CN1103328C - Preparation of strontium-barium titanate film material - Google Patents

Abstract

The invention provides a preparation method of barium strontium titanate thin film material, the process is: mixing barium acetate, strontium acetate, butyl titanate, acetic acid and acetylacetone in a certain molar ratio to prepare a stable precursor solution , and then on the Pt/Ti/SiO ₂ /Si substrate, perform glue leveling and heat treatment, and apply an auxiliary electric field to the film at the same time during the heat treatment, and repeat the above process until the desired thickness is reached. The invention realizes heterogeneous nucleation and homoepitaxial growth by controlling the thickness of each layer of gel film after heat treatment to 8 to 20 nanometers, thereby forming a thin film material with large-size columnar grains. The thin film material of the invention is suitable for applications in dynamic random access memory, room temperature infrared focal plane array and the like.

Description

Preparation method of strontium barium titanate thin film material

The invention relates to a preparation method of barium strontium titanate thin film material, belonging to the field of functional information materials and devices.

Barium strontium titanate (Ba _x Sr _1-x TiO ₃ ) has a very high dielectric constant, and its Curie temperature can be adjusted between 30 and 400K by changing the composition. Infrared focal plane arrays have broad application prospects. Compared with many preparation methods, the sol-gel method has many advantages such as good uniformity, easy control of stoichiometric ratio, and simple equipment, and has been widely used in the preparation of thin film materials. In recent years, there have been many literature reports on the preparation of barium titanate (BaTiO ₃ ) and strontium barium titanate (Ba _x Sr _1-x TiO ₃ ) thin film materials by sol-gel method, such as: "Preparation and Characterization of Ba _x Sr _1-x TiO ₃ Thin Films by a Sol-Gel Technique", J.Am.Ceram.Soc.79, 1593-98(1996); "In-Situ Transmission Electron Microscopy Crystallization Studies of Sol-Gel-Derived Barium Titanate Thin Films", J.Am.Ceram.Soc.80, 2828-36(1997); "Microstructure of Columnar-Grained SrTiO ₃ and BaTiO ₃ Thin Films Prepared by Chemical Solution Deposition", J.Mater.Res.13, 2206- 17 (1998); "Control of Microstructure and Orientation in Solution-Deposited _BaTiO3 and _SrTiO3 ThinFilms", J. Am. Ceram. Soc. 82, 2359-67 (1999). From the results reported in these literatures, only when X=0 is BaTiO ₃ and X=1 is SrTiO ₃ , a thin film material with columnar grains and a grain size of 100 nm to 200 nm is grown, but when When 0<x<1, the grown Ba _x Sr _1-x TiO ₃ film is still composed of spherical grains, and its grain size is generally less than 70 nanometers. The Ba _x Sr _1-x TiO ₃ film composed of such grains , its dielectric properties and ferroelectric properties are still poor, and cannot meet the application requirements in the development of next-generation dynamic random access memories and room temperature infrared focal plane arrays.

The object of the present invention is to provide a kind of stable precursor solution, prepare Ba _x Sr _1-x TiO ₃ (0＜x＜1) thin film material with columnar crystal grain, grain size at 100～200 nanometers, make it It meets the application requirements in the development of next-generation dynamic random access memory, room temperature infrared detectors and room temperature infrared focal plane arrays.

In order to achieve the above object, the preparation of film material of the present invention adopts sol-gel method, and its process is as follows:

1. Stable precursor solution preparation:

According to X: (1-X), 0<x<1, weigh barium acetate ((CH ₃ COO) ₂ Ba) and strontium acetate ((CH ₃ COO) ₂ Sr) in molar ratio, put them into acetic acid together, and heat and stir until barium acetate and strontium acetate are completely dissolved; measure and add acetylacetone in an equimolar amount to ((CH ₃ COO) ₂ Ba+(CH ₃ COO) ₂ Sr) into the acetic acid solution of barium acetate and strontium acetate, and stir to make Mix evenly; measure butyl titanate in an equimolar amount to ((CH ₃ COO) ₂ Ba+(CH ₃ COO) ₂ Sr), add it to the mixed solution prepared above, stir evenly, and then dilute the solution with acetic acid The concentration of the solution is adjusted to 0.05-0.1 mol/liter, and it is left for 5-10 days to fully chelate it to obtain a stable precursor solution.

2. Preparation of film materials:

Pt/Ti/SiO ₂ /Si is used as the substrate, and the film is formed by rotating the glue-spinning method. The precursor solution is dropped on the surface of the substrate, and then the solution is evenly shaken off by a glue homogenizer. The glue-spinning speed is 3000-7000 Rotation per minute, and then put the gel film formed by spin-coating uniform gel into the annealing furnace together with the substrate for heat treatment, dry at 250-300°C, pyrolyze for 5-30 minutes, and then anneal at 600-750°C 5-30 minutes; during the annealing process, apply an auxiliary electric field of 2-4kv/cm to the film at the same time, control the thickness of each gel film after heat treatment at 8-20 nanometers, repeat the above spin coating and heat treatment process until the desired thickness So far, generally 300 to 800 nanometers.

In the present invention, acetylacetone is added in the preparation process of the precursor solution, so that the prepared precursor solution is relatively stable.

In the present invention, by controlling the thickness of each gel film after heat treatment between 8 and 20 nanometers, the heterogeneous nucleation and homoepitaxial growth of Ba _x Sr _1-x TiO ₃ are realized, columnar grains are formed, and the thickness of the film is reduced. crystallization temperature.

In the present invention, an auxiliary electric field of 2-4KV/cm is applied during the _{BaxSr1 -xTiO3 annealing} process, so that the film easily forms a tetragonal phase perovskite structure with (001) preferred orientation during the crystallization process.

The present invention has the following beneficial effects:

1. The preparation method of the film material of the present invention has simple production equipment and low production cost, which is beneficial to commercial application.

2. The thin film material preparation method of the present invention solves key technologies such as the preparation of a stable precursor solution, the thickness control of a single-layer gel film, heat treatment, and electric field-assisted annealing, so that the prepared Ba _x Sr _1-x TiO ₃ , (0 <x<1) Thin film materials have large-size columnar grains of 100-200 nanometers and excellent physical properties, making them widely used in the development of dynamic random access memory, room temperature infrared detectors and room temperature infrared focal plane arrays prospect.

The accompanying drawings of the present invention are as follows:

Figure 1 is a scanning electron micrograph of Ba _0.8 Sr _0.2 TiO ₃ thin film, (a) is the surface morphology, (b) is the cross-sectional morphology. The grain size of the thin film is between 100 and 200 nanometers, and the grain shape is columnar.

Figure 2 is the hysteresis loop of Ba _0.8 Sr _0.2 TiO ₃ film. The remnant polarization of the thin film is 3.5μC/cm ² , and the coercive electric field is 53KV/cm, showing good ferroelectricity.

Fig. 3 is the variation curve of the pyroelectric coefficient of Ba _0.8 Sr _0.2 TiO ₃ film with temperature. Between 10 and 100°C, the pyroelectric coefficient of the film is greater than 1.5×10 ^-4 C/m ² K, and the film is suitable for applications in pyroelectric detectors and infrared focal plane arrays.

Example 1.

Preparation of Ba _x Sr _1-x TiO ₃ (x=0.8) ferroelectric thin film material:

First, clean the utensils used: soak the flasks, beakers, weighing bottles, distillation tubes, pipettes, and syringes in aqua regia for 24 hours, then rinse them with deionized water for 10 times, and put the cleaned utensils at 80°C Bake for 5 hours under low temperature conditions and set aside.

1. Preparation of precursor solution:

Using analytically pure barium acetate ((CH ₃ COO) ₂ Ba), strontium acetate ((CH ₃ COO) ₂ Sr) and butyl titanate ((C ₄ H ₉ )O ₄ Ti) as raw materials, acetic acid as solvent, Acetylacetone (CH ₃ COCH ₂ COCH ₃ ) was used as a stabilizer.

(a). Weighing: Weigh 0.008 moles (2.0436 grams) of barium acetate and 0.002 moles (0.4294 grams) of strontium acetate into 20 ml of acetic acid, heat to 90 ° C, and stir at this temperature until barium acetate and strontium acetate completely dissolved;

(b). Measure 0.01 mole (1 milliliter) of acetylacetone, inject it in the acetic acid solution of barium acetate and strontium acetate, stir for 30 minutes, make it mix evenly, then distill until the solution concentration is 0.5 mole/liter;

(c). Measure 0.01 mole (3.5 ml) of butyl titanate, inject it into the solution prepared above, and stir for 30 minutes;

(d). Add appropriate amount of acetic acid to dilute to 0.1-0.05 mol/liter, and stir for 30-120 minutes to make it evenly mixed;

(e). Leave it for 5-10 days to fully chelate it, and then obtain a stable precursor solution.

2. Preparation of film materials:

1). Substrate processing:

(a). Use Pt/Ti/SiO ₂ /Si as the substrate, and gently scrub the surface of the substrate with acetone cotton balls repeatedly to remove organic matter on the surface;

(b). Put the scrubbed substrate into a mixed solution of NH ₄ OH: _{H 2} O ₂ :H ₂ O at a ratio of 1:4:20, heat to 60°C, and clean it in an ultrasonic cleaning tank for 5 minutes, further remove organic matter;

(c). Put the above-cleaned substrate into a mixed solution of HCl: _{H 2} O ₂ :H ₂ O (1:1:20), heat to 60°C, and clean it in an ultrasonic cleaning tank for 5 minutes to remove Ions and atomic impurities;

(d). Rinse with a large amount of deionized water until no more water drops hang on the surface of the substrate;

(e). Infrared drying for later use.

2). Thin film spin coating:

The film formation adopts the method of rotating and shaking the gel, dripping the precursor solution onto the surface of the substrate, and then throwing it away evenly with a glue homogenizer. The speed of the glue shaking is 5000 rpm for 40 seconds; then the gel film Put it into the annealing furnace together with the substrate for heat treatment, dry at 250°C, pyrolyze for 5 minutes, then anneal at 700°C for 10 minutes, apply an auxiliary electric field of 4KV/cm during the annealing process, repeat the above spin coating and heat treatment process Until the ideal thickness of 300 nanometers; finally put the film with a thickness of 300 nanometers into the annealing furnace, and anneal at 750 ° C for 5 minutes, which can be used for room temperature infrared detectors and room temperature infrared focal plane arrays. film material.

3. Material identification:

1) Structural and microstructural characterization:

(a). X-ray diffraction analysis shows that the prepared Ba _x Sr _1-x TiO ₃ (x=0.8) film is a polycrystalline film with a pure perovskite structure, which is tetragonal at room temperature.

(b). Scanning electron microscope test shows that: the prepared Ba _x Sr _1-x TiO ₃ (x=0.8) film has a grain size between 100 and 200 nanometers, and the grain shape is columnar. See attached picture 1.

2) Electrical performance characterization:

(a). The prepared Ba _x Sr _1-x TiO ₃ (x=0.8) film exhibits a remanent polarization of 3.5 μC/cm ² and a coercive electric field of 53 KV/cm at room temperature, showing good ferroelectric properties. See Figure 2 for the hysteresis loop.

(b). The pyroelectric coefficient of the prepared Ba _x Sr _1-x TiO ₃ (x=0.8) film between 10°C and 100°C is greater than 1.5×10 ^-4 C/m ² K. The change curve of pyroelectric coefficient with temperature is shown in Figure 3.

(c). The prepared Ba _x Sr _1-x TiO ₃ (x=0.8) film has a leakage current of less than 1×10 ^-7 A/cm ² under an electric field of 100 KV/cm.

The prepared Ba _x Sr _1-x TiO ₃ (x=0.8) thin film is suitable for application in the infrared focal plane at room temperature.

Example 2.

Preparation of Ba _x Sr _1-x TiO ₃ (x=0.65) dielectric film material:

The preparation process is the same as in Example 1. The Ba _x Sr _1-x TiO ₃ (x=0.65) thin film material is tested to have a relative permittivity ε _r > 600. Under an electric field of 100 kv/cm, the leakage of the thin film is The current is less than 1×10 ^-7 A/cm ² , which is suitable for the application of dynamic random access memory.

Claims (4)

1. strontium-barium titanate (Ba _xSr _1-xTiO ₃) preparation method of thin-film material, it is characterized in that this preparation method in turn includes the following steps:

(1). precursor solution preparation: according to X:(1-X), 0＜x＜1, mol ratio takes by weighing barium acetate ((CH ₃COO) ₂Ba), strontium acetate ((CH ₃COO) ₂Sr), put into acetic acid together, heating is also stirred, and dissolves fully until barium acetate, strontium acetate; Measure and ((CH ₃COO) ₂Ba+ (CH ₃COO) ₂Sr) methyl ethyl diketone of equimolar amount adds in the acetum of barium acetate, strontium acetate, stirs to make it to mix; Measure and ((CH ₃COO) ₂Ba+ (CH ₃COO) ₂Sr) the metatitanic acid fourth fat of equimolar amount joins in the mixing solutions for preparing above, stirs, and with concentration adjustment to 0.05～0.1 mol of acetic acid with solution, places 5～10 days then, makes it abundant chelating, promptly obtains stable precursor solution;

(2). the preparation of thin-film material: precursor solution is dropped on the substrate, with sol evenning machine solution is evenly thrown away, form gel-film, whirl coating speed is that per minute 3000 forwards 7000 commentaries on classics to, again substrate and gel-film being put into annealing furnace heat-treats, 250～300 ℃ of dryings, pyrolysis 5～30 minutes, annealed 5～30 minutes down at 600～750 ℃ then, in annealing process, apply the auxiliary electric field of 2～4kV/cm, gauge control after every layer of even glued membrane thermal treatment in 8～20 nanometers, is repeated above spin coating, heat treatment process is till film thickness is 300 to 800 nanometers.

2. strontium-barium titanate (Ba according to claim 1 _xSr _1-xTiO ₃) preparation method of thin-film material, it is characterized in that: described X span scope is 0.7＜x＜0.9, is applicable to the room temperature infrared focal plane array.

3. strontium-barium titanate (Ba according to claim 1 _xSr _1-xTiO ₃) preparation method of thin-film material, it is characterized in that: described X span scope is 0.5＜x≤0.7, is applicable to dynamic RAM.

4. strontium-barium titanate (Ba according to claim 1 _xSr _1-xTiO ₃) preparation method of thin-film material, it is characterized in that described substrate is Pt/Ti/SiO ₂/ Si.

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