Bimodal memristor based on quantum dot / copolymer composite film and preparation method thereof

Abstract

The invention discloses a dual-mode memristor based on a quantum dot / copolymer composite film and a preparation method of the dual-mode memristor, and belongs to the technical field of nonvolatile memories. The structure of the device sequentially comprises an Al top electrode, a CsPbBr3 / EVA composite film functional layer and an FTO bottom electrode, and the whole device takes glass as a substrate; the method comprises the steps of synthesis and purification of quantum dots, preparation of a composite solution, preparation of the memristor and the like, perovskite CsPbBr3 and an ethylene-vinyl acetate copolymer EVA are combined to form a CsPbBr3 / EVA composite film resistive layer, and different resistance switch behaviors can be realized by adjusting applied voltage. The device has good cycle durability and long-time data retention capability; the simplification degree of the double-pulse simplification characteristic of the memristor prepared by the invention can reach 77.8% at most, which indicates that the memristor has relatively strong signal enhancement capability in the aspect of short-time synaptic plasticity and has wide application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-volatile memories, and particularly relates to a dual-mode memristor based on a quantum dot / copolymer composite film and a preparation method thereof. Background Art

[0002] With the continuous development of artificial intelligence, there is an increasing demand for the availability of large data sets and the use of graphics processing units to implement the backpropagation algorithm for training artificial neural networks. In particular, the interest in efficient and reliable storage devices for next-generation digital communications has grown rapidly, requiring special attention to new methods for storage devices. The field of neuromorphic computing may have a profound impact on next-generation computing and artificial intelligence.

[0003] Memristors have also emerged. Also known as resistive random access memories or memristive impedance devices, they belong to a type of non-volatile memory and are a new type of storage device based on the memristive effect. Its main structure is a sandwich structure composed of electrodes, a functional layer, and electrodes. The memristive effect refers to the existence of an internal state in a material, which can be reversibly changed under the action of an external voltage or current, thereby causing a change in the resistance of the material. Memristors utilize this effect to achieve the storage function of storage devices. Memristors have the advantages of fast erasing, low power consumption, and high-density integration, and are considered to be one of the important development directions of next-generation storage devices. It has broad application prospects in fields such as logic operations, neural networks, and pattern recognition, and is expected to be an important breakthrough in the future storage device field, promoting the development of computers and information technology. HP Labs first successfully fabricated an actual memristive device in 2008, verifying the memristive effect for the first time, opening up a new path for the physical implementation and application research of memristors. According to its switching characteristics, the switching behavior of memristors can be divided into two types: resistive switching (RS) and threshold switching (TS). RS-type memristors can stably maintain high-resistance and low-resistance states under the applied electric field, showing non-volatility. In contrast, TS-type memristors suddenly switch to the conductive state when the threshold voltage is reached, but once the voltage is removed, they return to the high-resistance state, showing volatile characteristics. The different resistance switching behaviors of these two types provide specific advantages for practical applications. Therefore, a dual-mode memristor that can exhibit RS and TS behaviors enhances the functional diversity of memristors and realizes more general storage and computing functions, which has great practical significance.

[0004] So far, the active layers of memristors have been fully expanded, such as metal oxides, organic polymer materials, transition metal compounds, two-dimensional materials, halide perovskites, and so on. Among them, halide perovskites have very broad application prospects in the field of memristors due to their adjustable bandgap, high absorption coefficient, high defect tolerance, long carrier diffusion coefficient, outstanding optoelectronic properties, and easy processing characteristics. Summary of the Invention

[0005] The object of the present invention is to provide a dual-mode (RS and TS) memristor based on a quantum dot / copolymer composite film and a preparation method thereof. The present invention combines perovskite quantum dots (CsPbBr3) with ethylene-vinyl acetate copolymer (EVA) to form a composite resistive switching layer, and different resistive switching behaviors can be achieved by adjusting the applied voltage. The device has good cycle durability ( Figure 3 ) and long-term data retention ability ( Figure 4 ), and can also mimic a variety of important neural synapse functions ( Figure 5 , Figure 6 ), having broad application prospects.

[0006] The preparation method of a dual-mode memristor based on a quantum dot / copolymer composite film according to the present invention comprises the following steps:

[0007] S1: Synthesis and purification of quantum dots

[0008] (1) Preparation of cesium oleate (Cs-OA) precursor solution: Add 800-850 mg of cesium carbonate (Cs2CO3), 2-3 mL of oleic acid (OA) and 30 mL of octadecene (ODE) into a three-necked flask to remove moisture and oxygen in the system; then heat the system to 110-130 °C in a vacuum environment and keep it warm for 0.5-2.0 h, and then introduce N2 and heat to 140-160 °C until the cesium carbonate solid is completely dissolved; finally, seal the obtained Cs-OA precursor solution and store it in the refrigerator for later use;

[0009] (2) Synthesis of quantum dots: Add 90-110 mg of lead bromide (PbBr2), 180-220 mg of zinc bromide (ZnBr2) and 10 mL of octadecene (ODE) into a three-necked flask to remove moisture and oxygen in the system; then heat the system to 110-130 °C in a vacuum environment and keep it warm for 0.5-2.0 h, and then add 1 mL of oleic acid and 1 mL of oleylamine that have been treated for water removal. After the solid is completely dissolved, heat it to 170-190 °C and immediately inject the Cs-OA precursor solution prepared in step (1) that has been heated to 90-110 °C. After reacting for 20-40 s, immediately transfer the reaction system to an ice-water bath and cool it to room temperature to complete the preparation of the quantum dot solution;

[0010] (3) Purification of quantum dots: After shaking the quantum dot solution prepared in step (2), put it into a centrifuge tube and centrifuge at a rate of 4000 - 6000 rpm for 8 - 15 min to separate the excess reactants and by-products that did not participate in the reaction; pour out the supernatant, dissolve the obtained precipitate in 1 - 2 mL of toluene, then add 1 - 2 mL of methyl acetate, and centrifuge at a speed of 8000 - 12000 rpm for 8 - 15 min; pour out the supernatant again, and dissolve the obtained precipitate in 1 - 2 mL of toluene to form a quantum dot solution;

[0011] S2: Preparation of composite solution

[0012] Add 200 - 300 mg of EVA and 5 - 10 mL of toluene solution into a glass bottle, react at 40 - 50 °C on a hot stage for 20 - 40 min until all the EVA is dissolved to obtain a polymer solution, and store it at room temperature; add the quantum dot solution purified in step S1 into the polymer solution and stir vigorously to make the quantum dots evenly mixed in the polymer solution to obtain a composite solution;

[0013] S3: Preparation of memristive device

[0014] (1) Substrate pretreatment: First, rub the surface of the FTO conductive glass substrate with scouring powder, after rinsing it clean, ultrasonically clean it with deionized water, ethanol, acetone, and isopropanol for 8 - 15 min respectively; after cleaning, blow it dry under a N2 gas stream, and then perform ultraviolet treatment in a plasma cleaner at a power of 40 - 60 W for 10 - 20 min;

[0015] (2) Preparation of composite film: Under the condition that both the moisture and oxygen content are lower than 0.1 ppm, spin-coat the composite solution obtained in step S2 on the FTO conductive glass substrate, and after the spin-coating is completed, transfer the FTO conductive glass substrate to a hot stage at 110 - 130 °C for annealing for 8 - 15 min to obtain a CsPbBr3 / EVA composite film with a thickness of 180 - 220 nm; where EVA is ethylene-vinyl acetate copolymer;

[0016] (3) Deposition of top electrode: Place a mask plate with a round hole diameter of 400 - 600 μm on the CsPbBr3 / EVA composite film, vacuum deposit an 80 - 120 nm thick Al top electrode, and control the vacuum degree below 10 -4 Pa, and keep the evaporation rate at Thus, the described dual-mode memristor based on perovskite quantum dot / copolymer composite film is obtained.

[0017] Furthermore, in step S1, the three-necked flask is connected and sealed with a vacuum pump and a N2 device; then, the operations of evacuating and introducing N2 are alternately carried out at room temperature to remove the moisture and oxygen in the system;

[0018] Further, in step S3, the vacuum degree is controlled below 10 -4 Pa, and the evaporation rate is maintained at

[0020] A dual - mode memristor based on a quantum dot / copolymer composite film according to the present invention is prepared by the above - mentioned method. Description of the Drawings

[0021] Figure 1 It is a schematic structural diagram of the Al / CsPbBr3 - EVA / FTO memristor prepared in Example 1 of the present invention;

[0022] Figure 2 It is a high - resolution transmission electron microscope picture of the CsPbBr3 / EVA film prepared in Example 1 of the present invention;

[0023] Figure 3 The current - voltage characteristic curve of the Al / CsPbBr3 - EVA / FTO memristor prepared in Example 1 of the present invention in 1 to 400 cycles;

[0024] Figure 4 It is the retention performance curve of the Al / CsPbBr3 - EVA / FTO memristor prepared in Example 1 of the present invention at a voltage of 0.02V;

[0025] Figure 5 It is the excitatory postsynaptic current effect curve of the Al / CsPbBr3 - EVA / FTO memristor prepared in Example 1 of the present invention;

[0026] Figure 6 It is the double - pulse facilitation characteristic curve of the Al / CsPbBr3 - EVA / FTO memristor prepared in Example 1 of the present invention. Detailed Embodiments

[0027] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] Example 1

[0029] As Figure 1As shown in the figure, a dual-mode memristor based on a quantum dot / copolymer composite film. The device structure sequence is the top electrode, the functional layer, and the bottom electrode. The entire device uses glass as the substrate. The top electrode is Al, the functional layer is a CsPbBr3 / EVA composite film, and the bottom electrode is FTO. The technical solution of the present invention is as follows:

[0030] S1: Synthesis and purification of quantum dots

[0031] (1) Preparation of cesium oleate (Cs-OA) precursor solution: Add 814 mg of cesium carbonate (Cs2CO3), 2.6 mL of oleic acid (OA), and 30 mL of octadecene (ODE) into a 100 mL three-necked flask. Connect the three-necked flask to a vacuum pump and an N2 device, seal the connection with vaseline and fix it with a buckle to prevent air leakage. Subsequently, alternately perform vacuum pumping and N2 injection operations at room temperature to remove moisture and oxygen in the system. Then, heat the system to 120 °C in a vacuum environment and keep it warm for 1 h, then inject N2 and heat to 150 °C until the Cs2CO3 solid is completely dissolved. Finally, seal the obtained Cs-OA precursor solution and store it in the refrigerator for later use;

[0032] (2) Synthesis of quantum dots: Add 100 mg of lead bromide (PbBr2), 200 mg of zinc bromide (ZnBr2), and 10 mL of octadecene (ODE) into a 50 mL three-necked flask. Connect the three-necked flask to a vacuum pump and an N2 device, seal the connection with vaseline and fix it with a buckle to prevent air leakage. Subsequently, alternately perform vacuum pumping and N2 injection operations at room temperature to remove moisture and oxygen in the system. Then, heat the system to 120 °C in a vacuum environment and keep it warm for 1 h, then add 1 mL of oleic acid and 1 mL of oleylamine that have been treated for water removal. After the solid is completely dissolved, heat it to 180 °C and immediately inject the Cs-OA precursor solution prepared in step (1) that has been heated to 100 °C. After reacting for 30 s, immediately transfer the reaction system to an ice-water bath and cool it to room temperature to complete the preparation of the quantum dot solution;

[0033] (3) Purification of quantum dots: Shake the quantum dot solution prepared in step (2) and put it into a centrifuge tube, centrifuge at a rate of 5000 rpm for 10 min to separate the excess reactants and by-products that did not participate in the reaction. Pour off the supernatant, dissolve the obtained precipitate in 1 mL of toluene, then add 1 mL of methyl acetate, and centrifuge at a speed of 10000 rpm for 10 min. Pour off the supernatant again, and dissolve the obtained precipitate in 1 mL of toluene to form a quantum dot solution;

[0034] S2: Preparation of composite solution

[0035] Add 250 mg of EVA and 5 mL of toluene solution into a 10 mL glass bottle, react at 45 °C on a hot stage for 30 min until all the EVA is dissolved to obtain a polymer solution, and store it at room temperature; add the quantum dot solution purified in step S1 into the polymer solution and stir vigorously to make the quantum dots uniformly mixed in the polymer solution to obtain a composite solution;

[0036] S3: Preparation of memristive device

[0037] (1) Substrate pretreatment: First, scrub the surface of the FTO conductive glass substrate with scouring powder, and after rinsing it clean, ultrasonically clean it with deionized water, ethanol, acetone, and isopropanol for 10 min respectively; after cleaning, blow it dry under a N2 gas stream, and then perform ultraviolet treatment in a plasma cleaner at a power of 50 W for 15 min;

[0038] (2) Preparation of composite film: Under the condition that the water content and oxygen content are both lower than 0.1 ppm, place the FTO conductive glass substrate on a spin coater, use a pipette to suck an appropriate amount of the composite solution obtained in step S3 and drop it on the FTO conductive glass substrate and spin coat it. After the spin coating is completed, transfer the FTO conductive glass substrate to a 120 °C hot stage for annealing for 10 min to obtain a CsPbBr3 / EVA composite film with a thickness of 200 nm;

[0039] (3) Deposition of top electrode: Place a mask plate with a round hole diameter of 500 μm on the CsPbBr3 / EVA composite film, vacuum deposit a 100 nm thick Al top electrode, control the vacuum degree below 10 -4 Pa, and keep the evaporation rate at Thus, the described dual-mode memristor based on perovskite quantum dot / copolymer composite film is obtained.

[0040] Example 2

[0041] In this example, the memristor prepared in Example 1 is tested in this example. The electrical performance of the memristor is evaluated using a digital source meter combined with a probe station. The voltage applied to the top electrode Al is defined as the forward voltage, and vice versa is defined as the negative voltage. The device test is carried out in a room temperature and atmospheric environment.

[0042] The memristor prepared in Example 1 was subjected to a durability cycle test. To avoid device breakdown, a limit current of 1 mA was set, and the device was tested for current-voltage using a scanning sequence of 0 V → -4 V → 0 V → 3 V → 0 V. The initial state of the device was the high-resistance state. When a negative bias voltage was applied, the current of the device gradually increased, and at approximately -3 V, the current increased sharply to reach the limit current, and the device changed from the high-resistance state to the low-resistance state. This process was the turn-on process, and the corresponding voltage was defined as the turn-on voltage. The device remained in the low-resistance state in this state. Subsequently, a positive voltage was applied, and the current gradually decreased. When the voltage reached approximately 2 V, the device changed back from the low-resistance state to the high-resistance state. This process was the turn-off process, and the corresponding voltage was defined as the turn-off voltage. Figure 3 The current-voltage curves of the device in 400 cycles are shown, indicating that the device has bipolar switching behavior and can maintain relatively stable performance during long-term use;

[0043] The memristor prepared in Example 1 was subjected to a retention performance test. As Figure 4 shown, the retention curves of the high-resistance state and the low-resistance state of the device were obtained at a voltage of 0.02 V. It can be seen that the device has a switching ratio of 10 3 , and after the device was tested for 4×10 4 seconds, the statistical results of the high-resistance state and the low-resistance state showed no significant changes, indicating that the device has the ability to retain data for a long time, proving its high reliability and stability;

[0044] The memristor prepared in Example 1 was subjected to synaptic behavior simulation. An electrical pulse was applied to the top of the device using a source meter. As Figure 5 shown, when the device was stimulated by a square wave pulse of -1 V and 10 μs, the current suddenly increased, and after the pulse ended, the current gradually decayed back to the initial state within 300 μs, indicating that the device can successfully simulate the excitatory postsynaptic current effect. On this basis, two square wave pulses of -1 V and 10 μs were successively applied to the device, and the pulse interval was 10 μs. As Figure 6 shown. The current response (A2) induced by the second pulse was significantly greater than the current response (A1) induced by the first pulse, indicating that the device can successfully simulate the paired-pulse facilitation property, and its facilitation degree can be represented by the paired-pulse facilitation index. The specific formula is: (A2 - A1) / A1 × 100%. The maximum facilitation degree of the paired-pulse facilitation property of the memristor prepared in the present invention can reach 77.8%, indicating that the device has a strong signal enhancement ability in short-term synaptic plasticity.

[0045] In summary, the present invention provides a preparation method of a dual-mode memristor based on a quantum dot / copolymer composite film, and the beneficial effects are as follows:

[0046] (1) The present invention provides a memristor based on a CsPbBr3 / EVA composite film, which can achieve bipolar resistive switching behavior of negative voltage writing and positive voltage erasing, and can perform stable cycling ( Figure 3 );

[0047] (2) This memristor exhibits excellent retention performance and can maintain for more than 10 3 seconds at a high switching ratio (> 10 4 ) ( Figure 4 );

[0048] (3) By adjusting the applied voltage mode, this memristor can effectively simulate synaptic behaviors such as excitatory postsynaptic current effect ( Figure 5 ) and paired-pulse facilitation property ( Figure 6 ), further demonstrating its potential in neuromorphic computing.

[0049] The foregoing has shown and described the basic principles, main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes within the meaning and scope of the equivalent elements of the claims in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0050] In addition, it should be understood that although this specification is described according to embodiments, not each embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A preparation method of a dual-mode memristor based on a quantum dot / copolymer composite film, characterized in that: The steps are as follows: S1: Synthesis and purification of quantum dots (1) Preparation of cesium oleate precursor solution: Add 800 - 850 mg of cesium carbonate, 2 - 3 mL of oleic acid, and 30 mL of octadecene into a three-necked flask, and remove the moisture and oxygen in the system; then heat the system to 110 - 130 °C under vacuum and keep it warm for 0.5 - 2.0 h, then introduce N2 and heat to 140 - 160 °C until the cesium carbonate solid is completely dissolved; finally, seal the obtained Cs-OA precursor solution and store it in the refrigerator for later use; (2) Synthesis of quantum dots: Add 90 - 110 mg of lead bromide, 180 - 220 mg of zinc bromide, and 10 mL of octadecene into a three-necked flask, and remove the moisture and oxygen in the system; then heat the system to 110 - 130 °C under vacuum and keep it warm for 0.5 - 2.0 h, then add 1 mL of oleic acid and 1 mL of oleylamine that have been treated to remove water, and after the solid is completely dissolved, heat to 170 - 190 °C and immediately inject the Cs-OA precursor solution prepared in step (1) that has been heated to 90 - 110 °C, and after reacting for 20 - 40 s, immediately transfer the reaction system to an ice-water bath to cool to room temperature, thus completing the preparation of the quantum dot solution; (3) Purification of quantum dots: Shake the quantum dot solution prepared in step (2), put it into a centrifuge tube, and centrifuge at a rate of 4000 - 6000 rpm for 8 - 15 min to separate the excess reactants and by-products that did not participate in the reaction; pour out the supernatant, dissolve the obtained precipitate in 1 - 2 mL of toluene, then add 1 - 2 mL of methyl acetate, and centrifuge at a speed of 8000 - 12000 rpm for 8 - 15 min; pour out the supernatant again, and dissolve the obtained precipitate in 1 - 2 mL of toluene to form a quantum dot solution; S2: Preparation of composite solution Add 200 - 300 mg of ethylene-vinyl acetate copolymer and 5 - 10 mL of toluene solution into a glass bottle, react at 40 - 50 °C on a hot stage for 20 - 40 min until the ethylene-vinyl acetate copolymer is completely dissolved to obtain a polymer solution, and store it at room temperature; add the quantum dot solution purified in step S1 into the polymer solution and stir vigorously to make the quantum dots evenly mixed in the polymer solution to obtain a composite solution; S3: Preparation of memristive device (1) Substrate pretreatment: First, rub the surface of the FTO conductive glass substrate with detergent powder, and after rinsing it clean, ultrasonically clean it with deionized water, ethanol, acetone, and isopropanol for 8 - 15 min respectively; after cleaning, blow it dry under a N2 gas flow, and then perform ultraviolet treatment in a plasma cleaner at a power of 40 - 60 W for 10 - 20 min; (2) Preparation of composite film: Under the condition that the moisture and oxygen content are both lower than 0.1 ppm, spin-coat the composite solution obtained in step S2 on the FTO conductive glass substrate, and after the spin-coating is completed, transfer the FTO conductive glass substrate to a hot stage at 110 - 130 °C and anneal it for 8 - 15 min to obtain a CsPbBr3 / EVA composite film with a thickness of 180 - 220 nm; where EVA is ethylene-vinyl acetate copolymer; (3) Depositing the top electrode: Place a mask plate with a circular hole diameter of 400 - 600 μm on the CsPbBr3 / EVA composite film, and vacuum deposit an Al top electrode with a thickness of 80 - 120 nm to obtain the dual-mode memristor based on the quantum dot / copolymer composite film.

2. The preparation method of a dual-mode memristor based on a quantum dot / copolymer composite film according to claim 1, wherein: In step S1, connect the three-neck flask to the vacuum pump and N2 device and seal it; then alternately perform vacuum pumping and N2 introduction operations at room temperature to remove moisture and oxygen in the system.

3. The preparation method of a dual-mode memristor based on a quantum dot / copolymer composite film according to claim 1, characterized in that: In step S3, the vacuum degree is controlled to be below 10 -4 Pa, and the evaporation rate is maintained at 4. A dual-mode memristor based on a quantum dot / copolymer composite film, characterized in that: It is prepared by the preparation method described in any one of claims 1 - 3.

Images