Preparation method of (100) oriented BTO crystal film

Abstract

The preparation method of the (100) oriented BTO crystal film comprises the following steps: S1, preparing a BTO precursor solution, S2, spin-coating the BTO precursor solution on a seed layer to obtain a wet film, and S3, putting the prepared wet film on a hot plate, carrying out multi-gradient pyrolysis, slowly heating to 200 DEG C, keeping the temperature for 10 minutes, and cooling to room temperature; slowly heating to 350 DEG C, keeping for 10 minutes, and cooling to room temperature; finally, the temperature is slowly increased to 450 DEG C, the temperature is kept for 10 minutes, then the temperature is slowly decreased to the room temperature, and an amorphous film is obtained; in the step S4, oxygen annealing is carried out; and slowly raising the temperature to 800 DEG C, keeping the temperature for 0.5 hour, and slowly reducing the temperature to room temperature to obtain the (100) oriented PZT crystal film. The preparation method provided by the invention is simple in steps and low in cost, and the prepared BTO film is high in quality and has excellent electro-optical performance.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor device preparation, and in particular relates to a method for preparing a (100) oriented BTO crystal film. Background Art

[0002] Barium titanate film, or BTO film, is a lead-free perovskite structured metal oxide with ultra-high electro-optical effect and special electro-optical modulation mechanism. It is a popular material for realizing ultra-high-speed electro-optical modulators. At present, the preparation of high-quality BTO crystal film is complicated, the equipment is expensive, and the cost is high. In the prior art, the preparation of BTO film includes the following methods:

[0003] Traditional preparation technologies, such as vacuum evaporation and sputtering deposition, need to ensure the uniformity and crystal quality of the film. To prepare high-quality BTO films, stricter process control and higher substrate temperatures are usually required, which increases the complexity of the preparation process, making the equipment complex and expensive, limiting the application of these technologies in large-area film preparation and mass production.

[0004] Innovative application of sol-gel method: When using the sol-gel method to prepare BTO thin film, metal alkoxide is usually used as a precursor, which is hydrolyzed in a solvent to form a sol, and the sol is coated on the substrate by spin coating or dipping, and then dried and heat treated to obtain the BTO thin film. The sol-gel method can mix precursors at the molecular level to ensure the uniformity of the film's composition. In addition, by controlling the spin coating parameters and heat treatment conditions, precise control of the film thickness and microstructure can be achieved. Compared with traditional methods such as vacuum evaporation and sputtering deposition, the sol-gel method has lower equipment and production costs. This method does not require complex vacuum equipment and is suitable for large-area and mass production.

[0005] (100)-oriented barium titanate is a material with a specific crystal orientation. Its excellent electro-optical and photorefractive properties make it widely used in nonlinear optical devices. Its excellent piezoelectric properties make it suitable for piezoelectric sensors, multilayer capacitors and memory devices. It has important application value in the fields of ferroelectric materials and piezoelectric materials.

[0006] Low-temperature preparation of barium titanate thin films by sol-gel-hydrothermal method, Materials Letters (IF 2.7) Pub Date: 1999-01-01, Barium titanate (BaTiO3) thin films were prepared on silicon substrates at low processing temperatures for the first time using sol-gel-hydrothermal (SG-HT) technology, combining the traditional sol-gel process with the hydrothermal method. The dried BaTiO3 gel film was used as a precursor film for post-hydrothermal treatment. Microstructural characteristics proved that the prepared BaTiO3 thin films with good crystallinity and good surface morphology transformed from amorphous phase to perovskite phase at extremely low processing temperatures of 100-200°C.

[0007] However, the sol-gel method faces problems in film preparation, such as poor uniformity, many defects, and easy cracking of the film, which leads to reduced film performance.

[0008] However, the sol-gel method forms a gel through a chemical reaction in a solution, and then forms a solid film through drying and heat treatment. Since it involves multiple solution treatments and thermal decomposition processes, improper control can easily lead to insufficient crystallinity, which can reduce optoelectronic performance. In the sol-gel process, it is difficult to control crystal growth. Small crystal size will cause electrons to face more scattering centers when transmitting in the material, reducing electron mobility and affecting the electrical performance of the device. Smaller grains may also lead to higher grain boundary density, thereby affecting the mechanical stability and durability of the material. This is not conducive to applications that require long-term stable operation. Due to its multiple solution treatment and heat treatment steps, the sol-gel method is prone to introduce impurities and defects, such as bubbles, cracks, and uneven component distribution. These defects can become electron traps, capture electrons and reduce their mobility. Due to its low crystallinity, small crystal size, and more defects, BTO films prepared by the sol-gel method perform poorly in electro-optical applications, limiting their application in high-performance optoelectronic devices.

[0009] In the process of preparing BTO film by gel sol method, the pyrolysis method is single, the uniformity and stability of the precursor solution are poor, the quality of the prepared film is poor, resulting in more defects in the film, difficulty in preferential orientation, and even non-crystallization of the film. During the pyrolysis process, the film is easily cracked due to stress, the film quality is poor, and it is difficult to preferentially orient the film.

[0010] Therefore, how to solve the problem of poor film quality of the sol-gel method and provide a method for preparing BTO crystal film that retains the advantages of the sol-gel method, obtains (100) preferred orientation, improves the crystallinity of the BTO film, increases the crystal size, reduces defects, and improves its electro-optical effect and overall performance is a technical problem that needs to be solved urgently by technicians in this field. Summary of the invention

[0011] The purpose of the present invention is to provide a method for preparing a (100) oriented BTO crystal film in view of the problems in the prior art.

[0012] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0013] A method for preparing a (100)-oriented BTO crystal film, characterized by comprising the following steps:

[0014] S1, preparing a BTO precursor solution: mixing a barium source and a titanium source in an organic solvent, wherein the molar ratio of barium to titanium is 1.0:0.8-1.2, and reacting under nitrogen protection, adding acetylacetone and ethanolamine as stabilizers, heating and stirring, cooling and filtering, and obtaining a BTO precursor solution;

[0015] S2, spin coating the BTO precursor solution obtained in step S1 on the seed layer to obtain a wet film;

[0016] S3, placing the wet film obtained in step S2 on a hot plate, using multi-gradient pyrolysis, slowly heating to 200°C and holding for 10 minutes, then cooling to room temperature; then slowly heating to 350°C and holding for 10 minutes, then cooling to room temperature; finally slowly heating to 450°C and holding for 10 minutes, then slowly cooling to room temperature, to obtain an amorphous film;

[0017] In step S4, oxygen annealing is performed, and the amorphous film obtained in step S3 is placed in a tubular annealing furnace, and the temperature is slowly raised from room temperature to 450°C in an oxygen atmosphere and maintained for 10 minutes; then the temperature is slowly raised to 800°C, maintained for 0.5 hours, and then slowly lowered to room temperature to obtain a (100) oriented PZT crystal film.

[0018] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0019] As a preferred technical solution of the present invention: in step S1, barium acetate is selected as the barium source, and tetraisopropyl titanate is selected as the titanium source. 1.02 g of barium acetate with a molar weight of 4.0 mmol and 1.36 g of tetraethyl titanate with a molar weight of 4.0 mmol are added to 20 mL of glacial acetic acid under nitrogen protection, and 1.0 mL of acetylacetone is added. The mixture is heated to 120° C., stirred for 3 hours, cooled, and filtered to obtain a BTO precursor solution.

[0020] As a preferred technical solution of the present invention: in step S2, the BTO precursor solution is spin-coated on the seed layer at a rotation speed of 3000 rpm for 20 seconds to form a wet film.

[0021] As a preferred technical solution of the present invention: in step S3, multi-gradient pyrolysis: place the wet film on a hot plate, slowly heat it to 200°C, keep it for 10 minutes, then cool it down to room temperature, then quickly heat it to 350°C, keep it for 10 minutes, then cool it down to room temperature, finally quickly heat it to 450°C, keep it for 10 minutes, and then slowly cool it down to room temperature.

[0022] Compared with the prior art, the present invention has the following beneficial effects: the method for preparing a (100) oriented BTO crystal film of the present invention provides a uniform medium through an organic solvent, so that the barium source and the titanium source can be fully mixed at the molecular level to achieve uniform distribution of metal ions, thereby ensuring the chemical uniformity and consistency of the final film; the higher boiling point of the organic solvent helps to control the volatilization rate of the solution during the heat treatment process and prevent component segregation or unevenness caused by too fast drying; acetylacetone and ethanolamine, as a chelating agent, can form a stable chelate with barium and titanium, reducing the metal ions in the solution. The free movement of the precursor solution reduces the possibility of precipitation and agglomeration, and improves the stability of the solution. Acetylacetone can also effectively inhibit the hydrolysis and condensation reactions of metal alkoxides, further ensuring the stability of the precursor solution over a long period of time, which is beneficial to the repeatability and controllability of the film preparation process. By precisely controlling the ratio of barium source and titanium source with suitable chemical reaction activity to obtain BTO film with an ideal stoichiometric ratio, the solution is prepared under nitrogen protection to reduce unnecessary oxidation and hydrolysis reactions, improve the stability and repeatability of the solution, and prevent the premature decomposition of sensitive source materials, ensuring that they remain active throughout the preparation process.

[0023] At the same time, the present invention adopts multi-gradient pyrolysis, and through multiple heating and cooling, and then heating again after cooling to room temperature, water, organic solvents and organic ligands in the film are gradually removed in batches, the holes generated by rapid heating of the film and the cracks generated by stress in the film are alleviated, and the problems of difficulty in preferential orientation and multiple defects of the film caused by holes and cracks in the film are improved, and the quality of the film is improved. Different temperatures are applied in real time at different stages to effectively control the thermal decomposition process of the material, promote the formation of amorphous structure, and achieve fine regulation of the microstructure of the film.

[0024] In this application, the choice of annealing temperature is also an important factor affecting the preferred orientation. The amorphous film is placed in a tubular annealing furnace, slowly heated from room temperature to 450°C and maintained for 10 minutes in an oxygen atmosphere, then slowly heated to 800°C and maintained for 30 minutes, and finally slowly cooled to room temperature. This process has a significant effect on the preferred orientation of the film. The above are all difficulties in preparing a preferred oriented film. In an oxygen atmosphere, as the temperature increases, the film begins to undergo structural changes. At 450°C, although the temperature is relatively low, it is sufficient to promote the local rearrangement of atoms or molecules inside the film, and some short-range ordered regions begin to form. This change is an initial sign of the film's transition from an amorphous state to a crystalline state. When the temperature continues to rise to 800°C, the atoms or molecules inside the film obtain sufficient energy for more extensive migration and rearrangement, which promotes the growth of crystals and the increase of grains. Keeping at this temperature for a period of time is conducive to the stability of the crystal structure and the further growth of grains, thereby forming a polycrystalline film with a (100) preferred orientation.

[0025] The present invention provides a method for preparing a BTO crystal film, which realizes the preparation of a high-quality BTO crystal film, has excellent piezoelectric effect and electro-optic modulation capability, and has an ultra-high electro-optic coefficient. Compared with the existing technology, the preparation method provided by the present invention has simple steps and low cost, and the prepared BTO film is of high quality and has excellent electro-optical performance, showing strong compatibility and high performance in the field of optical communications, and has great application prospects in the field of electro-optical integrated materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of a method for preparing a (100) oriented BTO crystal film of the present invention;

[0027] Figure 2 The Vπ test results of the MZ type electro-optic modulator prepared based on the BTO of the present invention are as follows;

[0028] Figure 3 This is the SEM cross-sectional image of a PZT thin film crystal, with a thickness of 193.5 nm;

[0029] Figure 4 is the XRD pattern of the prepared PZT film;

[0030] Figure 5 This is a larger defect on the BTO thin film crystal wafer. DETAILED DESCRIPTION

[0031] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] like Figure 1As shown, in a method for preparing a (100) oriented BTO crystal film of the present invention,

[0034] In step S1, the BTO precursor solution is prepared:

[0035] Take barium acetate (1.02g, 4.0mmol), tetraethyl titanate (1.36g, 4.0mmol), add to 20mL glacial acetic acid under nitrogen protection, add 1.0mL of a mixed solution of acetylacetone and ethanolamine, heat to 120℃, stir for 3 hours, cool, filter, and obtain a BTO precursor solution, which is orange-yellow and transparent, as follows Figure 1 The solution is relatively stable and can be stored at room temperature for 2 months.

[0036] By using high-purity barium and titanium sources with suitable chemical reactivity and precisely controlling the reaction conditions under nitrogen protection, a BTO precursor solution with stable quality can be prepared to prepare high-quality BTO thin films. In the preparation of BTO thin films:

[0037] 1) Spin coating: Spin the BTO solution onto the seed layer using a spin coating method (3000 rpm, 20 s) to form a wet film.

[0038] 2) Multi-gradient pyrolysis: Place the wet film on a hot plate, slowly heat it up to 200°C, hold it for 10 minutes, then cool it down to room temperature, then quickly heat it up to 350°C, hold it for 10 minutes, then cool it down to room temperature, finally quickly heat it up to 450°C, hold it for 10 minutes, then slowly cool it down to room temperature. 3) Oxygen annealing: Place the film in a tubular annealing furnace, slowly heat it up from room temperature to 450°C in a certain oxygen atmosphere, hold it for 10 minutes; then slowly heat it up to 800°C, hold it for 0.5 hours; finally slowly cool it down to room temperature to prepare a high-quality (100) oriented PZT crystal film.

[0039] First, the uniformity and stability of the precursor solution are poor, and the quality of the prepared film is poor, resulting in more film defects, difficulty in preferential orientation, and even non-crystallization of the film. Thirdly, during the pyrolysis process, the film is easily affected by stress and cracks are generated, resulting in difficulty in preferential orientation of the film. The multi-gradient pyrolysis of the present invention significantly improves this process. Finally, the choice of annealing temperature is also an important factor affecting preferential orientation. The above are all difficulties in preparing preferentially oriented films.

[0040] Heating on a high-precision hot plate can make the wet film heated at a uniform temperature, and controlling the pyrolysis temperature to be far lower than the crystallization temperature can avoid the formation of crystalline phases. The multi-gradient pyrolysis in the present invention gradually heats up to a peak at the beginning, then maintains a stable state for a period of time, and then the temperature slowly drops to room temperature, and then gradually heats up, maintains a stable state for a period of time, and then slowly cools down to room temperature again.

[0041] Test verification data and performance analysis

[0042] Electro-optic coefficient

[0043] In order to test the electro-optic coefficient of the BTO thin film crystal material, a Mach-Zehnder (MZ) electro-optic modulator was prepared on the BTO thin film crystal. The electro-optic coefficient of the electro-optic film was calculated by testing the half-wave voltage (Vπ) of the MZ electro-optic modulator. The Vπ of the MZ electro-optic modulator can be expressed as:

[0044]

[0045] Where λ is the wavelength, G is the distance between the two electrodes of the electro-optic modulator, n is the effective refractive index of the optical waveguide, Γ is the electro-optic overlap factor, γ 33 is the electro-optic coefficient of BTO thin film crystal material, and L is the electrode length.

[0046] The electro-optic coefficient γ of BTO thin film crystal material can be calculated from formula (1): 33 :

[0047]

[0048] The parameters of the electro-optic modulator tested are as follows: wavelength λ is 1550nm, the distance between electrodes is 6μm, the effective refractive index of the optical waveguide is 1.71, the electro-optical overlap factor is 0.7, the electrode length is 2mm, and its Vπ is 7.75V. The test results are as follows Figure 2 The electro-optic coefficient γ of the BTO electro-optic thin film crystal is calculated from the above data. 33 It is ~343pm / V.

[0049] Film thickness:

[0050] After the BTO film wafer is cleaved, a relatively neat cross section is obtained. The cross-sectional morphology is observed by electron beam microscopy (SEM) to obtain the thickness of the BTO film, such as Figure 3 As shown, the thickness of the top BTO thin film crystal is 193.5nm, the middle is a 2μm thick silicon dioxide layer, and the bottom is a silicon substrate.

[0051] XRD spectrum of the film:

[0052] like Figure 4As shown, through XRD testing, the preparation method of the BTO crystal film of the present invention has a high quality of the prepared BTO crystal film. As shown in the figure below, the film has a high (100) preferred orientation and a high peak intensity, indicating that the grain size is large (about 67nm) and the crystallinity is high (about 97%). Among them, the prepared BTO crystal film has excellent performance in both microstructure and macroscopic performance, with a crystallinity of up to 97%. Almost all BTO materials have formed a good crystal structure, which helps to improve the electrical and mechanical properties of the film; the grain size is about 67nm, which shows that the BTO film has a relatively uniform and delicate microstructure. The large grain size helps to reduce the grain boundary area, reduce the scattering of charges at the grain boundary, and improve the electron mobility. At the same time, it can also improve the mechanical stability and durability of the film. The preparation method of the BTO crystal film of the present invention has a high (100) preferred orientation, a large grain size and a high crystallinity, which proves that the film prepared by the preparation method of the present invention has excellent performance and indicates the application potential of the film in high-performance electronic devices.

[0053] Number of defects:

[0054] like Figure 5 As shown, the defects of the BTO thin film wafer of the present invention are observed through a microscope, and the defects are about 0.4 cm 2 There are about 3 particles in the range, and the whole wafer removes the edge defects, and the whole wafer particles are kept below 20. It can be seen that the preparation method of the BTO crystal film of the present invention successfully reduces surface defects, and the overall quality of the BTO film is high. This low defect density effectively improves the electrical properties and mechanical stability of the film.

[0055] The invention discloses a method for preparing a BTO crystal film, which comprises mixing a barium source and a titanium source in an organic solvent, adding acetylacetone as a stabilizer, and preparing a stable BTO precursor solution.

[0056] 2) Use multi-gradient pyrolysis to prepare amorphous films

[0057] 3) Under a certain oxygen atmosphere, short-term annealing is performed to obtain a high-quality BTO crystal film, which has excellent electro-optical properties.

[0058] The above-mentioned specific implementation methods are used to explain the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a (100) oriented BTO crystal film, characterized in that: The following steps are involved: S1, preparing a BTO precursor solution: mixing a barium source and a titanium source in an organic solvent, wherein the molar ratio of barium to titanium is 1.0:0.8-1.2, and reacting under nitrogen protection, adding acetylacetone and ethanolamine as stabilizers, heating and stirring, cooling and filtering, and obtaining a BTO precursor solution; S2, spin coating the BTO precursor solution obtained in step S1 on the seed layer to obtain a wet film; S3, placing the wet film obtained in step S2 on a hot plate, using multi-gradient pyrolysis, slowly heating to 200°C and holding for 10 minutes, then cooling to room temperature; then slowly heating to 350°C and holding for 10 minutes, then cooling to room temperature; finally slowly heating to 450°C and holding for 10 minutes, then slowly cooling to room temperature, to obtain an amorphous film; In step S4, oxygen annealing is performed, and the amorphous film obtained in step S3 is placed in a tubular annealing furnace, and the temperature is slowly raised from room temperature to 450°C in an oxygen atmosphere and maintained for 10 minutes; then the temperature is slowly raised to 800°C, maintained for 0.5 hours, and then slowly lowered to room temperature to obtain a (100) oriented PZT crystal film.

2. The method for preparing a (100)-oriented BTO crystal film according to claim 1, characterized in that: In step S1, the barium source is barium acetate, and the titanium source is tetraethyl titanate. Take 1.02 g of barium acetate with a molar weight of 4.0 mmol, 1.36 g of tetraethyl titanate with a molar weight of 4.0 mmol, add them to 20 mL of glacial acetic acid under nitrogen protection, add 1.0 mL of acetylacetone, heat to 120°C, stir for 3 hours, cool, and filter to obtain a BTO precursor solution.

3. The method for preparing a (100)-oriented BTO crystal film according to claim 1, characterized in that: In step S2, the BTO precursor solution is spin-coated on the seed layer at a rotation speed of 3000 rpm for 20 seconds to form a wet film.

4. The method for preparing a (100)-oriented BTO crystal film according to claim 1, characterized in that: In step S3, multi-gradient pyrolysis: the wet film is placed on a hot plate, slowly heated to 200°C and kept for 10 minutes, then cooled to room temperature; then slowly heated to 350°C and kept for 10 minutes, then cooled to room temperature; finally, slowly heated to 450°C and kept for 10 minutes, then slowly cooled to room temperature.

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