A magnetoelectric storage element based on PMN-PT ferroelectric / ferromagnetic composite film and its preparation method

Abstract

A magnetoelectric storage element based on a PMN-PT ferroelectric / ferromagnetic composite film and a preparation method thereof, belonging to the field of semiconductor integrated circuit technology, wherein the preparation of a small-sized FeCo ferromagnetic film is to mask a specific pattern on a PMN-PT single crystal substrate by using ion beam deposition combined with a photolithography process; the PMN-PT single crystal piezoelectric substrate and the Fe 65 Co 35 The alloy target is placed in a sputtering chamber, and ion beam sputtering is used to deposit a ferromagnetic thin film. Compared to traditional non-volatile memory, the magnetoelectric memory device produced by this invention offers advantages such as low power consumption and fast read / write speeds, which are crucial for meeting the practical needs of future memory devices. The use of ion beam sputtering to produce layered composite thin film devices is simple and compatible with semiconductor processes.

Description

Technical Field

[0001] The present invention particularly relates to a magnetoelectric storage element of a PMN-PT-based ferroelectric / ferromagnetic composite film and a preparation method thereof. Background Art

[0002] With the rapid development of information technology in today's society, storage technologies are required to provide memories with larger capacity, faster speeds, smaller size, longer lifespan, and lower power consumption. Traditional information storage methods include ferroelectric random access memory (FeRAM) and magnetic random access memory (MRAM). Ferroelectric random access memory utilizes the spontaneous polarization of ferroelectrics to store information. It offers advantages such as high durability, fast read / write speeds, low power consumption, and reliable multi-level polarization states, making it a mature and promising non-volatile memory. However, it suffers from two drawbacks: the destructive read process and limited storage density. Magnetic memory offers significant advantages in access time and durability, but suffers from a significant drawback in high write energy. These two storage methods significantly limit their application as memory devices. To this end, researchers in related fields are constantly exploring new devices, structures, and materials related to information functions, and new memory concepts are being designed. One promising approach is to utilize magnetoelectric coupling (ME coupling) and multiferroic materials.

[0003] Multiferroic magnetoelectric materials possess both ferromagnetic and ferroelectric properties. These multifunctional materials enable the design and development of novel devices with new functionalities. The magnetoelectric coupling effect between magnetic and electrical order allows for the control of polarization by applying a magnetic field and magnetization by applying an electric field. Therefore, multiferroic magnetoelectric materials hold great potential for future application. Magnetoelectric random access memory (MERAM) based on this magnetoelectric coupling effect uses an electric field to write information and a magnetic head to read it. The basic operation combines magnetoelectric coupling with the interfacial exchange coupling between the multiferroic material and the ferromagnetic layer. The magnetization of the ferromagnetic layer is controlled by the strength of the electric field, and the polarization of the multiferroic material can be controlled by changes in the magnetic field. The advantages of this new type of multi-level non-volatile magnetoelectric memory include: first, a relatively simple memory cell structure and ease of fabrication. Second, applying a voltage pulse between two electrodes allows for faster and more efficient write operations, significantly improving read and write speeds. Third, read operations are easier than with traditional FRAM, reducing destructive read operations.

[0004] Relaxor ferroelectric single crystal Pb(Mg 1 / 3 Nb 2 / 3)O3-PbTiO3(PMN-PT)(W Zhou, et al., ACS APPL MATERINTER., 2021) exhibits a large piezoelectric effect (d 33 >2000pC / N), and has been widely studied for its excellent tensile strain capacity. It also has the characteristics of electric field controllable, reversible and non-volatile strain. 65 Co 35 The alloy film has high saturation magnetization, large magnetocrystalline anisotropy and saturation magnetostriction, high magnetic permeability and good thermal stability.

[0005] The present invention relates to a magnetoelectric storage element of a ferroelectric / ferromagnetic composite film based on magnetoelectric effect, wherein Fe 65 Co 35 The alloy serves as the ferromagnetic layer, and the 0.7PMN-0.3PT single crystal with a large piezoelectric coefficient serves as the ferroelectric layer. This allows the ferroelectric layer to generate sufficiently large strain under an electric field and transfer it to the adjacent ferromagnetic layer. This results in an environmentally friendly magnetoelectric memory device with a large electroresistance switching effect. Summary of the Invention

[0006] The purpose of the present invention is to solve the above problems and provide a method for preparing a magnetoelectric memory element based on a PMN-PT ferroelectric / ferromagnetic composite film. 1 / 3 Nb 2 / 3 )O3]-0.3[PbTiO3] single crystal substrate and Fe 65 Co 35 Alloy target material is used as raw material and ion beam sputtering method is adopted to prepare magnetoelectric composite thin film devices. This storage element can maintain the polarization and magnetization state when external voltage is applied. Since the change of resistance state can be achieved by flipping the voltage between the upper and lower electrodes, it does not require the generation of large current and large magnetic field, and has the advantage of low power consumption.

[0007] The technical solution of the present invention:

[0008] A magnetoelectric storage element based on a PMN-PT ferroelectric / ferromagnetic composite film is prepared by depositing a ferromagnetic film on a PMN-PT single crystal substrate to form a laminated structure. The chemical structure of the ferroelectric layer with piezoelectric effect is 0.7[Pb(Mg 1 / 3 Nb 2 / 3 )O3]-0.3[PbTiO3](PMN-PT), thickness 0.5mm, Fe with magnetostrictive effect 65 Co 35 Thin film, thickness 20-40nm,

[0009] A method for preparing a magnetoelectric storage element of a ferroelectric / ferromagnetic thin film structure based on PMN-PT:

[0010] The preparation of small-sized FeCo ferromagnetic films is to use ion beam deposition combined with photolithography to mask specific patterns on PMN-PT single crystal substrates. Here, the patterns are squares of 200μm×200μm, 100μm×100μm, and 50μm×50μm. The specific steps are as follows:

[0011] 1. Base film treatment

[0012] (1) Cleaning: Use wet method and deionized water to remove debris;

[0013] (2) Drying and baking to dry the substrate surface to prevent moisture from weakening the adhesion of the photoresist.

[0014] 2. Glue throwing

[0015] (1) Place the PMN-PT single crystal substrate on a metal tray. There is a small hole on the tray surface that can be connected to the vacuum tube. The substrate is adsorbed on the tray.

[0016] (2) spraying a photoresist solution on the substrate surface;

[0017] (3) The first stage is set to accelerate the rotating tray to 800 r / min and maintain it for 10 seconds; then the second stage is set to accelerate the rotating tray to 3800 r / min and maintain it for 60 seconds.

[0018] 3. Pre-drying

[0019] Evaporate excess water on a hot plate until dry, so that the solvent trapped in the photoresist can fully escape to avoid contamination.

[0020] 4. Exposure

[0021] Align the mask plate with the photolithography machine, then adjust the appropriate UV light intensity, set the exposure time to 6s and other parameters for photolithography.

[0022] 5. Development

[0023] Mix developer and water in a ratio of 1:10. Then, place the exposed PMN-PT single crystal substrate in the developer for 15 seconds, rinse in clean water, and dry. The photoresist used is a positive photoresist. The exposed areas gradually dissolve in the developer, while the photoresist in other areas remains insoluble. This exposure process creates a pattern on the PMN-PT single crystal substrate.

[0024] 6. Hard membrane

[0025] In order to remove the residual organic solvent in the photoresist and enhance the adhesion between the photoresist and the substrate, the substrate is baked at a temperature of 100°C.

[0026] 7. Development inspection

[0027] Check the mask: the quality of the pattern; the quality of the photoresist layer; whether the mask is selected correctly.

[0028] 8. Inspection

[0029] First, visually inspect the film under white light to see if there are any large contaminants. Then, use a microscope to observe the integrity of the film and the clarity of the pattern after photolithography.

[0030] Ferromagnetic film is made of Fe 65 Co 35 The alloy target is prepared by ion beam sputtering, and the steps are as follows:

[0031] PMN-PT single crystal piezoelectric substrate and Fe 65 Co 35 The alloy target is placed in the sputtering chamber and the chamber is evacuated to 1×10 -4 ~2×10 -4 Pa, adjust the argon flow rate to 9.4sccm, set the 3cm Kaufman ion gun power supply, adjust the discharge voltage to about 70V, adjust the discharge filament current to 5A, preheat for five minutes, then slowly adjust the current until discharge occurs, and then set the acceleration voltage to 200V (the acceleration current at this time will show 6~10mA), and finally adjust the beam current, adjust the beam voltage to 500V, ensure that the beam current is about 15mA, sputter at room temperature for 30-60min, take out the sample, remove all the photoresist with acetone, and use isopropyl alcohol and ultrapure water to obtain a pure PMN-PT / FeCo composite film.

[0032] Technical analysis of the present invention:

[0033] The storage unit of the present invention uses a stacked magnetoelectric film as a medium. An external electric field changes the polarization state of the ferroelectric layer, and the magnetization state of the ferromagnetic layer is affected by the magnetoelectric coupling effect to realize electric field control of the resistance state. The writing medium is the electric field, and the storage medium is the resistance state of the ferromagnetic layer. The change of the electroresistance state is based on PMN-PT and Fe 65 Co 35 The present invention adopts PMN-PT with large piezoelectric coefficient and Fe with large magnetostrictive effect to realize the magnetoelectric effect of stress-strain mechanism. 65 Co 35Fabricating memory elements using stacked layers facilitates the realization of the electroresistive switching effect. Compared to traditional non-volatile memory, magnetoelectric memory devices offer advantages such as low power consumption and fast read / write speeds, making them crucial for meeting the practical needs of future memory devices. Fabricating layered composite thin film devices using ion beam sputtering is a simple process compatible with semiconductor technology.

[0034] The advantages of the present invention are: the storage element can maintain the polarization and magnetization state when an external voltage is applied. Since the change of the resistance state can be achieved by flipping the voltage between the upper and lower electrodes, it does not require the generation of large current and large magnetic field, and has the advantage of low power consumption; the storage unit can directly write information data using an electric field and read information using changes in resistance. The magnetoelectric composite thin film device has good ferroelectric, piezoelectric and ferromagnetic properties at room temperature, and obtains a maximum electric field-controlled resistance transition effect of 42% at an external bias voltage of 30V. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the stacked structure of the magnetoelectric storage element of Example 1.

[0036] Figure 2 The XRD pattern of Example 1 shows that the film is composed of 0.7[Pb(Mg 1 / 3 Nb 2 / 3 )O3]-0.3[PbTiO3](001)(111)(002)(003) and Fe 65 Co 35 (200)(211) phase composition.

[0037] Figure 3 This is the butterfly curve diagram of the piezoelectric effect of Example 1.

[0038] Figure 4 This is the normalized hysteresis loop diagram of Example 1.

[0039] Figure 5 This is a graph showing the electroresistance transition effect under different bias voltages in Example 1. DETAILED DESCRIPTION

[0040] The present invention uses 0.7[Pb(Mg 1 / 3 Nb 2 / 3 )O3]-0.3[PbTiO3](PMN-PT) single crystal and Fe 65 Co 35 Alloy target material is used as raw material, and magnetoelectric composite thin film devices are prepared by ion beam sputtering. The specific embodiment is as follows:

[0041] Example 1:

[0042] The steps for preparing 30nm ferromagnetic film by ion beam sputtering are as follows:

[0043] 1) Rinse the PMN-PT substrate with deionized water and dry it. Place the substrate in a spin coater and spin-coat the substrate with photoresist solution. Set the first stage to accelerate the rotating tray to 800 rpm and hold for 10 seconds; then, in the second stage, accelerate the rotating tray to 3800 rpm and hold for 60 seconds. Evaporate excess water on a hot plate until dry. Align the mask with the photolithography machine and set the exposure time to 6 seconds for photolithography. Mix the developer and water in a ratio of 1:10. Then, place the exposed PMN-PT single crystal substrate in the developer for 15 seconds, rinse it in clean water, and bake it at 100°C.

[0044] 2) PMN-PT single crystal piezoelectric substrate and Fe 65 Co 35 The alloy target is placed in the sputtering chamber and the chamber is evacuated to 1×10 -4 ~2×10 -4 Pa, adjust the argon flow rate to 9.4sccm, set the 3cm Kaufman ion gun power supply, adjust the discharge voltage to about 70V, adjust the discharge filament current to 5A, preheat for five minutes, then slowly adjust the current until discharge occurs, then set the acceleration voltage to 200V (the acceleration current at this time will show 6~10mA), finally adjust the beam current, adjust the beam voltage to 500V, ensure that the beam current is about 15mA, at room temperature, take out the composite film from the sputtering chamber after sputtering for 45min;

[0045] 3) After sputtering the FeCo film, remove all the photoresist with acetone.

[0046] Figure 1 A schematic diagram of the stacked structure of the magnetoelectric storage element is given. Figure 2 XRD analysis shows that the film is composed of 0.7[Pb(Mg 1 / 3 Nb 2 / 3 )O3]-0.3[PbTiO3](001)(111)(002)(003) and Fe 65 Co 35 (200)(211) phase composition. The piezoelectric effect butterfly curve obtained by testing is as follows Figure 3 The normalized hysteresis loop obtained by the test is shown as Figure 4 , the electroresistance transition effect is as follows Figure 5 It can be seen that the obtained magnetoelectric memory element has both ferroelectricity and ferromagnetism at room temperature, and has a large electroresistance switching effect.

[0047] Example 2:

[0048] The steps for preparing 20nm ferromagnetic film by ion beam sputtering are as follows:

[0049] 1) Rinse the PMN-PT substrate with deionized water and dry it. Place the substrate in a spin coater and spin-coat the substrate with photoresist solution. Set the first stage to accelerate the rotating tray to 800 rpm and hold for 10 seconds; then, in the second stage, accelerate the rotating tray to 3800 rpm and hold for 60 seconds. Evaporate excess water on a hot plate until dry. Align the mask with the photolithography machine and set the exposure time to 6 seconds for photolithography. Mix the developer and water in a ratio of 1:10. Then, place the exposed PMN-PT single crystal substrate in the developer for 15 seconds, rinse it in clean water, and bake it at 100°C.

[0050] 2) PMN-PT single crystal piezoelectric substrate and Fe 65 Co 35 The alloy target is placed in the sputtering chamber and the chamber is evacuated to 1×10 -4 ~2×10 -4 Pa, adjust the argon flow rate to 9.4sccm, set the 3cm Kaufman ion gun power supply, adjust the discharge voltage to about 70V, adjust the discharge filament current to 5A, preheat for five minutes, then slowly adjust the current until discharge occurs, then set the acceleration voltage to 200V (the acceleration current at this time will show 6~10mA), finally adjust the beam current, adjust the beam voltage to 500V, ensure that the beam current is about 15mA, at room temperature, take out the composite film from the sputtering chamber after sputtering for 30min;

[0051] 3) After sputtering the FeCo film, remove all the photoresist with acetone.

[0052] Example 3:

[0053] The steps for preparing 40nm ferromagnetic film by ion beam sputtering are as follows:

[0054] 1) Rinse the PMN-PT substrate with deionized water and dry it. Place the substrate in a spin coater and spin-coat the substrate with photoresist solution. Set the first stage to accelerate the rotating tray to 800 rpm and hold for 10 seconds; then, in the second stage, accelerate the rotating tray to 3800 rpm and hold for 60 seconds. Evaporate excess water on a hot plate until dry. Align the mask with the photolithography machine and set the exposure time to 6 seconds for photolithography. Mix the developer and water in a ratio of 1:10. Then, place the exposed PMN-PT single crystal substrate in the developer for 15 seconds, rinse it in clean water, and bake it at 100°C.

[0055] 2) PMN-PT single crystal piezoelectric substrate and Fe 65 Co 35 The alloy target is placed in the sputtering chamber and the chamber is evacuated to 1×10-4 ~2×10 -4 Pa, adjust the argon flow rate to 9.4sccm, set the 3cm Kaufman ion gun power supply, adjust the discharge voltage to about 70V, adjust the discharge filament current to 5A, preheat for five minutes, then slowly adjust the current until discharge occurs, then set the acceleration voltage to 200V (the acceleration current at this time will show 6~10mA), finally adjust the beam current, adjust the beam voltage to 500V, ensure that the beam current is about 15mA, at room temperature, take out the composite film from the sputtering chamber after sputtering for 60min;

[0056] 3) After sputtering the FeCo film, remove all the photoresist with acetone.

Claims

1. A method for preparing a magnetoelectric memory element with a ferroelectric / ferromagnetic thin film structure based on PMN-PT, characterized by: The magnetoelectric storage element is a laminated structure made by depositing a ferromagnetic film on a PMN-PT single crystal substrate. The chemical structure of the ferroelectric layer with piezoelectric effect is 0.7[Pb(Mg 1 / 3 Nb 2 / 3 )O3]-0.3[PbTiO3], thickness of 0.5mm, Fe with magnetostrictive effect 65 Co 35 The film has a thickness of 20-40 nm. The preparation method is as follows: The preparation of small-sized FeCo ferromagnetic films is to use ion beam deposition combined with photolithography to mask specific patterns on PMN-PT single crystal substrates; PMN-PT single crystal piezoelectric substrate and Fe 65 Co 35 The alloy target is placed in the sputtering chamber and the chamber is evacuated to 1×10 -4 ~2×10 -4 Pa, adjust the argon flow rate to 9.4sccm, set the 3cm Kaufman ion gun power supply, adjust the discharge voltage to 70V, adjust the discharge filament current to 5A, preheat for five minutes, then slowly adjust the current until discharge occurs, then set the acceleration voltage to 200V, the acceleration current shows 6~10mA, finally adjust the beam current, adjust the beam voltage to 500V, ensure that the beam current is 15mA, sputter at room temperature for 30-60min, take out the sample, remove all the photoresist with acetone, and use isopropyl alcohol and ultrapure water to obtain a pure PMN-PT / FeCo composite film.

2. The method for preparing a magnetoelectric memory element of a PMN-PT-based ferroelectric / ferromagnetic thin film structure according to claim 1, wherein: The steps for masking specific patterns on N-PT single crystal substrates are as follows: S1. Base film treatment (1) Cleaning: Use wet method and deionized water to remove debris; (2) Drying and baking to dry the substrate surface to prevent moisture from attenuating the adhesion of the photoresist; S2. Glue throwing (1) Place the PMN-PT single crystal substrate on a metal tray. There is a small hole on the tray surface that can be connected to the vacuum tube. The substrate is adsorbed on the tray. (2) spraying a photoresist solution on the substrate surface; (3) The first stage is to accelerate the rotating tray to 800 r / min and hold for 10 s; then the second stage is to accelerate the rotating tray to 3800 r / min and hold for 60 s; S3. Pre-drying Evaporate excess water on a hot plate until dry, so that the solvent trapped in the photoresist can escape fully to avoid contamination; S4. Exposure Align the mask with the photolithography machine, then adjust the appropriate UV light intensity and set the exposure time to 6s for photolithography; S5. Development Mix the developer and water in a ratio of 1:10, place the exposed PMN-PT single crystal substrate in the developer, set the development time to 15 seconds, then rinse and dry it in clean water. The photoresist used is a positive photoresist. The exposed positive photoresist gradually dissolves in the developer, while the photoresist in other areas does not dissolve in the developer solution. In this way, the PMN-PT single crystal substrate is developed into a pattern through exposure; S6. Hard membrane To remove the residual organic solvent in the photoresist and enhance the adhesion between the photoresist and the substrate, the substrate was baked at a temperature of 100°C; S7. Development inspection Check the mask: the quality of the pattern; the quality of the photoresist layer; whether the mask is selected correctly; S8. Inspection First, visually inspect the film under white light to see if there are any large contaminants, and then observe the integrity of the film and the clarity of the pattern after photolithography under a microscope.

3. The method for preparing a magnetoelectric memory element having a ferroelectric / ferromagnetic thin film structure based on PMN-PT according to claim 1, wherein: The pattern is a square of 200 μm × 200 μm, 100 μm × 100 μm, or 50 μm × 50 μm.

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