Multistate memory based on quasi-two-dimensional perovskite ferroelectric thin film and preparation method thereof

Abstract

The application relates to the technical field of ferroelectric thin film multi-state memory, in particular to a multi-state memory based on a quasi-two-dimensional perovskite ferroelectric thin film and a preparation method thereof. The multi-state memory comprises, from bottom to top, a substrate, a patterned conductive bottom electrode, a multi-state storage layer and a top electrode; the multi-state storage layer is a metal ion doped quasi-two-dimensional perovskite ferroelectric thin film, and under the control of an applied electric field, the multi-state storage layer shows multiple light emission intensities for representing multiple information recording states. The material of the quasi-two-dimensional perovskite in the metal ion doped quasi-two-dimensional perovskite ferroelectric thin film comprises (CHA)2CsPb2Br7, (BA)2CsPb2Br7 or (BA)2CuCl4, and the metal ion comprises but is not limited to any one of Mn, Er and Tm. The multi-state memory has the advantages of high integration level and strong controllability; under ultraviolet excitation, different voltages can be applied to show different light emission intensities, and multi-state light information storage is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ferroelectric thin film multi-state memory, and particularly relates to a multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin film and a preparation method thereof. BACKGROUND

[0002] The rapid development of the information age makes people more urgent demand for high-density memory. There are two ways to increase the storage density per unit area, which are to increase the storage state of a single device and to further reduce the device size. As the limit size of silicon-based memory approaches, the strategy of reducing the device size has become a technical problem that the entire industry is difficult to break through. In contrast, increasing the storage state of a single device shows greater advantages for the realization of high-density memory. Multi-state memory has become a research hotspot.

[0003] Ferroelectric materials have the characteristics of electric field switchable spontaneous polarization, and can be switched from one polarization state to another planned state, becoming an ideal material for non-volatile memory. Since the 19th century, ferroelectric materials have attracted widespread attention. Multi-state non-volatile memory based on ferroelectric materials has the advantages of high storage density, energy consumption and speed, and has great potential in the fields of future high-density storage, edge computing and embedded devices. However, multi-state non-volatile ferroelectric memory has great challenges in complex preparation process, high cost and device scaling. Therefore, it is necessary to develop a new type of ferroelectric multi-state memory, which is of great significance for high-density storage in the big data era.

[0004] Metal halide perovskites (MHPs) are similar in structure to traditional ferroelectric oxide perovskites, but MHPs are different from wide-bandgap insulating oxides and belong to a new type of semiconductor. Due to the large absorption cross section, tunable band gap, high quantum efficiency and other characteristics of MHPs, they have received unprecedented attention. Quasi-2D MHPs have high structural stability, chemical stability and good flexibility. More importantly, the synergistic effect of the ordered arrangement of the organic component and the relative displacement of the octahedron in 2D MHPs makes it easier to produce spontaneous polarization. At present, a variety of 2D MHPs have been confirmed to have ferroelectricity. At present, the research of 2D perovskite ferroelectrics mainly focuses on the preparation of bulk crystals, which leads to the difficulty of device integration. By preparing 2D MHPs thin films, taking advantage of excellent optical properties, and designing new multi-state memories on this basis, there is great application potential and commercial prospect. SUMMARY

[0005] The present application provides a multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin film and a preparation method thereof to solve the above problems.

[0006] The first object of the present application is to provide a multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin film, comprising a substrate, a patterned conductive bottom electrode, a multi-state storage layer and a top electrode which are sequentially stacked from bottom to top;

[0007] The multi-state storage layer is a metal ion doped quasi-two-dimensional perovskite ferroelectric thin film.

[0008] The multi-state storage layer exhibits multiple light emission intensities under the control of an applied electric field, which is used to represent multiple information recording states.

[0009] Preferably, the material of the quasi-two-dimensional perovskite in the metal ion doped quasi-two-dimensional perovskite ferroelectric thin film includes (CHA)2CsPb2Br7, (BA)2CsPb2Br7 or (BA)2CuCl4, and the metal ion includes but is not limited to any one of Mn, Er and Tm.

[0010] Preferably, the metal ion doped quasi-two-dimensional perovskite ferroelectric thin film is prepared by one-step spin coating with organic halide, cesium halide, lead halide and metal ion halide according to the chemical formula ratio, and dimethyl sulfoxide as the solvent.

[0011] Preferably, the top electrode material is Au, which is prepared by a thermal evaporation method and has a thickness of 80-110 nm.

[0012] Preferably, the thickness of the multi-state storage layer is 30-50 nm.

[0013] Preferably, the patterned conductive bottom electrode is a transparent ITO electrode, and the substrate is a glass substrate.

[0014] The second object of the present application is to provide a preparation method of a multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin film, which specifically comprises the following steps:

[0015] S1. A patterned conductive bottom electrode is prepared on a substrate by magnetron sputtering and photolithography, and then the patterned conductive bottom electrode is sequentially ultrasonically cleaned in deionized water, ethanol, acetone, isopropanol and ethanol for 8-15 minutes and dried by blowing.

[0016] S2. Organic halide, cesium halide, lead halide and metal ion halide are dissolved in dimethyl sulfoxide at a certain ratio, and then continuously stirred and heated at 28-32℃ for 10-15 hours to obtain a reaction precursor solution.

[0017] S3. A metal ion doped quasi-two-dimensional perovskite ferroelectric thin film is prepared by spin coating under N2 atmosphere, which specifically comprises the following sub-steps:

[0018] S31. The reaction precursor solution is dropped on the surface of the patterned conductive bottom electrode and spin coated at a speed of 3800-4500 rpm for 25-35 seconds, and a reverse solvent is added during the process.

[0019] S32. heat annealing at 110~130℃ for 15~25min, cooling, to obtain the polymorphic storage layer;

[0020] S4. preparing the top electrode on the surface of the polymorphic storage layer by thermal evaporation.

[0021] Preferably, before the step S1, the step S0 of sequentially ultrasonicating the substrate in deionized water, ethanol, acetone, isopropanol, and ethanol for 8~15min each and blowing dry is further included.

[0022] Preferably, in the step S31, spin coating is performed at a rotation speed of 4000 rpm for 30s, and the anti-solvent chlorobenzene is added dropwise at the 20th second.

[0023] Preferably, in the step S32, heat annealing is performed at 120℃ for 20min.

[0024] Compared with the prior art, the present application can achieve the following beneficial effects:

[0025] (1) The metal ion doped quasi-two-dimensional perovskite ferroelectric thin film of the present application causes lattice distortion at low voltage, and the change of the crystal field environment can cause the non-volatility of the luminescent intensity of the metal ions, which can produce long-time storage effect. Polymorphic storage is operated at low voltage, which reduces the power consumption of the operating device. The obtained polymorphic storage device can exhibit different, non-volatile and reversible regulated luminescent intensity under the light excitation of ultraviolet GaN LED under different voltages, realizing polymorphic optical information storage.

[0026] (2) The present application adopts the metal ion luminescence principle, generates ferroelectric polarization through voltage, changes the crystal field environment of the host, regulates the ion luminescent intensity, and enhances the controllability of the device.

[0027] (3) The storage device built by the metal ion doped quasi-two-dimensional perovskite ferroelectric thin film of the present application utilizes the excellent optical properties and ferroelectric properties of MHPs, combines the low defect characteristics, and makes it compatible with other semiconductors, improving the integration level of the device. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a structure schematic diagram of a polymorphic storage device based on a quasi-two-dimensional perovskite ferroelectric thin film according to an embodiment of the present application.

[0029] Figure 2 is a hysteresis loop of a quasi-two-dimensional perovskite ferroelectric thin film according to an embodiment of the present application.

[0030] Figure 3 is four luminescent states of a polymorphic storage device based on a quasi-two-dimensional perovskite ferroelectric thin film after applying different electric fields (0, 2, 4, 6 V voltage) according to an embodiment of the present application.

[0031] Reference signs:

[0032] 1. a substrate;

[0033] 2. a patterned conductive bottom electrode;

[0034] 3. a multi-state storage layer;

[0035] 4. a top electrode. DETAILED DESCRIPTION

[0036] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. In the following description, the same modules are denoted by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0037] In order to make the objectives, technical solutions, and advantages of the present application clearer, further detailed descriptions will be given below in combination with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not constitute a limitation on the present application.

[0038] Referring to Figure 1 , the present application provides a multi-state memory based on a quasi-two-dimensional perovskite ferroelectric thin film, comprising a substrate 1, a patterned conductive bottom electrode 2, a multi-state storage layer 3, and a top electrode 4 stacked in order from bottom to top;

[0039] Specifically, the substrate 1 is a glass substrate;

[0040] The patterned conductive bottom electrode 2 is a transparent ITO electrode;

[0041] The multi-state storage layer 3 is a metal ion doped quasi-two-dimensional perovskite ferroelectric thin film; the thickness of the multi-state storage layer 3 is 30-50 nm;

[0042] The material of the quasi-two-dimensional perovskite (2D MHPs) in the metal ion doped quasi-two-dimensional perovskite ferroelectric thin film includes (CHA)2CsPb2Br7, (BA)2CsPb2Br7, or (BA)2CuCl4, and the metal ion includes but is not limited to any one of Mn, Er, and Tm;

[0043] The preparation method of the metal ion doped quasi-two-dimensional perovskite ferroelectric thin film includes: preparing by one-step spin coating with dimethyl sulfoxide (DMSO) as a solvent according to a chemical formula ratio of organic halide, cesium halide, lead halide, and metal ion halide;

[0044] The material of the top electrode 4 is Au, which is prepared by a thermal evaporation method, and the thickness of the Au electrode is 80-110 nm;

[0045] The metal ion doped quasi-two-dimensional perovskite ferroelectric thin film can exhibit a variety of light emitting intensities under the control of an applied electric field, which is used to represent a variety of information recording states. By using this characteristic, a brand new multi-state memory based on the metal ion doped quasi-two-dimensional perovskite ferroelectric thin film is made.

[0046] The preparation method of the multi-state memory based on the quasi-two-dimensional perovskite ferroelectric thin film includes the following steps:

[0047] S0. The substrate is sequentially ultrasonically cleaned in deionized water, ethanol, acetone, isopropanol and ethanol for 8-15 minutes, and dried with nitrogen;

[0048] S1. An ITO thin film is prepared on the substrate by magnetron sputtering, and a patterned conductive bottom electrode is prepared by a photolithography method. The patterned conductive bottom electrode is sequentially ultrasonically cleaned in deionized water, ethanol, acetone, isopropanol and ethanol for 8-15 minutes to remove possible residual particles and impurities. Nitrogen is used for drying;

[0049] S2. The organic halide, cesium halide, lead halide and metal ion halide are dissolved in dimethyl sulfoxide (DMSO) in a certain proportion, continuously stirred and heated at 28-32℃ for 10-15h to obtain a reaction precursor solution;

[0050] In specific embodiments, the concentration of lead halide is 0.5 mol / L; continuously stirred and heated at 30℃ for 12h;

[0051] S3. The device prepared in step S1 is transferred into a glove box filled with N2, and a metal ion doped quasi-two-dimensional perovskite ferroelectric thin film is prepared by spin coating. The specific steps include the following sub-steps:

[0052] S31. 40 microliters of the reaction precursor solution is dropped on the surface of the patterned conductive bottom electrode, and spin-coated at a speed of 3800-4500 rpm for 25-35s. At the 20th second, 100 microliters of chlorobenzene is dropped as an anti-solvent to help film formation;

[0053] In specific embodiments, spin-coating is performed at a speed of 4000 rpm for 30s;

[0054] S32. Transfer to a hot stage, and perform thermal annealing at 110-130℃ for 15-25min, and then naturally cool to obtain a multi-state storage layer;

[0055] In specific embodiments, thermal annealing is performed at 120℃ for 20min;

[0056] S4. Transfer to a thermal evaporation device, and prepare a top electrode on the surface of the multi-state storage layer by thermal evaporation to complete the preparation of the multi-state memory based on the quasi-two-dimensional perovskite ferroelectric thin film;

[0057] In a specific embodiment, the top electrode material is Au.

[0058] Example 1

[0059] This embodiment provides a method for fabricating a multi-state memory based on a quasi-two-dimensional perovskite ferroelectric thin film, specifically including the following steps:

[0060] S0. The glass substrate was ultrasonicated in deionized water, ethanol, acetone, isopropanol and ethanol for 10 minutes each in sequence, and then dried with nitrogen gas.

[0061] S1. An ITO thin film is prepared on a glass substrate by magnetron sputtering, and then a patterned conductive bottom electrode is prepared by photolithography; the patterned conductive bottom electrode is ultrasonicated in deionized water, ethanol, acetone, isopropanol and ethanol for 10 minutes each to remove any possible residual particles and impurities; and then dried with nitrogen.

[0062] S2. Dissolve the organic halide (butylammonium bromide BABr), cesium halide (CsBr), lead halide (PbBr2), and metal ion halide (MnBr2) in DMSO solvent in a molar ratio of 2:1:2:1, wherein the concentration of lead halide is 0.5 mol / L. Stir continuously at 30°C and heat for 12 h to obtain the reaction precursor solution.

[0063] S3. Transfer the device prepared in step S1 to a glove box filled with N2, and prepare a metal ion-doped quasi-two-dimensional perovskite ferroelectric thin film by spin coating; specifically including the following sub-steps:

[0064] S31. Take 40 μL of the reaction precursor solution and drop it onto the patterned conductive bottom electrode surface. Spin coat it at 4000 rpm for 30 s. At the 20th s, drop 100 μL of chlorobenzene as an anti-solvent to help form a film.

[0065] S32. Transfer to a hot stage and perform thermal annealing at 120°C for 20 min, followed by natural cooling to obtain (BA)2CsPb2Br7:Mn thin film, i.e., multistate storage layer;

[0066] S4. Transfer to a thermal evaporation device to prepare an Au top electrode on the surface of the multistate storage layer by thermal evaporation, thus completing the fabrication of a multistate memory based on a quasi-two-dimensional perovskite ferroelectric thin film.

[0067] like Figure 2 As shown, the remanent polarization of the multi-state storage layer (BA2CsPb2Br7:Mn thin film) is approximately 5 µC / cm. 2 The coercive field is approximately 4.5 V. Under the influence of an external electric field, polarization can be generated along the direction of the electric field, which in turn causes a change in the crystal field environment of Mn, thereby causing a change in the luminescence intensity.

[0068] The memory based on the metal ion doped quasi-two-dimensional perovskite ferroelectric thin film prepared above was measured for its luminescent intensity under different voltages (0, 2, 4, 6 V), and as shown in FIG. 4, four distinguishable luminescent intensity states were obtained, and such a memory device with storage characteristics can be used as a basic element for multi-state storage. Figure 3

[0069] Embodiment 2

[0070] The embodiment provides a preparation method of a multi-state memory based on a quasi-two-dimensional perovskite ferroelectric thin film, which is different from the embodiment 1 in that:

[0071] The multi-state storage layer is a (CHA)2CuCl4:Tm thin film; and in step S2, the organic halide (cyclohexylammonium bromide CHABr), the metal ion compound (copper chloride CuCl2), and the metal ion halide (TmBr2) are dissolved in a DMSO solvent at a molar ratio of 4:2:1, wherein the concentration of the lead halide is 0.5 mol / L, and the reaction precursor solution is obtained by continuously stirring and heating at 30°C for 12 h.

[0072] The remaining steps are the same as those in the embodiment 1.

[0073] Embodiment 3

[0074] The embodiment provides a preparation method of a multi-state memory based on a quasi-two-dimensional perovskite ferroelectric thin film, which is different from the embodiment 1 in that:

[0075] The multi-state storage layer is a (CHA)2CuCl4:Tm thin film; and in step S2, the organic halide (cyclohexylammonium bromide CHABr), the metal ion compound (copper chloride CuCl2), and the metal ion halide (TmBr2) are dissolved in a DMSO solvent at a molar ratio of 4:2:1, wherein the concentration of the lead halide is 0.5 mol / L, and the reaction precursor solution is obtained by continuously stirring and heating at 30°C for 12 h.

[0076] The remaining steps are the same as those in the embodiment 1.

[0077] It should be understood that the various forms of flow shown above can be used to reorder, add or delete steps. For example, the steps described in the present disclosure can be executed in parallel, in sequence, or in a different order, as long as the desired results of the technical solutions of the present disclosure can be achieved, and the present disclosure is not limited herein.

[0078] ​The above detailed description does not limit the scope of the application. Various modifications, combinations, sub-combinations and alternatives can be made to the detailed description. Any modification, equivalent replacement and improvement etc. made within the spirit and principle of the application shall be included in the scope of the application.

Claims

1. A multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin films, characterized in that: The substrate, the patterned conductive bottom electrode, the multi-state storage layer and the top electrode are sequentially stacked from bottom to top. The multi-state storage layer is a metal ion doped quasi-two-dimensional perovskite ferroelectric thin film. The thickness of the multi-state storage layer is 30-50 nm. 2.The multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin film according to claim 1, wherein: The metal ion doped quasi-two-dimensional perovskite ferroelectric thin film is prepared by one-step spin coating method using dimethyl sulfoxide as a solvent. 3.The multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin film according to claim 1, wherein: The top electrode material is Au, which is prepared by a thermal evaporation method and has a thickness of 80-110 nm.

4. The multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin films according to claim 1, wherein: The patterned conductive bottom electrode is a transparent ITO electrode, and the substrate is a glass substrate.

5. A preparation method of the multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin film, for preparing the multi-state memory based on quasi-two-dimensional perovskite ferroelectric thin film according to claim 1, characterized in that: The method comprises the following steps: S1. A patterned conductive bottom electrode is prepared on a substrate by a magnetron sputtering and a photolithography method. S2. Organic halide, cesium halide, lead halide and metal ion halide are dissolved in dimethyl sulfoxide at a certain ratio, and the solution is continuously stirred and heated at 28-32℃ for 10-15 h to obtain a reaction precursor solution. S3. The metal ion doped quasi-two-dimensional perovskite ferroelectric thin film is prepared by a spin coating method in a N2 atmosphere. S31. The reaction precursor solution is dropped on the surface of the patterned conductive bottom electrode and spin coated at a speed of 3800-4500 rpm for 25-35 s, and a reverse solvent is added during the process. S32. Thermal annealing is performed at 110-130℃ for 15-25 min, and the multi-state storage layer is obtained after cooling. S4. The top electrode is prepared on the surface of the multi-state storage layer by a thermal evaporation method.

6. The method of claim 5, wherein the method further comprises: Before the step S1, the substrate is ultrasonically cleaned in deionized water, ethanol, acetone, isopropanol and ethanol for 8-15 min, and then dried.

7. The method of claim 5, wherein the method further comprises: In the step S31, the spin coating is performed at a speed of 4000 rpm for 30 s, and a reverse solvent chlorobenzene is added at the 20th second.

8. The method of claim 5, wherein the method further comprises: In the step S32, the thermal annealing is performed at 120℃ for 20 min.

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