Barium titanate film structure and preparation method thereof

Abstract

The invention relates to the technical field of perovskite thin film material preparation and structural design, and discloses a barium titanate thin film structure and a preparation method thereof. The barium titanate film structure comprises a substrate, an amorphous buried oxide layer, a silicon nitride or silicon core layer waveguide, a crystallized magnesium oxide buffer layer and a crystallized barium titanate layer. The amorphous buried oxide layer is arranged on the substrate, the silicon nitride or silicon core layer waveguide is located in the buried oxide layer, and the crystal buffer layer film is arranged on the amorphous buried oxide layer. Wherein the buffer layer film can directly grow and crystallize on an amorphous buried oxide layer (such as amorphous silicon dioxide), the barium titanate film takes the buffer layer as a growth template to perform growth and crystallization, the growth of barium titanate is not restrained by a substrate of a specific material or a crystal structure, and the preparation process from bottom to top is simple; and the used preparation means is low in cost and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of perovskite thin film material preparation and structural design technology, and particularly to a barium titanate thin film structure and its preparation method. Background Technology

[0002] Ferroelectric materials such as lithium niobate and barium titanate possess excellent electrical and nonlinear optical properties, making them ideal materials for integrated silicon photonics. In the past few decades, lithium niobate electro-optic modulators have made substantial progress, overcoming obstacles such as manufacturing difficulties, high waveguide losses, and low modulation bandwidth caused by wide electrode spacing. Barium titanate exhibits a large electro-optic response, with its electro-optic coefficient currently reported at approximately 1000 pm / V, more than 30 times that of lithium niobate (30 pm / V). Through structural design, it has the potential for lower half-wave voltage and higher response speed.

[0003] Barium titanate has been grown using various methods, such as sol-gel, metal-organic chemical vapor deposition, radio frequency magnetron sputtering, and pulsed laser deposition. Currently, the most common method for growing high-quality barium titanate epitaxial films is molecular beam epitaxy (MBE). However, it is expensive, the growth process is relatively slow, and it is not suitable for producing thicker barium titanate films for optical applications. Furthermore, it requires atomic sub-monolayer passivation of the semiconductor surface before preparing a buffer layer suitable for barium titanate growth. Radio frequency magnetron sputtering was considered for use in this study due to its fast deposition rate, low cost, large-area uniformity, and compatibility with CMOS for large-scale industrial production.

[0004] Achieving heterogeneous integration of barium titanate thin films with mature semiconductor materials such as silicon and germanium has become a research hotspot, potentially leading to numerous novel semiconductor functional devices. However, it also presents significant challenges. The main difficulty lies in the chemical reaction between the oxide thin film and the silicon / germanium interface, resulting in an amorphous layer and causing epitaxial failure. To address this issue, developed processes include: atomic sub-monolayer passivation of the semiconductor surface; and layer-by-layer growth to obtain high-quality perovskite or perovskite-like single-crystal buffer layers. However, the complexity of these processes limits their application in various fields. Summary of the Invention

[0005] The purpose of this invention is to provide a barium titanate thin film structure and its preparation method. A silicon or silicon nitride core layer transmits the light field, and an interlayer coupler is designed to couple the light field into the barium titanate layer. This method avoids the complexity of the process caused by etching the barium titanate thin film. Furthermore, the barium titanate thin film can be directly grown and crystallized on an amorphous silicon dioxide layer using a crystalline magnesium oxide thin film, thereby overcoming the complexity of current epitaxial growth processes for barium titanate thin films.

[0006] To achieve the above objectives, the following technical solution is adopted: In a first aspect, the present invention provides a barium titanate thin film structure, comprising a substrate, an amorphous buried oxide layer, a crystalline buffer layer and a crystalline barium titanate layer arranged sequentially from bottom to top. The crystallization buffer layer can be directly grown and crystallized on the amorphous buried oxide layer. The crystallization barium titanate layer is grown and crystallized using the crystallization buffer layer as a growth template. The lattice constant of the (100) crystal plane of the crystallization barium titanate layer is a1, and the lattice constant of the (100) crystal plane of the crystallization buffer layer is a2. The lattice matching relationship between the crystallization barium titanate layer and the crystallization buffer layer must satisfy any one of the following: a1∥a2, √2a1∥a2, a1∥√2a2; The refractive index of the crystalline barium titanate layer in the near-infrared band is n1, and the refractive index of the crystalline buffer layer in the near-infrared band is n2, where n1 ≥ n2. The crystalline buffer layer does not absorb light or absorbs less than a set threshold in the near-infrared band.

[0007] Furthermore, the crystallization buffer layer is configured as a magnesium oxide thin film.

[0008] Furthermore, the thickness H1 of the amorphous buried oxide layer is 2-10 μm; The thickness H2 of the crystallization buffer layer is 10-300 nm; The thickness H3 of the crystalline barium titanate layer is 50-1000 nm.

[0009] Furthermore, it also includes a silicon nitride or silicon core layer waveguide, which is located inside the amorphous buried oxide layer.

[0010] Furthermore, the thickness H4 of the silicon nitride or silicon core layer waveguide is 100-1000 nm; the width W1 of the silicon nitride or silicon core layer waveguide is 0.4-10 μm.

[0011] Furthermore, it also includes a silicon nitride or silicon core layer waveguide and an amorphous silicon dioxide capping layer; wherein the silicon nitride or silicon core layer waveguide is located on the surface of the amorphous buried oxide layer, the surface of the silicon nitride or silicon core layer waveguide is covered by a layer of the amorphous silicon dioxide capping layer, the crystalline buffer layer is disposed on the amorphous silicon dioxide capping layer, and the crystalline barium titanate layer is disposed on the crystalline buffer layer.

[0012] Furthermore, the thickness H5 of the amorphous silicon dioxide capping layer is 100-1000 nm.

[0013] Secondly, the present invention provides a method for preparing a barium titanate thin film structure, the method being used to prepare the barium titanate thin film structure as described above, comprising the following steps: (1) A layer of silicon dioxide buried oxide is grown on the surface of the substrate as an amorphous buried oxide layer; (2) The amorphous buried oxide layer is cleaned to obtain the processed sample; (3) Place the treated sample into the buffer layer sputtering chamber, heat it to 300-1000 ℃, and evacuate the chamber to a background vacuum of 10. -4 -10 -5 Pa; (4) Maintain the background vacuum and temperature in the chamber of step (3), stabilize the power of the chamber radio frequency source at 50~500W, and complete the growth of magnesium oxide thin film; (5) After growth is stopped, maintain the process parameters of step (4) and anneal the film in the chamber, and then allow the sample to cool down naturally to 80-200 ℃; (6) The sample is fed into the sputtering chamber of the barium titanate thin film, heated to 300~1000 ℃, and the background vacuum of the chamber is reduced to 10. -5 -10 -6 Pa; (7) Maintain the background vacuum and temperature in the chamber of step (6), stabilize the power of the chamber radio frequency source at 10-500W, and complete the growth of barium titanate thin film. (8) Maintain the process parameters of step (6) and anneal the film in the chamber. Then allow the sample to cool naturally to 80-200 °C and take out the sample to obtain the barium titanate film structure.

[0014] Thirdly, the present invention provides a method for preparing a barium titanate thin film structure, the method being used to prepare the barium titanate thin film structure as described above, comprising the following steps: (1) A layer of silicon dioxide buried oxide is grown on the surface of the substrate as an amorphous buried oxide layer; (2) The amorphous buried oxide layer is cleaned to obtain the processed sample; (3) Place the sample processed in step (2) into the chamber of chemical vapor deposition, deposit a silicon nitride thin film of 100-1000 nm, and etch a waveguide structure with a width of 1.1-2 μm. Deposit silicon dioxide to cover the silicon nitride waveguide. (4) Place the sample from step (3) into the buffer layer sputtering chamber, heat the sample to 300-1000 ℃, and evacuate the chamber to a background vacuum of 10 ℃. -4 -10 -5 Pa; (5) Maintain the background vacuum and temperature in the chamber of step (4), stabilize the power of the chamber radio frequency source at 50~500W, and complete the growth of magnesium oxide thin film; (6) After growth is stopped, maintain the process parameters of step (5) to anneal the magnesium oxide film in the chamber, and then allow the sample to cool down naturally to 80-200 ℃; (7) The sample is placed into the sputtering chamber of the barium titanate thin film and heated to 300-1000 ℃. The background vacuum of the chamber is then reduced to 10. -5 -10 -6 Pa; (8) Maintain the background vacuum and temperature in the chamber of step (7), stabilize the power of the chamber radio frequency source at 10-500W, and complete the growth of barium titanate thin film. (9) After growth is stopped, the process parameters of step (7) are maintained to anneal the film in the chamber. Then the sample is allowed to cool naturally to 80-200 °C and the sample is taken out to obtain the barium titanate film structure.

[0015] Fourthly, the present invention provides a method for preparing a barium titanate thin film structure, the method being used to prepare the barium titanate thin film structure as described above, comprising the following steps: (1) A layer of silicon dioxide buried oxide is grown on the surface of the substrate as an amorphous buried oxide layer; (2) The amorphous buried oxide layer is cleaned to obtain the processed sample; (3) Place the sample processed in step (2) into the chamber of chemical vapor deposition, deposit a silicon nitride thin film of 100-1000 nm, and etch a waveguide structure with a width of 1.1-2 μm. (4) Maintain the background vacuum and temperature in the chamber of step (3) and deposit a 100-1000 nm silicon dioxide buried oxide layer on the waveguide surface again. (5) Maintain the background vacuum and temperature in the chamber of step (4), stabilize the power of the chamber radio frequency source at 50-500W, and complete the growth of magnesium oxide thin film; (6) After growth is stopped, maintain the process parameters of step (5) to anneal the film in the chamber, and then allow the sample to cool down naturally to 80-200 °C. (7) The sample is placed into the sputtering chamber of the barium titanate thin film and heated to 300-1000 ℃. The background vacuum of the chamber is then reduced to 10. -5 -10 -6 Pa; (8) Maintain the background vacuum and temperature in the chamber of step (7), stabilize the power of the chamber radio frequency source at 10-500W, and complete the growth of barium titanate thin film. (9) Maintain the process parameters of step (7) to anneal the film in the chamber, and then let the sample cool down naturally to 80-200 ℃ before taking out the sample to complete the growth of barium titanate film.

[0016] The beneficial effects of this invention are reflected in: 1. The present invention sets silicon nitride or silicon core layer waveguide in amorphous oxide layer. This method of not etching crystalline barium titanate layer reduces the difficulty of the process. Through interlayer optical coupling process, part of the light in silicon nitride or silicon core layer waveguide can enter barium titanate layer to achieve optical field modulation.

[0017] 2. Traditional barium titanate electro-optic modulators often require the growth of barium titanate films on crystalline substrates (such as single-crystal silicon, single-crystal silicon-on-insulator, single-crystal strontium titanate, etc.) or the acquisition of barium titanate films through bonding transfer. The crystalline barium titanate film of this invention can be grown on an amorphous buried oxide layer (such as amorphous silicon dioxide). This bottom-up preparation method and film structure simplify the process and facilitate manufacturing. Furthermore, the crystal orientation of the crystalline barium titanate layer can be controlled by altering the growth process of the crystal buffer layer, resulting in a BTO(200) crystal peak with the highest electro-optic coefficient. Attached Figure Description

[0018] Figure 1 A barium titanate thin film structure provided in an embodiment of the present invention. Figure 1 ; Figure 2 A barium titanate thin film structure provided in an embodiment of the present invention. Figure 2 ; Figure 3 A barium titanate thin film structure provided in an embodiment of the present invention. Figure 3 ; Figure 4 X-ray diffraction pattern of magnesium oxide layer provided in an embodiment of the present invention; Figure 5 X-ray diffraction pattern of barium titanate layer grown on magnesium oxide layer provided in an embodiment of the present invention; Figure 6 X-ray diffraction pattern of barium titanate layer with peak value 200 provided in the embodiment of the present invention; Figure 7 The Raman spectrum of magnesium oxide and barium titanate layer provided in the embodiments of the present invention; Figure 8 X-ray diffraction pattern of barium titanate layer growth without magnesium oxide layer provided in an embodiment of the present invention. Detailed Implementation

[0019] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0020] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0021] Example 1: This invention provides a barium titanate thin film structure, such as... Figure 1 As shown, the barium titanate thin film structure includes a substrate 1, an amorphous buried oxide layer 2, a crystallization buffer layer 3, and a crystalline barium titanate layer 4 arranged sequentially from bottom to top. The crystallization buffer layer 3 can be directly grown and crystallized on the amorphous buried oxide layer 2. The crystalline barium titanate layer 4 is grown and crystallized using the crystallization buffer layer 3 as a growth template. The lattice constant of the (100) crystal plane of the crystalline barium titanate layer is a1, and the lattice constant of the (100) crystal plane of the crystallization buffer layer 3 is a2. The lattice matching relationship between the crystalline barium titanate layer 4 and the crystallization buffer layer 3 must satisfy any one of the following: a1∥a2, √2a1∥a2, a1∥√2a2. The refractive index of the crystalline barium titanate layer 4 in the near-infrared band is n1, and the refractive index of the crystallization buffer layer 3 in the near-infrared band is n2. n1≥n2. The crystallization buffer layer 3 has no absorption of light or absorption less than a set threshold in the near-infrared band.

[0022] Substrate 1 serves as the supporting substrate for the entire thin film structure. Its core function is to provide stable physical support and interfacial adhesion, ensuring the orderly growth of subsequent functional layers. The substrate needs to have good flatness and chemical stability; for example, silicon substrates or sapphire substrates can be selected to prevent substrate defects from being transmitted to the upper thin film and affecting the overall structural performance.

[0023] The core function of the amorphous buried oxide layer 2 (such as the SiO2 layer) is to achieve interface isolation. On the one hand, it isolates the chemical interaction between the substrate 1 and the upper functional layer, preventing metal ions in the substrate from diffusing to the barium titanate layer and causing performance degradation. On the other hand, it utilizes the insulating properties of the amorphous structure to provide electrical isolation for the subsequent barium titanate layer. However, the atomic arrangement of the amorphous structure is disordered and cannot be directly used as a growth template for the crystalline layer. Therefore, a crystalline buffer layer needs to be introduced to solve this contradiction.

[0024] The core design of the crystallization buffer layer 3 solves the problem of growing high-quality crystalline layers on amorphous layers. The irregular atomic arrangement of the amorphous buried oxide layer 2 leads to difficulties in nucleation and disordered crystallization during the subsequent growth of barium titanate layer. The crystallization buffer layer 3 has the characteristic of direct crystallization on the amorphous buried oxide layer. Its function is to construct an ordered atomic arrangement interface, providing a precise growth template for the upper crystalline barium titanate layer, and ensuring that the crystalline barium titanate layer 4 grows along the preset crystal orientation.

[0025] The crystalline barium titanate layer 4 serves as a functional carrier for the thin film, enabling dielectric, ferroelectric, and optical functions. Its crystal quality directly determines the overall performance. The crystalline barium titanate layer 4 uses the crystallization buffer layer 3 as a growth template. The ordered atomic arrangement of the crystallization buffer layer 3 guides the directional growth of barium titanate molecules, avoiding crystallization defects caused by autonomous nucleation, such as dislocations and disordered grain boundaries.

[0026] This embodiment defines the lattice matching relationship between the crystalline barium titanate layer 4 and the crystalline buffer layer 3, aiming to reduce the interfacial lattice mismatch. Lattice mismatch is a major source of defects (such as dislocations and stress) during thin film growth: if the lattice constants of the two layers differ too much, the atomic arrangement cannot transition continuously, resulting in lattice distortion at the interface, which in turn leads to problems such as cracks and grain breakage in the crystalline barium titanate layer. The above three matching relationships, through direct alignment (a1∥a2) or alignment at a ratio of √2 (√2a1∥a2, a1∥√2a2), can control the lattice mismatch to an extremely low range (<1%), ensuring the continuous growth of the barium titanate layer along the ordered structure of the buffer layer, forming a high-quality single crystal or polycrystalline preferred orientation structure.

[0027] The refractive index relationship between the crystalline barium titanate layer 4 and the crystalline buffer layer 3 is constrained to achieve the confinement and transmission of near-infrared light. In near-infrared applications (such as optical modulation and optical sensing), light needs to be primarily transmitted within the crystalline barium titanate layer 4 to reduce light leakage to the buffer layer or substrate. When n1 ≥ n2, near-infrared light undergoes total internal reflection or high internal reflection at the interface between the barium titanate layer and the buffer layer, confining the light within the barium titanate layer and improving the interaction efficiency between the light and the barium titanate layer, such as enhancing the dielectric-optical coupling effect.

[0028] In this embodiment, the crystalline buffer layer 3 is limited to having no absorption or absorption less than a set threshold in the near-infrared band to avoid energy loss during light transmission. If the buffer layer significantly absorbs near-infrared light, the light will be consumed before reaching the barium titanate layer, reducing overall light utilization efficiency. The low absorption design ensures that light can efficiently penetrate the buffer layer and enter the barium titanate layer, while avoiding the thermal effects caused by buffer layer absorption.

[0029] In some embodiments, the crystalline buffer layer 3 is a magnesium oxide thin film. The magnesium oxide thin film can be directly crystallized and grown on the amorphous layer. Since the lattice constant of the magnesium oxide thin film matches that of the barium titanate thin film, this solves the problem of the difficulty in growing a high-quality crystalline barium titanate layer on the amorphous layer. At the same time, the refractive index of the magnesium oxide thin film is lower than that of the barium titanate layer, and the refractive index of the magnesium oxide thin film in the near-infrared band is lower than that of the barium titanate thin film and has almost no absorption. This causes the near-infrared light to undergo total internal reflection or high internal reflection at the interface between the barium titanate layer and the buffer layer, confining the light within the barium titanate layer.

[0030] In some embodiments, the thickness H1 of the amorphous buried oxide layer 2 is 2-10 μm; the thickness H2 of the crystalline buffer layer 3 is 10-300 nm; and the thickness H3 of the crystalline barium titanate layer 4 is 50-1000 nm. The thicker amorphous buried oxide layer 2 can prevent light leakage into the substrate, and the thicker crystalline barium titanate layer 4 can enhance the efficiency of light interaction with the barium titanate layer.

[0031] In some embodiments, such as Figure 2 As shown, the barium titanate thin film structure also includes a silicon nitride or silicon core layer waveguide 5, which is located inside the amorphous buried oxide layer 2. The refractive index of silicon nitride or silicon is close to or slightly greater than that of the barium titanate thin film, allowing near-infrared light to couple well into the barium titanate layer when propagating in the silicon nitride or silicon core layer waveguide 5. Simultaneously, this optical waveguide structure avoids optical losses and other problems caused by etching the barium titanate layer.

[0032] In some embodiments, the thickness H4 of the silicon nitride or silicon core layer waveguide 5 is 100-1000 nm; the width W1 of the silicon nitride or silicon core layer waveguide 5 is 0.4-10 μm. The structural design of the silicon nitride or silicon core layer can achieve a greater amount of optical coupling into the barium titanate layer to achieve optical modulation while ensuring low optical transmission loss.

[0033] In some embodiments, such as Figure 3 As shown, the barium titanate thin film structure also includes a silicon nitride or silicon core waveguide 5 and an amorphous silicon dioxide capping layer 6. The silicon nitride or silicon core waveguide 5 is located on the surface of the amorphous buried oxide layer 2, and the surface of the silicon nitride or silicon core waveguide 5 is covered by an amorphous silicon dioxide capping layer 6. A crystalline buffer layer 3 is disposed on the amorphous silicon dioxide capping layer 6, and a crystalline barium titanate layer 4 is disposed on the crystalline buffer layer 3. This structure enables the growth of barium titanate thin films on conventional silicon nitride or silicon waveguide structures, and magnesium oxide and barium titanate thin films can be grown directly without surface planarization, which greatly reduces the complexity of the process.

[0034] In some embodiments, the thickness H5 of the amorphous silicon dioxide capping layer 6 is 100-1000 nm. The amorphous silicon dioxide capping layer 6 serves as the main functional layer for regulating the intensity of light entering the barium titanate thin film. When the amorphous silicon dioxide capping layer 6 is thinner, more light can enter the barium titanate layer for optical modulation; when the amorphous silicon dioxide capping layer 6 is thicker, the light can be confined within a silicon nitride or silicon waveguide to achieve low-loss transmission.

[0035] Example 2: This invention provides a method for preparing a barium titanate thin film structure, wherein the prepared barium titanate thin film structure is as follows: Figure 1 As shown, the preparation method includes the following steps: (1) A 2 μm buried oxide layer of silicon dioxide is grown on the surface of a silicon substrate using a thermal oxidation method well known in the art; (2) Send the silica buried oxide layer from step (1) into the plasma cleaning chamber, pump the base vacuum of the chamber to 40 Torr, power 40 W, clean the surface for 30-50 s, and remove the contaminants on the surface. (3) Place the sample processed in step (2) into the buffer layer sputtering chamber, heat the sample to 300 ℃, and evacuate the background vacuum of the chamber to 10 ℃. -4 Pa; (4) Maintain the background vacuum and temperature in the chamber of step (3), stabilize the power of the chamber radio frequency source at 300 W, and complete the growth of magnesium oxide thin film; (5) After growth is stopped, maintain the process parameters of step (4) and anneal the film in the chamber, and then allow the sample to cool down naturally to 80 °C. (6) Next, the sample is sent into the sputtering chamber of the barium titanate thin film, heated to 500 °C, and the background vacuum of the chamber is reduced to 10 °C. -5 Pa; (7) Maintain the background vacuum and temperature in the chamber of step (6), stabilize the power of the chamber radio frequency source at 200 W, and complete the growth of barium titanate thin film. (8) Maintain the process parameters of step (6) and anneal the film in the chamber. Then allow the sample to cool down naturally to 80 °C and take out the sample to complete the growth of barium titanate film.

[0036] Example 3: This invention provides a method for preparing a barium titanate thin film structure, wherein the prepared barium titanate thin film structure is as follows: Figure 2 As shown, the preparation method includes the following steps: (1) A 2 μm buried oxide layer of silicon dioxide is grown on the surface of a silicon substrate using a thermal oxidation method well known in the art; (2) The silica buried oxide layer from step (1) is sent into the plasma cleaning chamber, the background vacuum of the chamber is evacuated to 40 Torr, the power is 40 W, and the surface is cleaned for 30-50 s to remove contaminants from the surface.

[0037] (3) The sample after step (2) is placed in the chamber of chemical vapor deposition, a 200 nm silicon nitride thin film is deposited, and a waveguide structure with a width of 1.1 μm is etched. Then, silicon dioxide is deposited to cover the silicon nitride waveguide.

[0038] (4) Place the sample from step (3) into the buffer layer sputtering chamber, heat the sample to 300 ℃, and evacuate the background vacuum of the chamber to ~10 -4 Pa.

[0039] (5) Maintain the background vacuum and temperature in the chamber of step (4), stabilize the power of the chamber radio frequency source at 300 W, and complete the growth of magnesium oxide thin film; (6) After growth is stopped, maintain the process parameters of step (5) and anneal the film in the chamber, and then allow the sample to cool down naturally to 80 °C. (7) Next, the sample is sent into the sputtering chamber of the barium titanate thin film, heated to 500 °C, and the background vacuum of the chamber is reduced to ~10 °C. -5 Pa; (8) Maintain the background vacuum and temperature in the chamber of step (7), stabilize the power of the chamber radio frequency source at 200 W, and complete the growth of barium titanate thin film. (9) After stopping growth, maintain the process parameters of step (7) to anneal the film in the chamber, and then let the sample cool down naturally to 80 °C before taking out the sample to complete the growth of barium titanate film.

[0040] Example 4: This invention provides a method for preparing a barium titanate thin film structure, wherein the prepared barium titanate thin film structure is as follows: Figure 3 As shown, the preparation method includes the following steps: (1) A 2 μm buried oxide layer of silicon dioxide is grown on the surface of a silicon substrate using a thermal oxidation method well known in the art; (2) The silica buried oxide layer from step (1) is introduced into the plasma cleaning chamber, the base vacuum of the chamber is evacuated to 40 Torr, the power is 40 W, and the surface is cleaned for 30~50 s to remove surface contaminants; (3) The sample after step (2) is placed in the chamber of chemical vapor deposition to deposit a 300 nm silicon nitride thin film and etch a waveguide structure with a width of 2 μm.

[0041] (4) Maintain the background vacuum and temperature in the chamber of step (3) and deposit a 400 nm buried oxide layer of silicon dioxide on the waveguide surface again.

[0042] (5) Maintain the background vacuum and temperature in the chamber of step (4), stabilize the power of the chamber radio frequency source at 300 W, and complete the growth of magnesium oxide thin film; (6) After growth is stopped, maintain the process parameters of step (5) and anneal the film in the chamber, and then allow the sample to cool down naturally to 80 °C. (7) Next, the sample is sent into the sputtering chamber of the barium titanate thin film, heated to 500 °C, and the background vacuum of the chamber is reduced to ~10 °C. -5 Pa; (8) Maintain the background vacuum and temperature in the chamber of step (7), stabilize the power of the chamber radio frequency source at 200 W, and complete the growth of barium titanate thin film. (9) Maintain the process parameters of step (7) to anneal the film in the chamber, and then let the sample cool down naturally to 80 °C before taking out the sample to complete the growth of barium titanate film.

[0043] Based on the barium titanate thin film structure prepared in Example 2 of this invention, its structure is as follows: Figure 1 As shown, the barium titanate thin film structure and the magnesium oxide layer were characterized by Raman spectroscopy and grazing X-ray diffraction, and the following properties were determined: (1) such as Figure 4 As shown, the X-ray diffraction characterization of the magnesium oxide layer crystallized on the amorphous buried oxide layer has the following properties: the magnesium oxide film shows a strong crystallization peak at 42°, which is suitable as an epitaxial growth template for the barium titanate layer, where θ is the angle between the incident X-ray and the barium titanate crystal plane.

[0044] (2) such as Figure 5 As shown, X-ray diffraction characterization of the barium titanate layer on the crystalline magnesium oxide layer revealed that the barium titanate layer has good epitaxial crystallization peaks at 2θ~22° and 45°.

[0045] (3) such as Figure 6 As shown, X-ray diffraction characterization of the barium titanate layer revealed that among the epitaxial peaks at 45° of the barium titanate layer, the 200 and 002 peaks represent barium titanate with two different growth directions, namely out-of-plane and in-plane, respectively. The high content of the 200 peak can provide a stronger electro-optic coefficient, while the electro-optic coefficient of the 002 peak is weaker. Through fitting, it was found that the content of the 200 peak is about 90%, which can be used to prepare semiconductor devices.

[0046] (4) such as Figure 7As shown, the Raman spectral characterization of the barium titanate layer exhibits the following properties: due to the presence of long-range electrostatic forces, each optical phonon splits into transverse (TO) and longitudinal (LO) modes. In the tetragonal phase of ferroelectric barium titanate, the expression 3[A1(TO) + A1(LO)] + B1 + 4[E(TO) + E(LO)] represents all phonon modes. In this embodiment, the barium titanate thin film comprises: A1(LO1) ~ 170 cm⁻¹ -1 B1 / E(TO2) ~ 305 cm -1 E(LO) ~715 cm -1 These optical vibrations are caused by the Ti layer during its growth process. 4+ The spontaneous displacement demonstrates the existence of ferroelectric properties in the barium titanate thin film, which is the most important prerequisite for realizing electro-optic modulation of barium titanate thin films. The peak value of magnesium oxide is approximately 10³⁰ cm⁻¹. -1 .

[0047] like Figure 8 As shown, X-ray diffraction characterization of barium titanate layers grown on buffer layers without magnesium oxide films revealed that the 200 crystallization peak of barium titanate was very weak and contained many impurity peaks with 110 and 111 orientations, which weakened the electro-optic coefficient and was detrimental to device fabrication.

[0048] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A barium titanate thin film structure, characterized in that, It includes a substrate (1), an amorphous buried oxide layer (2), a crystal buffer layer (3), and a crystalline barium titanate layer (4) arranged sequentially from bottom to top. The crystallization buffer layer (3) can be directly grown and crystallized on the amorphous buried oxide layer (2). The crystallized barium titanate layer (4) is grown and crystallized using the crystallization buffer layer (3) as a growth template. The lattice constant of the (100) crystal plane of the crystallized barium titanate layer is a1, and the lattice constant of the (100) crystal plane of the crystallization buffer layer (3) is a2. The lattice matching relationship between the crystallized barium titanate layer (4) and the crystallization buffer layer (3) must satisfy any one of the following: a1∥a2, √2a1∥a2, a1∥√2a2; The refractive index of the crystalline barium titanate layer (4) in the near-infrared band is n1, and the refractive index of the crystalline buffer layer (3) in the near-infrared band is n2, where n1 ≥ n2. The crystalline buffer layer (3) does not absorb light or absorbs less than a set threshold in the near-infrared band.

2. The barium titanate thin film structure according to claim 1, characterized in that, The crystallization buffer layer (3) is configured as a magnesium oxide thin film.

3. The barium titanate thin film structure according to claim 1, characterized in that, The thickness H1 of the amorphous buried oxide layer (2) is 2-10 μm; The thickness H2 of the crystallization buffer layer (3) is 10-300 nm; The thickness H3 of the crystalline barium titanate layer (4) is 50-1000 nm.

4. The barium titanate thin film structure according to any one of claims 1 to 3, characterized in that, It also includes a silicon nitride or silicon core layer waveguide (5), which is located inside the amorphous buried oxide layer (2).

5. The barium titanate thin film structure according to claim 4, characterized in that, The thickness H4 of the silicon nitride or silicon core waveguide (5) is 100-1000 nm; the width W1 of the silicon nitride or silicon core waveguide (5) is 0.4-10 μm.

6. The barium titanate thin film structure according to any one of claims 1 to 3, characterized in that, It also includes a silicon nitride or silicon core layer waveguide (5) and an amorphous silicon dioxide capping layer (6); wherein the silicon nitride or silicon core layer waveguide (5) is located on the surface of the amorphous buried oxide layer (2), the surface of the silicon nitride or silicon core layer waveguide (5) is covered by a layer of the amorphous silicon dioxide capping layer (6), the crystalline buffer layer (3) is disposed on the amorphous silicon dioxide capping layer (6), and the crystalline barium titanate layer (4) is disposed on the crystalline buffer layer (3).

7. The barium titanate thin film structure according to claim 6, characterized in that, The thickness H5 of the amorphous silicon dioxide capping layer (6) is 100-1000 nm.

8. A method for preparing a barium titanate thin film structure, characterized in that, The preparation method is used to prepare the barium titanate thin film structure as described in any one of claims 1 to 3, and includes the following steps: (1) A layer of silicon dioxide buried oxide is grown on the surface of the substrate as an amorphous buried oxide layer; (2) The amorphous buried oxide layer is cleaned to obtain the processed sample; (3) Place the treated sample into the buffer layer sputtering chamber, heat it to 300-1000 ℃, and evacuate the background vacuum of the chamber to 10 ℃. -4 -10 -5 Pa; (4) Maintain the background vacuum and temperature in the chamber of step (3), stabilize the power of the chamber radio frequency source at 50~500 W, and complete the growth of magnesium oxide thin film; (5) After growth is stopped, maintain the process parameters of step (4) and anneal the film in the chamber, and then allow the sample to cool down naturally to 80-200 ℃; (6) The sample is fed into the sputtering chamber of the barium titanate thin film, heated to 300~1000 ℃, and the background vacuum of the chamber is reduced to 10. -5 -10 -6 Pa; (7) Maintain the background vacuum and temperature in the chamber of step (6), stabilize the power of the chamber radio frequency source at 10~500 W, and complete the growth of barium titanate thin film. (8) Maintain the process parameters of step (6) and anneal the film in the chamber. Then allow the sample to cool naturally to 80-200 °C and take out the sample to obtain the barium titanate film structure.

9. A method for preparing a barium titanate thin film structure, characterized in that, The preparation method is used to prepare the barium titanate thin film structure as described in any one of claims 4 to 5, and includes the following steps: (1) A layer of silicon dioxide buried oxide is grown on the surface of the substrate as an amorphous buried oxide layer; (2) The amorphous buried oxide layer is cleaned to obtain the processed sample; (3) Place the sample processed in step (2) into the chamber of chemical vapor deposition, deposit a silicon nitride thin film of 100-1000 nm, and etch a waveguide structure with a width of 1.1-2 μm. Deposit silicon dioxide to cover the silicon nitride waveguide. (4) Place the sample from step (3) into the buffer layer sputtering chamber, heat the sample to 300~1000 ℃, and evacuate the background vacuum of the chamber to 10. -4 -10 -5 Pa; (5) Maintain the background vacuum and temperature in the chamber of step (4), stabilize the power of the chamber radio frequency source at 50~500 W, and complete the growth of magnesium oxide thin film; (6) After growth is stopped, maintain the process parameters of step (5) to anneal the magnesium oxide film in the chamber, and then allow the sample to cool down naturally to 80-200 °C. (7) The sample is placed into the sputtering chamber of the barium titanate thin film and heated to 300-1000 ℃. The background vacuum of the chamber is then reduced to 10. -5 -10 -6 Pa; (8) Maintain the background vacuum and temperature in the chamber of step (7), stabilize the power of the chamber radio frequency source at 10-500 W, and complete the growth of barium titanate thin film. (9) After growth is stopped, the process parameters of step (7) are maintained to anneal the film in the chamber. Then the sample is allowed to cool naturally to 80-200 °C and the sample is taken out to obtain the barium titanate film structure.

10. A method for preparing a barium titanate thin film structure, characterized in that, The preparation method is used to prepare the barium titanate thin film structure as described in any one of claims 6 to 7, and includes the following steps: (1) A layer of silicon dioxide buried oxide is grown on the surface of the substrate as an amorphous buried oxide layer; (2) The amorphous buried oxide layer is cleaned to obtain the processed sample; (3) Place the sample processed in step (2) into the chamber of chemical vapor deposition, deposit a silicon nitride thin film of 100-1000 nm, and etch a waveguide structure with a width of 1.1-2 μm. (4) Maintain the background vacuum and temperature in the chamber of step (3) and deposit a 100-1000 nm silicon dioxide buried oxide layer on the waveguide surface again. (5) Maintain the background vacuum and temperature in the chamber of step (4), stabilize the power of the chamber radio frequency source at 50-500 W, and complete the growth of magnesium oxide thin film; (6) After growth is stopped, maintain the process parameters of step (5) to anneal the film in the chamber, and then allow the sample to cool down naturally to 80-200 °C. (7) The sample is placed into the sputtering chamber of the barium titanate thin film and heated to 300-1000 ℃. The background vacuum of the chamber is then reduced to 10. -5 -10 -6 Pa; (8) Maintain the background vacuum and temperature in the chamber of step (7), stabilize the power of the chamber radio frequency source at 10-500 W, and complete the growth of barium titanate thin film. (9) Maintain the process parameters of step (7) to anneal the film in the chamber, and then let the sample cool down naturally to 80-200 ℃ before taking out the sample to complete the growth of barium titanate film.

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