Lead-free perovskite photoelectric nerve synaptic device with multi-bit storage function and preparation method of lead-free perovskite photoelectric nerve synaptic device

Abstract

The invention relates to the technical field of semiconductors and resistive random access memories, and provides a lead-free perovskite photoelectric synapse device with a multi-bit storage function and a preparation method thereof. The lead-free perovskite photoelectric nerve synapse device comprises a substrate, wherein an electron transport layer, a photosensitive layer and an electrode layer are sequentially stacked on the substrate; the material of the electron transport layer is ZnO, and the material of the photosensitive layer is Cs2AgBiBr6. The lead-free perovskite photoelectric nerve synapse device disclosed by the invention shows excellent optical programming multi-bit storage capability under continuous 410nm light multi-pulse stimulation.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductors and resistive random access memory, and in particular to a lead-free perovskite photoelectric neural synapse device with a multi-bit storage function and a preparation method thereof. Background Art

[0002] With the deep integration of artificial intelligence and big data, the demand for rapid processing of massive data is growing, requiring higher computing efficiency and lower energy consumption. The memory and processing units of traditional von Neumann architecture computers are physically separated, so they cannot quickly process large amounts of information at the same time, resulting in data exchange between the two units that inevitably consumes a lot of time and energy. In contrast, retinal neurons in the human visual system can efficiently and accurately preprocess and transmit visual data, thereby reducing the amount of redundant information and improving the efficiency of information processing in the human brain. Therefore, it is crucial to develop a neuromorphic system that highly integrates the functions of perceiving external information, memory, and preprocessing.

[0003] In order to achieve efficient data processing and take advantage of the human visual system, optoelectronic synaptic devices are regarded as a promising new type of device. Although optoelectronic synaptic devices have made significant progress and achieved the simulation of synaptic potentials under light stimulation, the multi-resistance stable storage function under light stimulation has not yet been realized, which is crucial for light stimulation hardware chips that identify different resistance states. Switching from binary storage to multi-bit storage is an important way to solve the problem of memory capacity, but the current multi-bit storage programming based on light stimulation of light-induced synaptic devices cannot achieve stable multi-level storage. The present invention realizes the function of multi-bit storage under light stimulation based on lead-free perovskite. Summary of the invention

[0004] In view of this, the present invention proposes a lead-free perovskite optoelectronic synaptic device with excellent optically programmed multi-bit storage capability and a preparation method thereof.

[0005] The technical solution of the present invention is implemented as follows: On the one hand, the present invention provides a lead-free perovskite optoelectronic neural synaptic device with a multi-bit storage function, comprising: a substrate, on which an electron transport layer, a photosensitive layer and an electrode layer are sequentially stacked; the material of the electron transport layer is ZnO, and the material of the photosensitive layer is Cs 2 AG 6。

[0006] Specifically, ZnO / Cs 2 AG 6Under the stimulation of 410nm light, the photosensitive layer of the composite film generates a large number of photogenerated carriers, and the ZnO layer happens to have a large number of defects, thus capturing some of the carriers. After the light stimulation is removed, the photogenerated carriers begin to recombine, and the captured electrons are slowly released, resulting in this non-volatile property. ZnO provides defects, Cs 2 AG 6 Provide carriers, and the two synergistically strengthen to form synaptic properties. Therefore, the lead-free perovskite optoelectronic neural synaptic device of the present invention has a multi-bit storage capacity of light programming under 410nm light stimulation.

[0007] On the basis of the above technical solution, preferably, the thickness of the electron transport layer is 150-200 nm.

[0008] On the basis of the above technical solution, preferably, the thickness of the photosensitive layer is 300-500 nm.

[0009] On the basis of the above technical solution, preferably, the thickness of the electrode layer is 80nm-100nm.

[0010] On the other hand, the present invention also provides a method for preparing a lead-free perovskite optoelectronic neural synaptic device with a multi-bit storage function, comprising the following steps:

[0011] S1, depositing a ZnO thin film on a glass substrate by a magnetron sputtering method to prepare an electron transport layer;

[0012] S2, Cs 2 AG 6 The solution is spin-coated on the surface of the ZnO film and then annealed to obtain a photosensitive layer;

[0013] S3, gold is plated on the photosensitive layer to obtain an electrode layer.

[0014] Based on the above technical solution, preferably, the Cs in step S2 2 AG 6 The solution spin coating method is: the spin coating speed is 1500-2500rpm, the time is 50-55s, and the Cs 2 AG 6 The solution was spin-coated on the surface of the ZnO film, and in the last 10 seconds, isopropanol was added dropwise to continue spin coating.

[0015] Specifically, Cs 2 AG 6When the solution is spin-coated, the purpose of adding isopropanol is to promote the crystallization process of the perovskite precursor and improve the morphology and uniformity of the film. Isopropanol is a volatile solvent. After adding it, it can help the solvent in the solution evaporate quickly and promote the formation of more dense and uniform perovskite crystals. In addition, adding isopropanol in the final stage of spin coating helps control the crystallization kinetics of perovskite, thereby obtaining a film with better optoelectronic properties.

[0016] On the basis of the above technical solution, preferably, Cs 2 AG 6 The volume ratio of solution: isopropanol is 1:1.5-1.8.

[0017] On the basis of the above technical solution, preferably, in step S2, the annealing temperature is 250-300° C. and the time is 5-10 min.

[0018] On the basis of the above technical solution, preferably, Cs 2 AG 6 The solution is prepared by adding cesium bromide, bismuth bromide and silver bromide in a molar ratio of 2:1:1 to dimethyl sulfoxide, stirring at 60-70°C for more than 24 hours to form Cs 2 AG 6 Solution.

[0019] On the basis of the above technical solution, preferably, the preparation method of the electron transport layer is: depositing a ZnO thin film on a glass sheet by a magnetron sputtering method, the air pressure in the chamber is 0.3-0.6 Pa, the volume ratio of argon to oxygen is 3-5:1, and the sputtering power of the ZnO thin film is 120-150W.

[0020] The lead-free perovskite optoelectronic synaptic device with excellent optically programmed multi-bit storage capacity and the preparation method thereof of the present invention have the following beneficial effects compared with the prior art:

[0021] (1) The lead-free perovskite optoelectronic neural synaptic device (hereinafter referred to as "synaptic device") of the present invention has 11 distinguishable conductance states under the stimulation of 10 consecutive 410nm light multiple pulses, showing excellent light-programmed multi-bit storage capability.

[0022] (2) Under the induction of continuous light pulse (wavelength 410nm) signal, the synaptic device of the present invention has obvious pulse number dependent plasticity (SNDP) behavior, and with the increase of pulse number, the excitatory postsynaptic current (EPSC) gradually increases and then shows a stable trend, showing excellent pulse number dependent plasticity, indicating that repeated learning enhances the memory ability of the synaptic device.

[0023] (3) When the synaptic device of the present invention is stimulated by 100 light pulses (wavelength 410 nm), the postsynaptic current increases steadily and evenly. At the same time, the linearity of the synaptic weight change of the synaptic device is also very high, reflecting better application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 This is a structural diagram of a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function prepared in Example 1 of the present application, in which 1 is an electrode layer, 2 is a photosensitive layer, 3 is an electron transport layer, and 4 is a substrate.

[0026] Figure 2 This is a test diagram of synaptic performance caused by a single light stimulus of the lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function prepared in Example 1 of the present application;

[0027] Figure 3 This is a test diagram of synaptic performance caused by five consecutive light stimuli of the lead-free perovskite neural synaptic device with multi-bit storage function prepared in Example 1 of the present application;

[0028] Figure 4 This is a test diagram of the multi-bit storage function of the lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function prepared in Example 1 of the present application;

[0029] Figure 5 This is a test graph of the pulse number-dependent plasticity of the lead-free perovskite optoelectronic synaptic device with multi-bit storage function prepared in Example 1 of the present application;

[0030] Figure 6 This is a stability test diagram of the lead-free perovskite optoelectronic synaptic device with multi-bit storage function prepared in Example 1 of the present application under 100 light pulses;

[0031] Figure 7 For Comparative Example 2, Cs alone 2 AG 6 Performance test diagram for 5 consecutive light stimuli;

[0032] Figure 8 This is a test diagram of the multi-bit storage function of the lead-free perovskite optoelectronic synaptic device prepared in Example 1 of the present application under 1, 3, 5, and 10 light pulse stimulations;

[0033] Fig. 9 This is a test diagram of the multi-bit storage function of the lead-free perovskite photoelectric synaptic device prepared in Comparative Example 7 under 1, 3, 5, and 10 light pulse stimulations. DETAILED DESCRIPTION

[0034] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments 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.

[0035] like Figure 1 As shown, the lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function of the present invention includes a substrate, the substrate is made of glass, ZnO is deposited on the surface of the substrate to form an electron transport layer with a thickness of 150-200nm; Cs 2 AG 6 , forming a photosensitive layer with a thickness of 300-500nm; a gold electrode is deposited on the surface of the photosensitive layer to form an electrode layer with a thickness of 80-100nm.

[0036] The preparation method of the lead-free perovskite optoelectronic neural synapse device of the present invention is further described below in conjunction with the examples.

[0037] Example 1

[0038] The method for preparing the lead-free perovskite optoelectronic neural synapse device of this embodiment comprises the following steps:

[0039] S1, ZnO thin film was deposited on a clean glass substrate by magnetron sputtering method, the chamber pressure was 0.5Pa, the argon-oxygen volume ratio was 4:1, the ZnO thin film sputtering power was 135W, and the thickness of the electron transport layer was 180nm.

[0040] S2, Cs 2 AG 6 Preparation of precursor solution: 0.426 g of cesium bromide (CsBr) and 0.449 g of bismuth bromide (BiBr 3 ) and 0.188 g silver bromide (AgBr) were added to 2 mL dimethyl sulfoxide (DMSO) and stirred at 68 °C for more than 24 h to form Cs 2 AG 6 Solution.

[0041] Take 200 μL Cs 2 AG 6The solution was spin-coated on the surface of the ZnO film at a speed of 2000 rpm for 55 seconds. In the last 10 seconds, 350 μL of isopropanol was added and spin-coated continuously. The film was then heated at 285° C. for 5 minutes to obtain a photosensitive layer with a thickness of 450 nm.

[0042] S3, depositing a 90nm gold electrode onto the photosensitive layer through a magnetron sputtering process, and finally obtaining a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function.

[0043] Example 2

[0044] The method for preparing the lead-free perovskite optoelectronic neural synapse device of this embodiment comprises the following steps:

[0045] S1, ZnO thin film was deposited on a clean glass substrate by magnetron sputtering method, the chamber pressure was 0.3 Pa, the argon-oxygen volume ratio was 3:1, the ZnO thin film sputtering power was 120 W, and the thickness of the electron transport layer was 150 nm.

[0046] S2, Cs 2 AG 6 Preparation of precursor solution: 0.426 g of cesium bromide (CsBr) and 0.449 g of bismuth bromide (BiBr 3 ) and 0.188 g silver bromide (AgBr) were added to 2 mL dimethyl sulfoxide (DMSO) and stirred at 60 °C for more than 24 h to form Cs 2 AG 6 Solution.

[0047] Take 200 μL Cs 2 AG 6 The solution was spin-coated on the surface of the ZnO film at a speed of 2500 rpm for 50 seconds. In the last 10 seconds, 360 μL of isopropanol was added to continue spin coating. The film was then heated at 250° C. for 10 minutes to obtain a photosensitive layer with a thickness of 500 nm.

[0048] S3, depositing a 100nm gold electrode onto the photosensitive layer through a magnetron sputtering process, and finally obtaining a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function.

[0049] Example 3

[0050] The method for preparing the lead-free perovskite optoelectronic neural synapse device of this embodiment comprises the following steps:

[0051] S1, ZnO thin film was deposited on a clean glass substrate by magnetron sputtering method, the chamber pressure was 0.6Pa, the argon-oxygen volume ratio was 5:1, the ZnO thin film sputtering power was 150W, and the thickness of the electron transport layer was 200nm.

[0052] S2, Cs 2 AG 6 Preparation of precursor solution: 0.426 g of cesium bromide (CsBr) and 0.449 g of bismuth bromide (BiBr 3 ) and 0.188 g silver bromide (AgBr) were added to 2 mL dimethyl sulfoxide (DMSO) and stirred at 70 °C for more than 24 h to form Cs 2 AG 6 Solution.

[0053] Take 200 μL Cs 2 AG 6 The solution was spin-coated on the surface of the ZnO film at a speed of 1500 rpm for 53 seconds. In the last 10 seconds, 300 μL of isopropanol was added to continue spin coating. The film was then heated at 300°C for 8 minutes to obtain a photosensitive layer with a thickness of 300 nm.

[0054] S3, depositing 80nm gold electrode onto the photosensitive layer through magnetron sputtering process, and finally obtaining a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function.

[0055] 1. Performance test of multi-bit storage

[0056] The excitatory postsynaptic current-time test of the synaptic device was tested by Keithley 4200 digital source meter. A bias voltage of 3.0V was applied to the top electrode. Single, 5 consecutive or 10 consecutive 410nm light pulses were used to stimulate the excitatory postsynaptic current. The results are shown in Figure 2-4 .

[0057] Figure 2 As shown, the lead-free perovskite optoelectronic synaptic device obtained in Example 1, under the stimulation of a single 410nm light with a pulse width of 2s, caused a current change of 26.2% (the percentage difference between the steady-state current after the light stimulation was removed and the initial current).

[0058] Figure 3 As shown, the lead-free perovskite optoelectronic synaptic device obtained in Example 1, under 5 consecutive 410nm light stimulations with a pulse width of 0.5s and an interval of 0.5s, caused a current change of 25.4% (the percentage difference between the steady-state current after the light stimulation was removed and the initial current).

[0059] Figure 4As shown, the lead-free perovskite optoelectronic synaptic device obtained in Example 1 is stimulated by 10 consecutive 410nm light pulses, each light pulse lasts for 0.5s, and the pulse interval is 5s. The optoelectronic synaptic device has 11 distinguishable conductance states, showing its excellent light-programmed multi-bit storage capability.

[0060] 2. Device synaptic plasticity test

[0061] We simulated the number of pulses dependent plasticity (SNDP) by applying a bias voltage of 3.0 V to the top electrode. The duration of each light pulse (wavelength 410 nm) was 0.5 s, and the interval between pulses was 5 s. We used continuous light pulse signals to induce the device to produce SNDP behavior. The number of light pulses was 1, 5, 10, and 20, respectively. The results are shown in Figure 5 .

[0062] like Figure 5 As shown, it can be observed that the SNDP behavior of the lead-free perovskite optoelectronic synaptic device is obvious. With the increase of the number of pulses, the excitatory postsynaptic current (EPSC) gradually increases and then shows a stable trend, showing excellent pulse number-dependent plasticity, indicating that repeated learning enhances the memory ability of the device.

[0063] 3. Device stability test

[0064] like Figure 6 As shown in Figure 2, we simulated the device under the condition of 100 light pulse stimulation (wavelength 410nm), the duration of each light pulse is 0.5s, the interval between pulses is 0.5s, and the test results of the device's excitatory postsynaptic current are shown in Figure 2. Figure 6 .

[0065] from Figure 6 It can be seen that in the corresponding 100 stimulation intervals, the postsynaptic current increases steadily and evenly with each pulse stimulation. At the same time, the linearity of the synaptic weight change of the device is also very high, reflecting better application potential.

[0066] Comparative Example 1

[0067] Compared with Example 1, Comparative Example 1 lacks a photosensitive layer, and the rest of the contents are the same.

[0068] The results show that: since the absorption band of ZnO is in the ultraviolet, it has no optical effect on the visible light band. Under the stimulation of 410nm light, the device has no photocurrent, which does not conform to the simulation of our human eye vision.

[0069] Comparative Example 2

[0070] Compared with Example 1, Comparative Example 2 lacks an electron transport layer, and the rest of the contents are the same.

[0071] The performance of the prepared device was tested: 5 consecutive 410nm light stimulations with a pulse width of 0.5s and an interval of 0.5s. The results are shown in Figure 7 As shown in the figure, the device changes its current by 0.02% under light stimulation, and the steady-state current is almost the same as the initial current after the light stimulation is removed.

[0072] The results showed that due to its fast response speed, it did not exhibit non-volatile memory properties under the stimulation of light and did not meet the performance requirements of artificial synapses.

[0073] Comparative Examples 1 to 2 show that ZnO or Cs 2 AG 6 There is no current or almost no change in current under 410nm light pulse stimulation, which cannot meet the performance requirements of artificial synapses. It also proves that the light-stimulated synaptic properties of the lead-free perovskite photoelectric synaptic device of the present application are derived from ZnO and Cs 2 AG 6 Combination of ZnO and Cs 2 AG 6 role.

[0074] Comparative Example 3

[0075] Compared with Example 1, in Comparative Example 3, the thickness of the electron transport layer is 100 nm, and the rest of the contents are the same.

[0076] The results showed that the synaptic device obtained, under the stimulation of a single 410 nm light with a pulse width of 2 s, caused a current change of 13.2% (the percentage of the difference between the steady-state current after the light stimulation was removed and the initial current).

[0077] Comparative Example 4

[0078] Compared with Example 1, in Comparative Example 4, the thickness of the electron transport layer is 250 nm, and the rest of the contents are the same.

[0079] The results showed that the synaptic device obtained, under the stimulation of a single 410 nm light with a pulse width of 2 s, caused a current change of 15.1% (the percentage of the difference between the steady-state current after the light stimulation was removed and the initial current).

[0080] In the preparation of the electron transport layer (ZnO film), the thickness is controlled at 150-200nm in order to optimize its electron transport performance and interface matching. As shown in Comparative Examples 3 to 4, when the thickness of the electron transport layer is less than 150nm or greater than 200nm, the current change of the synaptic device is lower than that of Example 1 (26.2%). This is because: if the thickness of the ZnO film is less than 150nm, it will lead to poor electron transport because the thin layer contains defects or discontinuities, which affect charge migration. If the thickness is greater than 200nm, the length of the electron transport path will be increased, the resistance will be increased, the current transport efficiency will be reduced, and the storage performance of the device will be reduced.

[0081] Comparative Example 5

[0082] Comparative Example 5 Compared with Example 1, Cs 2 AG 6 When the solution is prepared, the rotation speed is 1000 rpm, and the rest of the contents are the same.

[0083] The results showed that the synaptic device induced a current change of 14.6% (the percentage of the difference between the steady-state current and the initial current after the light stimulation was removed) under a single 410nm light stimulation with a pulse width of 2s.

[0084] Comparative Example 6

[0085] Comparative Example 6 Compared with Example 1, Cs 2 AG 6 The solution was spin-coated at a rotation speed of 3000 rpm, and the rest of the contents were the same.

[0086] The results showed that the synaptic device obtained, under the stimulation of a single 410 nm light with a pulse width of 2 s, caused a current change of 15.4% (the percentage of the difference between the steady-state current after the light stimulation was removed and the initial current).

[0087] Comparative Examples 5 to 6 show that Cs 2 AG 6 Both slow and fast spin coating of the solution will reduce the current change of the device. This is because: if the spin coating speed is slow, the film will form a thicker and uneven film. This will lead to uneven crystallization and increased surface roughness inside the perovskite layer, affecting the transfer of charge and increasing the interface resistance; in addition, the uneven film may also have local crystal defects or voids, resulting in unclear current changes. If the spin coating speed is too fast, the film will become too thin and incomplete, resulting in a discontinuous perovskite layer covering the ZnO; this will cause an increase in interface defects and incompleteness of the electron transfer path, and may also affect the crystallization quality of the film, thereby reducing the current change and overall storage performance of the device. Therefore, accurate spin coating speed is one of the keys to ensure the optimal performance of the perovskite layer.

[0088] Comparative Example 7

[0089] Comparative Example 7 Compared with Example 1, Cs 2 AG 6 No isopropanol was added when the solution was spin coated, and the rest of the contents were the same.

[0090] The results are as follows Fig. 9 As shown in FIG. 1 , 3, 5, and 10 stimulations, the sample without isopropanol addition has almost no storage effect (the difference between the steady-state current after the light stimulation is removed and the initial current), and the current is even lower than the initial current. Figure 8 ), the current changes caused by it are all changed, and the storage effect is better.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lead-free perovskite optoelectronic synaptic device with multi-bit storage function, characterized in that: The method comprises: a substrate, on which an electron transport layer, a photosensitive layer and an electrode layer are sequentially stacked; The material of the electron transport layer is ZnO, and the material of the photosensitive layer is Cs2AgBiBr6.

2. A lead-free perovskite optoelectronic synaptic device with multi-bit storage function as claimed in claim 1, characterized in that: The thickness of the electron transport layer is 150-200 nm.

3. A lead-free perovskite optoelectronic synaptic device with multi-bit storage function as claimed in claim 1, characterized in that: The thickness of the photosensitive layer is 300-500 nm.

4. A lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function as claimed in claim 1, characterized in that: The thickness of the electrode layer is 80nm-100nm.

5. A method for preparing a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, depositing a ZnO thin film on a glass substrate by a magnetron sputtering method to prepare an electron transport layer; S2, spin coating Cs2AgBiBr6 solution on the surface of ZnO film, followed by annealing to obtain a photosensitive layer; S3, gold is plated on the photosensitive layer to obtain an electrode layer.

6. The method for preparing a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function according to claim 5, characterized in that: The spin coating method of the Cs2AgBiBr6 solution in step S2 is as follows: the spin coating speed is 1500-2500rpm, the time is 50-55s, and the Cs2AgBiBr6 solution is spin coated on the surface of the ZnO film. In the last 10s, isopropanol is added and the spin coating is continued.

7. The method for preparing a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function according to claim 6, characterized in that: The volume ratio of Cs2AgBiBr6 solution: isopropanol is 1:1.5-1.

8.

8. The method for preparing a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function according to claim 5, characterized in that: In step S2, the annealing temperature is 250-300°C and the time is 5-10 minutes.

9. The method for preparing a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function according to claim 5, characterized in that: The preparation method of Cs2AgBiBr6 solution is as follows: cesium bromide, bismuth bromide and silver bromide are added to dimethyl sulfoxide in a molar ratio of 2:1:1, and stirred at 60-70°C for more than 24 hours to form a Cs2AgBiBr6 solution.

10. The method for preparing a lead-free perovskite optoelectronic neural synaptic device with multi-bit storage function according to claim 5, characterized in that: The preparation method of the electron transport layer is: depositing a ZnO film on a glass sheet by a magnetron sputtering method, the air pressure in the chamber is 0.3-0.6 Pa, the volume ratio of argon to oxygen is 3-5:1, and the sputtering power of the ZnO film is 120-150W.

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