A ferroelectrically controlled two-terminal lead-free perovskite artificial optical synapse device and its preparation method

Abstract

The present invention discloses a ferroelectrically controlled, two-terminal, lead-free perovskite artificial optical synaptic device and its preparation method. The device is characterized by sequentially spin-coating a lead-free perovskite film and an organic ferroelectric polymer film on a lower electrode to form a semiconductor active functional layer, followed by thermal evaporation of an upper electrode on the functional layer to form a vertically layered, ferroelectrically controlled, two-terminal artificial synaptic device. The preparation process specifically includes preparing a spin-coating solution, spin-coating the lead-free perovskite film and the organic ferroelectric polymer film, and evaporating the upper electrode. Compared with existing technologies, the present invention has advantages such as picoampere-level operating current, zero power consumption, and long memory time. It can simulate typical biological synaptic functions under light stimulation of a specific wavelength and can be applied to construct artificial neural network systems. The preparation method is simple, low-cost, safe, and environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of artificial synaptic photoelectric devices, and in particular to a method for preparing a ferroelectrically controlled two-terminal lead-free perovskite artificial optical synaptic device. Background Art

[0002] The rise of the Internet of Things (IoT) has posed a severe challenge to traditional von Neumann architecture computers. Therefore, simulating the structure and working principles of the human brain and achieving brain-like parallelism, high efficiency, and low power consumption is one of the effective ways to solve this problem. The human brain consists of approximately 10 11 These neurons are connected by about 10 15 Synapses are interconnected, and synaptic plasticity is considered the biological basis of learning and memory. Research on electrically stimulated artificial synaptic devices and arrays has made significant progress. Compared with electrically stimulated artificial synapses, optical signal stimulation offers advantages such as high bandwidth, low power consumption, and low crosstalk, making it more attractive in neuromorphic vision systems.

[0003] All-inorganic, lead-free double perovskites, particularly Cs2AgBiBr6, have become one of the most promising alternatives to organic-inorganic hybrid perovskites in optoelectronic devices due to their environmental stability, low toxicity, and simple solution-based film formation methods. Their excellent mechanical flexibility makes them particularly suitable for applications requiring large-area, low-cost, or flexible electronic devices. Furthermore, ferroelectric materials are functional materials with spontaneous polarization properties, whose polarization state can be continuously and reversibly modulated by an applied electric field and exhibits non-volatility. Therefore, ferroelectric materials are considered to be a candidate material for the next generation of memory devices. Three-terminal transistor devices often use ferroelectric materials as gate insulators to control the device's conductance.

[0004] However, the complex manufacturing process and the introduction of gates pose challenges to device fabrication and power consumption. Therefore, leveraging the polarization of ferroelectric materials in two-terminal devices is an effective alternative, as the built-in electric field generated by ferroelectrics influences the generation and recombination of electron-hole pairs. Furthermore, different polarization states can affect the band structure at the ferroelectric-semiconductor interface. Summary of the Invention

[0005] The present invention aims to provide a ferroelectrically controlled, two-terminal, lead-free perovskite artificial synaptic device, its preparation method, and its application. By incorporating an organic ferroelectric polymer film, the device reduces energy consumption and improves light responsiveness. The device can simulate the behavior of biological synapses using light signals as stimulation, achieving functions such as paired-pulse facilitation (PPF), pulse-rate-dependent plasticity (SRDP), and the transition from short-term memory (STM) to long-term memory (LTM). Furthermore, the device boasts zero power consumption, fast response, long retention time, simple preparation, low cost, safety, and environmental friendliness. It can be applied to artificial intelligence hardware and artificial neural network hardware.

[0006] The specific technical solution for achieving the purpose of the present invention is: a ferroelectrically controlled two-terminal lead-free perovskite artificial optical synapse device, which is characterized in that a layer of lead-free perovskite film and an organic ferroelectric polymer are spin-coated on the lower electrode as functional layers, and then a layer of conductor is thermally evaporated on the functional layer as the upper electrode to form a vertical layered structure ferroelectrically controlled two-terminal artificial synapse device, which is applied to the hardware of artificial intelligence and artificial neural networks, wherein the lower electrode adopts indium tin oxide conductive glass; the upper electrode is a metal electrode made of gold, aluminum or platinum; the lead-free perovskite is cesium silver bismuth bromide or cesium silver bismuth chloride; the organic ferroelectric polymer is polyvinylidene fluoride or polyvinylidene fluoride-trifluoroethylene copolymer.

[0007] A method for preparing a ferroelectrically controlled two-terminal lead-free perovskite artificial optical synapse device is characterized in that the preparation of the two-terminal lead-free perovskite artificial optical synapse device specifically includes the following steps:

[0008] (1) Cleaning of substrate

[0009] The substrate was ultrasonically cleaned in deionized water, propanol, ethanol, and isopropanol for 10 to 20 minutes in sequence, and the substrate surface was dried with nitrogen and placed in a drying oven for later use.

[0010] (2) Preparation of spin coating solution

[0011] Cesium halide (CsX), silver halide (AgX) and bismuth halide (BiX3) were weighed in a molar ratio of 2:1:1 and dissolved in dimethyl sulfoxide (DMSO). The solution was heated to 70-75°C in an atmospheric environment and stirred for 2-3 hours to obtain a lead-free perovskite solution A with a concentration of 0.5 mol / L.

[0012] The organic ferroelectric polymer powder is dissolved in diethyl carbonate or butanone, and the solution is heated to 70-75°C in an atmospheric environment and stirred for 2-3 hours to obtain a colorless, clear and transparent organic ferroelectric polymer solution B with a mass fraction of 2.5 wt%.

[0013] (III) Preparation of lead-free perovskite films and organic ferroelectric polymer films

[0014] Use a pipette to take an appropriate amount of lead-free perovskite solution A and drop it on the substrate cleaned in step (1) at a rotating speed of 500-3000 r / s for 50-60s. Move the spin-coated film into a vacuum drying oven and evacuate for 5-10 minutes, then anneal at 200-285°C for 5-10 minutes to obtain a lead-free perovskite film. After the thin plate with the lead-free perovskite film deposited is cooled to room temperature, organic ferroelectric polymer solution B is added dropwise at a rotating speed of 500-4000 r / s, and annealed at 135-140°C for 2-4 hours to prepare an organic ferroelectric polymer film on the lead-free perovskite film.

[0015] (IV) Fabrication of artificial synaptic devices

[0016] The mask is covered on the surface of the organic ferroelectric polymer film, and a metal top electrode with a thickness of 50 to 60 nanometers is obtained by thermal evaporation technology. The device obtained is a two-terminal artificial synapse controlled by ferroelectricity. The vacuum degree of the thermal evaporation is 2 to 6×10 -4 Pa, the deposition rate is 0.5~0.9 angstroms per second, and the evaporation time is 25~30 minutes.

[0017] The organic ferroelectric polymer is polyvinylidene fluoride (PVDF) or polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)); the lead-free perovskite is cesium silver bismuth bromide (Cs2AgBiBr6) or cesium silver bismuth chloride (Cs2AgBiCl6); the substrate is a lower electrode of indium tin oxide conductive glass; the upper electrode is a metal such as gold, aluminum, or platinum; the thickness of the lead-free perovskite film is 150 to 250 nanometers; the thickness of the organic ferroelectric polymer is 60 to 300 nanometers.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects and significant improvements:

[0019] 1) The built-in electric field of the ferroelectric polarization of the organic ferroelectric polymer film is used to regulate the potential barrier at the interface between the lead-free perovskite film and the organic ferroelectric polymer film, thereby controlling the generation and recombination of photogenerated electrons and holes, thereby simplifying the device structure, reducing device energy consumption and improving the photocurrent retention time.

[0020] 2) The synapse can control the generation and recombination of interfacial photogenerated electrons and holes through the built-in electric field formed after the polarization of the organic ferroelectric polymer, and can maintain multiple continuous conduction states and prolong the retention time.

[0021] 3) The device simulates typical biological synaptic functions, including EPSC, SRDP, and STM to LTM transition. Its preparation method has simple operation steps, readily available raw materials, low cost, low energy consumption, high efficiency, and easy implementation; the entire preparation process is safe and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the structure of the artificial optical synapse device prepared in Example 1;

[0023] Figure 2 Schematic diagram of the decay time of the postsynaptic current of the device prepared in Example 1;

[0024] Figure 3 Schematic diagram of the pulse frequency-dependent plasticity of the device prepared in Example 1 of the present invention;

[0025] Figure 4 Schematic diagram of the process of transformation from short-term memory to long-term memory in the device prepared in Example 1. DETAILED DESCRIPTION

[0026] Below in conjunction with specific embodiment and accompanying drawing, the present invention is described in further detail.The process, conditions, reagents, experimental techniques etc. of implementing the present invention, except the content specifically mentioned below, are all common knowledge and common common sense in this area, and the present invention has no particular limitation content.Below by embodiment, the present invention is further elaborated, its purpose is in order to more thoroughly understand the content of the present invention, and all examples cited are not regarded as limitation to protection scope of the present invention.

[0027] Example 1

[0028] In this example, polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)) is used as an organic ferroelectric polymer and cesium silver bismuth bromide (Cs2AgBiBr6) is used as a lead-free perovskite to prepare an artificial synaptic device based on the lead-free perovskite and the organic ferroelectric polymer. The specific steps are as follows:

[0029] 1) The ITO substrate was ultrasonically cleaned in deionized water, propanol, ethanol, and isopropanol for 20 minutes in sequence. The substrate surface was blown dry with nitrogen and placed in a drying oven for later use.

[0030] 2) Cesium bromide (CsBr), silver bromide (AgBr), and bismuth bromide (BiBr3) were weighed in a molar ratio of 2:1:1 and dissolved in 1 ml of dimethyl sulfoxide (DMSO). The solution was heated to 75°C in an atmospheric atmosphere and stirred for 2 hours to obtain a clear, yellow Cs2AgBiBr6 solution with a concentration of 0.5 mol / L.

[0031] 3) Dissolving polyvinylidene fluoride-trifluoroethylene copolymer powder in diethyl carbonate to prepare a spin coating solution to obtain a P(VDF-TrFE) solution with a mass fraction of 2.5 wt%.

[0032] 4) Use a pipette to take 50 μL of Cs2AgBiBr6 solution and drop it onto a rotating ITO substrate at a rotation speed of 2500 r / s for 60 s. Move the spin-coated film into a vacuum drying oven and evacuate for 10 minutes. Then, anneal it at 285°C for 10 minutes to obtain a Cs2AgBiBr6 thin film.

[0033] 5) After the thin plate with the deposited Cs2AgBiBr6 film cooled to room temperature, 70 μL of P(VDF-TrFE) solution was added to the prepared Cs2AgBiBr6 film at a rotation speed of 3000 r / s and annealed at 135°C for 4 hours to obtain a Cs2AgBiBr6 film.

[0034] 6) A 50-nanometer-thick gold layer was deposited on the surface of the Cs2AgBiBr6 thin film using thermal evaporation technology as the upper electrode to produce a ferroelectrically controlled, two-terminal lead-free perovskite artificial synaptic device.

[0035] See attached Figure 1 The ferroelectrically controlled two-terminal lead-free perovskite artificial optical synapse device prepared in the above embodiment has a sandwich vertical structure.

[0036] See attached Figure 2 The artificial synaptic device prepared in the above embodiment was subjected to a light illumination intensity of 45.25 μW / cm 2 Using a 100-millisecond pulse width to simulate the behavior of a biological synapse, the device showed that the photocurrent reached ~27 picoamperes after light stimulation and then gradually decreased to its initial level. This change is similar to the change in the postsynaptic current of a biological synapse after external stimulation, demonstrating the device's ability to mimic biological synapses.

[0037] See attached Figure 3 , pulse frequencies of different frequencies were applied to the artificial synaptic device prepared in the above embodiment, and the test results showed that the greater the frequency, the greater the response current, showing stimulation frequency-dependent plasticity (SRDP).

[0038] See attached Figure 4 By applying light pulses of the same frequency but different light intensities to the artificial synaptic device prepared in the above embodiment, attenuation curves after stimulation with different light intensities are obtained. The device can simulate the process of transformation from short-term memory to long-term memory.

[0039] The artificial synaptic device produced in the above embodiment has been subjected to the aforementioned performance tests, and the results demonstrate that the device can simulate the functions of biological synapses and can be used to construct artificial neural network systems. The present invention is not limited to the above embodiment; modifications and advantages that may be conceived by those skilled in the art without departing from the spirit and scope of the inventive concept are encompassed by the present invention and are protected by the appended claims.

Claims

1. A ferroelectrically controlled two-terminal lead-free perovskite artificial optical synaptic device, characterized in that A lead-free perovskite film and an organic ferroelectric polymer film are spin-coated in sequence on the lower electrode to form a semiconductor active functional layer, and then a conductor is thermally evaporated on the functional layer as the upper electrode to form a vertical layered structure ferroelectrically regulated two-terminal artificial synaptic device, which can be used to construct an artificial neural network system. The lower electrode is indium tin oxide conductive glass; the upper electrode is a metal electrode made of gold, aluminum or platinum; the lead-free perovskite is cesium silver bismuth bromide or cesium silver bismuth chloride; the organic ferroelectric polymer is polyvinylidene fluoride or polyvinylidene fluoride-trifluoroethylene copolymer.

2. A method for preparing a ferroelectrically controlled two-terminal lead-free perovskite artificial optical synapse device, characterized in that The preparation of the two-terminal lead-free perovskite artificial optical synapse device specifically includes the following steps: (1) Cleaning of substrate The substrate is ultrasonically cleaned in deionized water, propanol, ethanol and isopropanol solutions for 10 to 20 minutes in sequence, and then the substrate surface is blown dry with nitrogen and placed in a drying oven for use. The substrate is the upper electrode of the indium tin oxide conductive glass; (2) Preparation of spin coating solution Cesium halide, silver halide, bismuth halide and dimethyl sulfoxide are mixed in a molar ratio of 2:1:1:25-50, and stirred at 70-75°C for 2-3 hours to prepare a lead-free perovskite solution A; Dissolve the organic ferroelectric polymer powder in diethyl carbonate or butanone, and stir at 70-75°C for 2-3 hours to prepare an organic ferroelectric polymer solution B. The mass volume ratio of the organic ferroelectric polymer to diethyl carbonate or butanone is 25-40 mg:1 ml. (3) Preparation of lead-free perovskite films The lead-free perovskite solution A is spin-coated on the cleaned substrate, and then vacuum-dried for 5 to 10 minutes, and then annealed at 200 to 285° C. for 5 to 10 minutes, and naturally cooled to room temperature to form a lead-free perovskite film with a thickness of 150 to 250 nanometers on the upper electrode layer. The spin speed is 500 to 3000 r / s, and the spin time is 50 to 60 seconds. (IV) Preparation of organic ferroelectric polymer films Spin coating the organic ferroelectric polymer solution B on the lead-free perovskite film, annealing at 135-140° C. for 2-4 minutes, and then naturally cooling to room temperature to form an organic ferroelectric polymer film with a thickness of 60-300 nm on the lead-free perovskite film, wherein the spin speed is 500-4000 r / s and the spin time is 20-30 s; (V) Preparation of artificial synaptic devices The mask is covered on the surface of the organic ferroelectric polymer film, and a metal upper electrode with a thickness of 50 to 60 nanometers is evaporated to obtain a device that is a ferroelectrically controlled two-terminal artificial synapse. The evaporation time is 25 to 30 minutes, and the vacuum degree of thermal evaporation is 2 to 6×10 -4 Pa, and the deposition rate is 0.5~0.9 angstroms per second.

3. The method for preparing the ferroelectrically controlled two-terminal lead-free perovskite artificial optical synapse device according to claim 2, characterized in that The organic ferroelectric polymer is polyvinylidene fluoride or polyvinylidene fluoride-trifluoroethylene copolymer.

4. The method for preparing the ferroelectrically controlled two-terminal lead-free perovskite artificial optical synapse device according to claim 2, characterized in that The lead-free perovskite is Cs2AgBiBr6 or Cs2AgBiCl6.

5. The method for preparing the ferroelectrically controlled two-terminal lead-free perovskite artificial optical synapse device according to claim 2, characterized in that The upper electrode is a metal electrode made of gold, aluminum or platinum.

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