Preparation method of piezoelectric film structure

Abstract

The invention relates to the technical field of semiconductor manufacturing, and discloses a preparation method of a piezoelectric film structure, and the preparation method comprises the steps: sequentially forming a first thermal oxide layer, a waveguide core and a first cladding on the surface of one side of a first substrate, and forming a waveguide substrate; the first cladding coats the surface of one side, back on to the second substrate, of the waveguide core and the side surface of the waveguide core; sequentially forming a second thermal oxidation layer, a first electrode layer, a buffer layer, a piezoelectric film layer and a second electrode layer on the surface of one side of a second substrate to form a piezoelectric film substrate; forming a bonding layer on the surface of one side of the first cladding or the second electrode layer; aligning and bonding the waveguide substrate and the piezoelectric film substrate up and down; the second electrode layer or the first wrapping layer is correspondingly contacted with the bonding layer and is connected with the bonding layer in a bonding manner; removing the second substrate and the second thermal oxide layer; and patterning to expose a part of the second electrode layer. Compared with the prior art, the quality and the piezoelectric performance of the piezoelectric film layer can be improved, and the performance and the reliability of the piezoelectric modulation device are further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a method for preparing a piezoelectric film structure. Background Art

[0002] The common preparation scheme of stress-optical modulator is to grow SiO2 cladding on the top of waveguide (Si, SiN, etc.), and then grow the lower electrode layer Pt, piezoelectric layer PZT and upper electrode layer Pt. By applying voltage between the two electrodes, a vertical electric field is generated in the PZT layer. Due to the inverse piezoelectric effect, the PZT layer expands and contracts in thickness and width between the two electrodes respectively. Since the PZT layer grows on the top of the waveguide, the contraction change will generate stress in the waveguide layer below. Under the action of stress-optical effect, the effective refractive index of the waveguide changes, thereby producing a modulation effect. Among them, since the SiO2 cladding is prepared by plasma enhanced chemical vapor deposition (PECVD), its film layer has problems such as looseness, large porosity, and high hydrogen content. When the Pt electrode and PZT piezoelectric film are prepared later, there will be gas (hydrogen, etc.) leakage, which will cause the Pt and PZT films to be damaged, affecting the crystal phase and consistency of the Pt and PZT film layers, thereby causing the piezoelectric performance of the PZT film to fail; in addition, there is a risk of gas overflow causing the film to rupture and contaminate the cavity, which cannot be applied on a large scale in industry. In addition, the use of low-pressure chemical vapor deposition (LPCVD) to prepare the SiO2 cladding can improve the cladding quality problem, but there are still orientation differences, making it difficult to grow high-quality PZT films, and the thick SiO2 cladding also leads to greater stress. There is also a coating treatment scheme, in which a layer of SiO2 film is prepared on the SiO2 cladding prepared by PECVD using LPCVD or ALD and other technologies, but this method still has the risk of gas leakage causing film damage and contamination of the cavity during the processing process.

[0003] In the prior art, the piezoelectric material and the target substrate are heterogeneously integrated, and the smart-cut (intelligent peeling technology) technology is used to inject hydrogen ions into the piezoelectric material substrate, and then anneal at high temperature after forming a damaged layer to peel off the piezoelectric material; this method will damage the upper piezoelectric material during the hydrogen ion injection process, affecting the piezoelectric performance; at the same time, for the preparation process of PZT thin film, the PZT thin film needs to be sputtered and deposited at a low temperature to achieve excellent piezoelectric performance. The smart-cut technology requires subsequent annealing treatment, and the higher annealing temperature will cause secondary damage to the PZT thin film. In other schemes, the lithium niobate electro-optical modulation material and the SiC waveguide substrate are heterogeneously integrated, and the surface plasma is activated and bonded at room temperature, and then annealed to enhance the bonding strength. This method has a low bonding strength. At the same time, the lithium niobate material is incompatible with the subsequent CMOS process, and it is easy to contaminate the equipment during the waveguide structure photolithography and etching process, and it cannot be processed for large-scale mass production. Summary of the invention

[0004] In view of this, the present invention provides a method for preparing a piezoelectric thin film structure to solve the problems in the related art that the PZT film layer prepared on a SiO2 film of poor quality is easily damaged and has poor consistency, which leads to failure of the piezoelectric performance of the PZT film and contamination of the cavity, and the smart-cut technology will damage the PZT film, and the higher annealing temperature will cause secondary damage to the PZT film.

[0005] In a first aspect, the present invention provides a method for preparing a piezoelectric film structure, the method comprising:

[0006] Providing a first substrate, and sequentially forming a first thermal oxide layer, a waveguide core, and a first cladding on a surface of one side of the first substrate to form a waveguide substrate; the first cladding covers a surface of the waveguide core that is away from the first substrate and a side surface of the waveguide core;

[0007] Providing a second substrate, and sequentially forming a second thermal oxide layer, a first electrode layer, a buffer layer, a piezoelectric film layer, and a second electrode layer on a surface of one side of the second substrate to form a piezoelectric film substrate;

[0008] Forming a bonding layer: forming a bonding layer on a surface of the first cladding layer side of the waveguide substrate or on a surface of the second electrode layer side of the piezoelectric film substrate;

[0009] Aligning the waveguide substrate and the piezoelectric film substrate up and down and bonding them together; the first cladding layer and the bonding layer are correspondingly contacted and bonded together, or the second electrode layer and the bonding layer are correspondingly contacted and bonded together;

[0010] removing the second substrate and the second thermal oxide layer;

[0011] The first electrode layer, the buffer layer and the piezoelectric film layer are patterned to expose a portion of the second electrode layer.

[0012] The preparation method of the piezoelectric film structure provided by the present invention, on the one hand, by preparing the waveguide substrate and the piezoelectric film substrate separately, the two can maintain the best electrical and optical properties, will not cause pollution to the cavity, and the piezoelectric film layer in the piezoelectric film substrate is grown on the second thermal oxide layer, which can improve the growth quality of the piezoelectric film layer; on the other hand, by bonding the two substrates together through the W2W (wafer to wafer, wafer-level bonding) method, the waveguide substrate and the piezoelectric film substrate are heterogeneously integrated, and the piezoelectric film layer is not damaged. The disadvantage of the smart-cut technology that the piezoelectric film is damaged can be improved, and the quality of the piezoelectric film layer is improved, thereby improving the reliability of the piezoelectric modulation device; in addition, after the piezoelectric film substrate and the waveguide substrate are integrated, a patterning process is performed, which is compatible with the CMOS process. Due to the inverse piezoelectric effect, the piezoelectric film layer expands and contracts in thickness and width between the two electrodes respectively. Under the action of the stress-optical effect, the effective refractive index of the waveguide changes, thereby producing a modulation effect. The preparation method of the piezoelectric film structure provided by the present invention can prevent damage to the piezoelectric film layer and cavity contamination, improve the quality and piezoelectric performance of the piezoelectric film layer, and further improve the performance and reliability of the piezoelectric modulation device. At the same time, it can be compatible with the CMOS process, improve process compatibility, and realize large-scale industrial application.

[0013] In an optional embodiment, the bonding layer is a BCB adhesive layer;

[0014] The step of forming a bonding layer includes: forming a BCB glue layer on a surface of one side of the first cladding layer of the waveguide substrate;

[0015] In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the second electrode layer and the BCB adhesive layer are correspondingly contacted and bonded together; the first cladding layer and the second electrode layer are indirectly bonded together through the BCB adhesive layer.

[0016] The preparation method of the piezoelectric thin film structure provided by the present invention forms a BCB adhesive layer as a bonding layer on the surface of one side of the first cladding of the waveguide substrate, so that the first cladding and the second electrode layer are indirectly bonded together through the BCB adhesive layer. The BCB adhesive layer is used as an organic intermediate to bond the first cladding and the second electrode layer. The PZT thin film substrate and the waveguide substrate are effectively bonded together by indirect bonding of the BCB adhesive layer. The flatness and roughness of the substrate surface are relatively low, and the process can be carried out at low temperature to avoid damage to the metal structure caused by high temperature and high pressure conditions, which can reduce process requirements and improve process efficiency and process costs.

[0017] In an optional embodiment, in the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together,

[0018] The bonding temperature is 180℃~200℃;

[0019] The bonding time is 1h to 2h.

[0020] In an optional embodiment, the bonding layer is a metal bonding layer; and a first metal adhesion layer is further included between the metal bonding layer and the first cladding layer;

[0021] The step of forming a bonding layer includes: sequentially forming a first metal adhesion layer and a metal bonding layer on a surface of one side of the first cladding layer of the waveguide substrate;

[0022] Before the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the method further includes:

[0023] Performing surface grinding and Ar plasma activation on the waveguide substrate and the piezoelectric film substrate;

[0024] In the step of aligning the waveguide substrate and the piezoelectric film substrate and bonding them together, the second electrode layer and the metal bonding layer are in corresponding contact and connected together through metal bonding.

[0025] The preparation method of the piezoelectric film structure provided by the present invention forms a first metal adhesion layer and a metal bonding layer on the surface of one side of the first cladding of the waveguide substrate in sequence, and the two substrates are in corresponding contact with the metal bonding layer through the second electrode layer and connected together through metal bonding; adopts the method of metal-to-metal hot pressing bonding, assisted by Ar plasma activation, combined with the mutual diffusion of atoms between metal interfaces, and relies on metal bonds and other factors to form an interconnection interface at the bonding interface. The low bonding temperature of this method is conducive to protecting the PZT thin film material. Due to the Ar plasma assistance, the bonding strength is relatively high. At the same time, this bonding method belongs to direct bonding, and no intermediate dielectric layer is introduced, thereby improving the reliability of the device.

[0026] In an optional embodiment, in the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together,

[0027] The bonding temperature is 300℃~350℃;

[0028] The bonding pressure is 2.5Mpa~3MPa;

[0029] The bonding time is 20min to 30min.

[0030] In an optional embodiment, the bonding layer is a second cladding layer;

[0031] The step of forming a bonding layer includes: forming a second cladding layer on a surface of a second electrode layer side of the piezoelectric film substrate;

[0032] Before the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the method further includes:

[0033] Performing surface grinding and oxygen plasma activation on the waveguide substrate and the piezoelectric film substrate;

[0034] In the step of aligning the waveguide substrate and the piezoelectric film substrate and bonding them together, the first cladding layer and the second cladding layer are in corresponding contact and connected together by thermocompression bonding.

[0035] The preparation method of the piezoelectric film structure provided by the present invention forms a second cladding on the surface of one side of the second electrode layer of the piezoelectric film substrate; the two substrates are in contact with the corresponding second cladding through the first cladding and the second cladding and connected together by thermocompression bonding. The thermocompression bonding method is adopted, and the number of hydroxyl groups on the target surface is increased by oxygen plasma activation to make the first cladding and the second cladding surfaces of the two substrates become hydrophilic surfaces. Combined with the low roughness of the surfaces of the two substrates (less than 1nm), pressure is then applied to the two substrates at a relatively low temperature, so that the two substrates are successfully bonded. The low bonding temperature of this method is beneficial to protecting the PZT thin film material. Due to the assistance of oxygen plasma, the bonding strength is relatively high. At the same time, this bonding method belongs to direct bonding, and no intermediate dielectric layer is introduced, thereby improving the reliability of the device.

[0036] In an optional embodiment, the material of the second cladding layer is SiO2.

[0037] In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together,

[0038] The bonding temperature is 200℃~250℃;

[0039] The bonding pressure is 2.5Mpa~3MPa;

[0040] The bonding time is 20min to 30min.

[0041] In an optional embodiment, the step of sequentially forming a second thermal oxide layer, a first electrode layer, a buffer layer, a piezoelectric film layer, and a second electrode layer on a surface of one side of the second substrate to form a piezoelectric film substrate includes:

[0042] A second thermal oxide layer, a second metal adhesion layer, a first electrode layer, a buffer layer, a piezoelectric film layer and a second electrode layer are sequentially formed on the surface of one side of the second substrate.

[0043] In an optional embodiment, the step of removing the second substrate and the second thermal oxide layer includes:

[0044] The second substrate, the second thermal oxide layer and the second metal adhesion layer are removed.

[0045] In an optional embodiment, after the step of patterning the first electrode layer, the buffer layer and the piezoelectric film layer to expose a portion of the second electrode layer, the step further includes:

[0046] A third cladding layer is formed on a surface of the second electrode facing away from the first substrate; the third cladding layer also covers a side surface of the first electrode layer, a side surface of the buffer layer, a side surface of the piezoelectric film layer, and a side surface of the first electrode layer facing away from the buffer layer;

[0047] Etching the side of the third cladding layer facing away from the second electrode layer to form a second electrode contact hole; etching the side of the third cladding layer facing away from the first electrode layer to form a first electrode contact hole;

[0048] A first electrode lead and a second electrode lead are prepared in the first electrode contact hole and the second electrode contact hole, respectively.

[0049] In an optional embodiment, the material of the first substrate and the material of the second substrate are silicon;

[0050] The material of the first thermal oxide layer, the material of the first cladding layer and the material of the second thermal oxide layer are SiO2;

[0051] The material of the waveguide core is silicon nitride;

[0052] The material of the first electrode layer and the material of the second electrode layer are Pt;

[0053] The material of the piezoelectric film layer is PZT;

[0054] The material of the buffer layer is LaNiO3. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the related technologies, the drawings required for use in the specific embodiments or the related technical descriptions will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0056] Figure 1 It is a schematic flow chart of a method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0057] Figure 2 It is a schematic diagram of a specific process of a method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0058] Figure 3 It is a schematic structural diagram of forming a waveguide substrate in a method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0059] Figure 4 It is a schematic structural diagram of forming a piezoelectric film substrate in a method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0060] Figure 5It is a structural schematic diagram of forming a BCB glue layer in a method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0061] Figure 6 It is a structural schematic diagram of aligning and bonding a waveguide substrate and a piezoelectric film substrate together in a method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0062] Figure 7 It is a structural schematic diagram of removing the second substrate, the second thermal oxide layer, and the second metal adhesion layer in a method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0063] Figure 8 It is a schematic diagram of a structure in which a portion of a second electrode layer is exposed by patterning in a method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0064] Fig. 9 It is a structural schematic diagram of forming a first electrode contact hole and a second electrode contact hole in a method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0065] Fig.10 It is a structural schematic diagram of a piezoelectric thin film structure prepared by a method for preparing a piezoelectric thin film structure according to an embodiment of the present invention.

[0066] Fig.11 It is a schematic diagram of a specific process of another method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0067] Fig.12 It is a structural schematic diagram of forming a second cladding layer in another method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0068] Fig.13 It is a structural schematic diagram of aligning and bonding a waveguide substrate and a piezoelectric film substrate together in a method for preparing another piezoelectric film structure according to an embodiment of the present invention.

[0069] Fig.14 1 is a schematic structural diagram of a piezoelectric film structure prepared by another method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0070] Fig.15 It is a schematic diagram of a specific process of another method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0071] Fig.16 It is a structural schematic diagram of forming a second cladding layer in another method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0072] Fig.17It is a structural schematic diagram of aligning and bonding a waveguide substrate and a piezoelectric film substrate together in a vertical direction in another method for preparing a piezoelectric film structure according to an embodiment of the present invention.

[0073] Fig.18 1 is a schematic structural diagram of a piezoelectric thin film structure prepared according to another method for preparing a piezoelectric thin film structure according to an embodiment of the present invention.

[0074] Reference numerals:

[0075] 10. First substrate; 11. First thermal oxide layer; 12. Waveguide core; 13. First cladding; 20. Second substrate; 21. Second thermal oxide layer; 22. Second metal adhesion layer; 23. First electrode layer; 24. Buffer layer; 25. Piezoelectric film layer; 26. Second electrode layer; 30. Third cladding; 311. First electrode contact hole; 312. Second electrode contact hole; 321. First electrode lead; 322. Second electrode lead; 41. BCB glue layer; 42. Second cladding; 43. Metal bonding layer; 44. First metal adhesion layer. DETAILED DESCRIPTION

[0076] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0077] In the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified for the purpose of clear expression, and some details may be omitted. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships between them are only exemplary, and may be deviated due to manufacturing tolerances or technical limitations in practice, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be a middle layer / element between them. In addition, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "under" the other layer / element.

[0078] In wafer-level CMOS-compatible processes, the photonic integration platform has ultra-low waveguide losses and a wide range of passive applications in the visible and infrared wavelength ranges. The platform has the advantages of low cost, low power consumption, and high reliability, and can be widely used in quantum information science and applications, optical communications, gyroscopes, microwave photonics, etc. These applications generally require high optical drive and modulation for tuning and control functions, including wavelength shift, swept frequency modulation, and phase shift; low optical insertion loss and large modulation bandwidth are also required. Currently, the commonly used modulation methods are thermo-optic modulation and electro-optic modulation. The modulator using thermo-optic modulation usually consumes 200mW to 500mW per modulator and has a modulation speed of 0.5kHz to 1kHz. For applications that require a large number of modulators, such as microwave photonics, the power consumption of the modulator needs to be reduced to the nW level; for applications that require fast modulation, thermo-optic modulation also has limitations. Electro-optic modulation can be performed using nonlinear materials such as lithium niobate. The electro-optic modulation method has a modulation bandwidth of more than 1GHz, but the optical loss is large, the power consumption is high, and it may have a limited material optical wavelength range. Stress-optical modulation using the photoelastic effect has low propagation loss and tuning power, wide optical bandwidth and low power consumption. The braking control of stress in the waveguide structure is achieved by depositing a thin layer of piezoelectric material on the top of the structure. The commonly used piezoelectric material is lead zirconate titanate (PZT) because it has a large effective lateral piezoelectric coefficient and is widely used in micro-electromechanical systems.

[0079] The common preparation scheme of stress-optical modulator is to grow SiO2 cladding on the top of waveguide (Si, SiN, etc.), and then grow the lower electrode layer Pt, piezoelectric layer PZT and upper electrode layer Pt. By applying voltage between the two electrodes, a vertical electric field is generated in the PZT layer. Due to the inverse piezoelectric effect, the PZT layer expands and contracts in thickness and width between the two electrodes respectively. Since the PZT layer grows on the top of the waveguide, the contraction change will generate stress in the waveguide layer below. Under the action of stress-optical effect, the effective refractive index of the waveguide changes, thereby producing a modulation effect. Among them, since the SiO2 cladding is prepared by plasma enhanced chemical vapor deposition (PECVD), its film layer has problems such as looseness, large porosity, and high hydrogen content. When the Pt electrode and PZT piezoelectric film are prepared later, there will be gas (hydrogen, etc.) leakage, which will cause the Pt and PZT films to be damaged, affecting the crystal phase and consistency of the Pt and PZT film layers, thereby causing the piezoelectric performance of the PZT film to fail; in addition, there is a risk of gas overflow causing the film to rupture and contaminate the cavity, which cannot be applied on a large scale in industry. In addition, the use of low-pressure chemical vapor deposition (LPCVD) to prepare the SiO2 cladding can improve the cladding quality problem, but there are still orientation differences, making it difficult to grow high-quality PZT films, and the thick SiO2 cladding also leads to greater stress. There is also a coating treatment scheme, in which a layer of SiO2 film is prepared on the SiO2 cladding prepared by PECVD using LPCVD or ALD and other technologies, but this method still has the risk of gas leakage causing film damage and contamination of the cavity during the processing process.

[0080] In the prior art, the piezoelectric material and the target substrate are heterogeneously integrated, and the smart-cut technology is used to inject hydrogen ions into the piezoelectric material substrate, and then annealing is performed at high temperature after forming a damaged layer to peel off the piezoelectric material; this method will damage the upper piezoelectric material during the process of injecting hydrogen ions, affecting the piezoelectric performance; at the same time, for the preparation process of PZT thin film, the PZT thin film needs to be sputtered and deposited at a low temperature to achieve excellent piezoelectric performance. The smart-cut technology requires subsequent annealing treatment, and the higher annealing temperature will cause secondary damage to the PZT thin film. In other schemes, the lithium niobate electro-optical modulation material and the SiC waveguide substrate are heterogeneously integrated, and the surface plasma is activated and bonded at room temperature, and then annealing is performed to enhance the bonding strength. This method has a low bonding strength. At the same time, the lithium niobate material is incompatible with the subsequent CMOS process, and it is easy to contaminate the equipment during the photolithography and etching process of the waveguide structure, and it cannot be processed for large-scale mass production.

[0081] In the existing scheme, an adhesion layer Ti, a lower electrode Pt and a buffer layer LNO are spaced between the PZT film and the waveguide structure or silicon oxide. These three layers are used to improve the growth quality of the PZT film (due to the large difference in the lattice constants of silicon oxide and the PZT film). In addition, since the silicon oxide cladding on the waveguide structure is usually prepared by PECVD technology, the quality is poor, which seriously affects the subsequent growth quality of the PZT film. At the same time, during the growth process, due to the high temperature, the silicon oxide film layer breaks, releasing residual hydrogen ions, which will cause pollution to the PZT film cavity.

[0082] like Figure 1 As shown, this embodiment provides a method for preparing a piezoelectric film structure, and the preparation method includes but is not limited to steps S101 to S106.

[0083] Step S101, providing a first substrate 10, sequentially forming a first thermal oxide layer 11, a waveguide core 12 and a first cladding layer 13 on one side surface of the first substrate 10 to form a waveguide substrate; the first cladding layer 13 covers a side surface of the waveguide core 12 facing away from the first substrate 10 and a side surface of the waveguide core 12, such as Figure 3 shown.

[0084] Step S102, providing a second substrate 20, and sequentially forming a second thermal oxide layer 21, a first electrode layer 23, a buffer layer 24, a piezoelectric film layer 25 and a second electrode layer 26 on one side of the second substrate 20 to form a piezoelectric film substrate, such as Figure 4 shown.

[0085] During specific implementation, in one example, the piezoelectric film layer 25 is a PZT film layer, and the piezoelectric film substrate is a PZT film substrate.

[0086] Step S103, forming a bonding layer: forming a bonding layer on the surface of the first cladding layer 13 of the waveguide substrate or on the surface of the second electrode layer 26 of the piezoelectric film substrate.

[0087] Step S104, aligning the waveguide substrate and the piezoelectric film substrate up and down and bonding them together; the first cladding layer 13 and the bonding layer are correspondingly contacted and bonded together, or the second electrode layer 26 and the bonding layer are correspondingly contacted and bonded together.

[0088] Step S105 , removing the second substrate 20 and the second thermal oxide layer 21 .

[0089] Step S106 , patterning the first electrode layer 23 , the buffer layer 24 and the piezoelectric film layer 25 to expose a portion of the second electrode layer 26 .

[0090] The preparation method of the piezoelectric film structure provided in the present embodiment, on the one hand, by preparing the waveguide substrate and the piezoelectric film substrate separately, the two can maintain the best electrical and optical properties, will not cause pollution to the cavity, and the piezoelectric film layer in the piezoelectric film substrate grows on the second thermal oxide layer, which can improve the growth quality of the piezoelectric film layer; on the other hand, by bonding the two substrates together through the W2W (wafer to wafer, wafer-level bonding) method, the waveguide substrate and the piezoelectric film substrate are heterogeneously integrated, and the piezoelectric film layer is not damaged. The disadvantage of the smart-cut technology that causes damage to the piezoelectric film can be improved, and the quality of the piezoelectric film layer is improved, thereby improving the reliability of the piezoelectric modulation device; in addition, after the piezoelectric film substrate and the waveguide substrate are integrated, a patterning process is performed, which is compatible with the CMOS process. Due to the inverse piezoelectric effect, the piezoelectric film layer expands and contracts in thickness and width between the two electrodes respectively. Under the action of the stress-optical effect, the effective refractive index of the waveguide changes, thereby producing a modulation effect. The method for preparing the piezoelectric film structure provided in this embodiment can prevent damage to the piezoelectric film layer and cavity contamination, improve the quality and piezoelectric performance of the piezoelectric film layer, and thereby improve the performance and reliability of the piezoelectric modulation device. At the same time, it can be compatible with the CMOS process, improve process compatibility, and realize large-scale industrial application.

[0091] The device is prepared by bonding to avoid growing PZT thin film on poor quality silicon oxide; although the bonding layer is introduced, the piezoelectric coefficient of the PZT thin film itself is large (e 31 >14C / m 2 ), will not affect the performance of the device, and the PZT film and silicon oxide layer in the existing solution also have a multi-layer structure.

[0092] In some optional embodiments, the bonding layer is a BCB adhesive layer 41;

[0093] The step of forming a bonding layer includes: forming a BCB adhesive layer 41 on one side surface of the first cladding layer 13 of the waveguide substrate;

[0094] In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the second electrode layer 26 and the BCB adhesive layer 41 are correspondingly contacted and bonded together; the first cladding layer 13 and the second electrode layer 26 are indirectly bonded together through the BCB adhesive layer 41.

[0095] The preparation method of the piezoelectric thin film structure provided in the present embodiment forms a BCB adhesive layer as a bonding layer on the surface of one side of the first cladding of the waveguide substrate, so that the first cladding and the second electrode layer are indirectly bonded together through the BCB adhesive layer. The BCB adhesive layer is used as an organic intermediate to bond the first cladding and the second electrode layer. The PZT thin film substrate and the waveguide substrate are effectively bonded together by indirect bonding of the BCB adhesive layer. The requirements for the flatness and roughness of the substrate surface are low, and the process can be carried out at low temperature to avoid damage to the metal structure caused by high temperature and high pressure conditions, thereby reducing process requirements and improving process efficiency and process costs.

[0096] In some optional embodiments, in the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together,

[0097] The bonding temperature is 180℃~200℃;

[0098] The bonding time is 1h to 2h.

[0099] In some optional embodiments, the bonding layer is a metal bonding layer 43; a first metal adhesion layer 44 is further included between the metal bonding layer 43 and the first cladding layer 13;

[0100] The step of forming the bonding layer includes: sequentially forming a first metal adhesion layer 44 and a metal bonding layer 43 on a surface of one side of the first cladding layer 13 of the waveguide substrate;

[0101] Before the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the method further includes:

[0102] The waveguide substrate and the piezoelectric film substrate are subjected to a surface grinding process and an Ar plasma activation process.

[0103] In the step of aligning the waveguide substrate and the piezoelectric film substrate and bonding them together, the second electrode layer 26 and the metal bonding layer 43 are in corresponding contact and connected together through metal bonding.

[0104] In some optional embodiments, after the surface grinding process, the roughness of the metal bonding layer 43 and the second electrode layer 26 is less than 1 nm.

[0105] The preparation method of the piezoelectric film structure provided in this embodiment forms a first metal adhesion layer and a metal bonding layer on the surface of one side of the first cladding layer of the waveguide substrate in sequence, and the two substrates are in corresponding contact with the metal bonding layer through the second electrode layer and connected together through metal bonding; adopts the method of metal-to-metal hot pressing bonding, assisted by Ar plasma activation, combined with the mutual diffusion of atoms between metal interfaces, and relies on metal bonds and other factors to form an interconnection interface at the bonding interface. The low bonding temperature of this method is conducive to protecting the PZT thin film material. Due to the Ar plasma assistance, the bonding strength is relatively high. At the same time, this bonding method belongs to direct bonding, and no intermediate dielectric layer is introduced, which improves the reliability of the device.

[0106] In some optional embodiments, in the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together,

[0107] The bonding temperature is 300℃~350℃;

[0108] The bonding pressure is 2.5Mpa~3MPa;

[0109] The bonding time is 20min to 30min.

[0110] In some optional embodiments, the bonding layer is a second cladding layer 42;

[0111] The step of forming the bonding layer includes: forming a second cladding layer 42 on a surface of one side of the second electrode layer 26 of the piezoelectric film substrate;

[0112] Before the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the method further includes:

[0113] Performing surface grinding and oxygen plasma activation on the waveguide substrate and the piezoelectric film substrate;

[0114] In the step of aligning the waveguide substrate and the piezoelectric film substrate and bonding them together, the first cladding layer 13 and the second cladding layer 42 are in contact with each other and connected together by thermocompression bonding.

[0115] In some optional embodiments, after the surface grinding process, the roughness of the first cladding layer 13 and the second cladding layer 42 is less than 1 nm.

[0116] The preparation method of the piezoelectric film structure provided in this embodiment is through forming a second cladding on the surface of one side of the second electrode layer of the piezoelectric film substrate; the two substrates are in contact with the corresponding second cladding through the first cladding and the second cladding and connected together by thermocompression bonding. The thermocompression bonding method is adopted, and the number of hydroxyl groups on the target surface is increased by oxygen plasma activation to make the first cladding and the second cladding surfaces of the two substrates become hydrophilic surfaces. Combined with the low roughness of the surfaces of the two substrates (less than 1nm), pressure is then applied to the two substrates at a relatively low temperature, so that the two substrates are successfully bonded. The low bonding temperature of this method is conducive to protecting the PZT thin film material. Due to the assistance of oxygen plasma, the bonding strength is relatively high. At the same time, this bonding method belongs to direct bonding, and no intermediate dielectric layer is introduced, which improves the reliability of the device.

[0117] In some optional embodiments, the material of the second cladding layer 42 is SiO2.

[0118] In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together,

[0119] The bonding temperature is 200℃~250℃;

[0120] The bonding pressure is 2.5Mpa~3MPa;

[0121] The bonding time is 20min to 30min.

[0122] In some optional embodiments, a second thermal oxide layer 21, a first electrode layer 23, a buffer layer 24, a piezoelectric film layer 25 and a second electrode layer 26 are sequentially formed on a surface of one side of the second substrate 20 to form a piezoelectric film substrate, comprising:

[0123] A second thermal oxide layer 21, a second metal adhesion layer 22, a first electrode layer 23, a buffer layer 24, a piezoelectric film layer 25 and a second electrode layer 26 are sequentially formed on one side surface of the second substrate 20 to form a piezoelectric film substrate.

[0124] In some optional embodiments, the step of removing the second substrate 20 and the second thermal oxide layer 21 includes:

[0125] The second substrate 20 , the second thermal oxide layer 21 and the second metal adhesion layer 22 are removed.

[0126] In some optional implementations, after the step of patterning the first electrode layer 23, the buffer layer 24 and the piezoelectric film layer 25 to expose a portion of the second electrode layer 26, the following steps are further included:

[0127] A third cladding layer 30 is formed on a surface of the second electrode layer 26 facing away from the first substrate 10; the third cladding layer 30 also covers a side surface of the first electrode layer 23, a side surface of the buffer layer 24, a side surface of the piezoelectric film layer 25, and a side surface of the first electrode layer 23 facing away from the buffer layer 24;

[0128] The side of the third cladding layer 30 facing away from the second electrode layer 26 is etched to form a second electrode contact hole 312; the side of the third cladding layer facing away from the first electrode layer is etched to form a first electrode contact hole 311;

[0129] A first electrode lead 321 and a second electrode lead 322 are prepared in the first electrode contact hole 311 and the second electrode contact hole 312 , respectively.

[0130] In some optional embodiments, the material of the first substrate 10 and the material of the second substrate 20 are silicon;

[0131] The material of the first thermal oxide layer 11, the material of the first cladding layer 13 and the material of the second thermal oxide layer 21 are SiO2;

[0132] The material of the waveguide core 12 is silicon nitride;

[0133] The material of the first metal adhesion layer 44 and the second metal adhesion layer 22 is Ti;

[0134] The material of the first electrode layer 23 and the material of the second electrode layer 26 are Pt;

[0135] The material of the piezoelectric film layer 25 is PZT;

[0136] The material of the buffer layer 24 is LaNiO 3 .

[0137] like Figure 2 The present invention also provides a specific schematic flow chart of a method for preparing a piezoelectric film structure, comprising the following steps:

[0138] Step S201, providing a first substrate 10, sequentially forming a first thermal oxide layer 11, a waveguide core 12 and a first cladding layer 13 on one side surface of the first substrate 10 to form a waveguide substrate; the first cladding layer 13 covers a side surface of the waveguide core 12 facing away from the first substrate 10 and a side surface of the waveguide core 12, such as Figure 3 shown.

[0139] The material of the first substrate 10 is silicon, the material of the first thermal oxide layer 11 is SiO2, the material of the waveguide core 12 is silicon nitride, and the material of the first cladding layer 13 is SiO2.

[0140] In the specific implementation, a 2μm to 15μm SiO2 film is thermally oxidized on a 4 / 6 / 8-inch Si substrate (500μm to 725μm thick); a waveguide layer is prepared on the SiO2 film using LPCVD technology with a thickness of 25nm to 350nm, and then a pattern structure is formed using a photolithography process; and a SiO2 upper cladding layer is prepared using PECVD technology with a thickness of 1 to 6μm. The waveguide substrate is subjected to chemical mechanical polishing (CMP) to reduce the surface roughness to less than 1nm.

[0141] Step S202, providing a second substrate 20, and sequentially forming a second thermal oxide layer 21, a second metal adhesion layer 22, a first electrode layer 23, a buffer layer 24, a piezoelectric film layer 25 and a second electrode layer 26 on one side of the second substrate 20 to form a piezoelectric film substrate, such as Figure 4 shown.

[0142] The second substrate 20 is made of silicon, the second thermal oxide layer 21 is made of SiO2, the second metal adhesion layer 22 is made of Ti, the first electrode layer 23 and the second electrode layer 26 are made of Pt, the buffer layer 24 is made of LaNiO3, and the piezoelectric film layer 25 is made of PZT.

[0143] In the specific implementation, a 100nm to 300nm SiO2 film is thermally oxidized on a 4 / 6 / 8-inch Si substrate (500μm to 725μm thick); a 10nm to 35nm adhesion layer Ti, a 100nm lower electrode Pt, and a 100nm buffer layer LaNiO3 (LNO) are sequentially prepared using magnetron sputtering technology; a 0.5μm to 2μm piezoelectric layer PZT is prepared using a sol-gel method or a magnetron sputtering method; finally, a 100nm upper electrode Pt is prepared using magnetron sputtering technology to cover the entire surface of PZT.

[0144] Step S203, forming a BCB adhesive layer 41 on one side of the first cladding layer 13 of the waveguide substrate; the bonding layer is the BCB adhesive layer 41, such as Figure 5 shown.

[0145] In a specific implementation, 2 μm of benzocyclobutene (BCB) polymer is spin-coated on the surface of the substrate.

[0146] Step S204, align the waveguide substrate and the piezoelectric film substrate up and down and bond them together; the second electrode layer 26 and the BCB adhesive layer 41 are in contact with each other and bonded together; the first cladding layer 13 and the second electrode layer 26 are indirectly bonded together through the BCB adhesive layer 41, as shown in FIG. Figure 6 shown.

[0147] During the specific implementation, the PZT thin film substrate is placed with the back side facing up on the waveguide substrate and pre-bonded (W2W) after alignment. The bonding surfaces are the BCB on the waveguide substrate and the electrode Pt on the PZT thin film substrate. Then the two substrates are placed on a stage and the waveguide substrate and the PZT thin film substrate are permanently bonded together at 180°C to 200°C for 1h to 2h.

[0148] Step S205, removing the second substrate 20, the second thermal oxide layer 21 and the second metal adhesion layer 22. Figure 7 shown.

[0149] In specific implementation, chemical mechanical polishing (CMP) and TMAH etching processes are used to completely remove the second substrate 20 on the back of the piezoelectric film substrate, and dry etching is used to remove the second thermal oxide layer 21 and the second metal adhesion layer 22 of the piezoelectric film substrate.

[0150] Step S206, the first electrode layer 23, the buffer layer 24 and the piezoelectric film layer 25 are patterned to expose a portion of the second electrode layer 26, such as Figure 8 shown.

[0151] In specific implementation, photoresist is spin-coated on the first electrode layer 23, and after development, the first electrode layer 23 and the buffer layer 24 are etched into the required graphic structure by dry etching, and then the piezoelectric film layer 25 is patterned by wet etching. The structural parameters are as follows: length 5mm~15mm, width 10μm~30μm, device spacing 40μm~50μm.

[0152] Step S207, forming a third cladding layer 30 on the surface of the second electrode layer 26 facing away from the first substrate 10; the third cladding layer 30 also covers the side surface of the first electrode layer 23, the side surface of the buffer layer 24, the side surface of the piezoelectric film layer 25, and the side surface of the first electrode layer 23 facing away from the buffer layer 24, such as Fig. 9 shown.

[0153] In a specific implementation, the third cladding layer 30 is prepared on the substrate by using chemical vapor deposition technology, and the material of the third cladding layer 30 is SiO2.

[0154] Step S208, etching the side of the third cladding layer 30 facing away from the second electrode layer 26 to form a second electrode contact hole 312; etching the side of the third cladding layer facing away from the first electrode layer to form a first electrode contact hole 311, such as Fig. 9 shown.

[0155] In a specific implementation, dry etching is adopted to form the electrode contact holes, and the electrode contact holes include a first electrode contact hole 311 and a second electrode contact hole 312 .

[0156] Step S209, preparing the first electrode lead 321 and the second electrode lead 322 in the first electrode contact hole 311 and the second electrode contact hole 312, respectively. Fig.10 shown.

[0157] In a specific implementation, the first electrode lead 321 and the second electrode lead 322 are prepared by metal stripping technology, and the first electrode lead 321 and the second electrode lead 322 are CrAu leads.

[0158] like Fig.11 As shown, the present invention also provides a specific flow chart of another method for preparing a piezoelectric film structure, which includes the following steps:

[0159] Step S301, providing a first substrate 10, sequentially forming a first thermal oxide layer 11, a waveguide core 12 and a first cladding layer 13 on one side surface of the first substrate 10 to form a waveguide substrate; the first cladding layer 13 covers a side surface of the waveguide core 12 facing away from the first substrate 10 and a side surface of the waveguide core 12, such as Figure 3 shown.

[0160] The material of the first substrate 10 is silicon, the material of the first thermal oxide layer 11 is SiO2, the material of the waveguide core 12 is silicon nitride, and the material of the first cladding layer 13 is SiO2.

[0161] Step S302, providing a second substrate 20, and sequentially forming a second thermal oxide layer 21, a second metal adhesion layer 22, a first electrode layer 23, a buffer layer 24, a piezoelectric film layer 25 and a second electrode layer 26 on one side of the second substrate 20 to form a piezoelectric film substrate, such as Figure 4 shown.

[0162] The second substrate 20 is made of silicon, the second thermal oxide layer 21 is made of SiO2, the second metal adhesion layer 22 is made of Ti, the first electrode layer 23 and the second electrode layer 26 are made of Pt, the buffer layer 24 is made of LaNiO3, and the piezoelectric film layer 25 is made of PZT.

[0163] Step S303, forming a second cladding layer 42 on one side of the second electrode layer 26 of the piezoelectric film substrate; the bonding layer is the second cladding layer 42, such as Fig.12 shown.

[0164] In a specific implementation, chemical vapor deposition technology is used to form the second cladding layer 42 on one side of the second electrode layer 26 of the piezoelectric film substrate. The material of the second cladding layer 42 is SiO2, and the thickness is 1 μm to 1.5 μm.

[0165] Step S304: performing a surface grinding process and an oxygen plasma activation process on the waveguide substrate and the piezoelectric film substrate.

[0166] In the specific implementation, the two substrates were first subjected to CMP treatment to make the surface roughness of the two substrates less than 1nm, and then the two substrates were cleaned for ten minutes each using RCA1 cleaning solution (NH4OH:H2O2:H2O=1:1:5~1:2:7) and RCA2 cleaning solution (HCl:H2O2:H2O=1:1:6~1:2:8), and rinsed with deionized water, and then spin dried. Secondly, the two substrates were activated by oxygen plasma, and the activation parameters were as follows: oxygen flow rate 100sccm, pressure 90mTorr, DC bias 300V, RF power 100W, and exposure time 30s.

[0167] Step S305, align the waveguide substrate and the piezoelectric film substrate up and down and bond them together; the first cladding layer and the second cladding layer are in contact with each other and connected together by thermal compression bonding, such as Fig.13 shown.

[0168] In the specific implementation, the PZT thin film substrate is placed on the waveguide substrate with the back side facing up, and pre-bonded (W2W) is performed after alignment. The bonding surface is silicon oxide and silicon oxide layer. Then the two substrates are placed on the stage, and hot pressing bonding is performed at 200℃~250℃, applying 2.5Mpa~3Mpa pressure, and the bonding time is 20min~30min. After the bonding is completed, the sample is annealed at 200℃ for 1h~2h to remove residual water molecules.

[0169] Step S306 , removing the second substrate 20 , the second thermal oxide layer 21 and the second metal adhesion layer 22 .

[0170] Step S307 , patterning the first electrode layer 23 , the buffer layer 24 and the piezoelectric film layer 25 to expose a portion of the second electrode layer 26 .

[0171] Step S308, forming a third cladding layer 30 on the surface of the second electrode layer 26 facing away from the first substrate 10; the third cladding layer 30 also covers the side surface of the first electrode layer 23, the side surface of the buffer layer 24, the side surface of the piezoelectric film layer 25 and the side surface of the first electrode layer 23 facing away from the buffer layer 24.

[0172] Step S309 , etching the side of the third cladding layer 30 facing away from the second electrode layer 26 to form a second electrode contact hole 312 ; etching the side of the third cladding layer 30 facing away from the first electrode layer 23 to form a first electrode contact hole 311 .

[0173] Step S310, preparing the first electrode lead 321 and the second electrode lead 322 in the first electrode contact hole 311 and the second electrode contact hole 312, respectively. Fig.14 shown.

[0174] like Fig.15As shown, the present invention also provides a specific flow chart of another method for preparing a piezoelectric film structure, which includes the following steps:

[0175] Step S401, providing a first substrate 10, sequentially forming a first thermal oxide layer 11, a waveguide core 12 and a first cladding layer 13 on one side surface of the first substrate 10 to form a waveguide substrate; the first cladding layer 13 covers a side surface of the waveguide core 12 facing away from the first substrate 10 and a side surface of the waveguide core 12, such as Figure 3 shown.

[0176] The material of the first substrate 10 is silicon, the material of the first thermal oxide layer 11 is SiO2, the material of the waveguide core 12 is silicon nitride, and the material of the first cladding layer 13 is SiO2.

[0177] Step S402, providing a second substrate 20, and sequentially forming a second thermal oxide layer 21, a second metal adhesion layer 22, a first electrode layer 23, a buffer layer 24, a piezoelectric film layer 25 and a second electrode layer 26 on one side of the second substrate 20 to form a piezoelectric film substrate. Figure 4 shown.

[0178] The second substrate 20 is made of silicon, the second thermal oxide layer 21 is made of SiO2, the second metal adhesion layer 22 is made of Ti, the first electrode layer 23 and the second electrode layer 26 are made of Pt, the buffer layer 24 is made of LaNiO3, and the piezoelectric film layer 25 is made of PZT.

[0179] Step S403, a first metal adhesion layer 44 and a metal bonding layer 43 are sequentially formed on the surface of one side of the first cladding layer 13 of the waveguide substrate; the bonding layer is the metal bonding layer 43, such as Fig.16 shown.

[0180] The material of the first metal adhesion layer 44 is Ti, and the material of the metal bonding layer 43 is Pt.

[0181] In specific implementation, a first metal adhesion layer Ti with a thickness of 10nm-35nm is prepared on one side surface of the first cladding layer 13 of the waveguide substrate by magnetron sputtering technology, and then a metal bonding layer Pt with a thickness of 100nm-500nm is prepared as a bonding layer.

[0182] Step S404: performing a surface grinding process and a plasma activation process on the waveguide substrate and the piezoelectric film substrate.

[0183] In the specific implementation, the waveguide substrate and the PZT thin film substrate were CMP treated to make the surface roughness less than 1nm, and the thickness of the Pt film on the two substrates reached 100nm to 300nm. Then, the two substrates were cleaned for 10min each using RCA1 and RCA2 cleaning solutions, and then Ar plasma activation was performed after spin drying. The activation parameters were as follows: 180s at 200W power.

[0184] Step S405, align the waveguide substrate and the piezoelectric film substrate up and down and bond them together; the second electrode layer 26 and the metal bonding layer 43 are in contact with each other and connected together through metal bonding, such as Fig.17 shown.

[0185] In the specific implementation, the two substrates are aligned and pre-bonded (W2W), with the bonding surface being the metal layer Pt. The two substrates are then placed on a stage and permanently bonded together at 300°C to 350°C with a pressure of 2.5Mpa to 3MPa applied for a bonding time of 20min to 30min.

[0186] Step S406 , removing the second substrate 20 , the second thermal oxide layer 21 and the second metal adhesion layer 22 .

[0187] Step S407 , patterning the first electrode layer 23 , the buffer layer 24 and the piezoelectric film layer 25 to expose a portion of the second electrode layer 26 .

[0188] Step S408, forming a third cladding layer 30 on the surface of the second electrode layer 26 facing away from the first substrate 10; the third cladding layer 30 also covers the side surface of the first electrode layer 23, the side surface of the buffer layer 24, the side surface of the piezoelectric film layer 25 and the side surface of the first electrode layer 23 facing away from the buffer layer 24.

[0189] Step S409 , etching the side of the third cladding layer 30 facing away from the second electrode layer 26 to form a second electrode contact hole 312 ; etching the side of the third cladding layer 30 facing away from the first electrode layer 23 to form a first electrode contact hole 311 .

[0190] Step S410, preparing the first electrode lead 321 and the second electrode lead 322 in the first electrode contact hole 311 and the second electrode contact hole 312, respectively. Fig.18 shown.

[0191] In the description of this specification, the description with reference to the terms "this embodiment", "one embodiment", "some embodiments", "example", "specific example", or "some examples" 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 a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples, unless otherwise clearly and specifically defined. In addition, the terms "first" and "second" are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" can explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0192] In the above description, the technical details of the patterning and etching of each layer are not described in detail. However, those skilled in the art should understand that various technical means can be used to form layers, regions, etc. of desired shapes. In addition, in order to form the same structure, those skilled in the art can also design methods that are not completely the same as the methods described above. In addition, although the various embodiments are described above separately, this does not mean that the measures in the various embodiments cannot be used in combination to advantage.

[0193] The above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described above, and that various obvious changes, readjustments, combinations and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention is described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may also include more other equivalent embodiments without departing from the concept of the present invention. The scope of protection of the present invention is determined by the scope of the attached claims.

Claims

1. A method for preparing a piezoelectric thin film structure, characterized in that: include: Providing a first substrate, and sequentially forming a first thermal oxide layer, a waveguide core, and a first cladding on a surface of one side of the first substrate to form a waveguide substrate; The first cladding layer covers a surface of the waveguide core facing away from the first substrate and a side surface of the waveguide core; Providing a second substrate, and sequentially forming a second thermal oxide layer, a first electrode layer, a buffer layer, a piezoelectric film layer, and a second electrode layer on a surface of one side of the second substrate to form a piezoelectric film substrate; Forming a bonding layer: forming a bonding layer on a surface on one side of the first cladding layer of the waveguide substrate or on a surface on one side of the second electrode layer of the piezoelectric film substrate; The waveguide substrate and the piezoelectric film substrate are aligned and bonded together; the first cladding layer and the bonding layer are correspondingly contacted and bonded together, or the second electrode layer and the bonding layer are correspondingly contacted and bonded together; removing the second substrate and the second thermal oxide layer; The first electrode layer, the buffer layer and the piezoelectric film layer are patterned to expose a portion of the second electrode layer.

2. The method for preparing a piezoelectric thin film structure according to claim 1, characterized in that: The bonding layer is a BCB adhesive layer; The step of forming the bonding layer includes: forming the BCB adhesive layer on the surface of one side of the first cladding layer of the waveguide substrate; In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the second electrode layer and the BCB adhesive layer are in corresponding contact and bonded together; the first cladding layer and the second electrode layer are indirectly bonded together through the BCB adhesive layer.

3. The method for preparing a piezoelectric thin film structure according to claim 2, characterized in that: In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, The bonding temperature is 180℃~200℃; The bonding time is 1h to 2h.

4. The method for preparing a piezoelectric thin film structure according to claim 1, characterized in that: The bonding layer is a metal bonding layer; a first metal adhesion layer is further provided between the metal bonding layer and the first cladding layer; The step of forming the bonding layer includes: sequentially forming the first metal adhesion layer and the metal bonding layer on the surface of one side of the first cladding layer of the waveguide substrate; Before the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the method further includes: Performing a surface grinding process and an Ar plasma activation process on the waveguide substrate and the piezoelectric film substrate; In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the second electrode layer and the metal bonding layer are in corresponding contact and connected together through metal bonding.

5. The method for preparing a piezoelectric thin film structure according to claim 4, characterized in that: In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, The bonding temperature is 300℃~350℃; The bonding pressure is 2.5Mpa~3MPa; The bonding time is 20min to 30min.

6. The method for preparing a piezoelectric thin film structure according to claim 1, characterized in that: The bonding layer is a second cladding layer; The step of forming the bonding layer includes: forming the second cladding layer on the surface of the second electrode layer of the piezoelectric film substrate; Before the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the method further includes: Performing a surface grinding process and an oxygen plasma activation process on the waveguide substrate and the piezoelectric film substrate; In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, the first cladding layer and the second cladding layer are in corresponding contact and connected together by thermocompression bonding.

7. The method for preparing a piezoelectric thin film structure according to claim 6, characterized in that: The material of the second cladding layer is SiO2; In the step of aligning and bonding the waveguide substrate and the piezoelectric film substrate together, The bonding temperature is 200℃~250℃; The bonding pressure is 2.5Mpa~3MPa; The bonding time is 20min to 30min.

8. The method for preparing a piezoelectric thin film structure according to claim 1, characterized in that: The step of sequentially forming a second thermal oxide layer, a first electrode layer, a buffer layer, a piezoelectric film layer, and a second electrode layer on a surface of one side of the second substrate to form a piezoelectric film substrate includes: A second thermal oxide layer, a second metal adhesion layer, a first electrode layer, a buffer layer, a piezoelectric film layer and a second electrode layer are sequentially formed on one side surface of the second substrate.

9. The method for preparing a piezoelectric film structure according to claim 8, characterized in that: The step of removing the second substrate and the second thermal oxide layer includes: The second substrate, the second thermal oxide layer and the second metal adhesion layer are removed.

10. The method for preparing a piezoelectric thin film structure according to claim 1, characterized in that: After the step of patterning the first electrode layer, the buffer layer and the piezoelectric film layer to expose a portion of the second electrode layer, the step further includes: A third cladding layer is formed on a surface of the second electrode facing away from the first substrate; the third cladding layer also covers a side surface of the first electrode layer, a side surface of the buffer layer, a side surface of the piezoelectric film layer, and a side surface of the first electrode layer facing away from the buffer layer; Etching a side of the third cladding layer facing away from the second electrode layer to form a second electrode contact hole; etching a side of the third cladding layer facing away from the first electrode layer to form a first electrode contact hole; A first electrode lead and a second electrode lead are prepared in the first electrode contact hole and the second electrode contact hole, respectively.

11. The method for preparing a piezoelectric thin film structure according to claim 1, characterized in that: The material of the first substrate and the material of the second substrate are silicon; The material of the first thermal oxide layer, the material of the first cladding layer and the material of the second thermal oxide layer are SiO2; The material of the waveguide core is silicon nitride; The material of the first electrode layer and the material of the second electrode layer are Pt; The material of the piezoelectric film layer is PZT; The material of the buffer layer is LaNiO3.

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