Light control artificial synaptic device based on two-dimensional ReS2 material

Abstract

The invention belongs to the field of two-dimensional materials and synaptic devices, and particularly relates to a two-dimensional ReS2 synaptic device, a preparation method and application of the two-dimensional ReS2 synaptic device in computer image recognition. Comprising preparation of a two-dimensional ReS2 thin film and preparation of a ReS2 synaptic device, the prepared ReS2 semiconductor thin film has inherent S defects, electrons in ReS2 generate capture / decapture behaviors, and therefore the unique conductive behavior is shown. In addition, the invention also proves the correlation between the optical response of the ReS2 device and the number of light pulses, so that the controllable light modulation behavior can realize the multi-stage response of the device, and the memory characteristics of the brain can be effectively simulated. When the method is used in computer image recognition, an adjustable conductivity range can be realized from hardware.

Description

Technical Field

[0001] The present invention belongs to the field of two-dimensional materials and electronic information devices, and specifically relates to a two-dimensional ReS2 synaptic device, a preparation method thereof, and an application thereof in computer image recognition. Background Art

[0002] The ability to identify detailed information in images is critical to addressing the growing demand for data processing. The surge in data volume has increased the requirements for intelligent vision systems. On the hardware side, the delay effects and high power consumption caused by signal transmission between sensors, memory units, and processors can be solved by using artificial synaptic devices for in-sensor computing. However, traditional oxide films have difficulty responding to optical signals quickly and stably, indicating that new materials and device structures are urgently needed.

[0003] In order to develop new intelligent vision system hardware, it is urgently necessary to build synaptic devices with ultra-high light responsiveness, multi-level conductance states and good stability. Summary of the invention

[0004] Based on the above analysis, the present invention proposes a two-dimensional ReS2 synaptic device and a preparation method thereof and an application in computer image recognition. The first technical solution of the present application discloses a preparation method of a two-dimensional ReS2 synaptic device, comprising the following steps:

[0005] Preparation of ReS2 semiconductor film: Using SiO2 / Si as substrate, ReS2 semiconductor film was prepared by salt-assisted chemical vapor deposition method;

[0006] Preparation of ReS2 semiconductor devices: Cr / Au electrodes are deposited on the ReS2 semiconductor film to obtain a ReS2 synaptic device.

[0007] Furthermore, the salt used as the auxiliary salt is sodium chloride.

[0008] Furthermore, the salt-assisted chemical vapor deposition method is to react sulfur powder with rhenium dioxide and sodium chloride to form a ReS2 film under a chemical deposition method.

[0009] And, the ReS2 synaptic device prepared according to the above preparation method.

[0010] The second technical solution of the present application discloses the application of the above-mentioned ReS2 synaptic device as an optical sensor in the field of computer vision, which is used for image recognition.

[0011] The beneficial effects of the present invention are:

[0012] (1) The method of the present invention adopts salt-assisted chemical vapor deposition to synthesize a two-dimensional ReS2 thin film. The analysis of the photoelectron peak area under XPS proves the inherent S defects of the material itself. This inherent S defect causes the electrons in ReS2 to capture / de-capture behavior, causing it to exhibit unique conductivity behavior.

[0013] (2) The ReS2-based device demonstrated the correlation between the optical response and the number of light pulses. The device illuminated by 6 sets of light pulses with different numbers can show 6 different response conductance levels. The memory retention rate increases with the number of pulses. Therefore, the controllable light modulation behavior can achieve a multi-level response of the device, effectively mimicking the memory characteristics of the brain.

[0014] (3) The light-regulated artificial synaptic device based on two-dimensional ReS2 material prepared by the method of the present invention has the advantage of multi-level light response, thereby realizing an adjustable conductance range in hardware. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic diagram of chemical vapor deposition;

[0016] Figure 2 This is an optical picture of a two-dimensional ReS2 material;

[0017] Figure 3 XPS spectrum of 2D ReS2;

[0018] Figure 4 is the optical response of the device under various optical stimulation conditions;

[0019] Figure 5 It is the multi-level memory state of the device under stimulation of different pulse numbers. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments 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 creative work are within the scope of protection of the present invention.

[0021] Unless otherwise specifically stated, the relative arrangement of the parts and steps set forth in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the application. The technology, method and equipment known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology, method 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 exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, and therefore, once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0022] To this end, the first technical solution of the present application discloses a method for preparing a two-dimensional ReS2 synaptic device, comprising the following steps:

[0023] Preparation of ReS2 semiconductor film: Using SiO2 / Si as substrate, ReS2 semiconductor film was prepared by salt-assisted chemical vapor deposition method;

[0024] Preparation of ReS2 semiconductor devices: Fixing Cr / Au electrodes on the ReS2 semiconductor film to obtain ReS2 synaptic devices.

[0025] In this embodiment, the inert gas introduced in the chemical vapor deposition method is Ar gas. During the whole process, S powder is placed in an upstream quartz boat, rhenium dioxide (ReO2) and sodium chloride (NaCl) are placed in a downstream quartz boat, and the S powder is heated and evaporated by the Ar gas and transported to the downstream quartz boat to react with ReO2 and NaCl to form a ReS2 semiconductor film.

[0026] In the above process, the role of NaCl is to act as a promoter to help ReO2 sublime and accelerate the efficiency of ReS2 semiconductor film formation.

[0027] In the above process, the heating temperature zone was heated from room temperature to 150°C and 780°C at a rate of 2.9°C / min and 17.6°C / min, respectively. The reaction lasted for 12 minutes for growth, after which the heating was stopped and gradually cooled to room temperature.

[0028] In a further embodiment, the ReS2 synaptic device is prepared from a ReS2 semiconductor film, specifically:

[0029] S1. Spin coating photoresist: Spin coating photoresist on the original substrate of ReS2 thin layer, the photoresist is methyl methacrylate (PMMA, 950A4), and after spin coating, drying is performed to obtain PMMA film.

[0030] S2. Wet transfer: After the PMMA film is peeled off from the SiO2 / Si substrate, it is immersed in a KOH solution and wet-transferred to a new marked silicon-based material covered with 285nm SiO2. Step S1 is repeated to cover the sample surface with photoresist.

[0031] S3. Etching: The sample obtained in S2 is exposed to the left / right electrodes according to a predetermined pattern by electron beam lithography (EBL), and the electrode is deposited by thermal evaporation technology to obtain a SnS2 synaptic device.

[0032] The second embodiment of the present application discloses the application of the ReS2 synaptic device as an optical sensor in the field of computer vision, which is used for image recognition: the ReS2 semiconductor film in the ReS2 synaptic device obtained by the above-mentioned preparation method has its own inherent S defects, which causes the electrons in the ReS2 to produce capture / decapture behavior, thereby exhibiting unique conductivity behavior. In addition, the present application also proves the correlation between the optical response of the ReS2 device and the number of light pulses, so that the controllable light modulation behavior can achieve multi-level response of the device, effectively imitating the memory characteristics of the brain. When used in computer image recognition, an adjustable conductivity range can be achieved from the hardware.

[0033] The technical effects of the present application will be further explained below through specific embodiments and drawings.

[0034] Example 1 Preparation of two-dimensional ReS2 thin film by chemical vapor deposition

[0035] The chemical vapor deposition system uses a dual-temperature zone tube furnace for heating, and the entire reaction process is carried out in an atmospheric pressure environment. Figure 1As shown. High-purity sulfur powder (S, Aladdin, 99.999%), rhenium dioxide (ReO2, Macklin, 99.5%), and NaCl were selected as solid precursors and placed in a quartz boat. S powder (~120 mg) was placed in temperature zone 1 as the S source, and a mixed powder of ReO2 (3.4 mg) and NaCl (1 mg) was placed in temperature zone 2 as the Re source, where NaCl acts as a promoter to help ReO2 sublime. The polished surface of the SiO2 / Si substrate was placed face down above the bottom of the downstream quartz boat. Before each reaction, argon (Ar) was purged for 5 minutes at a flow rate of 200 sccm to remove the air in the tube, and then 40 sccm of Ar gas was introduced as a carrier gas to bring the sublimated S powder downstream to react with ReO2 to generate a ReS2 film and deposit it on the SiO2 / Si substrate. Temperature zone 1 and temperature zone 2 were heated from room temperature to 150 and 780°C at a rate of 2.9°C / min and 17.6°C / min, respectively, and the reaction lasted for 12 minutes. After the reaction, the tube furnace was naturally cooled to room temperature and the ReS2 sample was taken out. A two-dimensional ReS2 film was obtained. The optical microscope image of the ReS2 film is shown in Figure 2. Figure 2 As shown. It can be seen that the size of the obtained two-dimensional ReS2 can reach 40μm, which improves the design freedom.

[0036] Then the XPS spectrum of ReS2 is obtained, such as Figure 3 As shown in Figure 1, the atomic ratio of S to Re is calculated to be 1.94:1 based on the integral of the peak intensity, which indicates the presence of S defects in the ReS2 sample grown by CVD. This intrinsic S defect can produce significant electronic effects in ReS2, causing it to exhibit unique conductive behavior.

[0037] Example 2 Preparation of ReS2 Synaptic Device

[0038] Preparation method:

[0039] First, the ReS2 thin layer was transferred from the original substrate to the 300 nm SiO2 / Si substrate using a wet transfer method. The specific implementation method is: first, polymethyl methacrylate (PMMA) 950A4 was spin-coated on the original substrate on which the ReS2 thin layer was grown (the PMMA spin coating process was carried out at a rotation speed of 500 rpm for the first 10 seconds, and then at a speed of 4000 rpm for the next 60 seconds). Subsequently, the sample was baked on a hot plate at 180°C for 2 minutes. Then, the PMMA-covered substrate was soaked in a potassium hydroxide (KOH) solution, and the PMMA film carrying ReS2 was transferred to a new 300 nm SiO2 / Si substrate after it fell off. Next, the left / right electrodes were exposed by electron beam lithography (EBL), and the target pattern was designed in advance according to the sample situation, and then the electrode patterning was completed by the development process. Finally, the Cr / Au (5 nm / 50 nm) electrodes were deposited by thermal evaporation technology, and the excess gold metal was stripped by acetone for 3 hours, and finally the device preparation based on the ReS2 film was completed.

[0040] Performance Testing:

[0041] The current-time measurement and IT curves were obtained using a Keithley 4200A-SCS semiconductor parameter analyzer with a cryogenic probe system, where the bias voltage between the source and drain was 0.1V.

[0042] like Figure 4 As shown, the optical response of the ReS2-based synaptic device under various optical stimulation conditions was tested. Three different wavelengths of light (blue: 450 nm, green: 520 nm, and red: 650 nm) were used, and it was found that short-term synaptic plasticity behaviors triggered by light pulses could be displayed over a wide spectral range. Figure 4 vii shows that the optical response of the device is more sensitive to blue light, so in this work, blue light is selected as the typical light source for other measurements based on its excellent light absorption properties and high response efficiency, thus providing technical support for the light regulation function in neuromorphic computing. Figure 4 i-iii show that as the pulse width, power density and number of pulses increase, the photocurrent gradually accumulates, making it difficult for the trapped electrons to escape from the trapped state. Therefore, the peak value of the triggered postsynaptic current is higher, and the current is maintained longer after the light is removed. This phenomenon directly verifies the ultra-high light responsiveness of the device in simulating neural synaptic signal transmission, and is consistent with the computing logic of the human brain: high intensity, fast frequency and frequent stimulation correspond to intense and difficult to dissipate postsynaptic currents.

[0043] like Figure 5As shown in the figure, 6 groups of different numbers of light pulses (pulse width = 1s, Δt = 1s) were applied to the device, and the device showed 6 different current / conductance levels, which were retained within 50s. This result not only shows that the device can achieve multi-level conductance states under light stimulation, but also further shows that it has good conductance stability within a certain time range. Specifically, with the increase in the number of light pulses, the memory retention rate of the device is significantly improved. This shows that the device can gradually enhance its photoelectric response under the repeated stimulation of optical pulses, simulating a process similar to the brain's memory enhancement. This phenomenon can be attributed to the enhancement of the electron trapped mechanism in the device and the characteristics of the multi-level conductance state, which enables it to accurately record and distinguish optical stimulation of different intensities. This multi-level conductance state provides support for the weight update and memory behavior of the simulated synapse, while its good stability ensures the reliability of the simulated memory characteristics.

[0044] Although the content of the present invention has been described in detail through the above-mentioned implementation cases, it should be appreciated that the above-mentioned description should not be considered as limiting the present invention. After reading the above-mentioned content, it will be obvious for those skilled in the art to make various modifications and substitutions to the present invention. Therefore, the protection scope of the present invention should be limited by the attached claims.

Claims

1. A method for preparing a two-dimensional ReS2 synaptic device, characterized in that: The steps include: Preparation of ReS2 semiconductor film: Using SiO2 / Si as substrate, ReS2 semiconductor film was prepared by salt-assisted chemical vapor deposition; Preparation of ReS2 semiconductor devices: Cr / Au electrodes are deposited on the ReS2 semiconductor film to obtain a ReS2 synaptic device.

2. The preparation method according to claim 1, characterized in that: The salt used as the auxiliary salt is sodium chloride.

3. The preparation method according to claim 1, characterized in that: The salt-assisted chemical vapor deposition method is to react sulfur powder with rhenium dioxide and sodium chloride to form a ReS2 film under a chemical deposition method.

4. A ReS2 synaptic device prepared according to any one of the preparation methods described in claims 1-3.

5. The application of the ReS2 synaptic device according to claim 4 as an optical sensor in the field of computer vision, which is used for image recognition.

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