Two-dimensional SnS2 synaptic device with dynamic recognition characteristic
By introducing synaptic devices based on two-dimensional SnS2 materials into CMOS image sensors, the problem of limited frame rate and time resolution in motion recognition of traditional CMOS image sensors is solved, and multi-time scale functions and higher recognition accuracy are achieved.
Patent Information
- Application Number
- CN202411935147.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-26
- Publication Date
- 2025-04-25
AI Technical Summary
Traditional CMOS image sensors are limited by limited frame rate and time resolution in motion recognition, resulting in blurred motion recognition and loss of information, and cannot achieve accurate motion recognition and classification.
A synaptic device constructed based on two-dimensional SnS2 material was used to prepare a SnS2 semiconductor thin film by salt-assisted chemical vapor deposition method, and the electrode path was etched through electron beam exposure technology to form a SnS2 synaptic device with dynamic modulation conductance value.
The multi-time scale function of synaptic devices is realized, which can adjust the conductivity under different light stimuli, improve the resolution of CMOS in-memory computing for movements on different time scales, and improve classification accuracy and recognition accuracy.
Smart Images
Figure CN119894359A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of two-dimensional materials and synaptic computing, and specifically relates to a two-dimensional SnS2 synaptic device with dynamic recognition characteristics. Background Art
[0002] In-memory computation and real-time learning for motion recognition is an important and emerging field in computer vision, providing the necessary intelligence for machines to understand the complex motion patterns around them. On the hardware side, the performance of traditional complementary metal oxide semiconductor (CMOS) image sensors is limited by their limited frame rate and temporal resolution. Using them for in-memory computation can lead to blurred motion recognition and information loss, hindering accurate motion recognition and classification.
[0003] To develop hardware compatible with widely controllable dynamics and achieve an adjustable dynamic range, optoelectronic devices with ultra-high responsiveness, high sensitivity, and excellent stability are urgently needed. Synaptic devices constructed from two-dimensional semiconductor materials have the ability to be tunable over a certain time scale, adjusting their conductivity within a controllable dynamic range. This allows for an adjustable dynamic range in hardware, potentially improving the classification and recognition accuracy of in-memory computing based on traditional CMOS. Summary of the Invention
[0004] Based on the above analysis, the present invention proposes a two-dimensional SnS2 synaptic device with dynamic recognition characteristics, whose conductance value can be dynamically modulated and can be used to improve the classification accuracy of traditional CMOS in-memory computing.
[0005] To this end, the first technical solution of the present application discloses a method for preparing a two-dimensional SnS2 synaptic device, comprising the following steps:
[0006] Preparation of SnS2 semiconductor thin film: Using SiO2 / Si as substrate, SnS2 semiconductor thin film was prepared by salt-assisted chemical vapor deposition;
[0007] Preparation of SnS2 semiconductor devices: Spin-coating photoresist on the surface of the prepared SnS2 film, etching electrode paths on the SnS2 semiconductor film using electron beam exposure technology, and then evaporating Cr / Au electrodes through thermal evaporation technology to obtain SnS2 synaptic devices.
[0008] Furthermore, potassium iodide is used for the salt-assisted reaction.
[0009] Furthermore, the salt-assisted chemical vapor deposition method is to react sulfur powder with tin oxide and potassium iodide to form a SnS2 thin film under a chemical deposition method.
[0010] Furthermore, the mass ratio of tin oxide to potassium iodide is 5:1.
[0011] Furthermore, the reaction is carried out in a hot environment, wherein the temperature of the hot environment is 200° C. in the sulfur powder temperature zone and 700° C. in the tin oxide and potassium iodide temperature zone.
[0012] And, the SnS2 synaptic device prepared according to the above preparation method.
[0013] The second technical solution of the present application discloses a dynamically adjustable light response of a SnS2 synaptic device, which can be used in the field of computer vision and dynamic recognition applications.
[0014] The beneficial effects of the present invention are:
[0015] (1) The method of the present invention adopts a salt-assisted chemical vapor deposition method to synthesize a two-dimensional SnS2 thin film. The EDS spectrum of the SnS2 thin film under TEM proves the inherent S defects in the material itself. This inherent S defect affects the electron transport properties of SnS2, causing it to exhibit unique conductivity behavior.
[0016] (2) The SnS2-based synaptic device demonstrated the correlation between the optical response and the duration of light stimulation. Under short-term irradiation, it exhibited excellent optical sensing performance and achieved a fast response of 1.5ms / 8.5ms. Under long-term irradiation, it exhibited a sustained optical response. By further changing the light power density, pulse width, and number of pulses, the SnS2-based synaptic device achieved a transition from short-term potentiation (STP) to long-term potentiation (LTP). Therefore, the controllable light-modulated conductance behavior can be used to represent the time scale of dynamic changes in the light response, thereby realizing the multi-timescale function of the synaptic device.
[0017] (3) The two-dimensional semiconductor device fabricated by the method of the present invention has the advantage of multiple time scales, thereby achieving an adjustable dynamic range in hardware. Under different light stimuli, it has a certain time scale and adjustable photoelectric response capability, and its conductivity can be adjusted within a controllable dynamic range, thus having an adjustable dynamic range in hardware. It can be used to improve the resolution of motion at different time scales in CMOS memory reservoir calculations. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 This is a scanning electron microscope (SEM) image of a two-dimensional SnS2 thin film prepared by chemical vapor deposition;
[0019] Figure 2 EDS characterization of the grown two-dimensional SnS2 film;
[0020] Figure 3 SEM image of SnS2 synaptic device fabricated based on two-dimensional SnS2 thin film;
[0021] Figure 4 is the photoelectric response of the SnS2 synaptic device under short pulses;
[0022] Figure 5 is the photoelectric response of the SnS2 synaptic device under different light power densities;
[0023] Figure 6 is the photoelectric response of the SnS2 synaptic device under different light pulse durations;
[0024] Figure 7 is the photoelectric response of the SnS2 synaptic device under different pulse numbers. DETAILED DESCRIPTION
[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.
[0026] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the application. The technology, methods and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be considered as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of the exemplary embodiments can have different values. It should be noted that similar numbers and letters represent similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.
[0027] The first technical solution of the present application discloses a method for preparing a two-dimensional SnS2 synaptic device, comprising the following steps:
[0028] Preparation of SnS2 semiconductor thin film: Using SiO2 / Si as substrate, SnS2 semiconductor thin film was prepared by salt-assisted chemical vapor deposition;
[0029] Preparation of SnS2 synaptic device: Spin-coating photoresist on the surface of the prepared SnS2 film, etching electrode paths on the SnS2 semiconductor film using electron beam exposure technology, and then evaporating Cr / Au electrodes through thermal evaporation technology to obtain the SnS2 synaptic device.
[0030] In this embodiment, the inert gas introduced during the chemical vapor deposition (CVD) process is argon (Ar). During the entire process, sulfur powder (S) is placed in an upstream quartz boat, while tin oxide (SnO2) and potassium iodide (KI) are placed in a downstream quartz boat. The S is heated and evaporated to form sulfur vapor, which is then transported by the Ar to the downstream quartz boat to react with the SnO2 and KI to form a SnS2 semiconductor film. During this process, the upstream and downstream heating zones are heated to 200°C and 700°C, respectively, within 20 minutes and maintained for 20 minutes for growth. Afterwards, heating is stopped and the film is allowed to cool naturally to room temperature.
[0031] In a further embodiment, the method for preparing the SnS2 synaptic device is specifically as follows:
[0032] S1. Spin-coating photoresist: The photoresist is methyl methacrylate (PMMA, 950A4), which is spin-coated and then dried to obtain a PMMA film.
[0033] S2. Wet transfer: The PMMA film loaded with SnS2 is peeled off from the SiO2 / Si substrate and immersed in a potassium hydroxide (KOH) solution for wet transfer. The grown SnS2 film is transferred to a newly marked silicon-based material covered with 285nm SiO2. Repeat step S1 to cover the sample surface with photoresist.
[0034] S3. Etching: The sample obtained in S2 was etched according to a predetermined pattern by electron beam lithography (EBL) and reactive ion etching (RIE, SHL 100μ-RIE) to obtain a SnS2 synaptic device.
[0035] It should be noted that the above preparation method is only the preferred preparation method of this application and is not intended to limit this application.
[0036] The second technical solution of this application discloses a dynamically adjustable optical response of a SnS2 synaptic device, which can be used in the field of computer vision and dynamic recognition applications. The SnS2 semiconductor film in the SnS2 synaptic device obtained by the above-mentioned preparation method has its own inherent S defects, which can affect the electron transport properties of the SnS2 synaptic device, causing it to exhibit unique conductivity behavior. At the same time, its optical response is correlated with the duration of light stimulation, showing excellent optical sensing performance, and can achieve a fast response of 1.5ms / 8.5ms. Under long-term irradiation, the synaptic device exhibits a continuous and adjustable optical response, thereby realizing the multi-time scale function of the device, and using it for dynamic recognition in the field of computer vision, and achieving an adjustable dynamic range from the hardware.
[0037] The technical effects of this application will be further explained below through specific embodiments and drawings.
[0038] Example 1 Preparation of two-dimensional SnS2 thin film by chemical vapor deposition
[0039] Using a dual-zone tube furnace, potassium iodide-assisted chemical vapor deposition (KI) was used to grow two-dimensional SnS2 triangles with side lengths up to 80μm. The specific implementation steps were: an excess of sulfur powder (99.999% Aladdin) was placed in one quartz boat, serving as the upstream zone; 10mg of tin oxide powder (99.99% Adamas SnO2) and 2mg of potassium iodide (99% Macklin KI) powder were placed in another quartz boat, with a clean SiO2 / Si substrate placed upside down on the boat, serving as the downstream zone. Ar was introduced at a flow rate of 500sccm for 20 minutes to expel excess water and air. The upstream and downstream zones were heated to 200°C and 700°C, respectively, over 20 minutes and held for 20 minutes for growth. During this process, sulfur evaporated and was transported downstream by the Ar to react with SnO2 and KI, forming a SnS2 film. Finally, the heating was stopped and the film was gradually cooled to room temperature to obtain a two-dimensional SnS2 thin film.
[0040] The obtained two-dimensional SnS2 film was characterized by scanning electron microscopy (SEM), and the image was obtained as follows Figure 1 As shown in the figure, it can be seen that the triangle side length of the two-dimensional SnS2 thin film prepared in Example 1 of the present application can reach 80μm.
[0041] Figure 2 The energy dispersive spectroscopy (EDS) of a two-dimensional SnS2 film obtained under a transmission electron microscope (TEM) shows that the atomic ratio of S to Sn in the grown sample is 1.94:1, indicating the presence of S defects in the SnS2 sample grown by chemical vapor deposition (CVD). This inherent S defect can produce significant electronic effects in SnS2, resulting in its unique conductive behavior.
[0042] Example 2 Preparation of SnS2 Synaptic Device and Characterization of Its Photoelectric Synaptic Performance
[0043] The SnS2 sample grown by CVD in Example 1 was transferred to a labeled SiO2 / Si substrate using wet transfer and EBL techniques and patterned. Cr / Au electrodes were then fabricated using EBL and thermal evaporation to complete the preparation of the SnS2 synaptic device. The preparation method is as follows:
[0044] The SnS2 synaptic device is fabricated from a SnS2 semiconductor thin film grown by CVD. Specifically, the SiO2 / Si substrate bearing the SnS2 thin film obtained in the aforementioned growth process is spin-coated with polymethyl methacrylate (PMMA, 950A4) in ambient air at room temperature. A pre-coating process is performed for 10 seconds at 500 rpm before the actual spin-coating, ensuring that the PMMA is evenly coated on the surface of the growth substrate obtained in the aforementioned process. After the pre-coating, the PMMA film is spin-coated for 60 seconds at 4000 rpm. After spin-coating, the PMMA film is dried on a hot plate at 180°C for 120 seconds to form a film. The growth substrate is then immersed in a potassium hydroxide (KOH) solution for a standard wet transfer step. Once the PMMA film bearing the SnS2 is peeled off from the growth substrate, the SnS2 film can be wet-transferred from the original growth substrate to a newly labeled silicon substrate coated with 285 nm SiO2. Subsequently, the sample is immersed in acetone and subjected to a standard lift-off procedure. After the PMMA on the sample surface is completely cleaned, the above spin coating and drying steps are repeated. After a newly covered PMMA film is obtained on the sample surface, a pattern etching procedure is performed. The sample pattern is etched by electron beam lithography (EBL) and reactive ion etching (RIE, SHL 100μ-RIE). First, a regular sample pattern is engraved by EBL technology. Through the development and fixing process, the unphotoetched PMMA film is left on the surface of the sample substrate. Then, RIE is used to perform reactive ion etching on the sample not covered with PMMA to remove the excess sample. Subsequently, a lift-off procedure is performed with acetone to obtain a patterned sample. After the sample patterning is completed, the above spin coating and drying processes are repeated, and EBL is used to etch the source and drain patterns. Finally, chromium and gold metal (5 / 50nm Cr / Au) were deposited by thermal evaporation technology as electrodes, and a lift-off procedure was performed with acetone to peel off the PMMA and metal outside the pattern, completing the preparation of the SnS2 thin film-based device. In this device, the Si substrate and 285nm SiO2 were used as the back control electrode (gate) and dielectric layer, respectively.
[0045] like Figure 3 A schematic diagram of a device array fabricated using grown SnS2 thin films, captured using a scanning tunneling microscope (SEM), shows chromium and gold (5 / 50nm Cr / Au) as the source and drain electrodes, while a Si substrate and 285nm SiO2 serve as the gate control electrode and dielectric layer, respectively.
[0046] The SnS2 device was tested and characterized using a cryogenic probe system and a Keithley 2636B source meter. Voltage-current measurements were performed to obtain IV curves, with a 1V bias voltage between the source and drain electrodes. These curves were used to measure the SnS2 synaptic device's response to light. Specifically, the device was illuminated with 450nm light and its photoelectric response was studied by varying the duration, power density, and number of light pulses.
[0047] Figure 4 The figure shows the optical response of the SnS2 synaptic device under illumination with a pulse width of 100ms. As can be seen from the figure, when the light pulse duration is 100ms, the SnS2 synaptic device reports rise and fall times of 1.5ms and 8.5ms, respectively. The rise time and fall time are defined as the time required for the photocurrent to fall within the range of 10% / 90% to 90% / 10% of the peak value. This result shows that the SnS2 synaptic device we prepared has a high optical response speed and is highly responsive to light.
[0048] Figure 5 The photoelectric response of the SnS2 synaptic device under different light power densities is shown in the figure. As can be seen from the figure, the current value (postsynaptic current) of the SnS2 synaptic device changes after the light is removed by varying the light power density. Specifically, increasing the applied light power density leads to an increase in the postsynaptic current value of the SnS2 synaptic device after the light is removed.
[0049] Figure 6 This is the photoelectric response of the SnS2 synaptic device under different light pulse durations. It can be seen from the figure that by increasing the light pulse duration, the postsynaptic current value of the SnS2 synaptic device increases after the light is removed.
[0050] Figure 7 This is the photoelectric response of the SnS2 synaptic device under stimulation with different numbers of light pulses. As can be seen from the figure, by increasing the number of light pulses, the postsynaptic current value of the SnS2 synaptic device increases after the light is removed.
[0051] from Figure 5 、 Figure 6 and Figure 7We found that the SnS2 synaptic device prepared by the present application has different photoelectric responses to different light power densities, light pulse times and light pulse numbers, which can effectively simulate the transition from short-term potentiation (STP) to long-term potentiation (LTP) in response to external stimuli in organisms. From a physical mechanism point of view, this transition is due to the different degrees of light applied to the SnS2 synaptic device, which produces different degrees of photogenerated carrier accumulation in the SnS2 synaptic device, thereby causing changes in the postsynaptic current. Therefore, the SnS2 synaptic device prepared by the present application can modulate the photoelectric response level of the synaptic device by precisely controlling external light stimulation. This memristive behavior modulated by external light indicates that the SnS2 synaptic device prepared by the present application has an adjustable photoresponse and has the ability to respond to external stimuli of varying time scales. Therefore, different intensities of light stimulation can be used for targets with different motion forms to improve the recognition and classification accuracy, thereby making up for the defect of inaccurate target classification in existing in-sensor reservoir computing.
[0052] Although the present invention has been described in detail through the above embodiments, it should be understood that the above description should not be considered as limiting the present invention. After reading the above, various modifications and substitutions of the present invention will be apparent to those skilled in the art. Therefore, the scope of protection of the present invention should be defined by the appended claims.
Claims
1. A method for preparing a two-dimensional SnS2 synaptic device, characterized in that: The steps include: Preparation of SnS2 semiconductor thin film: Using SiO2 / Si as substrate, SnS2 semiconductor thin film was prepared by salt-assisted chemical vapor deposition method; Preparation of SnS2 semiconductor devices: Spin-coating photoresist on the surface of the prepared SnS2 film, etching electrode paths on the SnS2 semiconductor film using electron beam exposure technology, and then evaporating Cr / Au electrodes using thermal evaporation technology to obtain SnS2 synaptic devices.
2. The preparation method according to claim 1, characterized in that: Potassium iodide was used for the salt assistance.
3. The preparation method according to claim 1 or 2, characterized in that: The salt-assisted chemical vapor deposition method is to react sulfur powder with tin oxide and potassium iodide to form a SnS2 film under a chemical deposition method.
4. The preparation method according to claim 3, characterized in that: The mass ratio of the tin oxide to potassium iodide is 5:
1.
5. The preparation method according to claim 3, characterized in that: The reaction is carried out in a hot environment, wherein the temperature of the hot environment is 200° C. in the sulfur powder temperature zone and 700° C. in the tin oxide and potassium iodide temperature zone.
6. A SnS2 synaptic device prepared according to any one of the preparation methods of claims 1-5.
7. Application of the SnS2 synaptic device according to claim 6 in the field of computer vision and dynamic recognition.