Bulk acoustic wave resonator integrated with double-layer temperature compensation structure and preparation method thereof

Abstract

The invention relates to the technical field of bulk acoustic wave resonators, and particularly provides a bulk acoustic wave resonator integrated with a double-layer temperature compensation structure and a preparation method thereof.The resonator comprises a first substrate, a bonding layer, a bottom electrode, a piezoelectric layer, a second temperature compensation layer and a top electrode which are sequentially connected from bottom to top, and the first substrate is provided with an air cavity; a first temperature compensation layer is wrapped in the bottom electrode, the boundary of the projection of the first temperature compensation layer in the overlook direction is located in the boundary of the projection of the air cavity in the overlook direction, and the temperature coefficients of the bottom electrode, the piezoelectric layer and the top electrode are all opposite to the temperature coefficients of the first temperature compensation layer and the second temperature compensation layer; the resonator can effectively avoid the conditions that the piezoelectric layer needs to be directly formed on the temperature compensation layer, and lattice mismatch exists between the temperature compensation layer and the piezoelectric layer, so that the crystal quality of the piezoelectric layer is poor, and leakage current is increased.

Description

A bulk acoustic resonator with integrated double-layer temperature-compensated structure and its fabrication method Technical Field

[0001] This application relates to the field of bulk acoustic wave resonator technology, and more specifically, to a bulk acoustic wave resonator with an integrated double-layer temperature-compensated structure and its fabrication method. Background Technology

[0002] With the rapid iteration of next-generation communication systems such as 5G / 6G and the Internet of Things, and the continuous evolution of communication technologies towards higher frequencies, higher speeds, and miniaturization, radio frequency (RF) front-ends are facing increasingly stringent requirements regarding device size, operating frequency, and power consumption. Bulk acoustic wave (BAW) devices, such as BAW filters, have become key components for achieving high-performance RF front-ends due to their small size, low insertion loss, high frequency, and ability to operate in frequencies above millimeter waves, and they occupy an important position in fields such as mobile communications.

[0003] However, traditional bulk acoustic wave (BAW) devices generally suffer from a high temperature coefficient of frequency, meaning that the resonant frequency of BAW devices drifts significantly with changes in ambient temperature. This frequency drift causes a significant deterioration in the passband characteristics of filters, severely limiting their reliability in wide-temperature environments or high-precision systems. To improve the temperature stability of devices, the industry often adopts a structural design that embeds a temperature compensation layer between the bottom electrode and the piezoelectric layer. However, because the formation of the piezoelectric thin film is later than the formation of the temperature compensation layer, and due to the lattice mismatch between the temperature compensation layer and the piezoelectric thin film materials, the piezoelectric thin film material lacks lattice guidance during formation. Therefore, traditional BAW devices suffer from poor crystal quality and increased leakage current in the piezoelectric thin film formed on the temperature compensation layer, thus affecting the electrical performance of the BAW device. Furthermore, existing single-layer temperature compensation structures offer limited improvement in temperature compensation effectiveness and are insufficient to meet the requirements for higher precision temperature stability.

[0004] There is currently no effective technical solution to the above problems. Summary of the Invention

[0005] The purpose of this application is to provide a bulk acoustic resonator with an integrated double-layer temperature-compensated structure and its fabrication method, which can effectively avoid the situation where the piezoelectric layer has poor crystal quality and increased leakage current due to the need to directly form a piezoelectric layer on the temperature-compensated layer and the lattice mismatch between the temperature-compensated layer and the piezoelectric layer.

[0006] In a first aspect, this application provides a bulk acoustic resonator with an integrated dual-layer temperature-compensated structure, comprising: a first substrate, a bonding layer, a bottom electrode, a piezoelectric layer, a second temperature-compensated layer, and a top electrode connected sequentially from bottom to top. An air cavity is provided on the first substrate, and the first temperature-compensated layer is wrapped inside the bottom electrode. The boundary of the projection of the first temperature-compensated layer in the top view direction is located within the boundary of the projection of the air cavity in the top view direction. The temperature coefficients of the bottom electrode, the piezoelectric layer, and the top electrode are all opposite in sign to the temperature coefficients of the first temperature-compensated layer and the second temperature-compensated layer.

[0007] This application provides a bulk acoustic wave resonator with an integrated dual-layer temperature-compensated structure. By wrapping the first temperature-compensated layer inside the bottom electrode and introducing a second temperature-compensated layer, a dual temperature compensation mechanism is achieved to effectively improve the temperature compensation effect and meet the requirements for higher precision temperature stability. This effectively improves the temperature stability of the bulk acoustic wave resonator. Since the first temperature-compensated layer of this application is wrapped by the bottom electrode, that is, the piezoelectric layer of this application is directly grown on the bottom electrode, this application can effectively avoid the situation where the piezoelectric layer needs to be directly formed on the temperature-compensated layer, and there is a lattice mismatch between the temperature-compensated layer and the piezoelectric layer, resulting in poor crystal quality of the piezoelectric layer and increased leakage current. This effectively improves the electrical performance of the bulk acoustic wave resonator.

[0008] Optionally, the bottom electrode includes a support portion and a wrapping portion, with the support portion located above the wrapping portion. The bottom surface of the support portion is connected to the top surface of the wrapping portion, and the support portion and the wrapping portion cooperate to wrap the first thermal compensation layer.

[0009] Optionally, the thickness of the support portion is greater than the thickness of the wrapping portion.

[0010] Optionally, the top surface of the second temperature compensation layer has a region exposed to the top electrode, and the bulk acoustic resonator with integrated double-layer temperature compensation structure also includes a passivation protection layer, which is connected to the regions of the top surface of the top electrode and the top surface of the second temperature compensation layer located outside the top electrode.

[0011] Because the passivation protective layer of this technical solution can effectively isolate the external environment from the erosion of the exposed areas of the top electrode and the second temperature compensation layer that are not covered by the top electrode, thus preventing performance degradation caused by oxidation, contamination or mechanical damage, this technical solution avoids the situation where the reliability of the bulk acoustic wave resonator with integrated double-layer temperature compensation structure decreases due to lack of protection during operation by setting the passivation protective layer. This effectively improves the long-term reliability and electrical performance stability of the bulk acoustic wave resonator, thereby effectively extending the service life of the bulk acoustic wave resonator and ensuring the continuous effectiveness of the temperature compensation function of the bulk acoustic wave resonator.

[0012] Optionally, the passivation protective layer is made of any one or more of silicon dioxide, silicon nitride, aluminum nitride, and aluminum oxide.

[0013] Optionally, the depth of the air cavity is 0.5-20 μm.

[0014] Optionally, the top surface of the bottom electrode has a region exposed to the piezoelectric layer, and the top surface of the top electrode has a region exposed to the passivation protection layer. The bulk acoustic resonator with integrated dual-layer temperature compensation structure also includes a first pad and a second pad. The first pad is connected to the region of the top surface of the bottom electrode outside the piezoelectric layer, and the second pad is connected to the region of the top surface of the top electrode outside the passivation protection layer.

[0015] Optionally, the piezoelectric layer is made of any one or more of monocrystalline aluminum nitride, polycrystalline aluminum nitride, scandium aluminum nitride, zinc oxide, lead zirconate titanate, lithium niobate, lithium tantalate, and barium strontium titanate; the bottom electrode and the top electrode are made of any one or more of molybdenum, nickel, gold, aluminum, platinum, titanium, tungsten, and ruthenium; and the first temperature compensation layer and the second temperature compensation layer are made of any one or more of phosphosilicate glass, borosilicate glass, and borophosphosilicate glass.

[0016] Secondly, this application also provides a method for fabricating a bulk acoustic wave resonator with an integrated dual-layer temperature-compensated structure, comprising the following steps: S1, forming a groove on a first substrate; S2, forming a first bonding structure on the top surface of the first substrate outside the groove; S3, sequentially forming a piezoelectric layer, a support portion, a first temperature-compensated layer, and an encapsulation portion on a second substrate; the support portion and the encapsulation portion cooperate to encapsulate the first temperature-compensated layer, and the support portion and the encapsulation portion form a bottom electrode; S4, forming a second bonding structure matching the first bonding structure on the top surface of the support portion to obtain a preliminary structure; S5, flipping the preliminary structure and bonding the preliminary structure to the first substrate through the first bonding structure and the second bonding structure; the first bonding structure and the second bonding structure form a bonding layer, the groove and the bottom electrode enclose an air cavity, and the boundary of the projection of the first temperature-compensated layer in the top view direction is located within the boundary of the projection of the air cavity in the top view direction; S6, removing the second substrate; S7, sequentially forming a second temperature-compensated layer and a top electrode on the piezoelectric layer; the temperature coefficients of the bottom electrode, the piezoelectric layer, and the top electrode are all opposite in sign to the temperature coefficients of the first temperature-compensated layer and the second temperature-compensated layer.

[0017] This application provides a method for fabricating a bulk acoustic wave resonator with an integrated dual-layer temperature-compensated structure. By wrapping a first temperature-compensated layer inside a bottom electrode and introducing a second temperature-compensated layer, a dual temperature compensation mechanism is achieved to effectively improve the temperature compensation effect and meet the requirements for higher precision temperature stability. This effectively improves the temperature stability of the bulk acoustic wave resonator. Since the first temperature-compensated layer of this application is wrapped by the bottom electrode, that is, the piezoelectric layer of this application is directly grown on the bottom electrode, this application can effectively avoid the situation where the piezoelectric layer needs to be directly formed on the temperature-compensated layer, and there is a lattice mismatch between the temperature-compensated layer and the piezoelectric layer, resulting in poor crystal quality of the piezoelectric layer and increased leakage current. This effectively improves the electrical performance of the bulk acoustic wave resonator.

[0018] Optionally, step S7 includes: S71, performing a film repair process on the top surface of the piezoelectric layer based on ion beam film repair technology; S72, sequentially forming a second temperature compensation layer and a top electrode on the piezoelectric layer.

[0019] This technical solution pre-treats the top surface of the piezoelectric layer using ion beam repair technology before forming the second temperature compensation layer and the top electrode, aiming to optimize the surface state of the piezoelectric layer. This repair process effectively removes surface roughness, impurities, and potential lattice defects from the top surface of the piezoelectric layer, providing a flat, clean interface with good crystal quality for subsequent thin film deposition. Because of this meticulous repair treatment of the piezoelectric layer's top surface, the second temperature compensation layer can form on the piezoelectric layer with superior adhesion and lower interface defects. This high-quality interface helps reduce lattice mismatch during thin film growth, ensuring that the second temperature compensation layer has uniform thickness and stable physicochemical properties. Furthermore, the formation of the top electrode also benefits from the flat and low-defect lower interface, ensuring good contact between the electrode and the temperature compensation layer and reducing contact resistance and leakage current.

[0020] As can be seen from the above, the bulk acoustic wave resonator with integrated double-layer temperature compensation structure and its fabrication method provided in this application realize a dual temperature compensation mechanism by wrapping the first temperature compensation layer inside the bottom electrode and introducing the second temperature compensation layer. This effectively improves the temperature compensation effect and meets the requirements for higher precision temperature stability, thereby effectively improving the temperature stability of the bulk acoustic wave resonator. Since the first temperature compensation layer of this application is wrapped by the bottom electrode, that is, the piezoelectric layer of this application is directly grown on the bottom electrode, this application can effectively avoid the situation where the piezoelectric layer has poor crystal quality and increased leakage current due to the lattice mismatch between the temperature compensation layer and the piezoelectric layer, which is caused by the need to directly form the piezoelectric layer on the temperature compensation layer. This effectively improves the electrical performance of the bulk acoustic wave resonator. Attached Figure Description

[0021] Figure 1 is a schematic diagram of a bulk acoustic resonator with an integrated double-layer temperature compensation structure provided in an embodiment of this application.

[0022] Figure 2 is a flowchart of a method for fabricating a bulk acoustic resonator with an integrated double-layer temperature-compensated structure provided in an embodiment of this application.

[0023] Figure 3 is a schematic diagram of a method for fabricating a bulk acoustic resonator with an integrated double-layer temperature-compensated structure provided in an embodiment of this application.

[0024] Reference numerals: 1. First substrate; 2. Bonding layer; 21. First bonding structure; 22. Second bonding structure; 3. Bottom electrode; 31. Support portion; 32. Encapsulation portion; 4. Piezoelectric layer; 5. Second temperature compensation layer; 6. Top electrode; 7. Air cavity; 8. First temperature compensation layer; 9. Passivation protection layer; 10. First pad; 11. Second pad; 12. Second substrate. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0026] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0027] In a first aspect, as shown in Figure 1, this application provides a bulk acoustic resonator with an integrated dual-layer temperature-compensated structure, comprising: a first substrate 1, a bonding layer 2, a bottom electrode 3, a piezoelectric layer 4, a second temperature-compensated layer 5, and a top electrode 6 connected sequentially from bottom to top. An air cavity 7 is provided on the first substrate 1, and the bottom electrode 3 is encapsulated within the first temperature-compensated layer 8. The boundary of the projection of the first temperature-compensated layer 8 in the top view direction is located within the boundary of the projection of the air cavity 7 in the top view direction. The temperature coefficients of the bottom electrode 3, the piezoelectric layer 4, and the top electrode 6 are all opposite in sign to the temperature coefficients of the first temperature-compensated layer 8 and the second temperature-compensated layer 5.

[0028] For ease of understanding, some key terms in this embodiment are explained below. The first substrate 1 in this embodiment is the base of the bulk acoustic wave resonator, serving to provide mechanical support. The material of the first substrate 11 in this embodiment is preferably one or more of silicon, sapphire, spinel, lithium tantalate (LT), lithium niobate (LN), LiGaO2, zinc oxide, and zirconium oxide ceramic. An air cavity 7 is provided on the first substrate 1, which effectively confines the acoustic wave energy within the resonant region to improve the quality factor and energy utilization efficiency of the resonator. The bonding layer 2 in this embodiment is an intermediate layer used to firmly connect different layers of materials (i.e., the first substrate 1 and the bottom electrode 3) together to ensure the mechanical stability and electrical connectivity of the device. The bonding layer 2 can be implemented using various bonding techniques, such as eutectic bonding and oxide bonding. In this embodiment, the bottom electrode 3 and the top electrode 6 are preferably made of metal materials with high electrical conductivity, high acoustic impedance and high Young's modulus (e.g., any one or more of gold, molybdenum, ruthenium and platinum). The material of the bottom electrode 3 in this embodiment is preferably the same as the material of the top electrode 6 in this embodiment. Specifically, when the top electrode 6 and the bottom electrode 3 are connected to an external signal source (equivalent to applying a voltage signal or an electrical signal to the top electrode 6 and the bottom electrode 3), an electric field is formed at both ends of the piezoelectric layer 4 to excite the bulk acoustic wave (equivalent to exciting the piezoelectric layer 4 to generate a longitudinal wave), thereby realizing the mutual conversion of electrical energy and mechanical energy and the frequency selection of the bulk acoustic resonator. In this embodiment, the bottom electrode 3 is encased in a first temperature compensation layer 8, and a second temperature compensation layer 5 is provided between the piezoelectric layer 4 and the top electrode 6. Since the temperature coefficients of the first temperature compensation layer 8 and the second temperature compensation layer 5 are opposite in sign to the temperature coefficients of the bottom electrode 3, the piezoelectric layer 4, and the top electrode 6, when the ambient temperature changes, if the resonant frequency drift direction of the bottom electrode 3, the piezoelectric layer 4, and the top electrode 6 is negative (i.e., the frequency decreases as the temperature increases), then the first temperature compensation layer 8 and the second temperature compensation layer 5 will provide a positive frequency drift (i.e., the frequency increases as the temperature increases), and vice versa. Through this characteristic of opposite temperature coefficients, the frequency drift caused by temperature changes in different material layers can cancel or compensate for each other, so that the overall resonant frequency of the bulk acoustic wave resonator remains stable over a wide temperature range. Therefore, this embodiment can effectively suppress the resonant frequency drift generated by the bottom electrode 3, the piezoelectric layer 4, and the top electrode 6 by wrapping the first temperature compensation layer 8 inside the bottom electrode 3 and setting the second temperature compensation layer 5 between the piezoelectric layer 4 and the top electrode 6, thereby effectively improving the temperature stability of the bulk acoustic wave resonator. This embodiment is equivalent to using a double-layer temperature compensation structure to compensate for the frequency temperature drift of the bulk acoustic wave resonator. Therefore, this embodiment can suppress the performance degradation of the bulk acoustic wave resonator caused by the frequency temperature drift of the bulk acoustic wave resonator as much as possible.

[0029] The working principle of this embodiment is as follows: Since the first temperature compensation layer 8 is wrapped by the bottom electrode 3, the first temperature compensation layer 8 does not directly contact the piezoelectric layer 4 when the piezoelectric layer 4 is formed. The second temperature compensation layer 5 is located above the piezoelectric layer 4, meaning that the formation time of the second temperature compensation layer 5 is later than the formation time of the piezoelectric layer 4. The second temperature compensation layer 5 will not affect the crystal quality of the piezoelectric layer 4. Therefore, this embodiment can effectively avoid the situation where the piezoelectric layer 4 is formed directly on the temperature compensation layer, and there is a lattice mismatch between the temperature compensation layer and the piezoelectric layer 4, resulting in poor crystal quality and increased leakage current of the piezoelectric layer 4. In other words, this application can effectively improve the crystal quality of the piezoelectric layer 4 and reduce the leakage current of the piezoelectric layer 4 while effectively compensating for the frequency drift of the bulk acoustic wave resonator caused by temperature changes, thereby effectively improving the electrical performance of the bulk acoustic wave resonator. Since this embodiment uses a double-layer temperature compensation structure to compensate for the temperature of the bulk acoustic wave resonator, the embodiment can effectively improve the temperature compensation effect to meet the requirements of higher precision temperature stability. It should be understood that, since the second temperature compensation layer 5 is formed later than the piezoelectric layer 4 in this embodiment, and the material of the second temperature compensation layer 5 is usually grown in an amorphous form, the film quality of the second temperature compensation layer 5 does not depend on the lattice structure of the lower layer (i.e., the piezoelectric layer 4). Therefore, the second temperature compensation layer 5 formed on the piezoelectric layer 4 will not experience a decrease in film quality or a limitation in temperature compensation effect due to the influence of the lower layer lattice structure.

[0030] Therefore, the bulk acoustic wave resonator with an integrated dual-layer temperature-compensated structure provided in this application achieves a dual temperature compensation mechanism by wrapping the first temperature-compensated layer 8 inside the bottom electrode 3 and introducing the second temperature-compensated layer 5. This effectively improves the temperature compensation effect and meets the requirements for higher precision temperature stability, thereby effectively improving the temperature stability of the bulk acoustic wave resonator. Since the first temperature-compensated layer 8 is wrapped by the bottom electrode 3, that is, the piezoelectric layer 4 is directly grown on the bottom electrode 3, this application can effectively avoid the situation where the piezoelectric layer 4 is directly formed on the temperature-compensated layer, and there is a lattice mismatch between the temperature-compensated layer and the piezoelectric layer 4, resulting in poor crystal quality of the piezoelectric layer 4 and increased leakage current. This effectively improves the electrical performance of the bulk acoustic wave resonator. In addition, since the boundary of the projection of the first temperature-compensated layer 8 in the top view direction is located within the boundary of the projection of the air cavity 7 in the top view direction, this application is equivalent to making the first temperature-compensated layer 8 effectively act on the resonant region of the bulk acoustic wave resonator to optimize the sound wave propagation path and temperature compensation effect of the bulk acoustic wave resonator.

[0031] In some preferred embodiments, the bottom electrode 3 includes a support portion 31 and a wrapping portion 32. The support portion 31 is located above the wrapping portion 32, and the bottom surface of the support portion 31 is connected to the top surface of the wrapping portion 32. The support portion 31 and the wrapping portion 32 cooperate to wrap the first temperature compensation layer 8. In this embodiment, the bottom electrode 3 includes a support portion 31 and a wrapping portion 32. The support portion 31 is the main structure of the bottom electrode 3, providing mechanical support and electrical connection, while the wrapping portion 32 serves as an auxiliary structure, cooperating with the support portion 31 to wrap the first temperature compensation layer 8. That is, this embodiment is equivalent to using the support portion 31 and the wrapping portion 32 to encapsulate the first temperature compensation layer 8. This embodiment refines the structure of the bottom electrode 3 into a support portion 31 and a wrapping portion 32. The tight connection and synergistic effect of the support portion 31 and the wrapping portion 32 achieve a firm wrapping of the first temperature compensation layer 8. In other words, this embodiment can stably fix the first temperature compensation layer 8 within the bottom electrode 3. Therefore, this embodiment can effectively prevent the first temperature compensation layer 8 from being accidentally displaced during the operation of the bulk acoustic wave resonator. That is, the first temperature compensation layer 8 in this embodiment always remains in a preset position to ensure that the temperature compensation function of the first temperature compensation layer 8 can be continuously and effectively performed, thereby maintaining the frequency stability of the bulk acoustic wave resonator over a wide temperature range, and thus effectively improving the reliability of the bulk acoustic wave resonator in practical applications.

[0032] In some preferred embodiments, the thickness of the support portion 31 is greater than the thickness of the wrapping portion 32. In this embodiment, the support portion 31 needs to bear the weight and stress of its upper structure (such as the piezoelectric layer 4, the second thermal compensation layer 5, and the top electrode 6), and the thickness design of the support portion 31 is crucial to its mechanical strength and stability. In this embodiment, the wrapping portion 32 cooperates with the support portion 31 to wrap the first thermal compensation layer 8. The thickness of the wrapping portion 32 affects its wrapping effect on the first thermal compensation layer 8, the thermal conductivity, and the local stress distribution. This embodiment effectively improves the mechanical strength of the support portion 31 by designing it to have a larger thickness, so that the support portion 31 can more stably support the upper structure and effectively reduce the deformation or stress concentration that may occur in the bottom electrode 3 during temperature changes or manufacturing process. This embodiment reduces the overall structural weight and local stress of the bottom electrode 3 by designing the wrapping portion 32 to have a smaller thickness, while firmly wrapping the first temperature compensation layer 8, so that the bottom electrode 3 has a more uniform stress distribution. Therefore, this embodiment is equivalent to effectively improving the structural reliability and temperature stability of the bulk acoustic resonator by optimizing the thickness of the support portion 31 and the wrapping portion 32.

[0033] In some preferred embodiments, the top surface of the second temperature compensation layer 5 has a region exposed outside the top electrode 6. The bulk acoustic wave resonator with integrated double-layer temperature compensation structure also includes a passivation protection layer 9, which is connected to the regions of the top surface of the top electrode 6 and the top surface of the second temperature compensation layer 5 located outside the top electrode 6. In this embodiment, the passivation protection layer 9 can be a dielectric thin film. The main function of the passivation protection layer 9 is to provide physical and chemical protection for the device. The passivation protection layer 9 is typically made of a material with good insulation, chemical stability, and mechanical strength. That is, the passivation protection layer 9 in this embodiment can effectively block moisture, oxygen, ionic contaminants, and mechanical damage from the external environment. Since the passivation protection layer 9 in this embodiment is connected to the regions of the top surface of the top electrode 6 and the top surface of the second temperature compensation layer 5 located outside the top electrode 6, this embodiment is equivalent to covering the upper surface of the top electrode 6 and the exposed areas of the upper surface of the second temperature compensation layer 5 not covered by the top electrode 6 with the passivation protection layer 9. Since the passivation protection layer 9 of this embodiment can effectively isolate the external environment from the erosion of the exposed areas of the top electrode 6 and the second temperature compensation layer 5 that are not covered by the top electrode 6, and prevent performance degradation caused by oxidation, contamination or mechanical damage, this embodiment avoids the situation where the reliability of the bulk acoustic wave resonator with integrated double-layer temperature compensation structure decreases due to lack of protection during operation by setting the passivation protection layer 9 as much as possible. This effectively improves the long-term reliability and electrical performance stability of the bulk acoustic wave resonator, thereby effectively extending the service life of the bulk acoustic wave resonator and ensuring the continuous effectiveness of the temperature compensation function of the bulk acoustic wave resonator.

[0034] In some preferred embodiments, the passivation protective layer 9 is made of any one or more of silicon dioxide, silicon nitride, aluminum nitride, and aluminum oxide. Silicon dioxide (SiO2), as a commonly used dielectric material, possesses excellent insulation properties, good chemical stability, and high dielectric strength, effectively blocking moisture and ion contamination. Silicon nitride (Si3N4) has a higher density and stronger ability to block moisture and sodium ion diffusion compared to silicon dioxide, while also exhibiting good mechanical strength and chemical stability. Aluminum nitride (AlN) is a wide-bandgap semiconductor material with high thermal conductivity, high sound velocity, and good dielectric properties; as a passivation layer, it provides excellent mechanical protection and chemical stability. Aluminum oxide (Al2O3) has a high dielectric constant, high hardness, excellent chemical stability, and corrosion resistance, making it an ideal passivation and insulating material.

[0035] In some preferred embodiments, the depth of the air cavity 7 is 0.5-20 μm. This embodiment ensures effective reflection of sound waves within the bulk acoustic resonator by setting the depth of the air cavity 7 to 0.5-20 μm, thereby enabling the air cavity 7 to provide sufficient acoustic isolation, effectively reducing sound energy leakage and effectively improving the quality factor and electrical performance of the bulk acoustic resonator. Furthermore, this embodiment also allows the air cavity 7 to function as an effective thermal resistance layer by setting its depth to 0.5-20 μm. This thermal resistance layer effectively mitigates the thermal impact of external temperature changes on the core structure of the bulk acoustic resonator, thereby effectively reducing the drift of the resonant frequency with temperature changes.

[0036] In some preferred embodiments, the top surface of the bottom electrode 3 has a region exposed to the piezoelectric layer 4, and the top surface of the top electrode 6 has a region exposed to the passivation protection layer 9. The bulk acoustic wave resonator with integrated dual-layer temperature-compensated structure also includes a first pad 10 and a second pad 11. The first pad 10 is connected to the region of the top surface of the bottom electrode 3 outside the piezoelectric layer 4, and the second pad 11 is connected to the region of the top surface of the top electrode 6 outside the passivation protection layer 9. In this embodiment, the first pad 10 and the second pad 11 are both interface structures for realizing the electrical connection between the bulk acoustic wave resonator and external circuits. These two pads are preferably made of a metal material (e.g., aluminum, gold, copper, nickel, or titanium) with good conductivity and reliability. The arrangement of the first pad 10 and the second pad 11 is designed to provide a robust and low-resistance electrical path to ensure effective signal transmission and normal operation of the bulk acoustic wave resonator. In this embodiment, the first pad 10 is connected to the area outside the air cavity 7 on the top surface of the bottom electrode 3. This connection ensures that the first pad 10 can establish a reliable electrical contact with the bottom electrode 3. Since the area outside the air cavity 7 on the top surface of the bottom electrode 3 is usually a more robust and stable part of the device structure, away from the suspended structure of the air cavity 7, this embodiment can avoid connection failures caused by mechanical stress or structural fragility, so that the electrical signal of the bottom electrode 3 can be effectively led out to the external circuit. In this embodiment, the second pad 11 is connected to the area outside the passivation protection layer 9 on the top surface of the top electrode 6. This connection is intended to provide an external electrical interface for the top electrode 6. It should be understood that the passivation protection layer 9 in this embodiment usually covers the device surface to provide protection, but in order to achieve electrical connection, the top electrode 6 needs to be exposed in a specific area. The second pad 11 is connected to this exposed area, thereby allowing the electrical signal of the top electrode 6 to be accessed by the external circuit. Therefore, this embodiment is equivalent to protecting the top electrode 6 while ensuring the effective electrical connection of the top electrode 6.

[0037] In some preferred embodiments, the piezoelectric layer 4 is made of any one or more of monocrystalline aluminum nitride, polycrystalline aluminum nitride, scandium aluminum nitride, zinc oxide, lead zirconate titanate, lithium niobate, lithium tantalate, and barium strontium titanate; the bottom electrode 3 and the top electrode 6 are made of any one or more of molybdenum, nickel, gold, aluminum, platinum, titanium, tungsten, and ruthenium; and the first temperature compensation layer 8 and the second temperature compensation layer 5 are made of any one or more of phosphosilicate glass, borosilicate glass, and borophosphosilicate glass. In this embodiment, the piezoelectric layer 4 is responsible for converting electrical signals into acoustic vibrations or vice versa. To ensure the performance of the piezoelectric layer 4, the material of the piezoelectric layer 4 needs to have excellent piezoelectric effect and good crystal structure stability. Specifically, the optional materials for the piezoelectric layer 4 include, but are not limited to, single-crystal aluminum nitride, polycrystalline aluminum nitride, scandium aluminum nitride, zinc oxide, lead zirconate titanate, lithium niobate, lithium tantalate, and barium strontium titanate. These materials all have significant piezoelectric characteristics. Therefore, this embodiment can ensure that the bulk acoustic resonator can achieve efficient electromechanical coupling by selecting these materials as the materials for the piezoelectric layer 4. It should be understood that those skilled in the art can also select any combination of two or more of these materials according to specific application requirements to form a composite piezoelectric thin film material to further optimize device performance. In this embodiment, the bottom electrode 3 and top electrode 6 serve as electrodes of the bulk acoustic wave resonator. Their main function is to apply an electric field and collect electrical signals. Simultaneously, they act as a reflective layer for sound waves. The electrode materials need to possess good conductivity, thermal stability, and interface compatibility with adjacent layers. Specifically, the materials of the bottom electrode 3 and top electrode 6 in this embodiment can be any one or more of molybdenum, nickel, gold, aluminum, platinum, titanium, tungsten, and ruthenium. These metallic materials all have low resistivity and good thermal conductivity. Therefore, this embodiment can effectively reduce the ohmic loss of the bulk acoustic wave resonator by selecting these materials as the materials of the bottom electrode 3 and top electrode 6, thereby ensuring the effective transmission of electrical signals. The first temperature compensation layer 8 and the second temperature compensation layer 5 in this embodiment are key structures for achieving temperature compensation of the bulk acoustic wave resonator. The temperature coefficients of these temperature compensation layer materials are opposite in sign to those of the piezoelectric layer 4, the bottom electrode 3, and the top electrode 6. They offset the change in resonant frequency with temperature through their thermal expansion or contraction effects. Specifically, the materials of the first temperature compensation layer 8 and the second temperature compensation layer 5 in this embodiment can be any one or more of phosphosilicate glass, borosilicate glass, and borosilicate glass. These glass materials have adjustable positive temperature coefficients. For example, the temperature coefficient of phosphosilicate glass (PSG) can be precisely controlled by changing the doping content, thereby achieving effective compensation for the temperature drift of the resonator frequency.

[0038] As can be seen from the above, the bulk acoustic wave resonator with an integrated dual-layer temperature compensation structure of this application realizes a dual temperature compensation mechanism by wrapping the first temperature compensation layer 8 inside the bottom electrode 3 and introducing the second temperature compensation layer 5, so as to effectively improve the temperature compensation effect and meet the requirements of higher precision temperature stability, thereby effectively improving the temperature stability of the bulk acoustic wave resonator. Since the first temperature compensation layer 8 of this application is wrapped by the bottom electrode 3, that is, the piezoelectric layer 4 of this application is directly grown on the bottom electrode 3, this application can effectively avoid the situation that the piezoelectric layer 4 is poor in crystal quality and increased in leakage current due to the need to directly form the piezoelectric layer 4 on the temperature compensation layer and the lattice mismatch between the temperature compensation layer and the piezoelectric layer 4, thereby effectively improving the electrical performance of the bulk acoustic wave resonator.

[0039] Secondly, as shown in Figures 2 and 3, this application also provides a method for fabricating a bulk acoustic wave resonator with an integrated double-layer temperature-compensated structure, comprising the following steps: S1, forming a groove on a first substrate 1; S2, forming a first bonding structure 21 on the top surface of the first substrate 1 outside the groove; S3, sequentially forming a piezoelectric layer 4, a support portion 31, a first temperature-compensated layer 8, and an encapsulation portion 32 on a second substrate 12; the support portion 31 and the encapsulation portion 32 cooperate to encapsulate the first temperature-compensated layer 8, and the support portion 31 and the encapsulation portion 32 form a bottom electrode 3; S4, forming a second bonding structure 22 on the top surface of the support portion 31 that matches the first bonding structure 21, so as to... A preliminary structure is obtained; S5, the preliminary structure is flipped and bonded to the first substrate 1 through the first bonding structure 21 and the second bonding structure 22; the first bonding structure 21 and the second bonding structure 22 form a bonding layer 2, the groove and the bottom electrode 3 enclose an air cavity 7, and the boundary of the projection of the first temperature compensation layer 8 in the top view is located within the boundary of the projection of the air cavity 7 in the top view; S6, the second substrate 12 is removed; S7, the second temperature compensation layer 5 and the top electrode 6 are formed sequentially on the piezoelectric layer 4; the temperature coefficients of the bottom electrode 3, the piezoelectric layer 4 and the top electrode 6 are all opposite in sign to the temperature coefficients of the first temperature compensation layer 8 and the second temperature compensation layer 5.

[0040] The method for fabricating a bulk acoustic resonator with an integrated double-layer temperature-compensated structure provided in this embodiment is preferably used to fabricate the bulk acoustic resonator with an integrated double-layer temperature-compensated structure provided in the first aspect above. The principle of the method for fabricating a bulk acoustic resonator with an integrated double-layer temperature-compensated structure provided in this embodiment is the same as the principle of the bulk acoustic resonator with an integrated double-layer temperature-compensated structure provided in the first aspect above, and will not be repeated here.

[0041] The core innovation of this embodiment lies in avoiding the lattice mismatch problem caused by direct deposition of the temperature compensation layer and piezoelectric layer 4 by encasing the first temperature compensation layer 8 inside the bottom electrode 3 and cooperating with the second temperature compensation layer 5 through a specific sequence of preparation steps. Specifically, after the piezoelectric layer 4 is independently formed on the second substrate 12, the first temperature compensation layer 8 is then encased by the support portion 31 and the encapsulation portion 32 to form the bottom electrode 3, ensuring high-quality growth of the piezoelectric layer 4 without interference from the temperature compensation layer; subsequently, the second temperature compensation layer 5 is added on the piezoelectric layer 4 to achieve a dual temperature compensation mechanism. Since the piezoelectric layer 4 is independently formed on the second substrate 12, the lattice mismatch caused by direct contact deposition of the temperature compensation layer and piezoelectric layer 4 in conventional processes is avoided, thereby effectively preventing the decline in the crystal quality of the piezoelectric thin film and the increase in leakage current. At the same time, the temperature coefficients of the bottom electrode 3, the piezoelectric layer 4, and the top electrode 6 are opposite in sign to the temperature coefficients of the first temperature compensation layer 8 and the second temperature compensation layer 5. By precisely controlling the thickness and material parameters of each layer, the positive and negative temperature coefficient effects cancel each other out, significantly improving the frequency temperature stability. Furthermore, this application forms the air cavity 7 structure through wafer bonding, eliminating the traditional filling and etching release process of the sacrificial layer, thereby avoiding potential damage to the device and temperature compensation layer by the etchant, and further improving the stability and reliability of the device structure.

[0042] In some preferred embodiments, the specific process of the fabrication method of a bulk acoustic wave resonator with an integrated dual-layer temperature-compensated structure provided in this application is as follows: A1. A groove is formed on a first substrate 1 using photolithography or etching; A2. A bonding layer 2 material is deposited on the first substrate 1 using magnetron sputtering, and then the deposited bonding layer 2 material is patterned to remove the bonding layer 2 material located in the groove and retain the bonding layer 2 material located outside the groove, so as to obtain a first bonding structure 21; A3. A single crystal aluminum nitride is deposited on a second substrate 12 using magnetron sputtering to form a piezoelectric layer 4; A4. A bottom electrode 3 material is deposited on the piezoelectric layer 4 using magnetron sputtering, and then the bottom electrode 3 material deposited on the piezoelectric layer 4 is patterned to obtain a support portion 31; A5. A temperature-compensated layer material is deposited on the support portion 31 using chemical vapor deposition, and then the temperature-compensated layer material deposited on the support portion 31 is patterned. A6. Perform patterning processing to obtain a first temperature compensation layer 8; A7. Deposit electrode material on the first temperature compensation layer 8 using magnetron sputtering equipment, and then remove excess electrode material using patterning processing to obtain an encapsulation portion 32; A8. Form a second bonding structure 22 matching the first bonding structure 21 on the top surface of the support portion 31 using magnetron sputtering and patterning processing to obtain a preliminary structure; A9. Flip the preliminary structure and bond the preliminary structure to the first substrate 1 through the first bonding structure 21 and the second bonding structure 22; A0. Etch the second substrate 12 using an etchant to remove the second substrate 12; A11. Deposit a temperature compensation layer material on the piezoelectric layer 4 using chemical vapor deposition to form a second temperature compensation layer 5; A12. Deposit electrode material on the second temperature compensation layer 5 using magnetron sputtering, and then pattern the electrode material deposited on the second temperature compensation layer 5 to obtain a top electrode 6.

[0043] In some preferred embodiments, step S7 includes: S71, performing a film repair treatment on the top surface of the piezoelectric layer 4 based on ion beam film repair technology; S72, sequentially forming a second temperature compensation layer 5 and a top electrode 6 on the piezoelectric layer 4.

[0044] The process of repairing the top surface of the piezoelectric layer 4 using ion beam repair technology refers to the process of using a high-energy ion beam to bombard the surface of the piezoelectric layer 4 and remove surface atoms through physical sputtering or chemical reaction, thereby achieving surface planarization, defect repair or modification. This technology aims to optimize the surface morphology and crystal structure of the top surface of the piezoelectric layer 4 to reduce surface roughness and eliminate or reduce lattice defects, impurities and damaged layers.

[0045] This embodiment optimizes the surface condition of the piezoelectric layer 4 by pretreating its top surface with ion beam repair technology before forming the second temperature compensation layer 5 and the top electrode 6. This repair process effectively removes surface roughness, impurities, and potential lattice defects from the top surface of the piezoelectric layer 4, providing a flat, clean interface with good crystal quality for subsequent thin film deposition. This meticulous repair process allows the second temperature compensation layer 5 to form on the piezoelectric layer 4 with superior adhesion and lower interface defects. This high-quality interface helps reduce lattice mismatch during thin film growth, ensuring the second temperature compensation layer 5 has uniform thickness and stable physicochemical properties. Furthermore, the formation of the top electrode 6 also benefits from the flat and low-defect lower interface, ensuring good contact between the electrode and the temperature compensation layer and reducing contact resistance and leakage current. Overall, this approach fundamentally improves the growth quality and interface characteristics of subsequent thin films by pre-treating them before the formation of the second temperature compensation layer 5 and the top electrode 6, thereby enhancing the overall electrical performance and temperature compensation effect of the bulk acoustic resonator with the integrated double-layer temperature compensation structure.

[0046] In some preferred embodiments, the fabrication method of the bulk acoustic resonator with integrated dual-layer temperature compensation structure further includes the following steps performed after step S7: S8, forming a passivation protection layer 9 on the top surface of the top electrode 6 and the top surface of the second temperature compensation layer 5 outside the top electrode 6; S9, forming a first pad 10 on the top surface of the bottom electrode 3 outside the piezoelectric layer 4, and forming a second pad 11 on the top surface of the top electrode 6 outside the passivation protection layer 9.

[0047] As can be seen from the above, the bulk acoustic wave resonator with integrated double-layer temperature compensation structure and its fabrication method provided in this application realize a dual temperature compensation mechanism by wrapping the first temperature compensation layer 8 inside the bottom electrode 3 and introducing the second temperature compensation layer 5. This effectively improves the temperature compensation effect and meets the requirements for higher precision temperature stability, thereby effectively improving the temperature stability of the bulk acoustic wave resonator. Since the first temperature compensation layer 8 of this application is wrapped by the bottom electrode 3, that is, the piezoelectric layer 4 of this application is directly grown on the bottom electrode 3, this application can effectively avoid the situation where the piezoelectric layer 4 is directly formed on the temperature compensation layer, and there is a lattice mismatch between the temperature compensation layer and the piezoelectric layer 4, resulting in poor crystal quality of the piezoelectric layer 4 and increased leakage current. This effectively improves the electrical performance of the bulk acoustic wave resonator.

[0048] In the embodiments provided in this application, it should be understood that relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0049] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A bulk acoustic resonator with an integrated double-layer temperature-compensated structure, characterized in that, The integrated dual-layer temperature-compensated bulk acoustic resonator includes, from bottom to top, a first substrate, a bonding layer, a bottom electrode, a piezoelectric layer, a second temperature-compensated layer, and a top electrode. An air cavity is provided on the first substrate. The bottom electrode is encapsulated within the first temperature-compensated layer. The boundary of the projection of the first temperature-compensated layer in the top view direction is located within the boundary of the projection of the air cavity in the top view direction. The temperature coefficients of the bottom electrode, the piezoelectric layer, and the top electrode are all opposite in sign to the temperature coefficients of the first temperature-compensated layer and the second temperature-compensated layer.

2. The bulk acoustic resonator with integrated double-layer temperature-compensated structure according to claim 1, characterized in that, The bottom electrode includes a support portion and a wrapping portion. The support portion is located above the wrapping portion, and the bottom surface of the support portion is connected to the top surface of the wrapping portion. The support portion and the wrapping portion cooperate to wrap the first temperature compensation layer.

3. The bulk acoustic resonator with integrated double-layer temperature-compensated structure according to claim 2, characterized in that, The thickness of the support portion is greater than the thickness of the wrapping portion.

4. The bulk acoustic resonator with integrated double-layer temperature-compensated structure according to claim 1, characterized in that, The top surface of the second temperature compensation layer has a region exposed outside the top electrode. The bulk acoustic resonator with the integrated dual-layer temperature compensation structure also includes a passivation protection layer, which is connected to the regions of the top surface of the top electrode and the top surface of the second temperature compensation layer located outside the top electrode.

5. The bulk acoustic resonator with integrated double-layer temperature-compensated structure according to claim 4, characterized in that, The passivation protective layer is made of any one or more of silicon dioxide, silicon nitride, aluminum nitride, and aluminum oxide.

6. The bulk acoustic resonator with integrated double-layer temperature-compensated structure according to claim 1, characterized in that, The depth of the air cavity is 0.5-20 μm.

7. The bulk acoustic resonator with integrated double-layer temperature-compensated structure according to claim 4, characterized in that, The bottom electrode has a region exposed outside the piezoelectric layer on its top surface, and the top electrode has a region exposed outside the passivation protection layer on its top surface. The integrated dual-layer temperature-compensated bulk acoustic resonator further includes a first pad and a second pad. The first pad is connected to the region of the bottom electrode top surface outside the piezoelectric layer, and the second pad is connected to the region of the top electrode top surface outside the passivation protection layer.

8. The bulk acoustic resonator with integrated double-layer temperature-compensated structure according to claim 1, characterized in that, The piezoelectric layer is made of any one or more of the following materials: single-crystal aluminum nitride, polycrystalline aluminum nitride, scandium aluminum nitride, zinc oxide, lead zirconate titanate, lithium niobate, lithium tantalate, and barium strontium titanate. The bottom electrode and the top electrode are made of any one or more of the following materials: molybdenum, nickel, gold, aluminum, platinum, titanium, tungsten, and ruthenium. The first temperature compensation layer and the second temperature compensation layer are made of any one or more of the following materials: phosphosilicate glass, borosilicate glass, and borophosphosilicate glass.

9. A method for fabricating a bulk acoustic resonator with an integrated double-layer temperature-compensated structure, characterized in that, The fabrication method of the integrated dual-layer temperature-compensated bulk acoustic wave resonator includes the following steps: S1, forming a groove on a first substrate; S2, forming a first bonding structure on the top surface of the first substrate outside the groove; S3, sequentially forming a piezoelectric layer, a support portion, a first temperature-compensated layer, and an encapsulation portion on a second substrate; the support portion and the encapsulation portion cooperate to encapsulate the first temperature-compensated layer, and the support portion and the encapsulation portion form a bottom electrode; S4, forming a second bonding structure matching the first bonding structure on the top surface of the support portion to obtain a preliminary structure; S5, flipping the preliminary structure and... The first bonding structure and the second bonding structure bond the preliminary structure to the first substrate; the first bonding structure and the second bonding structure form a bonding layer, the groove and the bottom electrode enclose an air cavity, and the boundary of the projection of the first temperature compensation layer in the top view direction is located within the boundary of the projection of the air cavity in the top view direction; S6, remove the second substrate; S7, form a second temperature compensation layer and a top electrode sequentially on the piezoelectric layer; the temperature coefficients of the bottom electrode, the piezoelectric layer and the top electrode are all opposite in sign to the temperature coefficients of the first temperature compensation layer and the second temperature compensation layer.

10. The method for fabricating a bulk acoustic resonator with an integrated double-layer temperature-compensated structure according to claim 9, characterized in that, Step S7 includes: S71, performing a film repair process on the top surface of the piezoelectric layer based on ion beam film repair technology; S72, sequentially forming a second temperature compensation layer and a top electrode on the piezoelectric layer.

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