Temperature-compensated resonator, filter and multiplexer based on polarity-inverted bimorphs

Abstract

The application discloses a temperature compensation type resonator based on polarity inversion double piezoelectric layers, a filter and a multiplexer, and belongs to the technical field of bulk acoustic wave resonators, and comprises a bottom electrode, a top electrode and a composite piezoelectric stack structure arranged between the bottom electrode and the top electrode, wherein the composite piezoelectric stack structure comprises two piezoelectric layers and a temperature compensation layer arranged between the two piezoelectric layers; the crystal polarity directions of the two piezoelectric layers are opposite, and the thicknesses are arranged according to a preset ratio, so that the temperature compensation layer is located in a vibration displacement minimum value region of the composite piezoelectric stack structure in a resonant state. The temperature compensation type resonator aims to solve the problem that the existing bulk acoustic wave resonator is difficult to balance between temperature stability and electrical performance, and lacks optimal design of polarity configuration of the piezoelectric layer, and cannot fully utilize the performance potential of the piezoelectric material, thereby limiting the performance improvement of the temperature compensation type resonator, and achieves the balance between temperature stability and electrical performance, and realizes the unity of high performance and high stability.

Description

Technical Field

[0001] This invention belongs to the field of bulk acoustic resonator technology, and specifically relates to a temperature-compensated resonator, filter and multiplexer based on a polarity-reversed double piezoelectric layer. Background Technology

[0002] In the field of bulk acoustic wave (BAW) resonator technology, temperature compensation is a key technology for achieving device frequency stability. Traditional temperature-compensated BAW resonators typically employ a structure where a silicon dioxide temperature compensation layer is directly inserted between the electrode and the piezoelectric layer. While this structure utilizes the positive temperature coefficient of silicon dioxide to compensate for the negative temperature coefficient of the piezoelectric material, it suffers from serious performance defects. Because the temperature compensation layer is located at the electrode-piezoelectric interface region where the electric field strength and acoustic energy density are highest, its non-piezoelectric characteristics significantly reduce the effective electric field strength, leading to a substantial decrease in the electromechanical coupling coefficient. Simultaneously, the acoustic impedance mismatch between silicon dioxide and adjacent materials induces significant acoustic scattering and reflection, causing acoustic energy loss and further deteriorating the resonator's quality factor. These structural defects make it difficult for traditional temperature-compensated resonators to balance temperature stability and electrical performance, severely limiting their performance in high-frequency applications such as filters and multiplexers. Furthermore, existing technologies lack optimized designs for the polarity configuration of the piezoelectric layer, failing to fully utilize the performance potential of piezoelectric materials.

[0003] Therefore, existing technologies need to be improved and developed. Summary of the Invention

[0004] The purpose of this invention is to provide a temperature-compensated resonator, filter, and multiplexer based on a polarity-reversed double piezoelectric layer. This invention aims to solve the problems of existing bulk acoustic wave resonators, which struggle to balance temperature stability and electrical performance, and lack optimized design for the piezoelectric layer polarity configuration, thus failing to fully utilize the performance potential of piezoelectric materials and limiting the performance improvement of temperature-compensated resonators. This invention achieves a balance between temperature stability and electrical performance, realizing a unity of high performance and high stability.

[0005] In a first aspect, the present invention provides a temperature-compensated resonator based on a polarity-reversed double piezoelectric layer, comprising a bottom electrode, a top electrode, and a composite piezoelectric stack structure disposed between the bottom electrode and the top electrode, wherein the composite piezoelectric stack structure comprises a first piezoelectric layer, a second piezoelectric layer, and a temperature compensation layer located between the first piezoelectric layer and the second piezoelectric layer. The crystal polarity directions of the first piezoelectric layer and the second piezoelectric layer are opposite. The thicknesses of the first piezoelectric layer and the second piezoelectric layer are set according to a preset ratio so that the temperature compensation layer is located in the region of minimum vibration displacement of the composite piezoelectric stack structure in the resonant state.

[0006] The temperature-compensated resonator based on polarity-reversed double piezoelectric layers provided by this invention introduces a polarity-reversed double piezoelectric layer structure and optimizes the position of the temperature compensation layer so that it is located in the region of minimum vibration displacement. This effectively reduces the impact of the temperature compensation layer on the electromechanical coupling coefficient and quality factor of the resonator, solves the performance defects of traditional temperature-compensated resonators, and achieves a balance between temperature stability and electrical performance.

[0007] Furthermore, the first piezoelectric layer and the second piezoelectric layer have the same thickness, so that the temperature compensation layer is located at the geometric center of the composite piezoelectric stack structure, thereby placing the temperature compensation layer in the region of minimum vibration displacement of the composite piezoelectric stack structure in the resonant state.

[0008] Furthermore, the composite piezoelectric stack structure also includes a first adapter layer disposed between the temperature compensation layer and the first piezoelectric layer, and a second adapter layer disposed between the temperature compensation layer and the second piezoelectric layer; the thickness of both the first adapter layer and the second adapter layer is less than 5 nm, and both are used to improve the acoustic impedance matching between the temperature compensation layer and the corresponding piezoelectric layer.

[0009] Furthermore, both the first piezoelectric layer and the second piezoelectric layer are made of aluminum nitride, zinc oxide, or lithium niobate.

[0010] Furthermore, both the first piezoelectric layer and the second piezoelectric layer are made of aluminum nitride, zinc oxide, or lithium niobate materials doped with any one or more elements selected from scandium, yttrium, and magnesium.

[0011] Furthermore, the temperature compensation layer is made of a dielectric material with a positive frequency temperature coefficient.

[0012] Furthermore, the dielectric material having a positive frequency temperature coefficient includes silicon dioxide and silicon oxynitride.

[0013] Furthermore, the dielectric material having a positive frequency temperature coefficient includes fluorine-doped silicon dioxide and fluorine-doped silicon oxynitride.

[0014] Secondly, the present invention provides a filter, including the temperature-compensated resonator based on the polarity-reversed double piezoelectric layer described above.

[0015] Thirdly, the present invention provides a multiplexer, including the temperature-compensated resonator based on the polarity-reversed double piezoelectric layer described above.

[0016] As can be seen from the above, the temperature-compensated resonator based on a polarity-reversed double piezoelectric layer provided by this invention effectively solves the problem of severe degradation of the electromechanical coupling coefficient and quality factor caused by the temperature compensation layer in the prior art by employing a unique polarity-reversed double piezoelectric layer structure and cleverly placing the temperature compensation layer in the region of minimum vibration displacement of the composite piezoelectric stack structure in the resonant state. Specifically, since the temperature compensation layer is located in the region of minimum vibration displacement, its influence on the effective electric field strength and acoustic energy density of the resonator is significantly reduced, thereby greatly improving the electromechanical coupling coefficient and quality factor. At the same time, the polarity-reversed double piezoelectric layer design not only optimizes the performance potential of the piezoelectric material, but also provides a more flexible control mechanism for temperature compensation. Accordingly, this application overcomes the defect of existing temperature-compensated resonators in that it is difficult to balance temperature stability and electrical performance, achieving a unity of high performance and high stability, and providing a better solution for high-frequency applications such as filters and multiplexers.

[0017] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing embodiments of the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cross-sectional structure of a temperature-compensated resonator based on a polarity-reversed double piezoelectric layer, provided as an embodiment of the present invention.

[0019] Label Explanation: 100 Bottom electrode; 200 Top electrode; 300 Composite piezoelectric stacked structure; 310 First piezoelectric layer; 320 Second piezoelectric layer; 400 Temperature compensation layer; 510 First adapter layer; 520 Second adapter layer. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0023] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0024] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0025] In the temperature compensation design of bulk acoustic resonators, when the temperature compensation layer is placed in the interface region between the electrode and the piezoelectric layer, the non-piezoelectric characteristics of the temperature compensation layer cause the effective electric field to be shunted due to the high-intensity electric field and high-density acoustic energy distribution in this region, leading to a decrease in the electromechanical coupling coefficient. Simultaneously, the acoustic impedance difference between the temperature compensation layer and adjacent materials causes acoustic wave scattering and reflection, resulting in acoustic energy loss and thus a deterioration of the quality factor. This structural defect creates an irreconcilable contradiction between the resonator's frequency temperature stability and key performance indicators such as bandwidth and insertion loss, specifically manifested as a mutual constraint between the temperature compensation effect and the high-frequency electroacoustic conversion efficiency.

[0026] For example, in the manufacturing process of RF filters used in 5G communication systems, when the silicon dioxide temperature compensation layer is placed at the contact interface between the bottom electrode and the aluminum nitride piezoelectric layer, the acoustic wave encounters a significant impedance discontinuity interface on the propagation path, generating additional acoustic scattering loss. This increases the passband insertion loss of the filter and reduces its out-of-band rejection performance. Furthermore, this phenomenon is particularly pronounced when the resonator operates at high frequencies, causing the device to fail to simultaneously meet the technical requirements of temperature drift suppression and signal selectivity, thereby affecting the overall functionality of the RF front-end module.

[0027] If the above problems are not solved, it will be difficult for resonators to achieve synergistic optimization of temperature stability and high-frequency electroacoustic performance, which will reduce the reliability of RF front-end modules in complex electromagnetic environments and limit their applicability in broadband communication applications. Specifically, the continuous accumulation of acoustic energy loss will increase the difficulty of device thermal management, while the decrease in electromechanical coupling efficiency will weaken the bandwidth expansion capability of filters, ultimately hindering the engineering application of high-performance RF devices.

[0028] For reference, see the appendix. Figure 1The present invention provides a temperature-compensated resonator based on a polarity-reversed double piezoelectric layer, including a bottom electrode 100, a top electrode 200, and a composite piezoelectric stack structure 300 disposed between the bottom electrode 100 and the top electrode 200. The composite piezoelectric stack structure 300 includes a first piezoelectric layer 310, a second piezoelectric layer 320, and a temperature compensation layer 400 located between the first piezoelectric layer 310 and the second piezoelectric layer 320. The crystal polarity directions of the first piezoelectric layer 310 and the second piezoelectric layer 320 are opposite. The thicknesses of the first piezoelectric layer 310 and the second piezoelectric layer 320 are set according to a preset ratio so that the temperature compensation layer 400 is located in the region of minimum vibration displacement of the composite piezoelectric stack structure 300 in the resonant state.

[0029] For ease of understanding, the following explains some key terms in this embodiment: Bottom electrode 100 and top electrode 200: These two electrodes are the basic components of the resonator, used to apply an electric field and extract the resonant signal. They are typically made of conductive materials, such as thin metal films, and formed through processes such as physical vapor deposition. The bottom electrode 100 is usually deposited on a substrate, while the top electrode 200 is located at the top of the entire stacked structure.

[0030] Composite piezoelectric stack structure 300: This structure is the core functional layer of this application and is disposed between the bottom electrode 100 and the top electrode 200. It consists of multiple functional layers, including a piezoelectric layer and a temperature compensation layer, and its overall design is intended to achieve specific acoustic and electrical properties.

[0031] First piezoelectric layer 310 and second piezoelectric layer 320: These two piezoelectric layers are key components of the composite piezoelectric stack structure 300. They can convert electrical energy into mechanical energy and vice versa, thereby achieving a resonant function. The crystal structure of the piezoelectric material determines its polarity direction, which is crucial for achieving polarity reversal in this application.

[0032] Temperature compensation layer 400: This layer is located between the first piezoelectric layer 310 and the second piezoelectric layer 320. Its main function is to offset the inherent frequency temperature coefficient of the piezoelectric material, thereby improving the frequency stability of the resonator at different temperatures. This layer is usually made of a dielectric material with specific thermodynamic properties.

[0033] In one embodiment, the bottom electrode 100 and the top electrode 200 can be made of a variety of conductive materials, such as aluminum, molybdenum, tungsten, copper, or alloys thereof. The thickness of these electrodes can be adjusted according to the design frequency and impedance matching requirements of the resonator. For example, the bottom electrode 100 can be formed on a substrate using physical vapor deposition techniques such as magnetron sputtering or electron beam evaporation, followed by the top electrode 200 formed over the composite piezoelectric stack structure 300.

[0034] The crystal polarity directions of the first piezoelectric layer 310 and the second piezoelectric layer 320 are opposite. This polarity reversal can be achieved in various ways. For example, by precisely controlling the precursor flow rate, substrate temperature, or applying a bias voltage during the growth process using processes such as metal-organic chemical vapor deposition or reactive magnetron sputtering, directional growth of crystal polarity can be achieved. Specifically, after depositing the first piezoelectric layer 310, specific surface treatments (e.g., using ion beam-assisted deposition to bombard the surface of the first piezoelectric layer 310 with a specific ion beam before growing the second piezoelectric layer 320 to change its surface polarity) or seed layer techniques (e.g., introducing silane for silicon doping to form an extremely thin, heavily doped layer at the interface to induce polarity reversal) can be used to make the crystal c-axis direction of the subsequently deposited second piezoelectric layer 320 opposite to that of the first piezoelectric layer 310. Specifically, the first piezoelectric layer 310 can be an aluminum-polar aluminum nitride thin film, while the second piezoelectric layer 320 can be an nitrogen-polar aluminum nitride thin film. Another approach is to select two different piezoelectric materials with opposite default polarization directions (epitaxially grown using substrate templates with different crystal orientations) as the first piezoelectric layer 310 and the second piezoelectric layer 320.

[0035] The thicknesses of the first piezoelectric layer 310 and the second piezoelectric layer 320 are set according to a preset ratio so that the temperature compensation layer 400 is located in the region of minimum vibration displacement of the composite piezoelectric stack structure 300 in the resonant state. This thickness ratio setting is based on acoustic theory and simulation analysis. For example, the standing wave modes of sound waves under different thickness ratios can be simulated using finite element analysis (FEA) software to determine the precise placement of the temperature compensation layer 400. In one implementation, the physical thicknesses of the first piezoelectric layer 310 and the second piezoelectric layer 320 can be adjusted so that the temperature compensation layer 400 is located near the strain node of the sound wave thickness extension mode. For example, if the sound velocities of the first piezoelectric layer 310 and the second piezoelectric layer 320 are similar, their physical thicknesses can be adjusted so that the temperature compensation layer 400 is located at the geometric center of the composite piezoelectric stack structure 300, thus placing it in the region of minimum vibration displacement.

[0036] When the resonator is operating, the electric field applied between the bottom electrode 100 and the top electrode 200 excites the first piezoelectric layer 310 and the second piezoelectric layer 320 to generate mechanical vibrations. Since the crystal polarities of the first piezoelectric layer 310 and the second piezoelectric layer 320 are opposite, this configuration helps to form a specific acoustic standing wave mode within the composite piezoelectric stack structure 300. By precisely designing the thickness ratio of the first piezoelectric layer 310 to the second piezoelectric layer 320, the temperature compensation layer 400 can be precisely located in the region of minimum vibration displacement of this acoustic standing wave mode, i.e., near the strain node of the acoustic wave. At the strain node, the acoustic energy density is extremely low, thus minimizing the scattering and reflection effects of the temperature compensation layer 400 on the acoustic wave, thereby significantly reducing acoustic losses and improving the quality factor of the resonator. Simultaneously, since the temperature compensation layer 400 is no longer located at the electrode-piezoelectric layer interface where the electric field strength is highest, its shunting effect on the effective electric field is also reduced, thus maintaining a high electromechanical coupling coefficient.

[0037] Through the aforementioned structure and working principle, this resonator successfully places the temperature compensation layer 400 in the region with minimal impact on resonator performance. This achieves effective temperature compensation while avoiding the problems of decreased electromechanical coupling coefficient and deteriorated quality factor found in traditional solutions. This design not only improves the frequency-temperature stability of the resonator but also optimizes its key performance indicators such as bandwidth and insertion loss.

[0038] Compared to traditional temperature compensation schemes, the technical concept of this application makes a significant technical contribution. Traditional schemes place the temperature compensation layer between the electrode and the piezoelectric layer. This region has a high electric field intensity and high acoustic energy density, resulting in a strong shunting effect of the temperature compensation layer on the electric field, a decrease in the electromechanical coupling coefficient, and acoustic impedance mismatch causing sound wave scattering, thus deteriorating the quality factor. This application introduces a polarity-reversed double piezoelectric layer structure and precisely controls the thickness of each layer, placing the temperature compensation layer 400 in the region of minimum vibration displacement of the composite piezoelectric stack structure 300 in the resonant state. This innovative layer sequence and polarity design fundamentally resolves the contradiction between temperature stability and high-frequency electroacoustic performance in traditional schemes. By placing the temperature compensation layer 400 in a region of extremely low acoustic energy density, this application can minimize its interference with sound wave transmission, thereby significantly reducing acoustic losses and improving the quality factor of the resonator. Simultaneously, since the temperature compensation layer 400 is no longer directly located in the high electric field region, its shunting effect on the effective electric field is also reduced, thus maintaining high electromechanical coupling efficiency. This optimization not only improves the frequency-temperature stability of the resonator (the absolute value of the negative frequency temperature coefficient (TCF) can be optimized to within 5 ppm / ℃), but also provides a foundation for broadband filter design and promises to achieve lower insertion loss and higher out-of-band rejection. Furthermore, the polarity-reversed double-layer piezoelectric structure itself supports higher harmonic operating modes, giving the device greater design freedom and allowing for higher operating frequencies or better power tolerance with the same physical thickness.

[0039] In some embodiments, the first piezoelectric layer 310 and the second piezoelectric layer 320 have the same thickness, so that the temperature compensation layer 400 is located at the geometric center of the composite piezoelectric stack structure 300, thereby placing the temperature compensation layer 400 in the region of minimum vibration displacement of the composite piezoelectric stack structure 300 in the resonant state.

[0040] The equal thickness of the first piezoelectric layer 310 and the second piezoelectric layer 320 means that the physical dimensions of the first piezoelectric layer 310 and the second piezoelectric layer 320 are identical in the direction perpendicular to their plane. This equal thickness setting aims to ensure the acoustic symmetry of the composite piezoelectric stack structure 300, providing a basis for the precise centering of the temperature compensation layer 400. This equal thickness can be achieved by precisely controlling the parameters of the thin film deposition process (e.g., magnetron sputtering, pulsed laser deposition, or atomic layer deposition) to keep the growth rate and time of the two layers consistent, thereby obtaining the same physical thickness; or by finely adjusting the thickness of the two layers after deposition through post-processing processes such as etching or chemical mechanical polishing to achieve equality. Positioning the temperature compensation layer 400 at the geometric center of the composite piezoelectric stack structure 300 means precisely placing the temperature compensation layer 400 at the midpoint of the composite piezoelectric stack structure 300 in the thickness direction, i.e., on the physical axis of symmetry. This setting aims to provide a physical basis for subsequent operation in the region of minimum vibrational displacement under resonant conditions. This positioning can be achieved by precisely calculating the thickness of each layer during the design phase and ensuring that the thicknesses of the first piezoelectric layer 310 and the second piezoelectric layer 320 are equal, thus ensuring that the deposition location of the temperature compensation layer 400 is exactly at the geometric center of the entire stacked structure. Alternatively, during manufacturing, high-precision measuring equipment (e.g., ellipsometer, scanning electron microscope, or X-ray reflectometer) can be used to monitor the thickness of each layer in real time and adjust deposition or etching parameters to ensure that the temperature compensation layer 400 is ultimately located at the geometric center. This places the temperature compensation layer 400 in the region of minimum vibration displacement of the composite piezoelectric stacked structure 300 in the resonant state. This region refers to the area where the amplitude of sound wave vibration within the composite piezoelectric stacked structure 300 is minimal when the resonator is operating, typically corresponding to the strain node of the sound wave. This setup aims to minimize the impact of the temperature compensation layer 400 on the acoustic performance of the resonator, reduce acoustic energy loss, and improve the quality factor. This effect can be achieved by modeling and analyzing the composite piezoelectric stack structure 300 using acoustic simulation software (e.g., finite element analysis (FEA) or the transfer matrix method) to predict the vibration displacement distribution of sound waves under a specific resonance mode, thereby verifying whether the temperature compensation layer 400 is in the region of minimum vibration displacement; or by experimentally measuring (e.g., using a laser Doppler vibrometer or a scanning acoustic microscope) the surface vibration mode of the resonator at resonance, indirectly inferring the internal vibration displacement distribution to confirm the effective position of the temperature compensation layer 400.

[0041] The solution in this application ensures the acoustic symmetry of the composite piezoelectric stack structure 300 by setting the thicknesses of the first piezoelectric layer 310 and the second piezoelectric layer 320 to be equal. In this symmetrical structure, the temperature compensation layer 400 is precisely positioned at the geometric center of the composite piezoelectric stack structure 300. Since the region of minimum vibration displacement of a resonator in the resonant state is usually located at or near the geometric center of the structure, placing the temperature compensation layer 400 at the geometric center allows it to naturally be located in the region of minimum acoustic wave vibration amplitude. This design avoids the uncertainties that may arise from the complex calculations and preset ratios in traditional solutions, providing a more direct and reliable way to ensure that the temperature compensation layer 400 is located in the region of minimum vibration displacement. In the above-mentioned temperature-compensated resonator based on polarity-reversed dual piezoelectric layers, the crystal polarity directions of the first piezoelectric layer 310 and the second piezoelectric layer 320 are opposite, and their thicknesses are set according to a preset ratio so that the temperature compensation layer 400 is located in the region of minimum vibration displacement. The solution presented in this application further clarifies an optimized design for this "preset ratio," namely, by making the thicknesses of the first piezoelectric layer 310 and the second piezoelectric layer 320 equal, the inherent symmetry of the structure is utilized to ensure that the temperature compensation layer 400 is precisely located at the geometric center, thereby stably remaining in the region of minimum vibration displacement. This method not only simplifies the design and manufacturing process but also improves the consistency and stability of the resonator's performance.

[0042] In some embodiments, reference is made to the appendix. Figure 1 The composite piezoelectric stacked structure 300 further includes a first adapter layer 510 disposed between the temperature compensation layer 400 and the first piezoelectric layer 310, and a second adapter layer 520 disposed between the temperature compensation layer 400 and the second piezoelectric layer 320; the thickness of the first adapter layer 510 and the second adapter layer 520 is less than 5nm, and both are used to improve the acoustic impedance matching between the temperature compensation layer 400 and the corresponding piezoelectric layer.

[0043] Specifically, the first adapter layer 510 and the second adapter layer 520 are thin film layers disposed between two different material interfaces to improve interface characteristics (such as acoustic impedance matching and adhesion). These adapter layers can be fabricated from various materials, such as aluminum nitride (AlN), silicon nitride (Si3N4), or alumina (Al2O3), and their selection is usually based on acoustic properties, compatibility with adjacent layers, and the maturity of the deposition process. As an acoustic transition layer, its main function is to smooth the impedance changes of sound waves propagating at the interface of different media, reduce sound wave reflection and scattering, thereby reducing energy loss. At the same time, the adapter layer can also enhance the bonding force between different material layers and improve the mechanical stability of the structure. Limiting the thickness of the adapter layer to a very small range (less than 5 nm) is to ensure that while improving acoustic impedance matching, it does not introduce significant additional acoustic losses or negatively affect the overall resonant frequency and quality factor of the resonator. The extremely thin adapter layer can maximize the preservation of the acoustic performance of the resonator. Improved acoustic impedance matching enables sound waves to be transmitted more effectively at the interface between the temperature compensation layer 400 and the piezoelectric layer, reducing the reflection and scattering of acoustic energy, thereby reducing the insertion loss of the resonator and improving its quality factor.

[0044] This structural configuration allows the first adapter layer 510 and the second adapter layer 520 to be precisely inserted between the temperature compensation layer 400 and the two piezoelectric layers (first piezoelectric layer 310 and second piezoelectric layer 320) as acoustic transition layers. When the resonator is operating, sound waves propagate within the composite piezoelectric stack structure 300, passing sequentially through the piezoelectric layer, the adapter layer, and the temperature compensation layer. Because the material properties of the first adapter layer 510 and the second adapter layer 520 are chosen to be intermediate between those of the temperature compensation layer 400 and the corresponding piezoelectric layer, they effectively smooth abrupt changes in acoustic impedance. This smoothing effect reduces sound wave reflection and scattering at the interface, allowing acoustic energy to be transferred more efficiently from the piezoelectric layer to the temperature compensation layer, and vice versa. Simultaneously, the thickness of both the first adapter layer 510 and the second adapter layer 520 is strictly controlled to an extremely thin range of less than 5 nm. This ensures that the adapter layers provide acoustic impedance matching without introducing significant additional acoustic losses or negatively impacting the overall resonant characteristics of the resonator. In this way, the solution proposed in this application significantly reduces acoustic energy loss while maintaining the temperature compensation effect, thereby improving the quality factor of the resonator.

[0045] In one specific implementation, the composite piezoelectric stack structure 300 may include a first adapter layer 510 disposed between the temperature compensation layer 400 and the first piezoelectric layer 310, and a second adapter layer 520 disposed between the temperature compensation layer 400 and the second piezoelectric layer 320. The first adapter layer 510 and the second adapter layer 520 may be made of aluminum nitride or silicon nitride. These materials possess good acoustic properties and deposition processes compatible with both the piezoelectric layer and the temperature compensation layer. For example, after depositing the first piezoelectric layer 310, an aluminum nitride thin film with a thickness of less than 5 nm can be precisely deposited on the surface of the first piezoelectric layer 310 as the first adapter layer 510 using techniques such as atomic layer deposition or magnetron sputtering. Similarly, after the temperature compensation layer 400 is deposited, an aluminum nitride thin film with a thickness of less than 5 nm can be deposited on its surface as the second adapter layer 520 using the same or similar methods. In this way, the first adapter layer 510 and the second adapter layer 520 can serve as acoustic transition layers, effectively improving the acoustic impedance matching between the temperature compensation layer 400 and the corresponding piezoelectric layer, while ensuring that their extremely thin thickness will not adversely affect the overall performance of the resonator.

[0046] Through the above technical solution, in the temperature-compensated resonator based on polarity-reversed double piezoelectric layers, a first adapter layer 510 is provided between the temperature compensation layer 400 and the first piezoelectric layer 310, and a second adapter layer 520 is provided between the temperature compensation layer 400 and the second piezoelectric layer 320, and the thickness of these adapter layers is less than 5 nm, thereby effectively improving the acoustic impedance matching between the temperature compensation layer 400 and the corresponding piezoelectric layer. This improvement significantly reduces the reflection and scattering of sound waves at different material interfaces, reducing the loss of acoustic energy. Therefore, the solution of this application can effectively improve the quality factor of the resonator while achieving temperature compensation, avoiding the performance degradation problem caused by acoustic impedance mismatch in traditional temperature compensation schemes, so that the resonator has lower insertion loss and better filtering performance while maintaining temperature stability.

[0047] In some embodiments, both the first piezoelectric layer 310 and the second piezoelectric layer 320 are made of aluminum nitride, zinc oxide, or lithium niobate.

[0048] In some preferred embodiments, both the first piezoelectric layer 310 and the second piezoelectric layer 320 are made of aluminum nitride, zinc oxide or lithium niobate material doped with any one or more elements of scandium, yttrium and magnesium.

[0049] Doping with scandium can significantly improve the piezoelectric constant of piezoelectric materials, thereby enhancing the electromechanical coupling coefficient. Similar to scandium, doping with yttrium can improve the crystal structure and piezoelectric properties of piezoelectric materials, thus increasing the piezoelectric response. Doping with magnesium can adjust the lattice structure and electronic properties of piezoelectric materials, thereby affecting the piezoelectric coefficient and temperature stability.

[0050] The solution in this application addresses the problems of low piezoelectric coefficient and insufficient temperature stability of undoped piezoelectric materials by employing aluminum nitride, zinc oxide, or lithium niobate doped with one or more elements selected from scandium, yttrium, and magnesium in the first piezoelectric layer 310 and the second piezoelectric layer 320. In the composite piezoelectric stack structure 300, the first piezoelectric layer 310 and the second piezoelectric layer 320 are the core components for generating the piezoelectric effect and driving resonance. Doping elements can optimize the lattice structure of the piezoelectric material, enhance its piezoelectric constant, and enable the piezoelectric layer to generate greater mechanical deformation under the same electric field excitation, thereby improving the electromechanical coupling coefficient of the resonator. A higher electromechanical coupling coefficient means that the resonator can more effectively convert electrical energy into acoustic energy, and vice versa, which is crucial for realizing wide-bandwidth and low-insertion-loss filters. At the same time, these doping elements can also improve the temperature characteristics of the piezoelectric material, reducing the sensitivity of its natural frequency to temperature changes, thereby reducing the temperature drift of the resonator. The synergistic effect of this improved piezoelectric layer and the temperature compensation layer 400 in the composite piezoelectric stack structure 300 enables the entire resonator to achieve superior frequency-temperature stability while maintaining a high electromechanical coupling coefficient. By precisely placing the temperature compensation layer 400 in the region of minimum vibration displacement, its impact on the resonator's quality factor can be minimized, while the doped piezoelectric layer further enhances the overall performance of the resonator.

[0051] In some embodiments, the temperature compensation layer 400 is made of a dielectric material with a positive frequency temperature coefficient, including silicon dioxide and silicon oxynitride.

[0052] In some preferred embodiments, the dielectric material having a positive frequency temperature coefficient includes fluorine-doped silicon dioxide and fluorine-doped silicon oxynitride.

[0053] Specifically, fluorine-doped silicon dioxide refers to the introduction of fluorine into a silicon dioxide (SiO2) matrix. The introduction of fluorine can alter the physicochemical properties of the material, such as density, sound velocity, coefficient of thermal expansion, and dielectric constant, thereby affecting its frequency temperature coefficient and acoustic impedance characteristics. Fluorine-doped silicon dioxide can be achieved in various ways. For example, it can be formed using plasma-enhanced chemical vapor deposition (PECVD) technology, where fluorine-containing gases (such as silicon tetrafluoride SiF4 or trifluoromethane CHF3) are introduced during the deposition process to react with a silicon source (such as silane SiH4) and an oxygen source (such as nitrous oxide N2O or oxygen O2); alternatively, it can be deposited using sputtering deposition technology with a fluorine-containing silicon dioxide target. Fluorine-doped silicon oxynitride refers to the introduction of fluorine into a silicon oxynitride (SiON) matrix. Similar to fluorine-doped silicon dioxide, fluorine doping can optimize the material properties of silicon oxynitride, resulting in superior performance when used as a temperature compensation layer at 400°C. Fluorine-doped silicon oxynitride can be prepared using PECVD technology, which involves co-depositing a fluorine-containing gas into a conventional silicon oxynitride precursor such as silane, ammonia (NH3), or nitrous oxide; or it can be prepared using atomic layer deposition (ALD) technology, which allows for precise composition control by alternating reactions of the fluorine-containing precursor with silicon, nitrogen, and oxygen sources.

[0054] The solution in this application optimizes the performance of the temperature compensation layer 400 by introducing fluorine-doped silicon dioxide and fluorine-doped silicon oxynitride as materials for the temperature compensation layer 400. In the temperature-compensated resonator based on polarity-reversed double piezoelectric layers, the composite piezoelectric stack structure 300 includes a first piezoelectric layer 310, a second piezoelectric layer 320, and a temperature compensation layer 400 located between the first piezoelectric layer 310 and the second piezoelectric layer 320. The crystal polarity directions of the first piezoelectric layer 310 and the second piezoelectric layer 320 are opposite, and their thicknesses are set according to a preset ratio so that the temperature compensation layer 400 is located in the region of minimum vibration displacement of the composite piezoelectric stack structure 300 in the resonant state. Furthermore, the temperature compensation layer 400 is made of a dielectric material with a positive frequency temperature coefficient, specifically fluorine-doped silicon dioxide or fluorine-doped silicon oxynitride. Fluorine doping effectively modulates the temperature coefficient of frequency (TFC) of materials, maintaining a stable and precise positive TFC over a wider temperature range. This more effectively counteracts the negative TFC of piezoelectric layers (such as aluminum nitride). Simultaneously, fluorine doping improves the acoustic impedance matching between the temperature compensation layer 400 and adjacent piezoelectric layers, reducing sound wave reflection and scattering at the interface and lowering acoustic energy loss. This optimization allows the temperature compensation layer 400 to achieve temperature compensation with lower losses and higher efficiency when located in the region of minimum vibration displacement, thereby improving the overall quality factor and frequency stability of the resonator.

[0055] The present invention provides a filter, including the temperature-compensated resonator based on polarity-reversed double piezoelectric layers in the above embodiments.

[0056] The present invention provides a multiplexer, including the temperature-compensated resonator based on polarity-reversed double piezoelectric layers in the above embodiments.

[0057] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0058] The above descriptions are merely some embodiments of the present invention. For those skilled in the art, various modifications and improvements can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A temperature-compensated resonator based on a polarity-reversed double piezoelectric layer, comprising a bottom electrode (100), a top electrode (200), and a composite piezoelectric stack structure (300) disposed between the bottom electrode (100) and the top electrode (200), characterized in that, The composite piezoelectric stack structure (300) includes a first piezoelectric layer (310), a second piezoelectric layer (320), and a temperature compensation layer (400) located between the first piezoelectric layer (310) and the second piezoelectric layer (320). The crystal polarity directions of the first piezoelectric layer (310) and the second piezoelectric layer (320) are opposite; The thicknesses of the first piezoelectric layer (310) and the second piezoelectric layer (320) are set according to a preset ratio so that the temperature compensation layer (400) is located in the region of minimum vibration displacement of the composite piezoelectric stack structure (300) in the resonant state.

2. The temperature-compensated resonator based on a polarity-reversed double piezoelectric layer according to claim 1, characterized in that, The first piezoelectric layer (310) and the second piezoelectric layer (320) have the same thickness, so that the temperature compensation layer (400) is located at the geometric center of the composite piezoelectric stack structure (300), thereby placing the temperature compensation layer (400) in the region of minimum vibration displacement of the composite piezoelectric stack structure (300) in the resonant state.

3. The temperature-compensated resonator based on a polarity-reversed double piezoelectric layer according to claim 1, characterized in that, The composite piezoelectric stack structure (300) further includes a first adapter layer (510) disposed between the temperature compensation layer (400) and the first piezoelectric layer (310), and a second adapter layer (520) disposed between the temperature compensation layer (400) and the second piezoelectric layer (320); the thickness of the first adapter layer (510) and the second adapter layer (520) is less than 5 nm, and both are used to improve the acoustic impedance matching between the temperature compensation layer (400) and the corresponding piezoelectric layer.

4. The temperature-compensated resonator based on a polarity-reversed double piezoelectric layer according to claim 1, characterized in that, Both the first piezoelectric layer (310) and the second piezoelectric layer (320) are made of aluminum nitride, zinc oxide or lithium niobate.

5. The temperature-compensated resonator based on a polarity-reversed double piezoelectric layer according to claim 4, characterized in that, Both the first piezoelectric layer (310) and the second piezoelectric layer (320) are made of aluminum nitride, zinc oxide or lithium niobate material doped with any one or more elements of scandium, yttrium and magnesium.

6. The temperature-compensated resonator based on a polarity-reversed double piezoelectric layer according to claim 1, characterized in that, The temperature compensation layer (400) is made of a dielectric material with a positive frequency temperature coefficient.

7. The temperature-compensated resonator based on a polarity-reversed double piezoelectric layer according to claim 6, characterized in that, The dielectric material with a positive frequency temperature coefficient includes silicon dioxide and silicon oxynitride.

8. The temperature-compensated resonator based on a polarity-reversed double piezoelectric layer according to claim 7, characterized in that, The dielectric material with a positive frequency temperature coefficient includes fluorine-doped silicon dioxide and fluorine-doped silicon oxynitride.

9. A filter, characterized in that, Including the temperature-compensated resonator based on polarity-reversed double piezoelectric layers as described in any one of claims 1-8.

10. A multiplexer, characterized in that, Including the temperature-compensated resonator based on polarity-reversed double piezoelectric layers as described in any one of claims 1-8.

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