Optoelectronic memristor and preparation method thereof

Abstract

The application provides a photoelectric memristor and a preparation method thereof. The photoelectric memristor sequentially has a LiNbO3 (lithium niobate) resistive change layer and a Pd upper electrode formed on a (111) Nb:STO (niobium-doped strontium titanate) substrate. The preparation method of the memristor comprises the following steps: cleaning and drying the substrate; growing the LiNbO3 (LNO) resistive change layer on the Nb:STO substrate through PLD (pulsed laser deposition); and growing the Pd upper electrode on the LiNbO3 resistive change layer. The application uses a LiNbO3 thin film as the resistive change layer of the memristor. The LiNbO3 is an important photoelectric material because of its excellent piezoelectric, pyroelectric, electromagnetic, acousto-optic and nonlinear optical characteristics. These characteristics make the LiNbO3 a promising candidate for many applications.

Description

Technical Field

[0001] This invention relates to the field of storage technology, specifically to a photoelectric memristor and its fabrication method. Background Technology

[0002] In recent years, the application of digital communication in big data and the Internet of Things has driven the development of next-generation storage devices. Integrated circuit technology has reached dimensions below 20 nanometers, and traditional non-volatile memory devices are approaching their physical limits. Developing next-generation non-volatile memory devices has become a hot research area for scientists worldwide. Currently, the main types of non-volatile memory devices include ferroelectric memory, magnetic memory, phase-change memory, and resistive random access memory (RRAM). Among them, RRAM is widely considered a strong contender for next-generation non-volatile memory due to its advantages such as simple structure, fast operation speed, good scalability, good robustness, low power consumption, fast read / write speed, good data retention, simple fabrication, and ease of integration. It is a promising next-generation memory technology.

[0003] The earliest observed resistive switching effect dates back to 1962, and subsequently, more materials were confirmed to possess resistive switching properties. In 2002, Zhuang et al. first fabricated a 64-bit resistive switching memory array using complementary metal-oxide-semiconductor (CMOS) technology. In 2005, Baek et al. successfully demonstrated a binary transition metal-oxide-semiconductor (BMOS) resistive switching memory, which sparked extensive research on resistive switching memories. After 2008, resistive switching memories were also known as memristors, considered the fourth type of basic passive circuit element besides resistors, capacitors, and inductors, and have been applied to emerging fields such as artificial synapses and logic operations. The general structure of a memristor is a typical sandwich structure, with upper and lower electrodes and a variable resistive material placed between the upper and lower electrodes that can generate resistive switching. Under the action of an applied bias voltage, the resistance state of the device will change from high to low resistance, thereby realizing the storage of 0 and 1. For memristors, the choice of different resistive switching layer materials has a significant impact on the device; it can be said that the resistive switching layer material is the core of the memristor.

[0004] Scientific research shows that there are many types of materials that can be used as resistive switching layers, currently mainly falling into four categories. First, transition metal oxides. Transition metal binary oxides have advantages such as simple composition, low cost, ease of preparation, and compatibility with CMOS processes. Second, solid electrolytes. These memristors typically have a sandwich structure, including an electrochemically active electrode (Ag, Cu, etc.), an electrochemically inert electrode (W, Pt, etc.), and a resistive switching layer composed of a solid electrolyte material. Their resistive switching characteristics are due to the formation and breakage of metal conductive filaments caused by the migration of metal cations generated by the electrochemical reaction of the active metal electrode material under the influence of an electric field. Third, organic materials. Currently, organic materials are simple to prepare and inexpensive, and research on using the bistable characteristics of organic materials to fabricate memristors is widespread. The biggest advantage of organic materials is their wide variety, offering a large selection. Finally, perovskite oxides. Perovskite materials are easy to prepare, have long carrier diffusion lengths, low binding energies, excellent electrical properties, and processing performance, making them very suitable for use as resistive switching layer materials in memristors. Summary of the Invention

[0005] The purpose of this invention is to provide a photoelectric memristor and its fabrication method, so as to provide a new high-performance non-volatile memristor with stable resistance, good storage performance, good memory characteristics, good fatigue resistance and durability, and fast read, write and erase operation speeds.

[0006] This invention is implemented as follows:

[0007] A photoelectric memristor is provided, wherein a LiNbO3 resistive switching layer and a Pd top electrode are sequentially formed on an Nb:STO substrate. The Nb:STO substrate has a (111) crystal plane structure.

[0008] The LiNbO3 resistive switching layer in the opto-memristor provided by this invention has a thickness of 100 nm and a sputtering time of 60 min.

[0009] The photoelectric memristor provided by this invention has a Pd upper electrode thickness of 40 nm and a sputtering time of 10 min.

[0010] This invention also discloses a method for fabricating a photomemristor, comprising the following steps:

[0011] (a) Pretreatment of Nb:STO substrate;

[0012] (b) A LiNbO3 resistive switching layer was grown on an Nb:STO substrate using PLD (pulsed laser deposition);

[0013] (c) Fabrication of Pd top electrode on LiNbO3 resistive switching layer.

[0014] Preferably, step (a) specifically involves: first immersing the Nb:STO substrate in an acetone solution for ultrasonic cleaning for 10 minutes to remove surface contaminants, then immersing it in an alcohol solution for ultrasonic cleaning for 10 minutes, and finally drying it with high-purity nitrogen gas for later use.

[0015] Preferably, step (b) specifically involves: preparing the treated Nb:STO substrate, attaching it to the substrate holder using silver adhesive tape, placing it into the cavity of the PLD instrument, and evacuating the air pressure in the cavity to 5 × 10⁻⁶. -4 The pressure is then increased to 7.6 Pa, and the temperature is maintained at 550°C. The laser energy is 230 mJ, forming a LiNbO3 resistive switching layer. Annealing begins in the cavity under a flowing oxygen atmosphere, with the temperature decreasing by 5°C per minute.

[0016] Preferably, step (c) specifically involves: placing a mask on the substrate where the LiNbO3 resistive switching layer is formed, and evacuating the cavity to a vacuum level of 2 × 10⁻⁶. -4 Pa, introduce Ar gas at a flow rate of 25 sccm into the cavity, adjust the interface valve to maintain the pressure in the cavity at 1 Pa, turn on the DC source to control the Pd target ignition, adjust the AC source power to 10W to ignite the Pd target, and pre-sputter for 1 min; then perform formal sputtering to form the Pd top electrode on the LiNbO3 resistive switching layer.

[0017] In the preparation method provided by the present invention, the annealing in step (b) refers to vacuum annealing at 550°C, with the annealing time decreasing by 5°C per minute.

[0018] In the preparation method provided by the present invention, the mask in step (c) has circular holes with a diameter of 100-120 μm evenly distributed on it.

[0019] In the preparation method provided by the present invention, the thickness of the Pd electrode in step (c) is 40 nm and the sputtering time is 10 min.

[0020] The method for fabricating a photoelectric memristor provided by the present invention first processes an Nb:STO substrate, then grows a LiNbO3 resistive switching layer on the Nb:STO substrate by pulsed laser deposition, and finally grows a Pd top electrode on the LiNbO3 resistive switching layer by magnetron sputtering.

[0021] The fabrication method provided by this invention is simple, easy to implement, and highly operable. Performance testing of the fabricated memristor demonstrates its excellent resistive switching characteristics, exhibiting a relatively stable resistance change. Electrical testing reveals a small current, achieving low power consumption. Furthermore, this memristor exhibits superior fatigue resistance in both high and low resistance states.

[0022] In summary, the memristor provided by this invention uses a LiNbO3 thin film as the resistive switching layer. LiNbO3 has a high remanent polarization intensity and a small coercive electric field. When used to prepare opto-memristors, it exhibits good performance and is a material with more stable storage performance, stronger durability, and broader application prospects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the photoelectric memristor provided in Embodiment 1 of the present invention.

[0024] Figure 2 The image shows the XRD pattern of the Nb:STO / LiNbO3 heterojunction of the memristor prepared in Example 2 of this invention.

[0025] Figure 3 The image shows the IV curves of the memristor Pd / LiNbO3 / Nb:STO prepared in Example 2 of this invention at voltages from -2V to 7V.

[0026] Figure 4 The image shows the IV curve of the memristor Pd / LiNbO3 / Nb:STO prepared in Example 2 of this invention at voltages from -2V to 2V. Detailed Implementation

[0027] The following examples are provided to further illustrate the present invention, but the examples do not limit the present invention in any way.

[0028] Example 1: A photomemristor.

[0029] The structure of the photoelectric memristor provided by this invention is as follows: Figure 1 As shown, its structure includes a bottom substrate Nb:STO (strontium niobate titanate), which has a (111) crystal plane structure; a LiNbO3 (lithium niobate) resistive switching layer is grown on the Nb:STO substrate, and a Pd top electrode is grown on the LiNbO3 resistive switching layer.

[0030] The thickness of the LiNbO3 resistive switching layer is 100 nm, the thickness of the Pd upper electrode is 40 nm, and the diameter of the Pd upper electrode is 100-120 μm.

[0031] Example 2: A method for fabricating a photoelectric memristor.

[0032] The method for fabricating a photoelectric memristor provided by this invention includes the following steps:

[0033] (1) First, place the Nb:STO substrate in acetone solution and ultrasonically clean it for 10 minutes to remove the stains on its surface. Then, place it in alcohol solution and ultrasonically clean it for 10 minutes. After taking it out, blow it dry with high-purity nitrogen gas for later use.

[0034] (2) The Nb:STO substrate was bonded to the heater tray using silver paste.

[0035] (3) Place the heater tray with the substrate attached into the cavity of the PLD instrument. After closing the cavity's sealing door, turn on the mechanical pump, then slowly open the bypass valve. Once the pressure inside the cavity drops below 5 Pa, close the bypass valve. Turn on the molecular pump start switch, then slowly open the fore-stage valve and the gate valve until the pressure reaches 5 × 10⁻⁶ Pa. -4 Pa. Adjust the gate valve to a slightly open position and inject oxygen into the chamber at a flow rate of 50 sccm. Adjust the gate valve to stabilize the pressure inside the chamber at 7.6 Pa. Adjust the heating program to increase the temperature to 550℃ at a rate of 20℃ / min. To remove contaminants from the target surface, perform a 10-min pre-deposition before formally depositing the thick LiNbO3 film. Then sputter for 60 min to generate a 100 nm thick LiNbO3 film. After film deposition, close the molecular pump valve and switch, and fill the chamber with oxygen to bring the pressure to 5 × 10⁻⁶ Pa. -4 Pa, then set the cooling rate to 5℃ / min, and cool down to room temperature.

[0036] (4) Place a mask on the substrate on which the LiNbO3 thin resistive switching layer is formed. The mask has circular holes with a diameter of 100–120 μm evenly distributed on it. Evacuate the cavity to 5 × 10⁻⁶. -4 Pa, introduce Ar gas at a flow rate of 25 sccm into the cavity, adjust the interface valve to maintain the pressure in the cavity at 1 Pa, turn on the AC source to control the Pd target ignition, adjust the DC source power to 10W to ignite the Pd target, and pre-sputter for 1 min; then perform formal sputtering for 10 min to form a Pd top electrode with a thickness of 40 nm on the LiNbO3 resistive switching layer.

[0037] The structure of the memristor prepared by this invention can be represented as Pd / LiNbO3 / Nb:STO. This device is an opto-memristor device. The key point is that a resistive switching layer of LiNbO3 was obtained on the substrate Nb:STO by pulsed laser deposition.

[0038] The above-described embodiments are any one of the preparation methods protected by this invention. As long as the process parameters described in the claims and specification are within the range (such as the substrate being an Nb:STO substrate, the cavity vacuum degree of pulsed laser deposition, the RF source power, the pre-sputtering time, and the formal sputtering time, etc.), the memristor to be protected in Embodiment 1 of this invention can be obtained, and the prepared memristor has basically similar performance to the device prepared in this embodiment.

[0039] Performance testing

[0040] like Figure 2 As shown, Figure 2This is the XRD pattern of the LiNbO3 / Nb:STO memristor prepared in Example 2. From... Figure 2 As can be seen, two characteristic peaks appeared sequentially in the scanning range of 30-50°, namely LiNbO3 (0006) and Nb:STO (111), indicating that the LiNbO3 thin film was grown on the Nb:STO substrate at 550°C by pulsed laser deposition, achieving preferential growth.

[0041] like Figure 3 As shown, Figure 3 This is the IV spectrum of the memristor Pd / LiNbO3 / Nb:STO prepared in Example 2 at voltages from -2V to 7V. Figure 3 As can be seen, when a relatively large voltage is initially applied, the device undergoes a forming process.

[0042] like Figure 4 As shown, Figure 4 This is the IV curve of the memristor Pd / LiNbO3 / Nb:STO prepared in Example 2 at voltages from -2V to 2V. Figure 4 As can be seen, after the device undergoes a forming process, it can maintain a small voltage after that, indicating that the device has good stability.

[0043] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for fabricating a photoelectric memristor, characterized in that, Includes the following steps: (1) Pretreatment of Nb:STO substrate; (2) A LiNbO3 resistive switching layer was grown on a Nb:STO substrate using pulsed laser deposition. (3) A Pd top electrode was prepared on a LiNbO3 resistive switching layer; Step (2) specifically involves: preparing the treated Nb:STO substrate, attaching it to the substrate holder using silver adhesive tape, placing it into the cavity of the PLD instrument, and evacuating the air pressure in the cavity to 5×10⁻⁶. -4 Pa, then oxygen is introduced into it to maintain its pressure at 7.6 Pa and its temperature at 550 °C, with a laser energy of 230 mJ, to form a LiNbO3 resistive switching layer; then high-temperature annealing is performed; the high-temperature annealing specifically involves annealing in a cavity under a flowing oxygen atmosphere, with the temperature decreasing by 5 °C per minute; In step (3), when preparing the Pd top electrode, a mask is first placed on the substrate on which the LiNbO3 resistive switching layer is formed. The mask has circular holes with a diameter of 100~120μm. Then, a vacuum is drawn, Ar gas is introduced into the cavity, and the pressure and DC power are adjusted to form the Pd top electrode on the LiNbO3 resistive switching layer. In step (3), the sputtering time of the Pd upper electrode is 10 min and the thickness is 40 nm.

2. A photoelectric memristor prepared according to the method of claim 1, characterized in that, A LiNbO3 resistive switching layer and a Pd top electrode are sequentially grown on an Nb:STO substrate.

3. The photomemristor according to claim 2, characterized in that, The Nb:STO substrate has a (111) crystal plane structure.

4. The photomemristor according to claim 2, characterized in that, The thickness of the LiNbO3 resistive switching layer is 100 nm, and the thickness of the Pd top electrode is 40 nm.

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