A method for preparing rare earth doped iron garnet thin film by liquid phase epitaxy

Abstract

The invention relates to the field of thin film materials and discloses a method for preparing a rare earth doped yttrium iron garnet thin film by using liquid phase epitaxy. The method comprises the following steps: weighing Gd2O3, Ga2O3, Fe2O3, Bi2O3 and a flux, putting them into a platinum crucible to melt and obtain a melt; cleaning a substrate; placing the cleaned substrate into a melt which has been cooled and is in a supersaturated metastable state, and growing a thin film by using a liquid phase epitaxy method, wherein the growth temperature is 700-900 DEG C, the substrate rotation speed is 30-80 rpm, the growth time is 5-10 hours, and after the growth is completed, cleaning and removing the residue. The invention adopts a lead-free liquid phase epitaxy process, uses calcium magnesium zirconium doped gadolinium gallium garnet as a substrate, uses B2O3, Bi2O3 and V2O5 as fluxes, adopts a suitable oxide ratio, and controls the growth temperature, substrate rotation speed and growth time to prepare the thin film.

Description

Technical Field

[0001] The invention belongs to the technical field of thin film materials, and in particular relates to a method for preparing a rare earth-doped iron garnet thin film by utilizing liquid phase epitaxy. Background Art

[0002] Yttrium iron garnet is a ferrite material with excellent magnetoelectric and optical properties. It is widely used in microwave devices and optical integrated devices due to its narrow ferromagnetic resonance line width, low damping, high resistivity, and high transmittance in the infrared band. At the same time, as a ferrimagnetic insulator, yttrium iron garnet is a hot material in the research of spintronic devices. With the continuous development of device integration and spintronic devices, the study of the microstructure of thin film ferrite materials and their influence on magnetic and electrical properties has also become the focus of yttrium iron garnet material research.

[0003] Liquid phase epitaxy refers to a process in which solids are precipitated from a melt and a single crystal film is formed on a substrate. The main principle of liquid phase epitaxy is to melt the required oxides and flux at high temperature. After they are fully reacted, the melt temperature is lowered to below the saturation temperature, and the solute will precipitate in the form of a solid. At this time, the substrate is immersed in the melt, and the precipitated solid will be deposited on the surface of the substrate, thereby forming a single crystal film on the surface of the substrate, and the film will also follow the lattice structure of the substrate. Based on the different substrates, liquid phase epitaxy is also divided into homoepitaxiality and heteroepitaxiality, but regardless of homoepitaxiality or heteroepitaxiality, the film will inherit the crystal structure of the substrate.

[0004] Using liquid phase epitaxy technology and using Bi 3+ Ion substitution of Y in yttrium iron garnet 3+ Ions can be used to grow bismuth-substituted garnet (Bi:YIG) films. The specific Faraday rotation angle of Bi:YIG film is much larger than that of pure YIG, and its easy magnetization axis is also easily regulated to an out-of-plane orientation, so that it can work under a smaller external magnetic field, thereby meeting the development needs of miniaturization and energy saving of magneto-optical devices. However, Bi 3+ The ionic radius is large, so simply increasing the Bi content is difficult to make the lattice constant of the epitaxial film match the lattice constant of the substrate.

[0005] In the existing liquid phase epitaxy process, the holding temperature of the melt is directly reduced to the growth temperature. A large temperature drop will cause the melt to be unstable, thus affecting the quality of the epitaxial film. In addition, in the liquid phase epitaxy process, the lead oxide system flux is a common flux, which has the following disadvantages: lead oxide is highly corrosive to the platinum crucible, causing crucible loss, and the Pt in the platinum crucible 2+ , Pt 4+ It is easy to enter the crystal lattice and affect product performance; the epitaxial film will contain impurities Pb from the flux 2+ , Pb 2+Occupying the 24c position will cause additional light absorption in the garnet film, and lead will also be present as Pb 2+ and Pb 4+ It exists in the membrane in the form of lead oxide, which will cause the valence of Fe ions in the membrane to be unstable; the melting point of lead oxide is 886℃, but it begins to volatilize at 750℃. As the temperature rises, its volatilization amount continues to increase. At 950℃, its volatilization amount has reached a large value, which is harmful to the human body and pollutes the environment. Summary of the invention

[0006] In order to solve the deficiencies mentioned in the above-mentioned background technology, the purpose of the present invention is to provide a method for preparing rare earth doped iron garnet film by liquid phase epitaxy, adopting a lead-free liquid phase epitaxy process, using calcium magnesium zirconium doped gadolinium gallium garnet as a substrate, B2O3, Bi2O3 and V2O5 as fluxes, Gd2O3, Ga2O3, Fe2O3, Bi2O3 as oxide raw materials and using a suitable oxide ratio, controlling the growth temperature, substrate rotation speed and growth time to prepare the rare earth doped iron garnet film.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A method for preparing a rare earth-doped iron garnet thin film by liquid phase epitaxy comprises the following steps:

[0009] S1. Weigh the oxide raw materials of Gd2O3, Ga2O3, Fe2O3 and Bi2O3 and the flux, mix them evenly and put them into a platinum crucible, melt them at 1050-1200°C for 12-24h, and then stir them for 8-12h to mix evenly to obtain a melt;

[0010] S2, cleaning the substrate;

[0011] S3, fixing the cleaned substrate on a substrate holder, with the substrate surface tilted at an angle to the melt surface, and then slowly placing the substrate into the melt that has been cooled and is in a supersaturated metastable state, and growing a thin film by liquid phase epitaxy, with a growth temperature of 700-900°C, a substrate rotation speed of 30-80rpm, and a growth time of 5-10h. After the growth is completed, cleaning and removing the residue, a rare earth-doped iron garnet thin film is obtained;

[0012] In step S1, the flux is B2O3, Bi2O3 and V2O5, the B2O3 is 0.5-10% of the total mass of the oxide raw material and the flux, the Bi2O3 is 40-60% of the total mass of the oxide raw material and the flux, and the V2O5 is 0.05-0.1% of the total mass of the oxide raw material and the flux.

[0013] Preferably, in step S1, the molar ratio of Gd2O3, Ga2O3, Fe2O3 and Bi2O3 is 1:1:1.67:15.

[0014] Preferably, the substrate used in step S2 is a calcium magnesium zirconium doped gadolinium gallium garnet substrate.

[0015] Preferably, the substrate cleaning process in step S2 is: the calcium magnesium zirconium doped gadolinium gallium garnet substrate is sequentially rinsed with trichloroethylene and deionized water; rinsed with potassium dichromate solution and deionized water; rinsed with alkaline solution and deionized water; rinsed with ammonia water and deionized water, and finally distilled with isopropanol.

[0016] Preferably, the cooling in step S3 is carried out in three stages, gradually lowering the melt temperature to the growth temperature, firstly lowering the temperature by 40-50°C until the crucible temperature reaches a stable state, then lowering the temperature by 30-40°C, and finally lowering the temperature to the growth temperature.

[0017] Preferably, the cooling rate is 0.3-0.6°C / min.

[0018] Preferably, in step S3, the substrate and the melt surface form an inclination angle of 9 to 11 degrees.

[0019] Beneficial effects of the present invention:

[0020] The present invention adopts lead-free liquid phase epitaxy process, uses calcium magnesium zirconium doped gadolinium gallium garnet as substrate, B2O3, Bi2O3 and V2O5 as flux, Gd2O3, Ga2O3, Fe2O3, Bi2O3 as oxide raw materials and adopts appropriate oxide ratio to prepare rare earth doped iron garnet film. The present invention adopts Bi-Gd co-doping to completely replace Y to reduce lattice mutation, and at the same time, Ga is doped 3+ To partially replace the Fe on the 24d site of the tetrahedral lattice 3+ , used to reduce the saturation magnetization intensity, and the composition of the single crystal garnet film was (BiGd)3(GaFe)5O 12 After adding flux B2O3, Bi2O3 and V2O5, the growth rate of the film decreased significantly, and the saturation temperature decreased, indicating that at the same growth temperature, the precipitation rate of the substance in the melt decreased, that is, the solubility of the solute increased. At the same time, V2O5 can reduce the corrosion of the platinum crucible and inhibit a small amount of Pt 2+ Entering the film lattice effectively improves the viscosity of the melt and improves the surface quality of the film. When the growth temperature is between 700 and 900 °C, the lattice matching between the film and the substrate is good, the mirror effect of the sample film is good, the defects in the film are reduced, and the surface roughness is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 is an XRD test diagram of the film prepared in Example 3 of the present invention;

[0023] Figure 2 is a graph showing the relationship between the liquid phase epitaxial growth temperature and the growth rate of the thin film prepared in Example 3 of the present invention;

[0024] Figure 3 is a graph showing the relationship between the liquid phase epitaxial growth temperature and the growth rate of the thin film prepared in Comparative Example 1 of the present invention;

[0025] Figure 4 It is an optical microscope picture of the thin film obtained in Example 3, Comparative Example 1 and Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0027] Embodiment 1 A method for preparing a rare earth-doped iron garnet thin film by liquid phase epitaxy comprises the following steps:

[0028] S1. Weigh Gd2O3, Ga2O3, Fe2O3, Bi2O3 oxide raw materials and flux in a molar ratio of 1:1:1.67:15, mix them evenly, put them into a platinum crucible, melt them at 1050°C for 24 hours, and then stir them for 8 hours to mix evenly to obtain a melt, wherein the flux is B2O3, Bi2O3 and V2O5, B2O3 is 0.5% of the total mass of the oxide raw materials and flux, Bi2O3 is 40% of the total mass of the oxide raw materials and flux, and V2O5 is 0.05% of the total mass of the oxide raw materials and flux;

[0029] S2. Soak the calcium magnesium zirconium doped gadolinium gallium garnet substrate in trichloroethylene at 80°C for 5 minutes, and then soak it in deionized water at 80°C for 5 minutes; soak the substrate treated in the previous step in a mixture of potassium dichromate, concentrated sulfuric acid and water at 80°C for 10 times, each soaking time is 1~2 seconds, wherein the mass concentration of potassium dichromate in the mixture is 18g / L, and the molar concentration of concentrated sulfuric acid is 10mol / L, and then soak it in deionized water at 80°C for 2 minutes, take it out and soak it in another deionized water at 80°C for 5mi n; sodium phosphate, sodium carbonate and potassium hydroxide in a mass ratio of 1:1:1 are prepared into a mixed alkali solution with a solute mass concentration of 15 g / L, and the substrate treated in the previous step is soaked in the prepared alkali solution at 80°C for 5 minutes, and then soaked in deionized water at 80°C for 5 minutes; the substrate treated in the previous step is placed in a 25% ammonia solution by volume at room temperature for 5 minutes, and then soaked in deionized water at room temperature for 5 minutes; the substrate treated in the previous step is cleaned under isopropanol vapor condensation reflux conditions for 5 minutes;

[0030] S3, the holding temperature of the melt is cooled to 720°C in three stages, first from 1050°C to 1010°C, wait until the crucible temperature reaches a nearly stable state, then drop to 1070°C, and finally drop the temperature to 720°C, the cooling rate is 0.4°C / min, reach the growth temperature point, fix the cleaned substrate on the substrate holder, the substrate surface forms an inclination angle of 10° with the melt surface, then slowly put the substrate into the melt that has been cooled and is in a supersaturated metastable state, and grow the film by liquid phase epitaxy, the growth temperature is 720℃, substrate rotation speed is 30rpm, growth time is 7h. After the growth is completed, the substrate is quickly lifted from the melt surface and rotated at a rate of 120rpm to shake off the residual melt on the substrate, and then the substrate is slowly lifted from the epitaxial furnace to avoid film cracking caused by thermal expansion. Finally, the obtained substrate is immersed in a solution of nitric acid and deionized water in a ratio of 1:1 until the residual melt on the surface of the epitaxial film is completely peeled off from the epitaxial film, and then the epitaxial film is removed from the growth fixture to obtain a rare earth-doped iron garnet film.

[0031] Embodiment 2 A method for preparing a rare earth-doped iron garnet thin film by liquid phase epitaxy comprises the following steps:

[0032] S1. Weigh Gd2O3, Ga2O3, Fe2O3, Bi2O3 oxide raw materials and flux in a molar ratio of 1:1:1.67:15, mix them evenly, put them into a platinum crucible, melt them at 1100°C for 24 hours, and then stir them for 10 hours to mix evenly to obtain a melt, wherein the flux is B2O3, Bi2O3 and V2O5, B2O3 accounts for 0.6% of the total mass of the oxide raw materials and flux, Bi2O3 accounts for 48% of the total mass of the oxide raw materials and flux, and V2O5 accounts for 0.08% of the total mass of the oxide raw materials and flux;

[0033] S2, substrate cleaning process is the same as in Example 1;

[0034] S3, the holding temperature of the melt is cooled to 840°C in three stages, first from 1100°C to 1050°C, wait until the crucible temperature reaches a nearly stable state, then drop to 1020°C, and finally drop the temperature to 840°C, the cooling rate is 0.5°C / min, reach the growth temperature point, fix the cleaned substrate on the substrate holder, the substrate surface forms an inclination angle of 10° with the melt surface, then slowly put the substrate into the melt that has been cooled and is in a supersaturated metastable state, and grow the film by liquid phase epitaxy, the growth temperature is 840℃, substrate rotation speed is 60rpm, growth time is 8h. After the growth is completed, the substrate is quickly lifted from the melt surface and rotated at a rate of 120rpm to shake off the residual melt on the substrate, and then the substrate is slowly lifted from the epitaxial furnace to avoid film cracking caused by thermal expansion. Finally, the obtained substrate is immersed in a solution of 1:1 nitric acid and deionized water until the residual melt on the surface of the epitaxial film is completely peeled off from the epitaxial film, and then the epitaxial film is removed from the growth fixture to obtain a rare earth-doped iron garnet film.

[0035] Embodiment 3 A method for preparing a rare earth-doped iron garnet thin film by liquid phase epitaxy comprises the following steps:

[0036] S1. Weigh Gd2O3, Ga2O3, Fe2O3, Bi2O3 oxide raw materials and flux in a molar ratio of 1:1:1.67:15, mix them evenly, put them into a platinum crucible, melt them at 1200°C for 14 hours, and then stir them for 12 hours to mix evenly to obtain a melt, wherein the flux is B2O3, Bi2O3 and V2O5, B2O3 accounts for 0.8% of the total mass of the oxide raw materials and flux, Bi2O3 accounts for 58% of the total mass of the oxide raw materials and flux, and V2O5 accounts for 0.1% of the total mass of the oxide raw materials and flux;

[0037] S2, substrate cleaning process is the same as in Example 1;

[0038] S3, the holding temperature of the melt is cooled to 900°C in three stages, first from 1200°C to 1150°C, wait until the crucible temperature reaches a nearly stable state, then drop to 1110°C, and finally drop the temperature to 900°C, with a cooling rate of 0.6°C / min, to reach the growth temperature point, fix the cleaned substrate on the substrate holder, the substrate surface forms an inclination angle of 10° with the melt surface, and then slowly put the substrate into the melt that has been cooled and is in a supersaturated metastable state, and grow a thin film using liquid phase epitaxy, the growth temperature is 900℃, substrate rotation speed is 80rpm, growth time is 5h. After the growth is completed, the substrate is quickly lifted from the melt surface and rotated at a rate of 120rpm to shake off the residual melt on the substrate, and then the substrate is slowly lifted from the epitaxial furnace to avoid film cracking due to thermal expansion. Finally, the obtained substrate is immersed in a solution of nitric acid and deionized water in a ratio of 1:1 until the residual melt on the surface of the epitaxial film is completely peeled off from the epitaxial film, and then the epitaxial film is removed from the growth fixture to obtain a rare earth-doped iron garnet film.

[0039] from Figure 1 It can be seen from the figure that the sample film prepared in this embodiment has no impurity phase. After doping with rare earth elements, the film achieves good lattice matching with the calcium magnesium zirconium doped gadolinium gallium garnet substrate.

[0040] Comparative Example 1 A method for preparing a rare earth-doped iron garnet thin film by liquid phase epitaxy comprises the following steps:

[0041] S1. Weigh Gd2O3, Ga2O3, Fe2O3 and Bi2O3 oxide raw materials in a molar ratio of 1:1:1.67:15, mix them evenly and put them into a platinum crucible, melt them at 1200°C for 14h, and then stir them for 12h to mix evenly to obtain a melt;

[0042] S2, substrate cleaning process is the same as in Example 1;

[0043] S3, the holding temperature of the melt is cooled to 900°C in three stages, first from 1200°C to 1150°C, wait until the crucible temperature reaches a nearly stable state, then drop to 1110°C, and finally drop the temperature to 900°C, with a cooling rate of 0.6°C / min, to reach the growth temperature point, fix the cleaned substrate on the substrate holder, the substrate surface forms an inclination angle of 10° with the melt surface, and then slowly put the substrate into the melt that has been cooled and is in a supersaturated metastable state, and grow a thin film using liquid phase epitaxy, the growth temperature is 900℃, substrate rotation speed is 80rpm, growth time is 5h. After the growth is completed, the substrate is quickly lifted from the melt surface and rotated at a rate of 120rpm to shake off the residual melt on the substrate, and then the substrate is slowly lifted from the epitaxial furnace to avoid film cracking due to thermal expansion. Finally, the obtained substrate is immersed in a solution of nitric acid and deionized water in a ratio of 1:1 until the residual melt on the surface of the epitaxial film is completely peeled off from the epitaxial film, and then the epitaxial film is removed from the growth fixture to obtain a rare earth-doped iron garnet film.

[0044] Comparative Example 2 A method for preparing a rare earth-doped iron garnet thin film by liquid phase epitaxy comprises the following steps:

[0045] S1. Weigh Gd2O3, Ga2O3, Fe2O3, Bi2O3 oxide raw materials and flux in a molar ratio of 1:1:1.67:15, mix them evenly, put them into a platinum crucible, melt them at 1200°C for 14 hours, and then stir them for 12 hours to mix evenly to obtain a melt, wherein the flux is B2O3, Bi2O3 and V2O5, B2O3 accounts for 0.8% of the total mass of the oxide raw materials and flux, Bi2O3 accounts for 58% of the total mass of the oxide raw materials and flux, and V2O5 accounts for 0.1% of the total mass of the oxide raw materials and flux;

[0046] S2, substrate cleaning process is the same as in Example 1;

[0047] S3. Directly reduce the holding temperature of the melt to 900°C at a cooling rate of 0.6°C / min to reach the growth temperature point, fix the cleaned substrate on the substrate holder, and form an inclination angle of 10° between the substrate surface and the melt surface. Then slowly place the substrate into the melt that has been cooled and is in a supersaturated metastable state. Use liquid phase epitaxy to grow a thin film at a growth temperature of 900°C, a substrate rotation speed of 80rpm, and a growth time of 5h. After the growth is completed, quickly lift the substrate from the melt surface and rotate it at a rate of 120rpm to shake off the residual melt on the substrate. Then slowly lift the substrate from the epitaxial furnace to avoid film cracking caused by thermal expansion. Finally, soak the obtained substrate in a solution of nitric acid and deionized water in a ratio of 1:1 until the residual melt on the surface of the epitaxial film is completely peeled off from the epitaxial film. Then remove the epitaxial film from the growth fixture to obtain a rare earth-doped iron garnet thin film.

[0048] like Figure 2-3 As shown, in Comparative Example 1, as the growth temperature decreases, the growth rate of the film increases with the degree of supercooling (Ts-Tg) and is linearly related. The growth saturation temperature (Ts) is 907.5°C. In Example 3, the sample with flux added has a growth saturation temperature (Ts) of 905.4°C. Figure 2 and Figure 3 By comparison, it can be seen that after adding flux B2O3, Bi2O3 and V2O5, the growth rate of the film decreases significantly and the saturation temperature decreases, indicating that at the same growth temperature, the precipitation rate of substances in the melt decreases, that is, the solubility of the solute increases, the grown film is more uniform, and has fewer internal defects.

[0049] Figure 4 The optical microscope pictures of the films obtained in Example 3 of the present invention, Comparative Example 1 and Comparative Example 2 show that the film obtained in Example 3 of the present invention has no cracks or pits and has a good mirror effect.

[0050] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0051] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for preparing rare earth doped iron garnet thin film by liquid phase epitaxy, characterized in that: The following steps are involved: S1. Weigh the oxide raw materials of Gd2O3, Ga2O3, Fe2O3 and Bi2O3 and the flux, mix them evenly and put them into a platinum crucible, melt them at 1050-1200°C for 12-24h, and then stir them for 8-12h to mix evenly to obtain a melt; S2, cleaning the substrate; S3, fixing the cleaned substrate on a substrate holder, with the substrate surface tilted at an angle to the melt surface, and then slowly placing the substrate into the melt that has been cooled and is in a supersaturated metastable state, and growing a thin film by liquid phase epitaxy, with a growth temperature of 700-900°C, a substrate rotation speed of 30-80rpm, and a growth time of 5-10h. After the growth is completed, cleaning and removing the residue, a rare earth-doped iron garnet thin film is obtained; In step S1, the flux is B2O3, Bi2O3 and V2O5, the B2O3 is 0.5-10% of the total mass of the oxide raw material and the flux, the Bi2O3 is 40-60% of the total mass of the oxide raw material and the flux, and the V2O5 is 0.05-0.1% of the total mass of the oxide raw material and the flux; In step S1, the molar ratio of Gd2O3, Ga2O3, Fe2O3 and Bi2O3 is 1:1:1.67:15; The substrate used in step S2 is a calcium magnesium zirconium doped gadolinium gallium garnet substrate; The cooling in step S3 is carried out in three stages, and the melt temperature is gradually reduced to the growth temperature. First, the temperature is reduced by 40-50°C until the crucible temperature reaches a stable state, then the temperature is reduced by 30-40°C, and finally the temperature is reduced to the growth temperature; the cooling rate is 0.3-0.6°C / min.

2. The method for preparing rare earth-doped iron garnet thin film by liquid phase epitaxy according to claim 1, characterized in that: The substrate cleaning process in step S2 is: the calcium magnesium zirconium doped gadolinium gallium garnet substrate is sequentially rinsed with trichloroethylene and deionized water; rinsed with potassium dichromate solution and deionized water; rinsed with alkaline solution and deionized water; rinsed with ammonia water and deionized water, and finally distilled with isopropanol.

3. The method for preparing rare earth-doped iron garnet thin film by liquid phase epitaxy according to claim 1, characterized in that: In step S3, the substrate and the melt surface form an inclination angle of 9-11°.

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