Film bulk acoustic resonator and preparation method thereof

Abstract

The invention discloses a film bulk acoustic resonator and a preparation method thereof. Comprising a substrate which comprises a first cavity; the first electrode is positioned on one side of the substrate; the first piezoelectric layer is located on the side, away from the substrate, of the first electrode; the second electrode is located on the side, away from the substrate, of the first piezoelectric layer; the second piezoelectric layer is located on the side, away from the substrate, of the second electrode; the third electrode is located on the side, away from the substrate, of the second piezoelectric layer; the temperature compensation layer is located between the second electrode and the second piezoelectric layer; along the thickness direction of the film bulk acoustic resonator, the first electrode, the first piezoelectric layer, the second electrode, the temperature compensation layer, the second piezoelectric layer and the third electrode are overlapped in an effective working area; the third electrode is connected in parallel with the second electrode. The temperature compensation layer is arranged between the middle electrode and the upper electrode, and the upper electrode is combined to lead out the middle electrode to realize a parallel structure, so that the resistance Rs of the upper electrode can be effectively reduced, and the Q value of the resonator is improved.

Description

Technical Field

[0001] This invention belongs to the field of acoustic resonators, and more specifically, relates to a thin-film bulk acoustic resonator and its fabrication method. Background Technology

[0002] Thin-film bulk acoustic resonators (FBARs), as core components of modern RF front-end filters, are widely used in mobile communications, wireless networks, and the Internet of Things (IoT) due to their small size, high quality factor, and ease of integration. However, the piezoelectric thin-film materials of FBARs (such as aluminum nitride (AlN) and aluminum-doped aluminum nitride (ScAlN)) have inherent temperature coefficients, causing their resonant frequencies to drift with changes in ambient temperature, resulting in insufficient frequency stability. Temperature drift can cause shifts in the filter's passband center frequency, passband overlap, or misalignment, ultimately affecting the system's selectivity and stability. Therefore, improving the temperature stability of resonators is a key focus of current research.

[0003] In existing technologies, common temperature compensation schemes mainly involve inserting temperature compensation materials between piezoelectric layers or electrode layers. Taking AlN-based FBARs as an example, since both the commonly used piezoelectric material AlN and the electrode material Mo have negative temperature drift coefficients, it is common practice to introduce a dielectric film with a positive temperature coefficient between the electrodes or piezoelectric layers, or to use a multilayer piezoelectric composite structure to offset the temperature characteristics of different materials. While these schemes can reduce the temperature drift of the resonant frequency to some extent, their drawbacks are also significant. First, the dielectric effect of the additional compensation layer introduces additional acoustic losses, leading to a decrease in energy transfer efficiency and thus a decline in the device's quality factor. Second, since the compensation layer occupies a limited stack thickness, the electrode thickness must be reduced, resulting in increased electrode resistance. If the compensation layer is located between electrodes, it will also affect the lattice coefficient of the electrode material, reducing crystal quality and similarly affecting conductivity and power handling performance. Third, the introduction of the compensation layer changes the acoustic energy propagation path and boundary conditions, weakening the energy conversion efficiency between the piezoelectric layer and the electrode, directly leading to a decrease in the electromechanical coupling coefficient. A decrease in the electromechanical coupling coefficient not only reduces the effective bandwidth of the filter, but also significantly degrades the overall performance of the device.

[0004] In summary, while existing temperature compensation schemes improve temperature drift, they inevitably introduce drawbacks such as increased device losses, higher electrode resistance, and reduced electromechanical coupling coefficients, making it difficult to achieve a balance between temperature stability and device performance. Therefore, there is an urgent need for a new temperature compensation structure that can improve temperature drift while avoiding a decrease in the electromechanical coupling coefficient and reducing electrode resistance, thereby maintaining the high-performance characteristics of the device. Summary of the Invention

[0005] To address the shortcomings of related technologies, the present invention aims to provide a thin-film bulk acoustic resonator and its fabrication method, which aims to improve temperature drift while avoiding a decrease in electromechanical coupling coefficient and reducing electrode resistance, thereby maintaining the high-performance characteristics of the device.

[0006] To achieve the above objectives, a first aspect of the present invention provides a thin-film bulk acoustic resonator, comprising: A substrate, the substrate including a first cavity; a first electrode located on one side of the substrate; A first piezoelectric layer is located on the side of the first electrode away from the substrate; a second electrode is located on the side of the first piezoelectric layer away from the substrate; a second piezoelectric layer is located on the side of the second electrode away from the substrate; a third electrode is located on the side of the second piezoelectric layer away from the substrate. A temperature compensation layer is located between the second electrode and the second piezoelectric layer; a thickening layer, which is made of a conductive material, is located between the second piezoelectric layer and the third electrode. Along the thickness direction of the thin-film bulk acoustic resonator, the first electrode, the first piezoelectric layer, the second electrode, the temperature compensation layer, the second piezoelectric layer, and the third electrode overlap in the effective working area; the third electrode is connected in parallel with the second electrode.

[0007] Optionally, the second electrode is connected to the thickened layer through at least one through-hole.

[0008] Optionally, the second electrode extends along a direction perpendicular to the thickness of the thin-film bulk acoustic resonator to form a lateral lead, which is connected to the thickened layer via an air bridge; the air bridge includes at least one metal pillar disposed along the thickness direction for forming an electrical connection between the second electrode and the thickened layer.

[0009] Optionally, a second cavity and a third cavity are provided between the thickened layer and the second piezoelectric layer.

[0010] Optionally, the second electrode material is made of one or more of the following: molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, or chromium.

[0011] Optionally, the temperature compensation layer is made of a material with the opposite temperature drift coefficient to that of the second electrode.

[0012] Optionally, the first piezoelectric layer is a monocrystalline piezoelectric material or a polycrystalline piezoelectric material, or a rare earth doped material containing the monocrystalline piezoelectric material or the polycrystalline piezoelectric material.

[0013] A second aspect of the present invention provides a method for fabricating the above-mentioned thin-film bulk acoustic resonator, comprising the following steps: A substrate including a first cavity is provided; a first sacrificial layer is grown in the first cavity and chemically mechanically polished to the surface of the substrate; A seed layer is prepared above the cavity; A first electrode is prepared above a portion of the seed layer; A first piezoelectric layer is prepared over the first electrode and the remaining portion of the seed layer; A second electrode is fabricated above a portion of the first piezoelectric layer; A temperature compensation layer is prepared above a portion of the second electrode; A second piezoelectric layer is prepared over the temperature compensation layer and the remaining portion of the second electrode and the first piezoelectric layer; A second sacrificial layer and a third sacrificial layer are prepared above the second piezoelectric layer. The second and third sacrificial layers are arranged along the direction perpendicular to the thickness of the thin film bulk acoustic resonator and are spaced apart. Etching a first through-hole, a second through-hole, and a third through-hole, wherein the projection position of the first through-hole on the device plane is located in the area where the second piezoelectric layer and the first piezoelectric layer are in direct contact, and penetrates the first piezoelectric layer and the second piezoelectric layer; the projection positions of the second through-hole and the third through-hole on the device plane are both located in the area where the second piezoelectric layer and the second electrode are in direct contact, and penetrate the second piezoelectric layer; A thickened layer is prepared above a portion of the second piezoelectric layer; A third electrode is fabricated on top of the thickened layer and the remaining portion of the second piezoelectric layer.

[0014] Release the first sacrificial layer, the second sacrificial layer, and the third sacrificial layer to obtain the first cavity, the second cavity, and the third cavity.

[0015] Optionally, the first electrode includes an interconnected body portion and an extension portion with an angle; along the first direction, the average thickness of the body portion is greater than the average thickness of the extension portion, the body portion overlaps with the first cavity, and the extension portion is located on the side of the body portion away from the center of the first cavity.

[0016] Optionally, the tilt angle ranges from 0 to 60°.

[0017] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: (1) It significantly increases the equivalent conductive cross-sectional area of ​​the upper electrode, thereby effectively reducing its equivalent series resistance Rs and improving the quality factor Q of the resonator in the high-frequency band; (2) In another embodiment of the present invention, an air bridge structure made of metal material is provided between the second electrode and the thickened layer, and a metal pillar is introduced in the air bridge as a support and electrical connection path, so that the second electrode and the third electrode are electrically connected in parallel. The metal pillar provides reliable mechanical support for the air bridge structure while realizing electrical connection, so that a stable void structure can be formed under the air bridge, thereby introducing a sudden change in acoustic impedance at the edge of the effective working area of ​​the resonator, which helps to suppress the diffusion of acoustic energy to the periphery of the device and further reduce energy leakage; (3) A temperature compensation layer is placed between the middle electrode and the upper electrode, which provides temperature compensation without reducing device performance. The main principle is based on the distribution of metal charge on the surface, so the main sandwich structure when the device is working is the middle electrode - the first piezoelectric layer - the lower electrode. Considering that the temperature compensation layer generally has a large dielectric constant, it will bring about a large loss. The design of this invention makes the temperature compensation layer not participate in the main resonance, thus successfully avoiding the large loss it brings and improving the frequency temperature stability of the resonator; (4) Since the electric field distribution is mainly between the middle electrode, the first piezoelectric layer and the bottom electrode, there is no interference from the TC layer in this interval. Therefore, the electromechanical coupling coefficient of the resonator is also significantly improved, which comprehensively improves the Q value of the resonator. Attached Figure Description

[0018] Figure 1 This is a schematic cross-sectional view of the first type of thin-film bulk acoustic resonator provided in this embodiment of the invention; Figure 2 This is a top view of the first type of thin-film bulk acoustic resonator provided in the embodiments of the present invention; Figure 3 This is a schematic diagram showing the impedance of the resonator in an embodiment of the present invention as a function of frequency; Figure 4 This is a schematic diagram showing the relationship between the thickness of the temperature compensation layer (TC layer) and the temperature frequency drift coefficient (TCF) in an embodiment of the present invention; Figure 5 This is a schematic diagram showing the Q value of the resonator in an embodiment of the present invention as a function of the operating frequency; Figure 6 This is a schematic cross-sectional view of the second type of thin-film bulk acoustic resonator provided in this embodiment of the invention; Figures 7A-7P This is a schematic diagram of the fabrication method of the thin-film bulk acoustic resonator provided in the embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0020] The following describes the contents involved in the above embodiments in conjunction with several preferred embodiments.

[0021] Figure 1 This is a schematic cross-sectional view of the first type of thin-film bulk acoustic resonator provided in an embodiment of the present invention. Figure 2 This is a top view. For example... Figure 1 As shown, the thin-film bulk acoustic resonator includes: a substrate 101, which includes a first cavity 102; a first electrode 105 located on one side of the substrate 101; a seed layer 104 located between the substrate and the first electrode; a first piezoelectric layer 106 located on the side of the first electrode 105 away from the substrate 101; a second electrode 107 located on the side of the first piezoelectric layer 106 away from the substrate 101; a second piezoelectric layer 109 located on the side of the second electrode 107 away from the substrate 101; and a third electrode 113 located on the side of the second piezoelectric layer 105 away from the substrate 101. 9. The side away from the substrate 101; a temperature compensation layer 108, located between the second electrode and the second piezoelectric layer; a thickening layer 112, the thickening layer 112 being made of a conductive material, preferably an electrode material, located between the second piezoelectric layer 109 and the third electrode 113; along the thickness direction of the thin-film bulk acoustic resonator, the first electrode 105, the first piezoelectric layer 106, the second electrode 107, the temperature compensation layer 108, the second piezoelectric layer 109, and the third electrode 113 overlap in the effective working area; the third electrode 113 is connected in parallel with the second electrode 107. Figure 2 As shown, the shape of the resonator with the central connection is not limited. It can be the same shape as the upper and lower electrodes (with parallel sides); it can also be circular, rectangular, etc., as long as it forms a connection, it is within the scope of protection of this invention.

[0022] Specifically, the substrate 101 can be made of single-crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.; the seed layer 104 can be made of AlN. A first cavity 102 is formed in the central region of the substrate 101 by removing the sacrificial layer 103, wherein the sacrificial layer 103 can be made of SiO2, silicate glass, etc. The first cavity 102 provides acoustic isolation, preventing vibrational energy from leaking into the substrate.

[0023] Specifically, the first electrode material is made of one or more of the following: molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, or chromium. The second and third electrode materials may be the same as or different from the first electrode material.

[0024] Optionally, the temperature compensation layer is made of a material with a temperature drift coefficient opposite to that of the piezoelectric layer or electrode layer.

[0025] Optionally, the first piezoelectric layer 106 is a single-crystal piezoelectric material, such as: single-crystal aluminum nitride, single-crystal gallium nitride, single-crystal lithium niobate, single-crystal lead zirconate titanate (PZT), single-crystal potassium niobate, single-crystal quartz film, or single-crystal lithium tantalate; or a polycrystalline piezoelectric material, such as polycrystalline aluminum nitride, zinc oxide, PZT; or a rare earth element doped material containing a certain atomic ratio of the above materials, for example, it can be doped aluminum nitride, which contains at least one rare earth element, such as scandium (Sc), yttrium (Y), magnesium (Mg), titanium (Ti), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), etc. The material of the second piezoelectric layer 109 may be the same as or different from that of the first piezoelectric layer. Optionally, the second piezoelectric layer may be a non-piezoelectric material, serving to protect the temperature compensation layer.

[0026] Optionally, the third electrode 113 may also have a passivation layer 114, a recessed layer 115, and a PAD layer 116 on the side opposite to the substrate. The passivation layer 114 may be made of materials with good corrosion resistance, such as SiO2, SiC, or SiN. The PAD layer 116 is generally made of Au.

[0027] Specifically, a second cavity 1182 and a third cavity 1183 are provided between the second piezoelectric layer 109 and the thickened layer 112. These two cavities are formed by releasing the second and third sacrificial layers located on the surface of the second piezoelectric layer 109. The sacrificial layer material can be SiO2, silicate glass, etc. The second cavity 1182 and the third cavity 1183 are arranged at intervals along a plane perpendicular to the thickness direction of the thin-film bulk acoustic resonator. The presence of the second cavity 110a and the third cavity 110b creates local acoustic impedance discontinuities, which play a role in suppressing parasitic modes and enhancing acoustic energy reflection during high-frequency acoustic wave propagation, similar to the effect of a phonon crystal structure. Moreover, it can further reduce the disturbance of the electrode structure to the master mode vibration and improve the quality factor Q of the resonator. In addition, this dual-cavity structure forms an additional air gap between the thickened layer 112 and the second piezoelectric layer 109, which can reduce parasitic capacitance and thus improve the out-of-band rejection capability of the device.

[0028] Specifically, the first electrode 105, the second electrode 107, and the third electrode 113 can be understood as the lower electrode, the middle electrode, and the upper electrode, respectively. The second electrode 107 establishes an electrical connection with the thickened layer 112 through a via structure, thereby forming a parallel relationship between the second electrode 107 and the third electrode 113. To achieve this parallel path, the lead-out area of ​​the second electrode 107 is etched to form at least one through structure, which extends through the second piezoelectric layer 109 to the thickened layer 112. The via is typically formed using reactive ion etching (RIE) or deep silicon etching techniques to ensure good sidewall perpendicularity and electrical contact area in the device thickness direction. Through this via structure, the potential of the second electrode 107 can be further transferred to the third electrode 113 through the thickened layer 112, thus the second and third electrodes are electrically connected in parallel.

[0029] In a preferred structure of this embodiment, two through holes—a second through hole 1112 and a third through hole 1113—are provided to connect the second electrode 107 and the thickened layer 112. The projection positions of the second through hole 1112 and the third through hole 1113 on the device plane are both located in the area where the second piezoelectric layer and the second electrode are in direct contact, and they penetrate the second piezoelectric layer, so that the metal surface of the second electrode 107 can be directly exposed.

[0030] The structural design of this embodiment has the following beneficial effects: (1) It significantly increases the equivalent conductive cross-sectional area of ​​the upper electrode, thereby effectively reducing the equivalent series resistance Rs of the third electrode 113 and improving the quality factor Q of the resonator in the high-frequency range. For example Figure 3 As shown, the impedance curve exhibits a relatively low impedance reduction Zs at the series resonator frequency, decreasing by 50% from 0.71 to 0.35. (2) A temperature compensation layer (TC layer) is placed between the intermediate electrode and the upper electrode to provide temperature compensation without reducing device performance. The main principle is that, since the charge distribution of the metal is on the surface, the main sandwich structure during device operation is: intermediate electrode - first piezoelectric layer - lower electrode. Considering that the temperature compensation layer generally has a large dielectric constant, which would lead to significant losses, in this invention, the temperature compensation layer does not participate in the main resonance, thus successfully avoiding the significant losses it causes and improving the frequency-temperature stability of the resonator. Figure 4 As shown, the TCF gradually improves as the TC layer gradually increases in thickness; (3) Since the electric field distribution is mainly between the middle electrode, the first piezoelectric layer, and the bottom electrode, and there is no interference from the TC layer in this interval, the electromechanical coupling coefficient of the resonator is significantly improved, thus comprehensively enhancing the Q value of the resonator. For example Figure 5 As can be seen from the Bode Q, this invention more than doubles the Q value of the series resonant frequency (from 496 to 1002).

[0031] Figure 6 This is a schematic cross-sectional view of another thin-film bulk acoustic resonator provided in an embodiment of the present invention. The second electrode extends along the thickness direction of the thin-film bulk acoustic resonator to form a lateral lead, which is connected to the thickened layer via an air bridge. Specifically, in this embodiment, to further reduce the equivalent resistance of the second electrode 107 and enhance its reflection capability for high-frequency sound waves, the selected structure no longer directly connects the second electrode 107 to the thickened layer 112 through a through-hole penetrating the second piezoelectric layer 109, but instead uses an air bridge for connection. After the second electrode 107 is formed, its edge region extends outward along a plane perpendicular to the thickness direction of the thin-film bulk acoustic resonator, forming a linear lateral lead.

[0032] An air bridge is further fabricated above the end of the lateral lead. The air bridge is formed by releasing a metallic material through a sacrificial layer, and is separated from the second piezoelectric layer 109 below, forming an air gap. The other end of the air bridge 120 is in direct contact with the thickened layer 112, realizing an electrical connection between the air bridge 120 and the thickened layer 112. Since the air bridge is suspended above the second piezoelectric layer 109, no additional dielectric load is introduced into the air bridge path, thereby avoiding parasitic losses caused by dielectric layer coupling.

[0033] With the air bridge, the second electrode 107 and the third electrode 113 continue to form a parallel structure. Compared with the traditional through-hole connection method, the air bridge in this embodiment has a lower wiring resistance and can be led out without damaging the flatness of the second piezoelectric layer 109, thereby reducing process interference and reducing local electric field distortion between the upper and lower electrodes.

[0034] The air bridge structure in this embodiment includes a vertically extending metal column. The metal column is positioned along the thickness direction of the thin-film bulk acoustic resonator, with its upper end electrically connected to the thickened layer 112 and its lower end electrically connected to the upper surface of the second electrode 107, thereby forming a stable conductive and support structure between the thickened layer 112 and the second electrode 107. It also works in conjunction with the air bridge structure and the cavity region below it to form a composite support and lead-out structure.

[0035] The metal pillar serves two purposes: firstly, it enables the vertical lead-out of the electrical connection path, ensuring that the second electrode 107 and the third electrode 113 are connected in parallel, while effectively increasing the conductive cross-sectional area and thus reducing the equivalent series resistance Rs of the electrodes; secondly, the metal pillar provides mechanical support to the cavity area, improving the overall stability of the cavity structure and preventing collapse during subsequent processes or operations.

[0036] Furthermore, due to the significant difference in acoustic impedance between metallic materials, piezoelectric materials, and air, sound waves undergo reflection and scattering effects when propagating to the metal pillar and its surrounding cavity region. This suppresses the lateral diffusion of vibrational energy to the periphery of the device, reducing energy leakage. Through the synergistic effect of the metal pillar and cavity structure, this embodiment achieves reliable electrical connection while improving sound wave reflection capability, which is beneficial for improving the quality factor Q of the thin-film bulk acoustic resonator under high-frequency operating conditions.

[0037] Figures 7A-7P A method for fabricating the thin-film bulk acoustic resonator in the first embodiment described above is provided, comprising the following steps: A substrate 101 is provided, wherein a first cavity 102 is pre-formed inside the substrate 101.

[0038] A first sacrificial layer is deposited in the first cavity 102, and the upper surface of the first sacrificial layer is polished to be flush with the surface of the surrounding substrate 101 by a chemical mechanical polishing (CMP) process, so that the surface of the first sacrificial layer forms a flat substrate that can be used for subsequent thin film deposition.

[0039] Above the first cavity 102, i.e. on the surface region of the substrate 101, a seed layer 104 is prepared to provide crystal orientation or surface energy conditions to improve the deposition quality of subsequent electrodes and piezoelectric layers.

[0040] A first electrode 105 is deposited above a portion of the seed layer. The first electrode 105 may be formed by physical vapor deposition or sputtering processes and covers the area above the first cavity 102.

[0041] A first piezoelectric layer 106 is deposited together over the first electrode 105 and the remaining area of ​​the seed layer 104 not covered by the first electrode.

[0042] A second electrode 107 is formed over a portion of the first piezoelectric layer 106.

[0043] A temperature compensation layer 108 is deposited over the target area of ​​the second electrode 107.

[0044] A second piezoelectric layer 109 is deposited on the temperature compensation layer 108 and the remaining uncovered area, including the first piezoelectric layer 106 and the second electrode 107.

[0045] A second sacrificial layer 1101 and a third sacrificial layer 1102 are sequentially prepared above the second piezoelectric layer 109. Both are arranged perpendicular to the thickness direction of the device and are spaced apart to form the second cavity and the third cavity in the subsequent release step.

[0046] The first through-hole 1111, the second through-hole 1112, and the third through-hole 1113 are formed by photolithography and etching processes. The projection position of the first through-hole on the device plane (i.e., the plane perpendicular to the thickness direction of the device) is located in the area where the second piezoelectric layer 109 and the first piezoelectric layer 106 are in direct contact, and it penetrates the first piezoelectric layer 106 and the second piezoelectric layer 109. The projection positions of the second through-hole and the third through-hole are both located in the area where the second piezoelectric layer 109 and the second electrode 107 are in contact, and they penetrate the second piezoelectric layer 109, so as to realize the electrical lead-out of the second electrode 107.

[0047] After the via etching is completed, a thickened layer 112 is deposited over a portion of the second piezoelectric layer 109. This thickened layer 112 is made of a conductive material. Subsequently, a third electrode 113 is deposited over the thickened layer 112 and the remaining uncovered areas of the second piezoelectric layer 109.

[0048] After the third electrode 113 is formed, a passivation layer 114 can be sequentially prepared on its outer region, a recessed layer 115 can be etched to form a PAD layer 116, and a via 117 can be etched to complete the protective encapsulation of the device, local stress adjustment, and construction of electrical connection interfaces.

[0049] Subsequently, the first, second, and third sacrificial layers are simultaneously released using wet or dry etching processes, thereby forming the first cavity 1181, the second cavity 1182, and the third cavity 1183, respectively. The formation of these cavities further enhances the sound wave reflection and vibration energy confinement effects, which is beneficial to improving the resonator performance.

[0050] Optionally, in some embodiments, the first electrode 105 may be designed to include an interconnected body portion and an extension portion with an angle. Along a first direction, the average thickness of the first electrode body portion is greater than the thickness of the extension portion. The body portion is located above and overlaps with the first cavity 102; while the extension portion is located on the side of the body portion away from the center of the first cavity 102. This structure helps improve the stress distribution of the first electrode 105, maintaining better mechanical stability in the cavity edge region, thereby further improving the overall reliability of the resonant structure. Optionally, the angle ranges from 0 to 60°.

[0051] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A thin-film bulk acoustic resonator, characterized in that, include: A substrate, wherein the substrate includes a first cavity; The first electrode is located on one side of the substrate; A first piezoelectric layer is located on the side of the first electrode away from the substrate; The second electrode is located on the side of the first piezoelectric layer away from the substrate; A second piezoelectric layer is located on the side of the second electrode away from the substrate; a third electrode is located on the side of the second piezoelectric layer away from the substrate. A temperature compensation layer is located between the second electrode and the second piezoelectric layer; a thickening layer, which is made of a conductive material, is located between the second piezoelectric layer and the third electrode. Along the thickness direction of the thin-film bulk acoustic resonator, the first electrode, the first piezoelectric layer, the second electrode, the temperature compensation layer, the second piezoelectric layer, and the third electrode overlap in the effective working area; the third electrode is connected in parallel with the second electrode.

2. The thin-film bulk acoustic resonator as described in claim 1, characterized in that, The second electrode is connected to the thickened layer through at least one through-hole.

3. The thin-film bulk acoustic resonator as described in claim 1, characterized in that, The second electrode extends along the thickness direction perpendicular to the film bulk acoustic resonator to form a lateral lead, which is connected to the thickened layer via an air bridge; the air bridge includes at least one metal pillar, which is disposed along the thickness direction to form an electrical connection between the second electrode and the thickened layer.

4. The thin-film bulk acoustic resonator as described in claim 2 or 3, characterized in that, A second cavity and a third cavity are provided between the thickened layer and the second piezoelectric layer.

5. The thin-film bulk acoustic resonator as described in claim 4, characterized in that, The second electrode material is made of one or more of the following: molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, or chromium.

6. The thin-film bulk acoustic resonator as described in claim 5, characterized in that, The temperature compensation layer is made of a material with the opposite temperature drift coefficient to that of the second electrode.

7. The thin-film bulk acoustic resonator as described in claim 4, characterized in that, The first piezoelectric layer is a monocrystalline piezoelectric material or a polycrystalline piezoelectric material, or a rare earth doped material containing the monocrystalline piezoelectric material or the polycrystalline piezoelectric material.

8. The method for fabricating a thin-film bulk acoustic resonator according to claim 1, comprising the following steps: A substrate including a first cavity is provided; a first sacrificial layer is grown in the first cavity and chemically mechanically polished to the surface of the substrate; A seed layer is prepared above the cavity; A first electrode is prepared above a portion of the seed layer; A first piezoelectric layer is prepared over the first electrode and the remaining portion of the seed layer; A second electrode is fabricated above a portion of the first piezoelectric layer; A temperature compensation layer is prepared above a portion of the second electrode; A second piezoelectric layer is prepared over the temperature compensation layer and the remaining portion of the second electrode and the first piezoelectric layer; A second sacrificial layer and a third sacrificial layer are prepared above the second piezoelectric layer. The second and third sacrificial layers are arranged along the direction perpendicular to the thickness of the thin film bulk acoustic resonator and are spaced apart. Etching a first through-hole, a second through-hole, and a third through-hole, wherein the projection position of the first through-hole on the device plane is located in the area where the second piezoelectric layer and the first piezoelectric layer are in direct contact, and penetrates the first piezoelectric layer and the second piezoelectric layer; the projection positions of the second through-hole and the third through-hole on the device plane are both located in the area where the second piezoelectric layer and the second electrode are in direct contact, and penetrate the second piezoelectric layer; A thickened layer is prepared above a portion of the second piezoelectric layer; A third electrode is fabricated above the thickened layer and the remaining portion of the second piezoelectric layer. Release the first sacrificial layer, the second sacrificial layer, and the third sacrificial layer to obtain the first cavity, the second cavity, and the third cavity.

9. The method for fabricating a thin-film bulk acoustic resonator according to claim 8, characterized in that: The first electrode includes an interconnected body portion and an extension portion with an angle; along the first direction, the average thickness of the body portion is greater than the average thickness of the extension portion, the body portion overlaps with the first cavity, and the extension portion is located on the side of the body portion away from the center of the first cavity.

10. The method for fabricating a thin-film bulk acoustic resonator according to claim 9, characterized in that: The tilt angle ranges from 0 to 60°.

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