Two-dimensional (4, 4-DFHHA) 2PbI4 memristor and preparation method and application thereof

Abstract

The invention discloses a two-dimensional (4, 4-DFHHA) 2PbI4 memristor and a preparation method and application thereof, and belongs to the technical field of memristors. The memristor comprises a conductive substrate, a (4, 4-DFHHA) 2PbI4 functional layer, a PMMA modification layer and a metal electrode, and the PMMA modification layer is arranged between the (4, 4-DFHHA) 2PbI4 functional layer and the metal electrode and used for isolating the metal electrode from the (4, 4-DFHHA) 2PbI4 functional layer and preventing the metal electrode and the (4, 4-DFHHA) 2PbI4 functional layer from chemical reaction. Different configurations can be achieved through polarization of different electric fields, the stability and reliability of the memristor are effectively improved, and the memristor has wide application prospects in the fields of neuromorphic calculation and the like.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of memristors, in particular to a two-dimensional (4,4-DFHHA)2PbI4 memristor and a preparation method and application thereof. BACKGROUND

[0002] In recent years, two-dimensional perovskite memristors have shown great potential in artificial synapse applications due to their unique physical and chemical properties. For example, CN116940220A discloses a preparation method of a new two-dimensional material and organic thin film mixed memristor, which has the structure of ITO / perovskite thin film / PMMA / Ag. However, the product has the following problems:

[0003] The product in the above-mentioned document does not have ferroelectricity and cannot be polarized under the action of an electric field, so it cannot generate an additional polarization electric field under the action of an electric field, thereby having a single configuration and being unable to realize multi-level information storage.

[0004] In addition, in the prior art, the electrode layer of the memristor is prone to react with the perovskite thin film, which affects the stability of the memristor to some extent. For example, in the ITO / (4,4-DFHHA)2PbI4 / Ag memristor, the electrode layer reacts with the perovskite thin film after long-term storage, resulting in a decrease in the performance of the device. Therefore, how to improve the stability of the memristor has become a technical problem to be solved in the field. SUMMARY

[0005] The purpose of the application is to overcome the problems in the prior art and provide a two-dimensional (4,4-DFHHA)2PbI4 memristor. By introducing two-dimensional (4,4-DFHHA)2PbI4, different configurations can be realized by different electric field polarizations, thereby realizing multi-level information storage. By introducing a PMMA modification layer, the electrode and the perovskite thin film are effectively isolated, and the stability and reliability of the memristor are improved.

[0006] The two-dimensional (4,4-DFHHA)2PbI4 memristor provided by the application comprises: a conductive substrate; a (4,4-DFHHA)2PbI4 polycrystalline functional layer is arranged on the conductive substrate; a PMMA modification layer is arranged on the (4,4-DFHHA)2PbI4 polycrystalline functional layer; and a metal electrode is arranged on the PMMA modification layer.

[0007] The charge conduction mechanism of the memristor includes space charge limited conduction and ionic conduction.

[0008] The PMMA modification layer forms a coordination bond with Pb 2 and vacancies in the (4,4-DFHHA)2PbI4 polycrystalline functional layer through a carbonyl (C-O) functional group, thereby passivating grain boundary defects.

[0009] The two-dimensional (4,4-DFHHA)2PbI4 memristor uses the ferroelectric material two-dimensional (4,4-DFHHA)2PbI4, and under the condition of electric field polarization, the polarization state changes, thereby changing the conductive state; by changing the thickness and coverage of the PMMA modification layer, the switching ratio of the memristor and the resistance state stability of the memristor can be changed.

[0010] The preparation method of the two-dimensional (4,4-DFHHA)2PbI4 memristor comprises the following steps:

[0011] S1, dissolving (4,4-DFHHA)2PbI4 powder in a mixed solvent composed of DMSO and NMP to obtain a precursor solution; dropping the precursor solution onto a conductive substrate for spin coating, adding anti-solvent chlorobenzene as an extraction solvent during the spin coating process to improve the quality of the thin film, and then annealing to obtain a (4,4-DFHHA)2PbI4 polycrystalline functional layer;

[0012] S2, dissolving PMMA powder in chlorobenzene, adjusting the concentration of the PMMA solution according to the switching ratio and resistance state stability of the target memristor to obtain a PMMA solution; dropping the PMMA solution onto the (4,4-DFHHA)2PbI4 polycrystalline functional layer for spin coating; and then annealing to obtain a PMMA modification layer;

[0013] S3, using a thermal evaporation method to prepare a metal electrode on the PMMA modification layer as the top electrode of the memristor.

[0014] Preferably, in S1, DMSO and NMP are mixed in a volume ratio of (10:1) to (3:1) to form the mixed solvent; when the mixed solvent is used to dissolve (4,4-DFHHA)2PbI4 powder, the concentration of (4,4-DFHHA)2PbI4 is 0.2-1 mol / L, and after oscillation and dissolution, the precursor solution is obtained by filtration.

[0015] Preferably, in S1, the precursor solution is dropped onto the conductive substrate, spin-coated at a speed of 3000 rpm for 40 s, chlorobenzene is added at the 35th second, and annealing is performed at 100°C for 20 min.

[0016] Preferably, in S2, the concentration of the PMMA solution ranges from 0.5 mg / mL to 10 mg / mL.

[0017] The switching ratio of the two-dimensional (4,4-DFHHA)2PbI4 memristor can be adjusted within 10 2 ~ 10 4 :

[0018] When a large switching of the memristor is required, a PMMA solution with a lower concentration in the concentration range is selected;

[0019] When a high resistance state stability of the memristor is required, a PMMA solution with a higher concentration in the concentration range is selected;

[0020] When the memristor is required to have a high-low resistance state fluctuation of less than 10% within 10 3 s, a PMMA solution with a concentration of 10 mg / mL is selected;

[0021] 100 μL of the PMMA solution is taken for spin coating, and the spin coating speed is 4000 rpm; the annealing is annealing at 100℃ for 10 min in a constant temperature environment.

[0022] Preferably, in S3, the metal electrode is a Cu, Ag or Au electrode with a thickness of 100-300 nm.

[0023] The application also provides application of the two-dimensional (4,4-DFHHA)2PbI4 memristor in a high-humidity environment, the high-humidity environment being a room-temperature high-humidity environment with a temperature of 30℃ and a humidity of 50%; the two-dimensional (4,4-DFHHA)2PbI4 memristor can still maintain the resistance change characteristic after being placed in the room-temperature high-humidity environment for one month.

[0024] Compared with the prior art, the two-dimensional (4,4-DFHHA)2PbI4 memristor of the application introduces a PMMA modification layer between the (4,4-DFHHA)2PbI4 functional layer and the metal electrode, effectively isolates the metal electrode and the perovskite film, avoids chemical reaction between the two, and improves the stability and reliability of the memristor. At the same time, the PMMA modification layer can also passivate grain boundary defects, reduce charge traps and recombination, and further optimize the performance of the device. In addition, by optimizing the PMMA concentration and the metal electrode material, the switching ratio and stability of the memristor are further improved, and the memristor has a wide application prospect in the field of neuromorphic computing. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 In S3, (a) is an SEM cross-section of the (4,4-DFHHA)2PbI4 film, (b) is a structural diagram of "ITO / (4,4-DFHHA)2PbI4 / Ag", and (c) is a crystal structure diagram of (4,4-DFHHA)2PbI4.

[0026] Figure 2 The I-V curve of the memristor device is cycled: (a) is a "ITO / (4,4-DFHHA)2PbI4 / PMMA / Ag" memristor, and (b) is an "ITO / (4,4-DFHHA)2PbI4" memristor.

[0027] Figure 3 Cycling I-V curves for the memristive devices: (a-c) for 5 mg / mL PMMA-modified (4,4-DFHHA)2PbI4devices, (b-d) for 10 mg / mL PMMA-modified devices;

[0028] Figure 4 Cycling stability test curves for the memristive devices, where (a) and (b) are I-V curves for the "ITO / (4,4-DFHHA)2PbI4 / PMMA / Au" memristive devices; (c) and (d) are 50-cycle I-V curves for the "ITO / (4,4-DFHHA)2PbI4 / PMMA / Au" memristive devices;

[0029] Figure 5 250-cycle I-V curves for the "ITO / (4,4-DFHHA)2PbI4 / PMMA / Ag" memristive devices;

[0030] Figure 6 Perovskite devices with added anti-solvent (0.5 mg / mL PMMA) for different storage times: (a) for 1 week in a high-temperature and high-humidity environment, (b) for 2 weeks in a high-temperature and high-humidity environment, (c) for 4 weeks in a high-temperature and high-humidity environment;

[0031] Figure 7 In (a), the high and low resistance state retention time of the "ITO / (4,4-DFHHA)2PbI4 / PMMA / Ag" memristive device, and in (b), the high and low resistance value distribution of the memristive device after multiple cycles.

[0032] Figure 8 In (a), the double logarithmic fitting curve of the conduction mechanism under positive voltage scanning, and in (b), the double logarithmic fitting curve of the conduction mechanism under negative voltage scanning. DETAILED DESCRIPTION

[0033] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings, but it should be understood that the scope of protection of the present application is not limited by the specific embodiments. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0034] As shown in Figure 1 The two-dimensional (4,4-DFHHA)2PbI4 memristive device provided by the present application comprises an ITO substrate, a (4,4-DFHHA)2PbI4 functional layer, a PMMA modification layer 3 and a metal electrode, and the PMMA modification layer is arranged between the (4,4-DFHHA)2PbI4 functional layer and the metal electrode.

[0035] (4,4-DFHHA)2PbI4 powder synthesis

[0036] In a vacuum glove box, 0.69 g of (4,4-difluorohexahydroazepine hydrochloride) and 0.92 g of high purity PbI2 were accurately weighed using a high precision analytical balance and placed in an agate mortar for mechanical-chemical grinding for 30 min before being left to react in solution inside a fume hood. A 25 mL solution of hydriodic acid with a concentration of 47% was taken and injected into a flask (containing 0.02% sodium hypophosphite stabilizer), after thorough mixing an orange-red flocculent precipitate was immediately formed in the flask. After waiting for 10 min the flask was connected to a high precision oil bath system and heated to 395 K at a rate of 5 °C / min, magnetic stirring (600 rpm) was applied until the solution was completely clear. After the solution had cleared, crystallization was performed using the gradient cooling method: in the first stage a decrease of 0.5 °C / min was applied to 353 K for 1 h to form the crystal nuclei, followed by a decrease of 0.2 °C / min to room temperature to promote the directional growth of the crystals. The final synthesis product was vacuum filtered using a 0.22 pm polyvinylidene fluoride filter membrane, washed three times with 99% pure anhydrous ethanol, and the resulting crystals were left to dry in a vacuum drying oven (10-3Torr, 323 K) for 5 h, obtaining an orange-red powder which was immediately sealed and stored in the vacuum glove box.

[0037] Device fabrication

[0038] 1. (4,4-DFHHA)2PbI4 functional layer fabrication: 720 mg of (4,4-DFHHA)2PbI4 powder was weighed and dissolved in 1000 mL of solvent mixed from DMSO and NMP in a 4:1 ratio, after 12 h of shaking it was filtered. 50 pL of precursor solution was dropped on ITO and spin-coated at 3000 rpm for 40 s (70 pL of anti-solvent CB was added at the 35th s), annealed at 100 °C for 20 min.

[0039] 2. PMMA modification layer fabrication: 0.5 mg, 5 mg or 10 mg of PMMA powder was weighed and sequentially dissolved in 1 mL of chlorobenzene solvent, after 5 h of stirring at a constant temperature of 60 °C, the solution of different concentrations was filtered. 100 pL of prepared solution was dropped on the (4,4-DFHHA)2PbI4 functional layer, then dynamic spin-coating was performed at a high speed of 4000 rpm to make it uniformly cover the (4,4-DFHHA)2PbI4 thin film, and then the substrate was annealed at a constant temperature of 100 °C for 10 min.

[0040] 3. Metal electrode fabrication: 120 nm thick Ag or Au metal contact dots and rectangles were prepared as the top electrode of the memristor using the thermal evaporation method.

[0041] The prepared two-dimensional (4,4-DFHHA)2PbI4 memristor comprises a conductive substrate, a (4,4-DFHHA)2PbI4 polycrystal functional layer, a PMMA modification layer and a metal electrode, wherein the PMMA modification layer is arranged between the (4,4-DFHHA)2PbI4 functional layer and the metal electrode, and is used for isolating the metal electrode and the (4,4-DFHHA)2PbI4 functional layer to avoid chemical reaction between the two.

[0042] The concentration of the PMMA modification layer is 0.5 mg / mL-10 mg / mL. By adjusting the concentration of PMMA, the performance of the memristor can be optimized. When the concentration of PMMA is 5 mg / mL, the switching ratio of the memristor is larger; and when the concentration of PMMA is 10 mg / mL, the resistance state of the memristor is more stable.

[0043] The metal electrode is a Cu, Ag or Au electrode. By comparing different metal electrodes, it is found that the memristor with an Au electrode has better stability.

[0044] Preferably, the preparation method of the (4,4-DFHHA)2PbI4 polycrystal functional layer comprises the following steps: dissolving (4,4-DFHHA)2PbI4 powder in a solvent mixed by DMSO and NMP at a ratio of 4:1, filtering after oscillation for 12 h, dropping the precursor solution on ITO, spin-coating at a speed of 3000 rpm for 40 s, dropping 70 μL of anti-solvent CB at the 35th second, and annealing at 100 ℃ for 20 min.

[0045] Preferably, the preparation method of the PMMA modification layer comprises the following steps: dissolving PMMA powder in chlorobenzene solvent, filtering after stirring at a constant temperature of 60 ℃ for 5 h, dropping 100 μL of the solution at the 35th second of spin-coating of the perovskite precursor solution, then spin-coating at a speed of 4000 rpm, and annealing at 100 ℃ for 10 min.

[0046] The prepared memristor has a bipolar resistance conversion characteristic, and the switching ratio is 10 2 ~10 4 Under an applied voltage of 0.5 V, the device can realize bipolar resistance conversion, the window value is 10 2 , and the HRS / LRS remains stable within 400 cycles.

[0047] The prepared memristor can still maintain the resistance change characteristic after being placed in a room temperature high humidity environment (RT-30 ℃, RH-50%) for one month. The electrical performance of the unpackaged device begins to obviously attenuate after being placed in the environment for one month, but the RS characteristic can still be realized.

[0048] The resistance state stability of the prepared memristor is good, and the resistance state remains stable within 10 3s, the resistance value fluctuation of high and low resistance state is less than 10%. In 10 3 s, the resistance value fluctuation of high and low resistance state is less than 10%. In 10 2 .

[0049] The charge conduction mechanism of the prepared memristor includes ohmic conduction and space charge limited current conduction. In the low voltage scanning area of the HRS state, the slope of LogI-LogV is about 1, which is ohmic conduction. With the increase of scanning voltage, the current changes nonlinearly, and the curve fitting slope increases to n>2, indicating space limited current conduction.

[0050] The prepared PMMA modification layer forms a coordination bond with Pb 2+ The vacancies form a coordination bond, passivating the grain boundary defects. This feature enables PMMA to reduce the traps and recombination of charges in the transmission process, thereby improving the efficiency and stability of the device.

[0051] Performance test

[0052] 1. Basic I-V characteristic test: Under the conditions of no light source, 30% humidity and 20℃ environment, the memristor was subjected to continuous bias cyclic scanning, the voltage scanning direction was (0V→0.5V→0V→-0.5V→0V), the scanning rate was 300mV / s, and the limit current was set to 50mA. The results showed that the device exhibited resistance switching phenomenon, the I-V curve exhibited an asymmetric "8" shaped hysteresis loop, and had non-volatile bipolar switching characteristics.

[0053] 2. Different concentration PMMA influence test: The devices modified by 5mg / mL and 10mg / mL PMMA solution were compared, and continuous bias cyclic scanning was applied in the dark environment, the voltage scanning direction was (0V→0.55V→0V→-0.8V→0V), and the scanning rate was 300mV / s. The results showed that when the PMMA concentration of the modification layer increased, the VSET and VRESET values of the device increased, the switching of the device modified by 5mg / mL PMMA was larger, and the resistance state of the device modified by 10mg / mL PMMA was more stable.

[0054] 3. Different electrode material influence test: The devices with evaporated gold (Au) electrode and Ag electrode were compared, and continuous voltage cyclic scanning was applied in the dark environment, the voltage scanning direction was (0V→1.2V→0V→-1.2V→0V), and the scanning rate was 300mV / s. The results showed that the I-V curves of the devices with different electrode materials were different, and the device with Au electrode had better stability.

[0055] 4. Multiple cycle test: The memristor was continuously scanned 250 times, and the results showed that the I-V curve remained basically unchanged before and after scanning, reflecting the good reliability and stability of the device.

[0056] 5. Aging test: The memristor was stored in a room temperature high humidity environment (RT~30℃, RH~50%), and was not packaged, and electrical tests were performed after the first week, the second week and the fourth week. The results show that as the storage time increases, the device window decreases, but the RS characteristics can still be achieved at the fourth week.

[0057] 6. Resistance state stability study: The HRS and LRS resistance values at Vread of 0.15V were read, and the device HRS had slight fluctuations while the LRS remained almost unchanged within 10 3 s of test time, and the window value maintained 10 2 , and the high and low resistance state resistance fluctuation was small.

[0058] 7. Charge conduction mechanism study: The I-V curve was processed by double logarithm, and the results show that in the low voltage scanning area of HRS state, it is ohmic conduction, and in the higher voltage scanning area, it is space charge limited conduction, and in the reset process, ohmic law dominates.

[0059] The two-dimensional (4,4-DFHHA)2PbI4 memristor of the application effectively solves the problem of device performance degradation caused by the reaction of the electrode and the perovskite film in the prior art by introducing a PMMA modification layer, improves the stability and reliability of the memristor, and has good application prospects.

[0060] Although embodiments of the application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the application.

Claims

1. A two-dimensional (4,4-DFHHA)2PbI4 memristor, characterized in that, It comprises: a conductive substrate; a (4,4-DFHHA)2PbI4 polycrystalline functional layer is arranged on the conductive substrate; a PMMA modification layer is arranged on the (4,4-DFHHA)2PbI4 polycrystalline functional layer; and a metal electrode is arranged on the PMMA modification layer; The charge conduction mechanism of the memristor comprises space charge limited conduction and ionic conduction. The PMMA modification layer forms a coordination bond with Pb in the (4,4-DFHHA)2PbI4 polycrystal functional layer through a carbonyl (C-O) functional group 2 + vacancy formation coordination bond, passivation of grain boundary defects.

2. The method for fabricating a two-dimensional (4,4-DFHHA)2PbI4 memristor according to claim 1, characterized in that, It comprises the following steps: S1, dissolving (4,4-DFHHA)2PbI4 powder in a mixed solvent composed of DMSO and NMP to obtain a precursor solution; dropping the precursor solution onto a conductive substrate for spin coating; adding a chlorobenzene extraction solvent during the spin coating process to improve the quality of the thin film; and then annealing to obtain a (4,4-DFHHA)2PbI4 polycrystalline functional layer; S2, dissolving PMMA powder in chlorobenzene; adjusting the concentration of the PMMA solution according to the switching ratio and resistance state stability requirements of the target memristor to obtain a PMMA solution; dropping the PMMA solution onto the (4,4-DFHHA)2PbI4 polycrystalline functional layer for spin coating; and then annealing to obtain a PMMA modification layer; S3, preparing a metal electrode on the PMMA modification layer by a thermal evaporation method as a top electrode of the memristor.

3. The preparation method of the two-dimensional (4,4-DFHHA)2PbI4 memristor according to claim 2, characterized in that: in S1, the mixed solvent is composed of DMSO and NMP in a volume ratio of (10:1) to (3:1); when the mixed solvent is used to dissolve the (4,4-DFHHA)2PbI4 powder, the concentration of the (4,4-DFHHA)2PbI4 is 0.2-1 mol / L; and after oscillation and dissolution, the precursor solution is obtained by filtration.

4. The preparation method of the two-dimensional (4,4-DFHHA)2PbI4 memristor according to claim 3, characterized in that: in S1, the precursor solution is dropped onto the conductive substrate, spin coated at a speed of 3000 rpm for 40 s, chlorobenzene is added at the 35th second, and annealing is performed at 100℃ for 20 min.

5. The preparation method of the two-dimensional (4,4-DFHHA)2PbI4 memristor according to claim 4, characterized in that: in S2, the concentration of the PMMA solution ranges from 0.5 mg / mL to 10 mg / mL; The on-off ratio of the two-dimensional (4,4-DFHHA)2PbI4 memristor is 10 2 ~ 10 4 Adjustable: when a larger switching ratio of the memristor is required, a PMMA solution with a lower concentration is selected from the concentration range; when a higher resistance state stability of the memristor is required, a PMMA solution with a higher concentration is selected from the concentration range; The memristor is required to have a high-low resistance state fluctuation of less than 10% within 10 3 s, and a PMMA solution with a concentration of 10 mg / mL is selected. 100 μL of the PMMA solution is taken for spin coating at a speed of 4000 rpm; and the annealing is performed at 100℃ for 10 min in a constant temperature environment.

6. The method of claim 4, wherein the two-dimensional (4,4-DFHHA)2PbI4 memristor is prepared by the steps of: in S3, the metal electrode is a Cu, Ag or Au electrode with a thickness of 100-300 nm.

7. Use of the two-dimensional (4,4-DFHHA)2PbI4 memristor according to claim 1 in high humidity environments, characterized in that, The high humidity environment is a room temperature high humidity environment with a temperature of 30℃ and a humidity of 50%.

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