Method for simultaneously realizing short-range enhancement and inhibition of synapses based on optoelectronic memristor

Abstract

The application discloses a method for simultaneously realizing short-range enhancement and inhibition of synapses based on a photoelectric memristor, the photoelectric memistor comprising a bottom electrode layer, a top electrode layer and an oxide layer between the two, wherein the oxide layer comprises an oxygen-rich layer and an oxygen-deficient layer, the oxygen-deficient layer is adjacent to the top electrode layer, and the oxygen-rich layer is adjacent to the bottom electrode layer, the method is to input a light signal through the top electrode layer, and the method comprises that the photoelectric memristor obtains a short-range enhancement mode and a short-range inhibition mode of the synapses through the light signal; in the short-range enhancement mode of the synapses, the light signal is visible light or infrared light; and in the short-range inhibition mode of the synapses, the light signal is ultraviolet light. The method can simultaneously realize the short-range enhancement and inhibition of the synapses by changing the light signal irradiating the top electrode layer.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of artificial synapse device preparation, and in particular to a method for simultaneously realizing short-range enhancement and inhibition of a synapse based on a photoelectric memristor. BACKGROUND

[0002] Memristor is the fourth basic passive electronic device in addition to resistor, capacitor and inductor. Memristor has a simple two-terminal structure and can realize data storage and processing in one, so it becomes an ideal device for building a non-von Neumann architecture computing system. In 1971, Professor Chua proposed the memristor, and in 2008, HP laboratory prepared the memristor. Since then, the memristor has been widely studied and developed rapidly. The memristor has nonlinear electrical characteristics, and its resistance state has non-volatility, so it can be applied to the simulation of brain synapses. The connection strength between synapses is called synaptic plasticity, which is divided into long-range plasticity and short-range plasticity. Short-range plasticity generally lasts only a few seconds or minutes, representing human short-term memory. Short-range plasticity is of great significance to the human nervous system to perform complex computing tasks. Short-range plasticity can be divided into two categories: one is short-range enhancement, and the other is short-range inhibition.

[0003] In recent years, artificial synapse devices based on electrically controlled memristors have developed rapidly, but they still face the problems of poor stability and high power consumption. Compared with electrically controlled memristor synapse devices, photoelectric memristor synapse devices can reduce the influence of electrical signal stimulation on device stability, which is conducive to reducing the power consumption of the device, so it has attracted the attention of many researchers. However, existing photoelectric memristor synapse devices can only realize short-range enhancement of synapses. So far, photoelectric memristors have not been able to realize short-range enhancement and short-range inhibition of synapses simultaneously using optical signals.

[0004] Chinese patent CN112436092A discloses a double-ended photoelectric artificial synapse device, a preparation method and an application. The feature is that an organic ferroelectric polymer and an organic semiconductor are arranged as functional layers between the upper and lower electrodes to form a thin-film structure light-controlled neural synapse device. The preparation method includes: sequentially evaporating the lower electrode, spin-coating the organic ferroelectric polymer, evaporating the organic semiconductor and the upper electrode on the substrate to obtain a thin-film structure light-controlled neural synapse device. The device is applied to build an artificial neural network system and can simulate the function of biological neural synapses.

[0005] A photovoltaic memristor type synapse device is disclosed in Chinese Patent Publication No. CN109037388A, which comprises a silicon substrate as a gate, an oxide layer, a quantum dot layer, a polymer layer, a semiconductor layer and a metal thin film top electrode arranged in order from bottom to top on the silicon substrate, and the material of the quantum dot layer is one or more of CsPbCl3, CsPbBr3 and CsPbI3. Since the CsPbX3 quantum dot has photoresponsivity, the value of the photo-generated current in the electronic device can be changed by simply adjusting the wavelength of the light, and the excitatory postsynaptic current enhancement effect in the human brain can be simulated, and the inhibitory postsynaptic current weakening effect can be realized by combining the reverse electric field stimulation.

[0006] The synapse devices disclosed in the above two patents can realize the short-range enhancement function of synapses under the action of light signals, but cannot realize the short-range enhancement and short-range inhibition of synapses at the same time by using light signals, which limits the application field of the photovoltaic memristor type synapse device. SUMMARY

[0007] The application discloses a method for simultaneously realizing short-range enhancement and inhibition of synapses based on a photovoltaic memristor.

[0008] A method for simultaneously realizing short-range enhancement and inhibition of synapses based on a photovoltaic memristor, the photovoltaic memristor comprising a bottom electrode layer, a top electrode layer and an oxide layer therebetween, the method being to input a light signal through the top electrode layer, the method comprising that the photovoltaic memristor obtains a short-range enhancement mode and a short-range inhibition mode of synapses through the light signal.

[0009] In the short-range enhancement mode of the synapses, the light signal is visible light or infrared light.

[0010] In the short-range inhibition mode of the synapses, the light signal is ultraviolet light.

[0011] The application can adjust the short-range plasticity of synapses by only changing the wavelength of the applied light signal, which comprises realizing the short-range enhancement function of synapses by using visible light and near-infrared light, and realizing the short-range inhibition function of synapses by using ultraviolet light.

[0012] The oxide layer comprises an oxygen-rich layer and an oxygen-deficient layer, wherein the oxygen-deficient layer is adjacent to the top electrode layer, and the oxygen-rich layer is adjacent to the bottom electrode layer. The oxygen-rich layer oxide is grown in a mixed atmosphere of oxygen and argon, has fewer oxygen vacancy defects inside the material, has good insulation, and plays a role in reducing the conductivity of the device; the oxygen-deficient layer oxide is grown in pure argon, produces a large number of oxygen vacancy defects, and has good conductivity. The combination of the two enables the device to simultaneously realize short-range enhancement and inhibition functions under different light signal stimulation. When visible light acts on the device, the oxygen-deficient layer oxide semiconductor mainly undergoes interband excitation with neutral oxygen vacancy ionization, and the generated photo-generated electrons are excited to the conduction band to become free electrons. As the light exposure time increases, the device current continuously increases, and the device exhibits a short-range enhancement function. When ultraviolet light is irradiated, the oxygen-rich layer and the oxygen-deficient layer oxide semiconductor mainly undergo intrinsic excitation, generating a large number of free electrons, and the device current suddenly increases. However, as the light exposure time increases, the large number of free electrons increases the recombination probability of the ionized oxygen vacancies in the oxygen-deficient layer, resulting in a decrease in free electrons, and the device current gradually decreases, and the device exhibits a short-range inhibition function.

[0013] The optoelectronic memristor further comprises a substrate, and the substrate is located below the bottom electrode layer.

[0014] The substrate is an insulating substrate, a semiconductor substrate or a conductive substrate, wherein the insulating substrate is a thermal oxide silicon wafer, glass, ceramic or plastic; the semiconductor substrate comprises silicon, oxide semiconductor or nitride semiconductor; and the conductive substrate comprises metal or graphite.

[0015] In consideration of compatibility with existing CMOS processes and application in the field of integrated electronics, further, the substrate is a silicon-based substrate, and further, the substrate is a thermal oxide silicon wafer.

[0016] The bottom electrode layer, the top electrode layer and the oxide layer are all prepared by a plating film process, and the plating film process comprises thermal evaporation, magnetron sputtering, sol-gel, chemical vapor deposition or coating method. A suitable plating film method is selected according to the material of the electrode layer and the oxide layer.

[0017] The material of the top electrode layer is one or more of metal, conductive oxide, conductive nitride and conductive carbon material.

[0018] Further, the material of the top electrode layer is one or more of gold, platinum, tungsten, copper, silver, aluminum, titanium, nickel, zinc, tin, manganese and iron.

[0019] The thickness of the top electrode layer is 1-200 nm.

[0020] The material of the oxide layer is one or more of zinc oxide, zirconium oxide, hafnium oxide, silicon oxide, tantalum oxide, titanium oxide, aluminum oxide, nickel oxide, tungsten oxide, tin oxide, indium oxide, indium tin oxide, indium gallium zinc oxide and indium gallium cadmium oxide.

[0021] The thickness of the oxide layer is 1-500 nm.

[0022] The thickness of the oxygen-deficient layer is 25-40 nm, and the thickness of the oxygen-rich layer is 28-35 nm. A heterojunction can be formed between the oxygen-deficient layer and the oxygen-rich layer of a certain thickness, and the Schottky barrier between the oxygen-deficient layer and the top electrode is eliminated, so that a Schottky barrier is formed between the oxygen-rich layer and the bottom electrode, which is conducive to realizing the short-range enhancement and short-range inhibition plasticity of the synapse at the same time.

[0023] The material of the bottom electrode layer is one or more of metal, conductive oxide, conductive nitride and conductive carbon material. Further, the material of the bottom electrode layer is metal, such as one or more of gold, platinum, tungsten, copper, silver, aluminum, titanium, nickel, zinc, tin, manganese and iron.

[0024] The thickness of the bottom electrode layer is 1-500 nm.

[0025] In the short-range enhancement mode, the light signal is blue light, and the wavelength of the blue light is 400-480 nm.

[0026] In the short-range inhibition mode, the light signal is ultraviolet light, and the wavelength of the ultraviolet light is 200-400 nm.

[0027] By inputting light of different wavelengths to the top electrode layer, the short-range enhancement and inhibition of the synapse are realized at the same time: the light signal for realizing the short-range enhancement of the synapse is visible light and near-infrared light; and the light signal for realizing the short-range inhibition of the synapse is ultraviolet light.

[0028] Further preferably, the material of the top electrode layer is gold, the material of the oxide layer is indium gallium zinc oxide, the material of the bottom electrode layer is platinum, the thickness of the top electrode layer is 8-15 nm, the thickness of the oxide layer is 50-55 nm, and the thickness of the bottom electrode layer is 170-178 nm. Visible light is used to realize the short-range enhancement of the synapse, and ultraviolet light is used to realize the short-range inhibition of the synapse. When ultraviolet light acts on the device, the intrinsic excitation of the oxygen-rich layer and the oxygen-deficient layer oxide occurs, a large number of free electrons are generated, and the current of the device suddenly increases; with the extension of the light irradiation time, the free electrons will be gradually captured by the oxygen vacancy defects in the oxygen-deficient layer, and the device exhibits short-range inhibition function. When visible light acts on the device, the interband excitation mainly with oxygen vacancy defect ionization occurs in the oxygen-deficient layer, and the device exhibits short-range enhancement function.

[0029] The working mechanism of the method for simultaneously realizing short-range enhancement and inhibition of a synapse based on a photoelectric memristor is as follows:

[0030] The energy of visible light is less than the band gap width of indium gallium zinc oxide (InGaZnO, IGZO), so the IGZO cannot generate intrinsic excitation under visible light irradiation, but the internal neutral oxygen vacancy can be ionized (as the oxygen vacancy concentration of the oxygen-deficient layer IGZO is much greater than that of the oxygen-rich layer IGZO, the oxygen-deficient layer IGZO is mainly considered), resulting in a gradual increase in the device current, which can be used to simulate the short-range enhancement of a synapse; under ultraviolet light irradiation, the oxygen-deficient layer and the oxygen-rich layer IGZO are mainly intrinsic excitation, a large number of free electrons are generated, the device current sharply rises, however, with the increase of the irradiation time, the large number of free electrons will increase the recombination probability of the ionized oxygen vacancies, so that part of the free electrons will be captured by the ionized oxygen vacancy defects, resulting in a gradual decrease in the device current, which is used to simulate the short-range inhibition of a synapse. Our experiments prove that the devices prepared by the single-layer oxygen-deficient layer IGZO or the single-layer oxygen-rich layer IGZO will not exhibit the above functions (the former has good conductivity, so the device has no obvious photoelectric response under light irradiation; the latter has fewer internal oxygen vacancy defects, so the neutral oxygen vacancy ionization under visible light irradiation can be ignored), so the double-layer structure composed of the oxygen-deficient layer and the oxygen-rich layer plays an important role in realizing the short-range enhancement and inhibition of a synapse for the photoelectric memristor.

[0031] Compared with the prior art, the present application has the following main advantages:

[0032] (1) The photoelectric memristor synapse can use light signals to simulate synaptic functions, has the characteristics of fast speed and strong anti-interference ability, and has more practical application value.

[0033] (2) The traditional electrically controlled memristor synapse needs an electric signal to simulate synaptic functions, which will cause changes in the microstructure of the device and generate a large amount of Joule heat, thus causing large fluctuations in the performance of the device. The light power density used in the photoelectric memristor in the present application is very low, and will not cause microstructure changes, and the Joule heat generated during operation is very small. Therefore, the method provided in the present application can improve the reliability and stability of the device.

[0034] (3) The existing reported photoelectric memristor artificial synapse can only use light signals to realize the short-range enhancement of a synapse, but cannot realize the short-range inhibition of a synapse. The method provided in the present application can use light signals to simultaneously realize the short-range enhancement and inhibition of a synapse, which is beneficial to broaden the application field of the device.

[0035] (4) Considering that the short-range enhancement and short-range inhibition behaviors caused by light signals in the biological visual system are essential, the regulation method of the memristor artificial synapse and the working mode of the biological synapse have higher similarity, so the present application has a broader application prospect in the field of artificial vision. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the memristor structure used in the embodiments of the present invention, wherein 1-top electrode layer, 2-oxygen-deficient layer, 3-oxygen-rich layer, 4-bottom electrode layer, and 5-substrate;

[0037] Figure 2 The current-voltage characteristic curve of the memristor prepared in Example 1 in DC mode, including the setting process and the reset process;

[0038] Figure 3 The image shows the short-range synaptic enhancement mode of the photomemristor prepared in Example 1, where the optical signal uses 450nm visible light and the optical power density is 83μW / cm². 2 ;

[0039] Figure 4 The diagram shows the short-range synaptic suppression mode of the photomemristor prepared in Example 1, where the optical signal uses 350nm ultraviolet light with an optical power density of 36μW / cm². 2 ;

[0040] Figure 5 To demonstrate the relationship between the short-range enhancement index and the optical pulse time interval in the photomemristor prepared in Example 1, 450 nm visible light was used, and the optical power density was 83 μW / cm². 2 ;

[0041] Figure 6 To demonstrate the relationship between the short-range enhancement index and the optical pulse time interval in the photomemristor prepared in Example 1, 350 nm visible light was used, with an optical power density of 36 μW / cm². 2 ;

[0042] Figure 7 To demonstrate the relationship between the short-range enhancement index and the optical pulse time interval in the photomemristor prepared in Example 2, 550 nm visible light was used, with an optical power density of 83 μW / cm². 2 .

[0043] Figure 8 The diagram shows the short-range synaptic suppression mode of the photomemristor prepared in Example 2, where the optical signal uses 250nm ultraviolet light with an optical power density of 36μW / cm². 2 . Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0045] The memristor structure of this invention is as follows: Figure 1 As shown, from bottom to top, the layers are: substrate 5, bottom electrode layer 4, oxygen-rich layer 3, oxygen-deficient layer 2 (dividing the intermediate dielectric layer into an oxygen-deficient layer and an oxygen-rich layer), and top electrode layer 1. In all the embodiments described below, the optical signal is input through the top electrode layer 1.

[0046] Example 1

[0047] The photoelectric memristor prepared in Example 1 includes a substrate, a bottom electrode layer, an oxide layer, and a top electrode layer. The substrate is a thermally oxidized silicon wafer; the bottom electrode layer is platinum with a thickness of 175 nm; the oxide layer is IGZO with a thickness of 53 nm, wherein the oxygen-rich layer has a thickness of 30 nm and the oxygen-deficient layer has a thickness of 23 nm; and the top electrode layer is gold with a thickness of 10 nm.

[0048] The method for fabricating the memristor in this embodiment is as follows:

[0049] (1) A 6nm thick titanium film is prepared on the substrate surface by electron beam evaporation as a buffer layer. Its main function is to increase the mechanical bonding force between the platinum film and the thermally oxidized silicon wafer and prevent the film from falling off.

[0050] The aforementioned substrate is a thermally oxidized silicon wafer, which is formed on a single-crystal silicon wafer using a thermal oxidation method. This thermally oxidized silicon wafer is then used as the insulating substrate for fabricating the memristor in this embodiment. A titanium thin film is formed on the side of the thermally oxidized silicon wafer where the silicon dioxide layer is grown.

[0051] A 175 nm thick platinum film was prepared on a titanium film using electron beam evaporation as the bottom electrode layer.

[0052] (2) IGZO thin films were prepared on the bottom electrode layer by magnetron sputtering combined with a mask.

[0053] The sputtering parameters are as follows:

[0054] IGZO was used as the sputtering target. Oxygen-enriched IGZO was sputtered in a high-purity argon and high-purity oxygen atmosphere, while oxygen-deficient IGZO was sputtered in a high-purity argon atmosphere. The substrate temperature was room temperature. IGZO thin films were prepared using sputtering power of 40–100 W and sputtering time of 1–120 min.

[0055] (3) A gold top electrode layer was fabricated on the IGZO thin film prepared in (2) by using electron beam evaporation combined with a mask. The thickness of the gold top electrode layer was 10 nm.

[0056] The structural schematic diagram of the memristor prepared in this embodiment is shown in Figure 1 As shown in the figure, the memristor sequentially comprises a substrate, a bottom electrode layer, an oxygen-rich layer, an oxygen-deficient layer and a top electrode layer from bottom to top, and light is input through the top electrode. The substrate is a thermal silicon oxide wafer; a buffer layer composed of a 6nm-thick titanium film is further included between the substrate and the bottom electrode layer, and the buffer layer is in contact with both the bottom electrode layer and the thermal oxidation layer of the thermal silicon oxide wafer; the bottom electrode layer is a 175nm-thick platinum film; the oxide layer comprises an oxygen-rich IGZO layer and an oxygen-deficient IGZO layer, and the total thickness is 53nm; the top electrode layer is a gold film with a thickness of 10nm.

[0057] The electrical test is performed on the memristor prepared in this embodiment, and the current-voltage characteristic curve of the memristor under a direct current mode of -2V to 2V is shown in Figure 2 As shown in the figure, the bottom electrode is grounded, voltage is applied to the top electrode, light is input through the top electrode, and the current-voltage characteristic curve includes the setting process and the resetting process. It can be seen that the device realizes the resistance transition under the direct current voltage scanning. Figure 3 The short-range enhancement of the memristor prepared in this embodiment is realized under 450nm visible light. Figure 4 The short-range suppression of the memristor prepared in this embodiment is realized under 350nm ultraviolet light. Figure 5 The relationship between the short-range enhancement index and the pulse interval time of the memristor prepared in this embodiment under 450nm visible light. Figure 6 The relationship between the short-range suppression index and the pulse interval time of the memristor prepared in this embodiment under 350nm ultraviolet light.

[0058] Embodiment 2

[0059] The process parameters of the photoelectric memristor used in this embodiment are the same as those in Embodiment 1, and the difference lies in the wavelength of the applied light pulse. In this embodiment, 550nm visible light is used to realize short-range enhancement, and 250nm ultraviolet light is used to realize short-range suppression. Figure 7 The short-range enhancement of the memristor prepared in this embodiment under 550nm visible light. Figure 8 The short-range suppression of the memristor prepared in this embodiment under 250nm ultraviolet light.

[0060] In addition, it should be understood that, after reading the above description of the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the claims attached to the present application.

Claims

1. A method for simultaneously implementing synaptic short-term potentiation and depression based on optoelectronic memristors, characterized in that, The optoelectronic memristor comprises a bottom electrode layer, a top electrode layer and an oxide layer between the two, wherein the oxide layer comprises an oxygen-rich layer and an oxygen-deficient layer, the oxygen-deficient layer is adjacent to the top electrode layer, and the oxygen-rich layer is adjacent to the bottom electrode layer, the method is inputting a light signal through the top electrode layer, and the method comprises that the optoelectronic memristor obtains a short-range enhancement mode and a short-range inhibition mode of a synapse through the light signal. In the short-range enhancement mode of the synapse, the light signal is a visible light or infrared light double pulse; When the visible light or infrared light double pulse is irradiated, the oxygen-deficient layer oxide semiconductor is mainly ionized with neutral oxygen vacancy excitation, the generated photo-generated electrons are excited to the conduction band to become free electrons, and with the extension of the light irradiation time, the device current continuously increases, and the device exhibits a short-range enhancement function; In the short-range inhibition mode of the synapse, the light signal is an ultraviolet light double pulse; when the ultraviolet light double pulse is irradiated, the oxygen-rich layer and the oxygen-deficient layer oxide semiconductor are mainly excited with intrinsic excitation, free electrons are generated, the device current increases, however, with the extension of the light irradiation time, the free electrons increase the recombination probability of ionized oxygen vacancies in the oxygen-deficient layer, resulting in a decrease in free electrons, and the device current gradually decreases, and the device exhibits a short-range inhibition function. The material of the top electrode layer is one or more of metal, conductive oxide, conductive nitride and conductive carbon material.

2. The method for simultaneous realization of synaptic short-term potentiation and depression based on optoelectronic memristor according to claim 1, wherein, The optoelectronic memristor further comprises a substrate, and the substrate is located below the bottom electrode layer.

3. The method for simultaneous realization of synaptic short-term potentiation and depression based on optoelectronic memristor according to claim 2, wherein, The substrate is an insulating substrate, a semiconductor substrate or a conductive substrate, wherein the insulating substrate is a thermal oxide silicon wafer, glass, ceramic or plastic; the semiconductor substrate comprises silicon, oxide semiconductor or nitride semiconductor; and the conductive substrate comprises metal or graphite.

4. The method for simultaneous realization of synaptic short-term potentiation and depression based on optoelectronic memristor according to claim 1, wherein, The bottom electrode layer, the top electrode layer and the oxide layer are all prepared by a film plating process, and the film plating process comprises thermal evaporation, magnetron sputtering, sol-gel, chemical vapor deposition or coating method.

5. The method of claim 1, wherein the optoelectronic memristor is implemented in a crossbar array. The material of the top electrode layer is one or more of gold, platinum, tungsten, copper, silver, aluminum, titanium, nickel, zinc, tin, manganese and iron.

6. The method of claim 1, wherein the optoelectronic memristor is implemented in a crossbar array. The material of the oxide layer is one or more of zinc oxide, zirconium oxide, hafnium oxide, silicon oxide, tantalum oxide, titanium oxide, aluminum oxide, nickel oxide, tungsten oxide, tin oxide, indium oxide, indium tin oxide, indium gallium zinc oxide and indium gallium cadmium oxide.

7. The method of claim 1, wherein the optoelectronic memristor is implemented in a complementary metal-oxide-semiconductor (CMOS) integrated circuit. The material of the bottom electrode layer is one or more of metal, conductive oxide, conductive nitride and conductive carbon material.

8. The method of claim 1, wherein the optoelectronic memristor is implemented in a photonic integrated circuit. In the short-range enhancement mode, the wavelength of the visible light is 400-780 nm, and in the short-range inhibition mode, the light signal is ultraviolet light, and the wavelength of the ultraviolet light is 200-400 nm.

9. The method of simultaneously implementing short-term synaptic potentiation and depression based on optoelectronic memristors according to any one of claims 1-8, wherein, The material of the top electrode layer is gold, the material of the oxide layer is indium gallium zinc oxide, the material of the bottom electrode layer is platinum, the thickness of the top electrode layer is 8-15 nm, the thickness of the oxide layer is 50-55 nm, wherein the thickness of the oxygen-deficient layer is 25-40 nm, and the thickness of the oxygen-rich layer is 28-35 nm, and the thickness of the bottom electrode layer is 170-178 nm, visible light is used to realize the short-range enhancement of the synapse, and ultraviolet light is used to realize the short-range inhibition of the synapse.

Images