag electrode located at the bottom of the device and an upper Ag electrode located at the top of the device. The MXene layer 104 provides a highly conductive channel to facilitate the rapid transport and extraction of photogenerated carriers; the ZnO layer 105 is used to construct a heterojunction and enhance the device's photoresponse capability in the ultraviolet band; the patterned Se layer 106 enhances the device's absorption capability in the visible light band and improves the device's wavelength selectivity and bifacial asymmetric photoresponse characteristics.

[0053] Tests showed that the device could generate a stable photocurrent response under 365 nm ultraviolet light irradiation and 0 V bias conditions; under pulsed light stimulation, the device exhibited obvious excitatory postsynaptic current characteristics and good short-term synaptic plasticity behavior.

[0054] Example 2: Fabrication of a thin ZnO layer MXene / ZnO / patterned Se heterostructure opto-synaptic device SiO2 / Si wafers of type N100 with an oxide layer thickness of 285 nm and an overall thickness of 500 μm from Lijing Electronics Co., Ltd. were sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 15 min each. After being dried with nitrogen, they were subjected to plasma treatment for 3 min to improve the hydrophilicity of the substrate surface, and then an 80 nm Ag electrode was sputtered by magnetron sputtering.

[0055] 2 g of LiF was dissolved in 20 mL of 9 mol / L HCl and magnetically stirred for 15 min. Then, 3 g of Ti3AlC2 powder was slowly added, and the mixture was continuously stirred at 40 °C for 48 h for etching. After etching, the resulting suspension was washed once with 5 mL of 2 mol / L HCl, centrifuged at 3000 rpm for 30 s, and the supernatant was discarded. The precipitate was then resuspended and washed with deionized water, and the centrifugation and supernatant discarding steps were repeated until the pH of the supernatant obtained by centrifugation was approximately 6. Subsequently, the resulting dispersion was sonicated for 1 h under an argon atmosphere and an ice-water bath, and the supernatant was collected by centrifugation to obtain the Ti3AlC2 MXene dispersion.

[0056] The treated substrate was placed on a heating stage heated to 100°C, and the spray gun was fixed 20 cm away from the substrate. MXene dispersion was sprayed onto the substrate surface to form a uniform MXene film with a thickness of 300 nm. Subsequently, commercial ZnO powder was ground for 1 h and dispersed in anhydrous ethanol. After sonication for 30 min, a ZnO dispersion was obtained. The ZnO dispersion was then sprayed onto the surface of the MXene layer at 100°C. By reducing the spraying time and number of sprays, a ZnO film with a thickness of 300 nm was formed, resulting in a thin ZnO layer MXene / ZnO bilayer structure.

[0057] The AZ5214E ​​photoresist from Suzhou Ruicai Semiconductor Co., Ltd. was spin-coated onto the surface of the prepared MXene / ZnO bilayer film. First, the photoresist was spin-coated at 600 rpm for 10 s, and then at 3000 rpm for 60 s to ensure uniform coverage of the sample surface. The photoresist was then pre-baked for 1 min and exposed to ultraviolet light using either a mask with a preset square pattern or a maskless exposure method to create a difference in solubility between the exposed and unexposed areas. Afterward, the photoresist was developed by immersion in a developer for 60 s to remove the photoresist in the corresponding areas, thereby forming a uniformly distributed square pattern window on the sample surface.

[0058] The sample with the patterned window was placed in a thermal evaporation apparatus, and a Se thin film was deposited under vacuum conditions using Se as the evaporation source; the thermal evaporation vacuum degree was 2 × 10⁻⁶. -4 The photoresist was removed at a rate of 1 nm / s and a thickness of 100 nm. The deposition process was carried out at room temperature. After evaporation, the sample was immersed in acetone to remove the photoresist, and the Se material on the photoresist was removed along with the photoresist, resulting in a uniformly distributed square patterned Se film. Electrode pattern windows were then formed on the device surface using the same photolithography process. The sample was then placed in a magnetron sputtering apparatus with an Ag target as the sputtering source, and magnetron sputtering deposition was performed in an Ar atmosphere. The base vacuum of the magnetron sputtering was 7 × 10⁻⁶. -4 The working pressure was 0.6 Pa, the sputtering power was 30 W, the substrate temperature was room temperature, and the thickness of the deposited Ag electrode was 80 nm. After deposition, the photoresist and the Ag material covering it were removed to form a patterned Ag electrode, and finally the MXene / ZnO / heterogeneous structure opto-synaptic device of the thin ZnO layer was obtained.

[0059] Test results show that the device can generate a stable photocurrent response under 365 nm ultraviolet light irradiation and 0 V bias conditions. Due to the reduced ZnO layer thickness, incident light can more easily pass through the ZnO layer and couple with the underlying interface, resulting in improved visible light-assisted response and interface carrier transport. In double-sided incident tests, the device also exhibits asymmetric photoresponse characteristics and good photosynaptic behavior.

[0060] Example 3: Fabrication of low-coverage patterned Se MXene / ZnO / heterogeneous optosynaptic devices SiO2 / Si wafers of type N100 with an oxide layer thickness of 285 nm and an overall thickness of 500 μm from Lijing Electronics Co., Ltd. were sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 10 min each. After being dried with nitrogen, they were subjected to plasma treatment for 5 min to improve the hydrophilicity of the substrate surface, and then an 80 nm Ag electrode was sputtered by magnetron sputtering.

[0061] 2 g of LiF was dissolved in 20 mL of 9 mol / L HCl and magnetically stirred for 15 min. Then, 3 g of Ti3AlC2 powder was slowly added, and the mixture was continuously stirred at 40 °C for 48 h for etching. After etching, 5 mL of 2 mol / L HCl was added to the resulting suspension for washing once. After centrifugation at 3000 rpm for 30 s, the supernatant was discarded. The precipitate obtained after centrifugation was then resuspended and washed with deionized water. The steps of centrifugation and discarding the supernatant were repeated until the supernatant obtained after centrifugation was dark green and the pH was approximately 6.

[0062] The resulting dispersion was then sonicated for 1 h under an argon atmosphere and an ice-water bath, and the supernatant was collected by centrifugation to obtain the Ti3AlC2 MXene dispersion.

[0063] The treated substrate was placed on a heating stage heated to 100°C, and the spray gun was fixed 20 cm away from the substrate. MXene dispersion was sprayed onto the substrate surface to form a uniform MXene film with a thickness of 300 nm. Subsequently, commercial ZnO powder was ground for 1 h and dispersed in anhydrous ethanol. After sonication for 30 min, a ZnO dispersion was obtained. The ZnO dispersion was then sprayed onto the surface of the MXene layer at 100°C to form a ZnO film with a thickness of 800 nm, resulting in an MXene / ZnO bilayer structure.

[0064] The AZ5214E ​​photoresist from Suzhou Ruicai Semiconductor Co., Ltd. was spin-coated onto the surface of the prepared MXene / ZnO bilayer film. Spin-coating was first performed at 600 rpm for 10 s, and then at 3000 rpm for 60 s to ensure uniform coverage of the photoresist on the sample surface. Subsequently, the photoresist was pre-baked for 1 min, and then exposed to ultraviolet light using a mask with a preset small and / or large-spaced square pattern window pattern or without a mask to create a difference in solubility between the exposed and unexposed areas of the photoresist. After that, the area was developed by immersion in a developer for 60 s to remove the photoresist in the corresponding areas, thereby forming uniformly distributed small and / or large-spaced square pattern windows on the sample surface to reduce the coverage of Se on the device surface.

[0065] The sample with the patterned window was placed in a thermal evaporation apparatus, and a Se thin film was deposited under vacuum conditions using Se as the evaporation source; the thermal evaporation vacuum degree was 2 × 10⁻⁶. -4 The evaporation rate was 1 nm / s, the deposition thickness was 100 nm, and the deposition process was carried out at room temperature. After evaporation, the sample was immersed in acetone to remove the photoresist, and the Se material on the photoresist was removed along with the photoresist, thus obtaining a low-coverage patterned Se film.

[0066] Subsequently, the same photolithography process was used to form electrode pattern windows on the device surface, and the sample was placed in a magnetron sputtering apparatus, using an Ag target as the sputtering source, to perform magnetron sputtering deposition in an Ar atmosphere; the base vacuum level of the magnetron sputtering was 7 × 10⁻⁶. -4 The working pressure was 0.6 Pa, the sputtering power was 30 W, the substrate temperature was room temperature, and the thickness of the deposited Ag electrode was 80 nm. After deposition, the photoresist and the Ag material covering it were removed to form a patterned Ag electrode, and finally the low-coverage patterned Se MXene / ZnO / heterogeneous structure optosynaptic device was obtained.

[0067] Test results show that under 520 nm visible light illumination and 0 V bias conditions, the device exhibits a small photocurrent output; under periodic light pulse stimulation, the device possesses certain photocurrent retention characteristics and synaptic plasticity response. Compared with Example 1, as the patterned Se coverage area decreases, the device's response in the visible light band weakens, and its wavelength selectivity deteriorates.

[0068] Comparative Example 1: MXene / ZnO heterostructure device without Se layer SiO2 / Si wafers of type N100 with an oxide layer thickness of 285 nm and an overall thickness of 500 μm from Lijing Electronics Co., Ltd. were sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 10 min each. After being dried with nitrogen, they were subjected to plasma treatment for 5 min to improve the hydrophilicity of the substrate surface, and then an 80 nm Ag electrode was sputtered by magnetron sputtering.

[0069] 2 g of LiF was dissolved in 20 mL of 9 mol / L HCl and magnetically stirred for 15 min. Then, 3 g of Ti3AlC2 powder was slowly added and etched by continuous stirring at 40 °C for 48 h.

[0070] After etching, 5 mL of 2 mol / L HCl was added to the resulting suspension for washing once. After centrifugation at 3000 rpm for 30 s, the supernatant was discarded. Deionized water was then added to the precipitate obtained by centrifugation for resuspending and washing. The steps of centrifugation and discarding the supernatant were repeated until the pH of the supernatant obtained by centrifugation was approximately 6. Subsequently, the resulting dispersion was sonicated for 1 h under an argon atmosphere and an ice-water bath. The supernatant was collected by centrifugation to obtain the Ti3AlC2 MXene dispersion.

[0071] The treated substrate was placed on a heating stage heated to 100°C, and the spray gun was fixed 20 cm away from the substrate. MXene dispersion was sprayed onto the substrate surface to form a uniform MXene film with a thickness of 300 nm. Subsequently, commercial ZnO powder was ground for 1 h and dispersed in anhydrous ethanol. After sonication for 30 min, a ZnO dispersion was obtained. The ZnO dispersion was then sprayed onto the surface of the MXene layer at 100°C to form a ZnO film with a thickness of 800 nm, resulting in an MXene / ZnO bilayer structure.

[0072] Subsequently, photolithography was used to form electrode pattern windows on the device surface, and the sample was placed in a magnetron sputtering apparatus. Using an Ag target as the sputtering source, magnetron sputtering deposition was performed in an Ar atmosphere; the base vacuum level of the magnetron sputtering was 7 × 10⁻⁶. -4 The working pressure was 0.6 Pa, the sputtering power was 30 W, the substrate temperature was room temperature, and the thickness of the deposited Ag electrode was 80 nm. After deposition, the photoresist and the Ag material covering it were removed to form a patterned Ag electrode, and finally an MXene / ZnO heterostructure device without a Se layer was obtained.

[0073] Test results show that the device can generate a certain photocurrent response under ultraviolet light irradiation, but has almost no response in the visible light band. Furthermore, due to the lack of absorption and interface modulation effects of the Se layer for visible light, the device's bifacial asymmetric photoresponse characteristics are not obvious, and its photosynaptic behavior is weak. These results indicate that introducing a Se layer helps to improve the device's visible light response capability, expand its spectral response range, and enhance its synaptic function.

[0074] Comparative Example 2: ZnO / patterned Se heterostructure device without MXene layer SiO2 / Si wafers of type N100 with an oxide layer thickness of 285 nm and an overall thickness of 500 μm from Lijing Electronics Co., Ltd. were sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 10 min each. After being dried with nitrogen, they were subjected to plasma treatment for 5 min to improve the hydrophilicity of the substrate surface, and then an 80 nm Ag electrode was sputtered by magnetron sputtering.

[0075] Commercial ZnO powder was ground for 1 h and dispersed in anhydrous ethanol. After sonication for 30 min, a ZnO dispersion was obtained. The treated substrate was then placed on a heating table heated to 100°C. The spray gun was fixed 20 cm away from the substrate, and the ZnO dispersion was directly sprayed onto the substrate surface to form a uniform ZnO film with a thickness of 800 nm.

[0076] Compared with Example 1, the preparation steps of the MXene film are omitted in this comparative example.

[0077] The ZnO thin film was spin-coated with AZ5214E ​​photoresist from Suzhou Ruicai Semiconductor Co., Ltd. The spin coating was first performed at 600 rpm for 10 s, then at 3000 rpm for 60 s, to ensure uniform coverage of the sample surface. The photoresist was then pre-baked for 1 min, followed by UV exposure using either a mask with a pre-set square pattern or no mask, to create a difference in solubility between the exposed and unexposed areas. Afterward, the area was developed by immersion in developer for 60 s to remove the photoresist from the corresponding areas, thus forming uniformly distributed square pattern windows on the sample surface.

[0078] The sample with the patterned window was placed in a thermal evaporation apparatus, and a Se thin film was deposited under vacuum conditions using Se as the evaporation source; the thermal evaporation vacuum degree was 2 × 10⁻⁶. -4 Pa, evaporation rate of 1 nm / s, deposition thickness of 100 nm, deposition process at room temperature.

[0079] After evaporation, the sample was immersed in acetone to remove the photoresist, and the Se material on the photoresist was removed along with the photoresist, thus obtaining a patterned Se thin film. Electrode pattern windows were then formed on the device surface using the same photolithography process, and the sample was placed in a magnetron sputtering apparatus with an Ag target as the sputtering source, and magnetron sputtering deposition was performed in an Ar atmosphere; the base vacuum of the magnetron sputtering was 7 × 10⁻⁶. -4 The working pressure was 0.6 Pa, the sputtering power was 30 W, the substrate temperature was room temperature, and the thickness of the deposited Ag electrode was 80 nm. After deposition, the photoresist and the Ag material covering it were removed to form a patterned Ag electrode, and finally a ZnO / patterned Se heterostructure device without an MXene layer was obtained.

[0080] Test results show that the device can generate photoresponse under both ultraviolet and visible light irradiation, but the overall photocurrent is small, the response speed is slow, and the device stability is poor. Analysis suggests that the lack of an MXene layer results in insufficient conductive channels, reduced transport and extraction efficiency of interfacial carriers, and increased recombination of photogenerated carriers. These results indicate that an MXene layer helps improve device conductivity, promotes carrier separation and transport, and enhances photoresponse performance.

[0081] Comparative Example 3: MXene / ZnO / Se heterostructure device with continuous Se thin film SiO2 / Si wafers of type N100 with an oxide layer thickness of 285 nm and an overall thickness of 500 μm from Lijing Electronics Co., Ltd. were sequentially ultrasonically cleaned in acetone, ethanol and deionized water for 10 min each. After being dried with nitrogen, they were subjected to plasma treatment for 5 min to improve the hydrophilicity of the substrate surface, and then an 80 nm Ag electrode was sputtered by magnetron sputtering.

[0082] 2 g of LiF was dissolved in 20 mL of 9 mol / L HCl and magnetically stirred for 15 min. Then, 3 g of Ti3AlC2 powder was slowly added, and the mixture was continuously stirred at 40 °C for 48 h for etching. After etching, 5 mL of 2 mol / L HCl was added to the resulting suspension for washing once. After centrifugation at 3000 rpm for 30 s, the supernatant was discarded. The precipitate obtained after centrifugation was then resuspended and washed with deionized water. The steps of centrifugation and discarding the supernatant were repeated until the pH of the supernatant obtained after centrifugation was approximately 6.

[0083] The obtained dispersion was then sonicated for 1 h under an argon atmosphere and an ice-water bath. The supernatant was collected by centrifugation to obtain a Ti3AlC2 MXene dispersion. The treated substrate was placed on a heating stage heated to 100°C, and the spray gun was fixed 20 cm away from the substrate. The MXene dispersion was sprayed onto the substrate surface to form a uniform MXene film with a thickness of 300 nm. Subsequently, commercial ZnO powder was ground for 1 h and dispersed in anhydrous ethanol. After sonication for 30 min, a ZnO dispersion was obtained. The ZnO dispersion was then sprayed onto the surface of the MXene layer at 100°C to form a ZnO film with a thickness of 800 nm, resulting in an MXene / ZnO bilayer structure. Instead of using photolithography to form patterned windows, the sample was directly placed in a thermal evaporation device. Using Se as the evaporation source, a continuous Se film was deposited on the ZnO film surface under vacuum conditions. The thermal evaporation vacuum degree was 2 × 10⁻⁶. -4 Pa, evaporation rate of 1 nm / s, deposition thickness of 100 nm, deposition process at room temperature.

[0084] Compared to Example 1, this comparative example omits the patterned Se thin film preparation step and instead directly deposits a continuous Se thin film. Electrode pattern windows are then formed on the device surface using photolithography, and the sample is placed in a magnetron sputtering apparatus with an Ag target as the sputtering source, performing magnetron sputtering deposition in an Ar atmosphere; the base vacuum level of the magnetron sputtering is 7 × 10⁻⁶. -4 The working pressure was 0.6 Pa, the sputtering power was 30 W, the substrate temperature was room temperature, and the thickness of the deposited Ag electrode was 80 nm. After deposition, the photoresist and the Ag material covering it were removed to form a patterned Ag electrode, and finally a continuous Se thin film MXene / ZnO / Se heterostructure device was obtained.

[0085] Tests showed that the device could generate a significant and repeatable photocurrent response under illumination, exhibiting typical photodetector characteristics. However, after the pulsed light stimulation was removed, the device current quickly returned to its initial state, making it difficult to maintain a significant residual conductance. The excitatory postsynaptic current decay process was short, and it hardly exhibited effective memory retention, making it difficult to achieve typical photosynaptic behavior.

[0086] Analysis suggests that the continuous Se thin film forms a large-area continuous conductive and light absorption channel on the device surface, making the generation, transport and recombination of photogenerated carriers more similar to conventional photoconductive response. This weakens the local interface modulation and charge trapping / slow release effect, causing the device to behave more like a conventional photodetector rather than a photosynaptic device with memory function.

[0087] The results indicate that a continuous thin-film structure of the Se layer is not conducive to the formation of stable and controllable synaptic weight changes in the device; while using a patterned Se thin film can effectively enhance the local interface effect and carrier control capability, thereby endowing the device with more obvious memory characteristics and photoelectric synaptic functions. Therefore, the patterned Se structure is an important improvement point for realizing the performance enhancement of the photoelectric synaptic device of this invention.

[0088] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for fabricating a heterogeneous opto-synaptic device, characterized in that, Includes the following steps: S11: Coat the substrate surface with an MXene aqueous dispersion and heat-treat at 80-120℃ for 30-60 s to form an MXene layer; S12: Coat the surface of the MXene layer with a ZnO alcohol dispersion and heat-treat at 80-120℃ for 60-90 s to form a ZnO layer; S13: Se layer and metal electrode are sequentially deposited on the surface of the ZnO layer to obtain the heterostructure photoelectric synapse device; both the Se layer and the metal electrode are patterned.

2. The preparation method according to claim 1, characterized in that: The preparation method of the MXene aqueous dispersion is as follows: S21: Add the metal carbide to an aqueous solution containing hydrochloric acid and lithium fluoride, and etch at 35-45℃ for 40-56 h to obtain an etching mixture; S22: Separate the solid and liquid components of the etching mixture, and disperse the obtained solid in water for 0.5-1.5 h to obtain a mixed dispersion; the dispersion conditions are a protective atmosphere and an ice-water bath. S23: Separate the solid and liquid components of the mixed dispersion and collect the liquid to obtain the MXene aqueous dispersion.

3. The preparation method according to claim 2, characterized in that: In step S22, the solid-liquid mixture is washed with hydrochloric acid before solid-liquid separation.

4. The preparation method according to claim 2, characterized in that: In steps S22 and S23, the solid-liquid separation is performed by centrifugation at a speed of 3000-5000 rpm for 150-210 s.

5. The preparation method according to claim 1, characterized in that: The substrate is a composite substrate composed of silicon, silicon dioxide and metal electrodes.

6. The preparation method according to claim 1, characterized in that: The ZnO alcohol dispersion was obtained by grinding ZnO and adding it to ethanol.

7. The preparation method according to claim 1, characterized in that: In step S13, the patterning process is as follows: S31: Photolithographic patterning is performed after photoresist is coated on the surface of the previous layer; S32: Deposit a Se or metal electrode on the pattern; S32: Remove the photoresist to complete the patterning process.

8. The preparation method according to claim 1, 5, or 7, characterized in that: The metal electrodes are all made of gold, silver, aluminum, or magnesium.

9. The preparation method according to claim 1 or 7, characterized in that: The Se deposition method is thermal deposition, and the metal electrode deposition method is magnetron sputtering.

10. A heterogeneous opto-synaptic device prepared by the preparation method according to any one of claims 1-9.

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