A very low temperature normally closed resistance switch and its preparation method

Abstract

The present invention relates to a very low-temperature normally-off resistance switch, comprising: a SrTiO3 substrate, a LaFeO3 thin film, and a LaAlO3 thin film. The LaFeO3 thin film is grown on the polished surface of the SrTiO3 substrate, the LaAlO3 thin film is grown on the LaFeO3 thin film, and the rough surface of the SrTiO3 substrate is plated with metal. The very low-temperature normally-off resistance switch of the present invention utilizes a back electrode / SrTiO3 / LaFeO3 / LaAlO3 heterojunction constructed by pulsed laser deposition and magnetron sputtering. It has a simple structure, low cost, minimal oxide lattice mismatch, high feasibility, and is amenable to large-scale production and industrialization, thus possessing strong practical value.

Description

Technical Field

[0001] The present invention relates to the technical field of resistance switches, and in particular to an extremely low-temperature normally-off resistance switch and a preparation method thereof. Background Art

[0002] The rapid development of quantum computer technology is driving the need for miniaturization and integration. Compared to traditional flash memory, resistive random access memory (RRAM), based on the resistive switching effect, offers advantages such as simple structure, lower power consumption, smaller size, higher speed, higher capacity, non-volatility, and high compatibility with CMOS processes. However, RRAM typically operates at room temperature, making it difficult to integrate with quantum computers operating below liquid helium temperatures for miniaturization. Therefore, the development of a resistive switch capable of operating at extremely low temperatures is urgently needed. Summary of the Invention

[0003] The purpose of the present invention is to solve the defects in the prior art and provide a very low temperature normally closed resistance switch and a preparation method thereof.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] An extremely low temperature normally closed resistance switch, comprising:

[0006] SrTiO3 substrate, LaFeO3 film and LaAlO3 film, wherein the LaFeO3 film is grown on the polished surface of the SrTiO3 substrate, the LaAlO3 film is grown on the LaFeO3 film, and the rough surface of the SrTiO3 substrate is plated with an adhesion layer and a back electrode.

[0007] Preferably, the SrTiO3 substrate is a single-sided polished single-crystal SrTiO3 substrate, the thickness of the single-crystal SrTiO3 substrate is ≤1 mm, and the single-crystal SrTiO3 substrate is a 001-oriented single-crystal SrTiO3 substrate.

[0008] Preferably, the LaFeO3 film grown on the polished surface of the SrTiO3 substrate is a LaFeO3 film with c-axis preferential orientation, and the thickness of the LaFeO3 film is 2-15 monolayers; the LaAlO3 film grown on the LaFeO3 film is a LaAlO3 film with c-axis preferential orientation, and the thickness of the LaAlO3 film is 2-5 monolayers.

[0009] Preferably, the adhesion layer is made of Ni, Ti or Al, and the back electrode is made of Pt or Au.

[0010] To achieve the above object, the present invention further provides a method for preparing an extremely low temperature normally closed resistance switch, comprising:

[0011] Pre-treating a SrTiO3 substrate, and performing pulsed laser deposition on the treated SrTiO3 substrate to epitaxially grow an oxide film;

[0012] performing magnetron sputtering on the SrTiO3 substrate on which the oxide film is grown, sputtering metal on the rough surface to form an adhesion layer, and sputtering metal on the adhesion layer as a back electrode to obtain a resistance switch;

[0013] The resistance switch is placed in an extremely low temperature environment, and a back gate electric field is applied and then removed to obtain a normally closed resistance switch.

[0014] Preferably, pre-treating the SrTiO3 substrate comprises:

[0015] The SrTiO3 substrate is cleaned, etched and annealed to obtain a polished surface with a high-quality step where the Ti-O layer cuts off.

[0016] Preferably, cleaning the SrTiO3 substrate comprises: placing the SrTiO3 substrate in acetone for ultrasonic cleaning to remove organic impurities on the surface of the substrate, and then performing ultrasonic cleaning in anhydrous ethanol to remove acetone and other impurities on the surface; wherein the cleaning time is not less than 5 minutes.

[0017] Preferably, generating the oxide film includes:

[0018] The annealed SrTiO3 substrate is placed in a pulsed laser deposition chamber, and the chamber is first vacuumed to a pressure of less than 10 -7 mbar; then fill the cavity with oxygen to 10 -5 -10 -3 mbar; heating the SrTiO3 substrate to 650-750°C, epitaxially growing 2-15 monolayers of LaFeO3 thin film on the substrate, and then epitaxially growing 2-5 monolayers of LaAlO3 thin film, and monitoring the number of film growth layers by a reflection high-energy electron diffractometer; wherein the pulsed laser wavelength sputtering on the LaFeO3 ceramic target and the LaAlO3 target is 248nm, and the energy density is 0.2-3J / cm 2 , frequency is 1-10Hz.

[0019] Preferably, obtaining the normally-off resistance switch includes:

[0020] The rough surface of the SrTiO3 substrate is sputtered with Ni, Ti or Al with a thickness of not less than 5 nm as an adhesion layer, and then Pt or Au with a thickness of not less than 5 nm is sputtered as a back electrode to obtain a resistance switch component.

[0021] Preferably, the resistive switching device is placed in an environment with a temperature not greater than 20K, a back gate electric field of not less than 2000V / cm is applied and then the back gate electric field is removed to obtain a normally closed resistive switching component, wherein the duration of the back gate electric field is not less than 500ms.

[0022] The beneficial effects of the present invention are:

[0023] (1) The ultra-low temperature normally-off resistance switch of the present invention is constructed by pulsed laser deposition and magnetron sputtering to form a back electrode / SrTiO3 / LaFeO3 / LaAlO3 heterojunction. It has a simple structure, low cost, small oxide lattice mismatch, high feasibility, can be prepared on a large scale, is easy to industrialize, and has strong practical value.

[0024] (2) The resistive switch material has good stability, an operating temperature window covering the operating range of quantum computers, significant resistance change, and a resistance switching ratio exceeding five orders of magnitude;

[0025] (3) LaFeO3 and LaAlO3 films are prepared by pulsed laser deposition, and their thickness can be monitored by reflection high-energy electron diffractometer (RHEED) to realize switching devices with different resistance switching ratios. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 This is a schematic structural diagram of an extremely low temperature normally closed resistance switch according to an embodiment of the present invention;

[0028] Figure 2 This is a graph showing the resistance variation over time of the extremely low temperature normally-off resistance switch at 2K regulated by the back gate electric field of an embodiment of the present invention;

[0029] Figure 3 This is a graph showing the variation of leakage current with back gate electric field strength at 2K for an extremely low temperature normally-off resistance switch according to an embodiment of the present invention;

[0030] Figure 4 1 is an output curve diagram of the ultra-low temperature normally-off resistance switch under different back gate voltages at 2K according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] like Figure 1 As shown, the present invention provides an ultra-low temperature normally-off resistance switch, comprising a single-sided polished and oriented single-crystal SrTiO3 substrate and a LaFeO3 film and a LaAlO3 film with c-axis preferential orientation epitaxially grown on the polished surface thereof, as well as Ti, Ni, Al and other metals sputtered on the rough surface thereof as an adhesion layer and Pt, Au and other metals as a back electrode. The resistance switching effect can be achieved by applying a back gate voltage on the back electrode for regulation.

[0034] Based on the analysis of the characteristics of the resistive switch samples prepared in the present invention, the best implementation case of the method for preparing an extremely low temperature normally closed resistive switch is described in detail below:

[0035] Example 1:

[0036] (1) SrTiO3 substrate cleaning: The SrTiO3 substrate was ultrasonically cleaned in acetone for 10 min to remove organic impurities on the surface, and then ultrasonically cleaned in anhydrous ethanol for 10 min to remove acetone and other impurities on the surface;

[0037] (2) SrTiO3 substrate etching annealing: The cleaned SrTiO3 substrate was ultrasonically reacted in deionized water for 30 minutes, then etched in BOE solution for 30 seconds, then rinsed in deionized water and the water adsorbed on the surface was blown dry with nitrogen. The etched substrate was annealed at 950°C for 90 minutes to obtain a Ti-O layer-terminated SrTiO3 substrate with a high-quality step surface.

[0038] (3) Epitaxial growth of oxide thin films: Place the annealed SrTiO3 substrate into the pulsed laser deposition chamber and evacuate the chamber to 10 -8 mbar; then fill the cavity with oxygen to 10 -4mbar; a SrTiO3 substrate was heated to 700°C, and a five-monolayer LaFeO3 film was epitaxially grown on the substrate. A five-monolayer LaAlO3 film was then epitaxially grown, and the number of film layers grown was monitored by reflection high-energy electron diffraction (RHEED). The pulsed laser wavelength was 248 nm and the energy density was 1 J / cm2, which was used to sputter the polycrystalline LaFeO3 ceramic target (99.99%) and the single-crystalline LaAlO3 target (99.99%) of the perovskite phase. 2 , frequency is 2Hz;

[0039] (4) The thin film-grown sample was placed in a magnetron sputtering chamber, and a 20 nm thick Ti was sputtered on the rough surface of the SrTiO3 substrate as an adhesion layer, and then a 20 nm thick Pt was sputtered as a back electrode to obtain a resistive switch component;

[0040] (5) The resistive switch device is placed in an extremely low temperature environment of 2K, and a back gate electric field of 4200V / cm is applied for 2s and then removed to obtain a normally-off resistive switch component.

[0041] The resistance-time characteristics of the prepared normally-off resistance switch component were tested to study its resistance switching characteristics.

[0042] Connect the source meter four-probe to the four corners of the sample surface, and use the Van der Pauw method to measure its resistance-time characteristics. At the same time, the positive electrode of the back gate electric field is connected to the Pt back electrode, and the negative electrode is connected to the sample surface. The change process of the back gate electric field is 0→4200V / cm→0→4200V / cm→0→4200V / cm→0. A data point is measured every 3s, such as Figure 2 As shown, it can be seen that the back gate electric field of 4200V / cm can cause the resistance of the sample to change by more than five orders of magnitude, and this change is non-volatile, indicating that the sample has good non-volatile switching characteristics at extremely low temperatures.

[0043] Furthermore, the leakage current test is performed on the back gate electric field. The change process of the back gate electric field is -4200V / cm→0→4200V / cm→0→-4200V / cm. Figure 3 As shown, it can be seen that the leakage current is ≤60nA, the surface sample capacitance characteristics are good, and it is not broken down.

[0044] Example 2:

[0045] (1) SrTiO3 substrate cleaning: The SrTiO3 substrate was ultrasonically cleaned in acetone for 10 min to remove organic impurities on the surface, and then ultrasonically cleaned in anhydrous ethanol for 10 min to remove acetone and other impurities on the surface;

[0046] (2) SrTiO3 substrate etching annealing: The cleaned SrTiO3 substrate was ultrasonically reacted in deionized water for 30 minutes, then etched in BOE solution for 30 seconds, then rinsed in deionized water and the water adsorbed on the surface was blown dry with nitrogen. The etched substrate was annealed at 950°C for 90 minutes to obtain a Ti-O layer-cutoff SrTiO3 substrate with a high-quality step surface;

[0047] (3) Epitaxial growth of oxide thin films: Place the annealed SrTiO3 substrate into the pulsed laser deposition chamber and evacuate the chamber to 10 -8 mbar; then fill the cavity with oxygen to 5*10 -5 mbar; a SrTiO3 substrate was heated to 700°C, and a two-monolayer LaFeO3 film was epitaxially grown on the substrate. A five-monolayer LaAlO3 film was then epitaxially grown, and the number of film layers grown was monitored by reflection high-energy electron diffraction (RHEED). The pulsed laser wavelength was 248 nm and the energy density was 1.5 J / cm2, which was used to sputter the polycrystalline LaFeO3 ceramic target (99.99%) and the single-crystalline LaAlO3 target (99.99%) of the perovskite phase. 2 , frequency is 2Hz;

[0048] (4) The thin film-grown sample was placed in a magnetron sputtering chamber, and a 20 nm thick Ti was sputtered on the rough surface of the SrTiO3 substrate as an adhesion layer, and then a 20 nm thick Pt was sputtered as a back electrode to obtain a resistive switch component;

[0049] (5) The resistive switch device is placed in an extremely low temperature environment of 10K, and a back gate electric field of 3000V / cm is applied for 10s and then removed to obtain a normally-off resistive switch component.

[0050] Example 3:

[0051] (1) SrTiO3 substrate cleaning: The SrTiO3 substrate was ultrasonically cleaned in acetone for 10 min to remove organic impurities on the surface, and then ultrasonically cleaned in anhydrous ethanol for 10 min to remove acetone and other impurities on the surface;

[0052] (2) SrTiO3 substrate etching annealing: The cleaned SrTiO3 substrate was ultrasonically reacted in deionized water for 30 minutes, then etched in BOE solution for 30 seconds, then rinsed in deionized water and the water adsorbed on the surface was blown dry with nitrogen. The etched substrate was annealed at 950°C for 90 minutes to obtain a Ti-O layer-terminated SrTiO3 substrate with a high-quality step surface.

[0053] (3) Epitaxial growth of oxide thin films: Place the annealed SrTiO3 substrate into the pulsed laser deposition chamber and evacuate the chamber to 10-8 mbar; then fill the cavity with oxygen to 10 -5 mbar; a SrTiO3 substrate was heated to 675°C, and a 10-monolayer LaFeO3 film was epitaxially grown on the substrate. A 2-monolayer LaAlO3 film was then epitaxially grown, and the number of film layers grown was monitored by reflection high-energy electron diffraction (RHEED). The pulsed laser wavelength was 248 nm and the energy density was 1 J / cm2, which was used to sputter the polycrystalline LaFeO3 ceramic target (99.99%) and single-crystalline LaAlO3 target (99.99%) of the perovskite phase. 2 , frequency is 3Hz;

[0054] (4) The thin film-grown sample was placed in a magnetron sputtering chamber, and a 20 nm thick Ti was sputtered on the rough surface of the SrTiO3 substrate as an adhesion layer, and then a 50 nm thick Au was sputtered as a back electrode to obtain a resistive switch component;

[0055] (5) The resistive switch device is placed in an extremely low temperature environment of 2K, and a back gate electric field of 4200V / cm is applied for 5s and then removed to obtain a normally-off resistive switch component.

[0056] like Figure 4 The output curves at different back gate voltages at 2K.

[0057] Another aspect of the present invention provides a method for controlling the opening and disconnection of a normally closed resistive switch component, which uses the ultra-low temperature normally closed resistive switch described in any of the aforementioned items, applies a back gate electric field, and injects carriers to make the normally closed resistive switch component open; after removing the back gate electric field, the normally closed resistive switch component returns to being disconnected; wherein: when controlling the opening and disconnection of the normally closed resistive switch component, its operating temperature is maintained at ≤20K, and the applied back gate electric field is ≥2000V / cm.

[0058] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A resistance switch that is normally closed at very low temperatures, characterized in that: include: A SrTiO3 substrate, a LaFeO3 film, and a LaAlO3 film, wherein the LaFeO3 film is grown on the polished surface of the SrTiO3 substrate, the LaAlO3 film is grown on the LaFeO3 film, and the rough surface of the SrTiO3 substrate is plated with an adhesion layer and a back electrode; The SrTiO3 substrate is a single-sided polished single-crystal SrTiO3 substrate, the thickness of the single-crystal SrTiO3 substrate is ≤1mm, and the single-crystal SrTiO3 substrate is a single-crystal SrTiO3 substrate with a 001 orientation; The LaFeO3 film grown on the polished surface of the SrTiO3 substrate is a LaFeO3 film with a preferred c-axis orientation, and the thickness of the LaFeO3 film is 2-15 monolayers; the LaAlO3 film grown on the LaFeO3 film is a LaAlO3 film with a preferred c-axis orientation, and the thickness of the LaAlO3 film is 2-5 monolayers; The adhesion layer is made of Ni, Ti or Al, and the back electrode is made of Pt or Au; The method for preparing the extremely low temperature normally closed resistance switch comprises: Pre-treating a SrTiO3 substrate, and performing pulsed laser deposition on the treated SrTiO3 substrate to epitaxially grow an oxide film; performing magnetron sputtering on the SrTiO3 substrate on which the oxide film is grown, sputtering metal on the rough surface to form an adhesion layer, and sputtering metal on the adhesion layer as a back electrode to obtain a resistance switch; The resistance switch is placed in an extremely low temperature environment, and a back gate electric field is applied and then removed to obtain a normally closed resistance switch.

2. The extremely low temperature normally closed resistance switch according to claim 1, characterized in that: The pretreatment of the SrTiO3 substrate includes: The SrTiO3 substrate is cleaned, etched and annealed to obtain a polished surface with a high-quality step where the Ti-O layer cuts off.

3. The extremely low temperature normally closed resistance switch according to claim 2, characterized in that: Cleaning the SrTiO3 substrate includes: placing the SrTiO3 substrate in acetone for ultrasonic cleaning to remove organic impurities on the surface of the substrate, and then performing ultrasonic cleaning in anhydrous ethanol to remove acetone and other impurities on the surface; wherein the cleaning time is not less than 5 minutes.

4. The extremely low temperature normally closed resistance switch according to claim 1 is characterized in that: Generating the oxide film comprises: The annealed SrTiO3 substrate is placed in a pulsed laser deposition chamber, and the chamber is first vacuumed to a pressure of less than 10 -7 mbar; then fill the cavity with oxygen to 10 -5 -10 -3 mbar; heating the SrTiO3 substrate to 650-750°C, epitaxially growing 2-15 monolayers of LaFeO3 thin film on the substrate, and then epitaxially growing 2-5 monolayers of LaAlO3 thin film, and monitoring the number of film growth layers by a reflection high-energy electron diffractometer; wherein the pulsed laser wavelength sputtering on the LaFeO3 ceramic target and the LaAlO3 target is 248nm, and the energy density is 0.2-3J / cm 2 , frequency is 1-10Hz.

5. The extremely low temperature normally closed resistance switch according to claim 1, characterized in that: Obtaining the normally-off resistance switch includes: The rough surface of the SrTiO3 substrate is sputtered with Ni, Ti or Al with a thickness of not less than 5 nm as an adhesion layer, and then Pt or Au with a thickness of not less than 5 nm is sputtered as a back electrode to obtain a resistance switch component.

6. The extremely low temperature normally closed resistance switch according to claim 1, characterized in that: The resistive switching device is placed in an environment with a temperature not greater than 20K, a back gate electric field of not less than 2000V / cm is applied and then the back gate electric field is removed to obtain a normally-off resistive switching component, wherein the duration of the back gate electric field is not less than 500ms.

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