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

Abstract

A magnetoelectric storage element based on a BZT-BCT ferroelectric / ferromagnetic composite film and a preparation method thereof, belonging to the field of semiconductor integrated circuit technology, wherein the storage unit uses a laminated magnetoelectric film as the medium, and an external electric field changes the polarization state of the ferroelectric layer, thereby affecting the magnetization state of the ferromagnetic layer through 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 resistance state is based on the BZT-BCT and Fe 65 Co 35 The present invention adopts BZT-BCT with large piezoelectric coefficient and Fe with large magnetostrictive effect to realize the magnetoelectric effect of stress-strain mechanism. 65 Co 35 Fabricating memory elements in layers facilitates the electroresistance switching effect, offering advantages over traditional non-volatile memory, such as low power consumption and faster read / write speeds. Furthermore, the layered composite thin film devices are fabricated using magnetron sputtering, a simple process compatible with semiconductor technology.

Description

Technical Field

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

[0002] With the continuous development of integrated circuit technology, semiconductor memory, as an indispensable part of the integrated circuit field, has attracted increasing attention. Among the more mature storage technologies in today's society, ferroelectric random access memory (FeRAM) uses the spontaneous polarization (P) of ferroelectrics to store information. It has the advantages of high durability, fast read and write speeds, low power consumption, and reliable multi-level polarization states. However, a major problem restricting the development of traditional FeRAM is the read operation. The read operation of FeRAM is generally destructive and requires a rewrite step. In addition, due to the limitation of capacitor size, its storage density is also limited. Therefore, finding a method to solve the destructive read problem and the storage density limitation has become the key to the development of FeRAM.

[0003] Multiferroic materials are a class of multifunctional materials that exhibit both ferroelectric and antiferromagnetic properties. The coexistence of multiple ferroic properties opens up the possibility of new device functions. Interestingly, there is a cross-coupling between ferroelectricity and ferromagnetism, called magnetoelectric coupling. This coupling can control the electric field polarization through a magnetic field, and conversely, the magnetization can be controlled through an electric field. Therefore, the magnetoelectric coupling effect can effectively overcome the destructive reading problem of P in FeRAM by combining fast electric field writing and non-destructive magnetic reading operations. And because the size of the storage cell does not affect the reading of the magnetoelectric coupling voltage, the storage density is not limited like in traditional FeRAM. At the same time, the application of multiferroic materials avoids large amounts of current in both read and write operations, so the power consumption is very low.

[0004] Therefore, magnetoelectric memory (MERAMs) uses the magnetoelectric coupling effect to combine magnetization and polarization, and realizes data storage through different states of magnetization and polarization. The resistance state of the ferromagnetic layer can also be regulated by the electric field, realizing a magnetoelectric coupling storage unit with high / low resistance state as the write data bit and electric field as the write field. In 2014, Han et al. constructed a PMN-PT / Ru / FeCo heterostructure model mediated by strain. When the pulse of ±2kV / cm was turned on / off, the high / low resistance state occurred and was maintained. A non-volatile magnetic storage unit with resistance and electric field as the medium was realized (HanX et al.,Applied Physics Letters.,2014,105(12):187202.). Zheng et al. measured the resistance of LCMO film using the four-probe method. When the ±2kV / cm pulse electric field was applied, the magnetic film maintained the high / low resistance state. If the state under negative electric field or positive electric field is defined as bit "1" or "0" respectively, data storage can be realized (Zheng M, et al. Physical Review B Condensed Matter & Materials Physics, 2014, 90 (22): 224420.). The present invention constructs a ferroelectric / ferromagnetic composite thin film magnetoelectric storage element based on the magnetoelectric coupling effect, and selects Fe 65 Co 35 The alloy is used as the ferromagnetic layer and BZT-BCT is used as the ferroelectric layer. It is an environmentally friendly magnetoelectric storage device with a large magnetoelectric coupling effect. The magnetoelectric composite thin film device involved in the present invention is proposed for the first time and there are no related reports at home and abroad. Summary of the Invention

[0005] 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 ferroelectric / ferromagnetic composite film of BZT-BCT. 0.2 Ti 0.8 )O3-(Ba 35 Ca 65 )TiO3 ceramic target and Fe 65 Co 35 Magnetoelectric composite thin film devices are prepared by magnetron sputtering and ion beam sputtering using alloy target materials as raw materials. The storage element is non-volatile and can maintain polarization and magnetization states when an external voltage is applied. Since the change in 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.

[0006] The technical solution of the present invention:

[0007] A magnetoelectric storage element based on a ferroelectric / ferromagnetic composite film of BZT-BCT is fabricated by sequentially depositing ferroelectric and ferromagnetic films on a Pt / Ti / SiO2 / Si composite substrate to form a laminated structure, wherein the composite substrate comprises Si, SiO2, Ti, and Pt bottom electrodes from bottom to top. The chemical structure of the ferroelectric film with piezoelectric effect is 0.5Ba(Zr 0.2 Ti 0.8 )O3-0.5(Ba 35 Ca 65 )TiO3(BZT-BCT), thickness is 200-400nm, the film with magnetostrictive effect is Fe 65 Co 35 , with a thickness of 20-40nm.

[0008] A method for preparing a magnetoelectric storage element based on a ferroelectric / ferromagnetic film structure of BZT-BCT, wherein the ferroelectric ceramic film is prepared by radio frequency magnetron sputtering, and the ferromagnetic film is prepared by Fe 65 Co 35 The alloy target is prepared by ion beam sputtering, and the steps are as follows:

[0009] 1) Place the Pt / Ti / SiO2 / Si substrate and BZT-BCT ceramic target into the sputtering chamber and evacuate to (1-2)×10 -4 Then, a mixed gas with a pressure of 1.5-2.5 Pa and a volume ratio of argon to oxygen of 20:15-30:20 is introduced, the substrate temperature is 500-700°C, the radio frequency power is 50-60W, and the sputtering time is 1.5-4h. After being taken out of the sputtering chamber, it is heat-treated at 500°C in an air atmosphere for 30 minutes to obtain a ferroelectric ceramic film;

[0010] 2) First, the prepared ferroelectric ceramic film is cleaned using a standard RCA cleaning process to remove organic and inorganic impurities on the film surface. Next, a layer of UV positive resist is spin-coated on the ferroelectric layer using a spinner and dried on a heating table. After cooling, it is exposed to UV light under the masking effect of a mask. Finally, it is developed in a developer (a mixed solution of tetramethylammonium hydroxide solution TMAH and water in a certain ratio) to obtain the desired pattern. The RCA cleaning process parameters are as follows:

[0011] 1. Clean with acetone, isopropyl alcohol, alcohol and ultrapure water for 15 minutes each;

[0012] 2. Pre-baking temperature 100℃, time 60s;

[0013] 3. The coating speed is 3800r / min, the coating time is 60s, and the photoresist thickness is 1μm;

[0014] 4. Hard film temperature 100℃, time 90s;

[0015] 5. Exposure UV intensity is 9.8, exposure time is 7s;

[0016] 6. Post-baking temperature 100℃, time 10s;

[0017] 7. Development: Prepare the developer solution by mixing TMAH and H2O in a ratio of 5:50 and the development time is 50s;

[0018] 8. Remove the glue and ultrasonically clean in acetone, alcohol, and ultrapure water for 30 seconds respectively;

[0019] 3) Using the ferroelectric ceramic film attached with the photoresist prepared above as the substrate and Fe 65 Co 35 The alloy target is placed in the ion beam sputtering chamber and vacuumed to (1-2)×10 -4 , then introduce argon gas, with an argon flow rate of 9.4 sccm, a discharge voltage of 75 V, a discharge current of 0.2 A, an acceleration voltage of 200 V, a beam voltage of 500 V, and a sputtering time of 10-60 min. After taking it out of the sputtering chamber and removing the photoresist, a magnetoelectric storage element of a ferroelectric / ferromagnetic composite film is obtained.

[0020] Technical analysis of the present invention:

[0021] 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 affects the magnetization state of the ferromagnetic layer through 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 resistance state is based on BZT-BCT and Fe 65 Co 35 The present invention adopts BZT-BCT with large piezoelectric coefficient and Fe with large magnetostrictive effect to realize the magnetoelectric effect of stress-strain mechanism. 65 Co 35 Fabricating 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 magnetron sputtering is a simple process compatible with semiconductor technology.

[0022] The advantages of the present invention are: the storage element is non-volatile and can maintain polarization and magnetization states when an external voltage is applied. Since the change in 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 fields, 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 effect of 13% at an external bias voltage of 14V. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the stacked structure of the magnetoelectric storage element of Example 1

[0024] Figure 2 The XRD analysis of Example 1 shows that the film is composed of perovskite phase Ba(Zr 0.2 Ti 0.8 )O3-(Ba 35 Ca 65 )TiO3(100)(110)(200) and Fe 65 Co 35 (110) is composed of two phases.

[0025] Figure 3 This is the normalized hysteresis loop diagram of Example 1.

[0026] Figure 4 This is the butterfly curve diagram of the piezoelectric effect of Example 1.

[0027] Figure 5 This is a graph showing the electroresistance transition effect under different bias voltages in Example 1. DETAILED DESCRIPTION

[0028] The present invention uses Ba(Zr 0.2 Ti 0.8 )O3-(Ba 35 Ca 65 )TiO3 ceramic target and Fe 65 Co 35 Alloy target material is used as raw material, and magnetoelectric composite thin film devices are prepared by magnetron sputtering. The specific embodiment is as follows:

[0029] Example 1:

[0030] (1) The steps for preparing 200 nm ferroelectric thin films by RF magnetron sputtering are as follows:

[0031] 1) Pt / Ti / Si / SiO2 substrate and Ba(Zr 0.2 Ti 0.8 )O3-(Ba 35 Ca 65)The TiO3 ceramic target is placed in the sputtering chamber and the sputtering chamber is evacuated to 1×10 -4 ~2×10 -4 Pa, adjust the argon-oxygen ratio to 30:20, heat the substrate to a substrate temperature of 500 ° C, and when the sputtering chamber pressure is 1.5 Pa, adjust the control power to 50 W to start sputtering. After sputtering for 2 hours, take out the film from the sputtering chamber;

[0032] 2) The ferroelectric thin film was heat treated at 500° C. in an air atmosphere for 30 minutes to obtain a ferroelectric ceramic thin film material.

[0033] (2) UV lithography steps are as follows:

[0034] 1) Cleaning: Ultrasonic cleaning with acetone, isopropyl alcohol, alcohol, and ultrapure water for 15 minutes each;

[0035] 2) Pre-baking: temperature 100°C, time 60s;

[0036] 3) Glue coating: high speed 3800r / min, time 60s, photoresist thickness 1μm;

[0037] 4) Hard film: temperature 100℃, time 90s;

[0038] 5) Exposure: UV intensity 9.8, exposure time 7s;

[0039] 6) Post-baking: temperature 100°C, time 10s;

[0040] 7) Development: TMAH and H2O are mixed into a developer at a ratio of 5:50, and the development time is 50s.

[0041] (3) The steps for preparing 20 nm ferromagnetic film by ion beam sputtering are as follows:

[0042] The ferroelectric ceramic thin film substrate with photoresist attached prepared in step (2) and the 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 9.4 sccm, the discharge voltage to 75 V, the discharge current to 0.2 A, the acceleration voltage to 200 V, and the beam voltage to 500 V. After sputtering for 30 min, take the film out of the sputtering chamber and remove the photoresist to obtain a composite film;

[0043] 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 perovskite phase Ba(Zr 0.2 Ti 0.8 )O3-(Ba 35 Ca65 )TiO3(100)(110)(200) and Fe 65 Co 35 (110) phases. The hysteresis loop obtained by the test is as follows Figure 3 The piezoelectric effect butterfly curve is shown as Figure 4 The electroresistance switching effect is shown in Figure 5 It can be seen that the obtained device has both ferroelectric and ferromagnetic properties at room temperature, and also has a large electroresistance switching effect.

[0044] Example 2:

[0045] (1) The steps for preparing 250nm ferroelectric thin films by RF magnetron sputtering are as follows:

[0046] 1) Pt / Ti / Si / SiO2 substrate and Ba(Zr 0.2 Ti 0.8 )O3-(Ba 35 Ca 65 )The TiO3 ceramic target is placed in the sputtering chamber and the sputtering chamber is evacuated to 1×10 -4 ~2×10 -4 Pa, adjust the argon-oxygen ratio to 30:20, heat the substrate to a substrate temperature of 500 ° C, and when the sputtering chamber pressure is 1.5 Pa, adjust the control power to 50 W to start sputtering. After sputtering for 2.5 hours, take out the composite film from the sputtering chamber;

[0047] 2) The composite film was heat treated at 500° C. in an air atmosphere for 30 minutes to obtain a ferroelectric ceramic thin film material.

[0048] (2) UV lithography steps are as follows:

[0049] 1) Cleaning: Ultrasonic cleaning with acetone, isopropyl alcohol, alcohol, and ultrapure water for 15 minutes each;

[0050] 2) Pre-baking: temperature 100°C, time 60s;

[0051] 3) Glue coating: high speed 3800r / min, time 60s, photoresist thickness 1μm;

[0052] 4) Hard film: temperature 100℃, time 90s;

[0053] 5) Exposure: UV intensity 9.8, exposure time 7s;

[0054] 6) Post-baking: temperature 100°C, time 10s;

[0055] 7) Development: TMAH and H2O are mixed into a developer at a ratio of 5:50, and the development time is 50s.

[0056] (3) The steps for preparing 30 nm ferromagnetic thin films by DC magnetron sputtering are as follows:

[0057] The ferroelectric ceramic thin film substrate with photoresist attached prepared in step (2) and the 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 9.4 sccm, the discharge voltage to 75 V, the discharge current to 0.2 A, the acceleration voltage to 200 V, and the beam voltage to 500 V. After sputtering for 45 min, take the film out of the sputtering chamber and remove the photoresist to obtain a composite film;

[0058] The test results of the magnetoelectric storage element of the prepared ferroelectric / ferromagnetic composite film are similar to those of Example 1.

[0059] Example 3:

[0060] (1) The steps for preparing 300nm ferroelectric thin films by RF magnetron sputtering are as follows:

[0061] 1) Pt / Ti / Si / SiO2 substrate and Ba(Zr 0.2 Ti 0.8 )O3-(Ba 35 Ca 65 )The TiO3 ceramic target is placed in the sputtering chamber and the sputtering chamber is evacuated to 1×10 -4 ~2×10 -4 Pa, adjust the argon-oxygen ratio to 30:20, heat the substrate to a substrate temperature of 500 ° C, and when the sputtering chamber pressure is 1.5 Pa, adjust the control power to 50 W to start sputtering. After sputtering for 3 hours, remove the ferroelectric film from the sputtering chamber;

[0062] 2) The composite film was heat treated at 500° C. in an air atmosphere for 30 minutes to obtain a ferroelectric ceramic thin film material.

[0063] (2) UV lithography steps are as follows:

[0064] 1) Cleaning: Ultrasonic cleaning with acetone, isopropyl alcohol, alcohol, and ultrapure water for 15 minutes each;

[0065] 2) Pre-baking: temperature 100°C, time 60s;

[0066] 3) Glue coating: high speed 3800r / min, time 60s, photoresist thickness 1μm;

[0067] 4) Hard film: temperature 100℃, time 90s;

[0068] 5) Exposure: UV intensity 9.8, exposure time 7s;

[0069] 6) Post-baking: temperature 100°C, time 10s;

[0070] 7) Development: TMAH and H2O are mixed into a developer at a ratio of 5:50, and the development time is 50s.

[0071] (3) The steps for preparing 40 nm ferromagnetic films by DC magnetron sputtering are as follows:

[0072] The ferroelectric ceramic thin film substrate with photoresist attached prepared in step (2) and the 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 9.4 sccm, the discharge voltage to 75 V, the discharge current to 0.2 A, the acceleration voltage to 200 V, and the beam voltage to 500 V. After sputtering for 1 h, take out the film from the sputtering chamber, and remove the photoresist to obtain a composite film.

[0073] The test results of the magnetoelectric storage element of the prepared ferroelectric / ferromagnetic composite film are similar to those of Example 1.

Claims

1. A method for preparing a magnetoelectric memory element based on a ferroelectric / ferromagnetic thin film structure of BZT-BCT, characterized by: The magnetoelectric storage element is a laminated structure made by sequentially depositing ferroelectric and ferromagnetic films on a Pt / Ti / SiO2 / Si composite substrate, wherein the composite substrate is composed of Si, SiO2, Ti and Pt bottom electrodes from bottom to top. The chemical structure of the ferroelectric film with piezoelectric effect is 0.5Ba(Zr 0.2 Ti 0.8 )O3-0.5(Ba 35 Ca 65 )TiO3(BZT-BCT), thickness is 200-400nm, the film with magnetostrictive effect is Fe 65 Co 35 , thickness is 20-40nm; Ferroelectric ceramic films are prepared by radio frequency magnetron sputtering. Ferromagnetic films are made of Fe 65 Co 35 The alloy target is prepared by ion beam sputtering, and the steps are as follows: 1) Placing a Pt / Ti / Si / SiO2 substrate and a BZT-BCT ceramic target into a sputtering chamber, evacuating the chamber, and then introducing a mixture of argon and oxygen. After radio frequency magnetron sputtering, the substrate is removed from the sputtering chamber and heat treated in an air atmosphere to produce a ferroelectric ceramic film. 2) First, the prepared ferroelectric ceramic film is cleaned using a standard RCA cleaning process to remove organic and inorganic impurities on the film surface; second, a layer of UV positive resist is spin-coated on the ferroelectric layer using a spinner and dried on a heating table; After cooling, it is exposed to UV light under the masking effect of the mask; finally, it is developed in a developer to obtain the required pattern; 3) The ferroelectric ceramic film with the photoresist prepared above is used as the substrate and Fe 65 Co 35 The alloy target material is placed in an ion beam sputtering chamber, evacuated and then introduced with argon gas. After ion beam sputtering, the chamber is taken out and the photoresist is removed to obtain a magnetoelectric storage element of a ferroelectric / ferromagnetic composite film. In step 1), the sputtering chamber is evacuated, and then a mixed gas with a pressure of 1.5-2.5 Pa and a volume ratio of argon to oxygen of 20:15-30:20 is introduced. The substrate temperature is 500-700°C, the RF power is 50-60W, and the sputtering time is 1.5-4h. After being removed from the sputtering chamber, it is heat treated at 500°C in an air atmosphere for 30 minutes; In step 3), the ion beam sputtering chamber was evacuated, the argon flow rate was 9.4 sccm, the discharge voltage was 75 V, the discharge current was 0.2 A, the acceleration voltage was 200 V, the beam voltage was 500 V, and the sputtering time was 10-30 min.

2. The method for preparing a magnetoelectric memory element of a ferroelectric / ferromagnetic thin film structure based on BZT-BCT according to claim 1, wherein: RCA cleaning process parameters are as follows: 1) Cleaning: Ultrasonic cleaning with acetone, isopropyl alcohol, alcohol and ultrapure water for 15 minutes respectively; 2) Pre-baking temperature 100°C, time 60s; 3) Glue coating at a high speed of 3800 r / min for 60 s, with a photoresist thickness of 1 μm; 4) Hardening temperature is 100℃ and time is 90s; 5) UV exposure, exposure time is 7s; 6) Post-baking temperature 100°C, time 10s; 7) Development: TMAH and H2O are mixed into a developing solution at a ratio of 5:50, and the developing time is 50s; 8) Remove the glue by ultrasonic cleaning in acetone, alcohol and ultrapure water for 30 seconds respectively.

3. The method for preparing a magnetoelectric memory element of a ferroelectric / ferromagnetic thin film structure based on BZT-BCT according to claim 1, wherein: The developer is obtained by mixing tetramethylammonium hydroxide solution TMAH and water in a certain proportion, and the ratio of TMAH to H2O is 5:50.

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