Bulk acoustic wave resonator and preparation method thereof

Abstract

The invention discloses a bulk acoustic wave resonator and a preparation method thereof, and relates to the technical field of resonators. The bulk acoustic wave resonator comprises a substrate, the upper surface of the substrate is recessed inwards to form a cavity, a first bottom electrode, a second bottom electrode, a piezoelectric layer and an upper electrode layer are sequentially arranged on the substrate, and the projection overlapping area of the first bottom electrode, the second bottom electrode, the piezoelectric layer and the cavity on the substrate is an effective resonance area. The effective resonance area comprises a central area and a peripheral area surrounding the periphery of the central area, in the central area, the first bottom electrode and the second bottom electrode are connected, and in the peripheral area, the first bottom electrode and the second bottom electrode are arranged at intervals in the stacking direction. According to the bulk acoustic wave resonator and the preparation method thereof, the resistance of the bottom electrode can be reduced while the heat dissipation capability of the bulk acoustic wave resonator can be improved, so that the working temperature rise and the frequency drift are reduced, and the power capacity, the long-term reliability and the quality factor are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resonators, in particular to a bulk acoustic resonator and a preparation method thereof. BACKGROUND

[0002] Film Bulk Acoustic Resonator (FBAR) is an important radio frequency micro-electro-mechanical system device, which is widely used in modern mobile communication systems, such as filters, duplexers and radio frequency front-end modules, due to its high working frequency, high Q value, small size and good compatibility with integrated circuits. With the development of 5G and even 6G communication technology, the working frequency band of radio frequency devices is constantly expanding to high frequency (such as n77, n79 and other frequency bands), and higher requirements are put forward for high power tolerance, frequency stability and long-term reliability.

[0003] A typical FBAR adopts a "sandwich" structure, including a cavity structure on a substrate, a bottom electrode, a piezoelectric layer and an upper electrode above the cavity. Among them, the cavity is used to realize acoustic isolation, so that the acoustic energy is effectively constrained in the resonant region composed of the piezoelectric layer and the electrode. However, under high power working conditions, a large amount of heat is generated due to Joule heat, dielectric loss and piezoelectric nonlinear effect in the device, which will cause the temperature of the device to rise rapidly if it cannot be removed in time, resulting in frequency drift, material degradation and even structural failure, which seriously affects its performance and service life.

[0004] The existing FBAR structure has a significant bottleneck in thermal management. First, commonly used piezoelectric materials such as aluminum nitride (AlN) or scandium-doped aluminum nitride (AlScN) have excellent piezoelectric properties, but their thermal conductivity is relatively low (AlN is about 200 W / m·K, and AlScN can be reduced to below 100 W / m·K with increasing doping concentration), limiting the efficiency of heat conduction in the vertical direction. Second, the bottom electrode and the upper electrode in the traditional structure are usually single-layer metal thin films (such as molybdenum, tungsten or aluminum), with a thickness of only a few hundred nanometers to a few microns, which has a certain transverse heat conduction capacity, but the overall heat diffusion path mainly depends on the vertical direction. Since the bottom of the device is usually an air cavity or a distributed Bragg reflector layer, these structures have poor thermal conductivity, forming a thermal resistance circuit, which seriously hinders the effective transfer of heat to the substrate.

[0005] In addition, the electrode structure design in the prior art focuses on the optimization of electrical performance, and lacks comprehensive consideration of thermal-electric collaborative management. Especially under high power density, the central region has serious heat accumulation, while the edge heat dissipation path is insufficient, resulting in large temperature gradient, which further aggravates the frequency temperature drift and stress mismatch. SUMMARY

[0006] The application aims to provide a bulk acoustic wave resonator and a preparation method thereof, which can improve the heat dissipation capacity of the bulk acoustic wave resonator, reduce the resistance of the bottom electrode, reduce the working temperature rise and frequency drift, improve the power capacity, long-term reliability and quality factor.

[0007] Embodiments of the application are implemented as follows: In a first aspect, the application provides a bulk acoustic wave resonator, comprising a substrate, a cavity formed in the upper surface of the substrate, a first bottom electrode, a second bottom electrode, a piezoelectric layer and an upper electrode layer arranged in sequence on the substrate, wherein the overlapping area of the first bottom electrode, the second bottom electrode, the piezoelectric layer and the cavity on the substrate is an effective resonance area, the effective resonance area comprises a central area and a peripheral area enclosed outside the central area, in the central area, the first bottom electrode and the second bottom electrode are connected, and in the peripheral area, the first bottom electrode and the second bottom electrode are arranged in the stacking direction.

[0008] As an implementable manner, in the peripheral area, an air cavity is formed between the first bottom electrode and the second bottom electrode.

[0009] As an implementable manner, in the central area, the second bottom electrode is recessed to connect with the first bottom electrode, and / or the first bottom electrode is protruded to connect with the second bottom electrode.

[0010] As an implementable manner, in the central area, the first bottom electrode or the second bottom electrode is thickened to connect the first bottom electrode and the second bottom electrode.

[0011] As an implementable manner, in the central area, a connecting electrode is arranged between the first bottom electrode and the second bottom electrode.

[0012] As an implementable manner, the shape of the central area comprises a circular shape, a polygonal shape or an irregular shape, or the central area comprises a plurality of sub-areas, and the plurality of sub-areas are arranged in sequence according to a closed figure.

[0013] As an implementable manner, a heat dissipation structure is further arranged between the first bottom electrode and the second bottom electrode outside the effective resonance area.

[0014] As an implementable manner, a cavity structure or an air wing is further arranged between the upper electrode and the piezoelectric layer outside the effective resonance area.

[0015] As an implementable manner, a seed layer is further arranged between the substrate and the first bottom electrode, and between the first bottom electrode and the second bottom electrode.

[0016] In a second aspect, the present application provides a method for manufacturing a bulk acoustic wave resonator, comprising: providing a substrate, forming a cavity on the substrate and filling a sacrificial material in the cavity; forming a first bottom electrode and a second bottom electrode on the substrate, wherein the first bottom electrode and the second bottom electrode are connected in a central region, and the first bottom electrode and the second bottom electrode are arranged in a stacked direction with a spacing in a periphery of the central region; sequentially forming a piezoelectric layer and an upper electrode layer on the second bottom electrode, a region in which the first bottom electrode, the second bottom electrode, the piezoelectric layer and the cavity are projected on the substrate and overlap is an effective resonance region, and the effective resonance region includes the central region and the periphery of the central region; etching to form a release hole, and releasing the sacrificial material through the release hole to form the cavity.

[0017] The beneficial effects of the embodiments of the present application include: The body acoustic wave resonator provided by the embodiment of the present application comprises a substrate, a cavity is formed in the upper surface of the substrate by concave forming, and a first bottom electrode, a second bottom electrode, a piezoelectric layer and an upper electrode layer are sequentially arranged on the substrate, wherein the area where the first bottom electrode, the second bottom electrode, the piezoelectric layer and the cavity overlap on the substrate is an effective resonance area, the effective resonance area comprises a central area and a peripheral area enclosed outside the central area, the heat generated by the body acoustic wave resonator during operation is mainly concentrated in the central area of the effective resonance area of the body acoustic wave resonator, in the central area, the first bottom electrode and the second bottom electrode are connected, and in the peripheral area, the first bottom electrode and the second bottom electrode are arranged in the stacking direction. The heat generated will be transmitted to the central area of the first bottom electrode along the stacking direction in the central area of the second bottom electrode, and will also be transmitted to the peripheral area along the horizontal direction; at the same time, the heat transmitted to the central area of the first bottom electrode will also be transmitted to the peripheral area along the horizontal direction, that is, in the peripheral area, two independent conductive layers are reserved, a horizontal heat diffusion network is constructed, and the heat on the first bottom electrode and the second bottom electrode is transmitted to the outside of the effective resonance area, and then is transmitted to the substrate. Compared with the prior art, the heat transmission path is increased, specifically, when the heat from the center spreads to the periphery through the piezoelectric layer and the bottom electrode, it can also be conducted to the periphery through the first bottom electrode layer and the second bottom electrode layer, which is equivalent to a double-channel horizontal heat dissipation. The heat in the central area can be quickly conducted to the substrate outside the periphery of the effective resonance area, thereby improving the heat dissipation capacity of the body acoustic wave resonator, reducing the operating temperature rise and frequency drift, improving the power capacity and long-term reliability. In addition, the bottom electrode of the body acoustic wave resonator of the embodiment of the present application comprises a first bottom electrode and a second bottom electrode, in the central area, the first bottom electrode and the second bottom electrode are connected, and in the peripheral area, the first bottom electrode and the second bottom electrode are arranged in the stacking direction. The bottom electrode comprises two parts connected in parallel, thereby effectively reducing the resistance of the bottom electrode, thereby improving the quality factor of the body acoustic wave resonator. Therefore, the body acoustic wave resonator of the embodiment of the present application can improve the heat dissipation capacity of the body acoustic wave resonator while reducing the resistance of the bottom electrode, thereby reducing the operating temperature rise and frequency drift, improving the power capacity and long-term reliability and the quality factor, and realizing the cooperation of electrical energy performance and thermal management. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0019] Figure 1 One of the structural schematic diagrams of the body acoustic wave resonator provided by the embodiment of the present application; Figure 2 This is a second schematic diagram of the structure of the bulk acoustic resonator provided in the embodiments of this application; Figure 3 This is the third schematic diagram of the structure of the bulk acoustic resonator provided in the embodiments of this application; Figure 4 Fourth schematic diagram of the structure of the bulk acoustic resonator provided in the embodiments of this application; Figure 5 Fifth schematic diagram of the structure of the bulk acoustic resonator provided in the embodiments of this application; Figure 6 This is the sixth schematic diagram of the structure of the bulk acoustic resonator provided in the embodiments of this application; Figure 7 This is the seventh schematic diagram of the structure of the bulk acoustic resonator provided in the embodiments of this application; Figure 8 Eighth schematic diagram of the structure of the bulk acoustic resonator provided in the embodiments of this application; Figure 9 Resistance diagram of the bulk acoustic resonator provided in the embodiments of this application compared with that of the prior art; Figure 10 Impedance curves of existing bulk acoustic resonators and existing technologies are shown. Figure 11 The frequency offset of the bulk acoustic resonator provided in the embodiments of this application compared with the prior art; Figure 12 A flowchart illustrating the method for fabricating a bulk acoustic resonator provided in this application embodiment; Figure 13 This is one of the state diagrams of the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 14 A second state diagram of the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 15 The third state diagram of the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 16 State diagram four of the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 17 The fifth state diagram of the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 18 State diagram six of the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 19 State diagram seven of the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 20 State diagram eight for the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 21State diagram nine of the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 22 State diagram ten for the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 23 Eleventh of the state diagrams for the fabrication method of the bulk acoustic resonator provided in the embodiments of this application; Figure 24 State diagram 12 for the bulk acoustic resonator fabrication method provided in the embodiments of this application; Figure 25 This is the thirteenth state diagram of the bulk acoustic resonator fabrication method provided in the embodiments of this application.

[0020] Icons: 100-Bulk Acoustic Resonator; 110-Substrate; 111-Cavity; 121-First Bottom Electrode; 122-Second Bottom Electrode; 123-Air Cavity; 124-Connecting Electrode; 130-Piezoelectric Layer; 140-Upper Electrode Layer; 150-Effective Resonant Region; 151-Central Region; 152-Outer Peripheral Region; 160-Heat Dissipation Structure; 171-Cavity Structure; 172-Air Wing; 173-Seed Layer; 181-Sacrificial Material; 182-Sacrificial Ring; 183-Sacrificial Block; 184-Thickening Layer; 185-Passivation Layer; 186-Protective Layer; 187-Release Hole; 188-Lead-out Hole. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. The described embodiments are only some embodiments of this application, not all embodiments. Similar reference numerals and letters in the following drawings indicate similar items. Once an item is defined in one drawing, it does not need to be further defined in other drawings.

[0022] The terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use. They are used only for the convenience of describing this application and should not be construed as limiting this application. The terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0023] Unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to connections within two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0024] The main working component of a bulk acoustic wave resonator is a sandwich structure. The piezoelectric layer in the sandwich structure has limited thermal conductivity, and the acoustic reflection structure below the sandwich obstructs the vertical heat dissipation path, making it difficult for heat to be transferred downward to the substrate, resulting in poor heat dissipation capacity of the bulk acoustic wave resonator.

[0025] This application provides a bulk acoustic resonator 100, such as... Figure 1 and Figure 2 As shown, the substrate includes a substrate 110, with a cavity 111 formed by a recess in the upper surface of the substrate 110. A first bottom electrode 121, a second bottom electrode 122, a piezoelectric layer 130, and an upper electrode layer 140 are sequentially disposed on the substrate 110. The area where the projections of the first bottom electrode 121, the second bottom electrode 122, the piezoelectric layer 130, and the cavity 111 on the substrate 110 overlap is an effective resonant region 150. The effective resonant region 150 includes a central region 151 and an outer peripheral region 152 surrounding the central region 151. The first bottom electrode 121 and the second bottom electrode 122 are connected within the central region 151, and the first bottom electrode 121 and the second bottom electrode 122 are spaced apart in the stacking direction within the outer peripheral region 152.

[0026] The bulk acoustic wave resonator 100 provided in this application embodiment has a first bottom electrode 121 and a second bottom electrode 122 connected in a central region 151 as a bottom electrode. The bottom electrode, the piezoelectric layer 130 and the upper electrode layer 140 form a sandwich structure as the working component of the bulk acoustic wave resonator 100. An alternating voltage is applied between the bottom electrode and the upper electrode layer 140 in the bulk acoustic wave resonator 100 to form a voltage difference on the piezoelectric layer 130. The piezoelectric layer 130 vibrates under the action of the piezoelectric effect. Specifically, the sound wave is reflected at the boundary of the effective resonance region 150, and the energy is accumulated to achieve resonance.

[0027] When the bulk acoustic wave resonator 100 is working, acoustic energy and Joule heat are mainly concentrated in the central region 151 of the effective resonant region of the bulk acoustic wave resonator 100. In this embodiment, the first bottom electrode 121 and the second bottom electrode 122 are connected in the central region 151. Thus, the generated heat is transferred from the second bottom electrode 122 in the central region 151 along the stacking direction to the central region 151 of the first bottom electrode 121, and also horizontally to the outer peripheral region 152. Simultaneously, the heat transferred to the central region 151 of the first bottom electrode 121 is also horizontally transferred to the outer peripheral region 152. That is, in the outer peripheral region 152, two independent conductive layers are retained, constructing a lateral heat diffusion network, such as... Figure 1 and Figure 2 As shown by the middle arrow, after the heat on the first bottom electrode 121 and the second bottom electrode 122 is transferred to the outside of the effective resonant region 150, it is transferred to the substrate 110. Compared with the prior art, this increases the heat transfer path. Specifically, when the heat diffuses from the center to the surroundings through the piezoelectric layer 130 and the bottom electrode, it can also be conducted to the outer periphery through the first bottom electrode 121 layer and the second bottom electrode 122 layer. This is equivalent to dual-channel lateral heat dissipation, which can quickly conduct the heat of the central region 151 to the substrate 110 on the outer periphery of the effective resonant region 150, thereby improving the heat dissipation capacity of the bulk acoustic wave resonator 100, reducing the operating temperature rise and frequency drift, and improving the power capacity and long-term reliability.

[0028] Furthermore, the bottom electrode of the bulk acoustic wave resonator 100 in this embodiment includes a first bottom electrode 121 and a second bottom electrode 122. The first bottom electrode 121 and the second bottom electrode 122 are connected in the central region 151, and the first bottom electrode 121 and the second bottom electrode 122 are spaced apart in the stacking direction in the outer peripheral region 152, so that the bottom electrode includes two parts connected in parallel, thereby effectively reducing the resistance of the bottom electrode and improving the quality factor of the bulk acoustic wave resonator 100.

[0029] In summary, the bulk acoustic wave resonator 100 of this application embodiment can improve the heat dissipation capacity of the bulk acoustic wave resonator 100 while reducing the resistance of the bottom electrode, thereby reducing the operating temperature rise and frequency drift, improving power capacity, long-term reliability and quality factor, and achieving synergistic optimization of power performance and thermal management.

[0030] In practical applications, since the bulk acoustic wave resonator 100 of this application embodiment can quickly conduct the heat of the central region 151 to the substrate 110 on the periphery of the effective resonant region 150, the temperature gradient is small, the thermal stress concentration is reduced, the risk of failure such as microcracks and delamination is reduced, and the device life is extended.

[0031] It is understandable that the first bottom electrode 121 and the second bottom electrode 122 are usually made of metallic materials, and therefore have good thermal conductivity.

[0032] Specifically, the specific materials used in each layer of this application embodiment are not limited, and those skilled in the art can make specific settings according to actual conditions. Specifically, the substrate 110 can be single-crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc. The first bottom electrode 121 can be a composite or alloy of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or the above metals. The second bottom electrode 122 can be a composite or alloy of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or the above metals. The second bottom electrode 122 can be the same as or different from the first bottom electrode 121. The piezoelectric layer 130 can be a single-crystal piezoelectric material, such as single-crystal aluminum nitride, single-crystal gallium nitride, single-crystal lithium niobate, single-crystal lead zirconate titanate, single-crystal potassium niobate, single-crystal quartz film, or single-crystal lithium tantalate, etc.; it can also be a polycrystalline piezoelectric material, such as polycrystalline aluminum nitride, zinc oxide, PZT, etc.; or it can be a rare earth element doped material containing a certain atomic ratio of the above materials, such as doped aluminum nitride, wherein the doped aluminum nitride contains at least one rare earth element, such as scandium, yttrium, magnesium, titanium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, etc. The upper electrode layer 140 can be molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a composite or alloy of the above metals, etc. The materials of the upper electrode layer 140 and the bottom electrode can be the same or different. Preferably, the upper electrode layer 140, the first bottom electrode 121 and the second bottom electrode 122 can all be the same.

[0033] In this embodiment, the first bottom electrode 121 is connected and disposed in the central region 151 and spaced apart in the outer peripheral region 152. This allows for dual-channel lateral heat dissipation of heat generated in the central region 151, enabling rapid heat transfer to the substrate 110 surrounding the effective resonant region 150, thereby improving the heat dissipation capability of the bulk acoustic wave resonator 100. Furthermore, the first bottom electrode 121 and the second bottom electrode 122 are spaced apart in the stacking direction, resulting in the bottom electrode comprising two parallel connected parts. This effectively reduces the resistance of the bottom electrode, thereby improving the quality factor of the bulk acoustic wave resonator 100.

[0034] Optional, such as Figure 1 and Figure 2 As shown, an air cavity 123 is formed between the first bottom electrode 121 and the second bottom electrode 122 within the outer peripheral region 152.

[0035] The air cavity 123 increases vertical thermal resistance, suppressing heat leakage along specific paths. Because air has extremely low thermal conductivity, the air cavity 123 introduced between the first bottom electrode 121 and the second bottom electrode 122 creates a high thermal resistance barrier locally, preventing heat from being directly conducted downwards through the electrodes to the cavity 111 region in the substrate 110, thus forcing heat to preferentially diffuse laterally. Meanwhile, the lateral heat conduction channels remain highly efficient, guiding heat to the edges for dissipation. The first bottom electrode 121 and the second bottom electrode 122, as independent metal layers, each act as a good lateral heat conductor, forming two parallel heat dissipation paths. Therefore, the overall system forms a directional heat flow control mechanism.

[0036] As an feasible approach, such as Figure 1 As shown, within the central region 151, the second bottom electrode 122 is recessed and connected to the first bottom electrode 121, and / or the first bottom electrode 121 is convex and connected to the second bottom electrode 122.

[0037] The first bottom electrode 121 and the second bottom electrode 122 are connected by the second bottom electrode 122 being recessed or the first bottom electrode 121 being convex. This makes the connection structure an integral structure with the first bottom electrode 121 or the second bottom electrode 122, which has good connection reliability and good thermal and electrical conductivity, thereby reducing contact resistance, making the current distribution uniform and the local temperature rise small.

[0038] Optionally, within the central region 151, the first bottom electrode 121 or the second bottom electrode 122 is thickened to connect the first bottom electrode 121 and the second bottom electrode 122.

[0039] The thickened first bottom electrode 121 or the second bottom electrode 122 forms a boss or columnar structure in the central region 151, which extends upward or downward to connect with the other bottom electrode, forming a direct metal-metal contact. The contact interface can be formed naturally through the deposition process without the need for additional bonding or filling materials.

[0040] As an feasible approach, such as Figure 2 As shown, a connecting electrode 124 is disposed between the first bottom electrode 121 and the second bottom electrode 122 within the central region 151.

[0041] In the central region 151, a connecting electrode 124 is provided as an independent conductive structure, which physically contacts both the first bottom electrode 121 and the second bottom electrode 122 simultaneously, forming an electrical path. The connecting electrode 124 can be a vertical conductive post, a metal plug, etc.

[0042] This makes the first bottom electrode 121 and the second bottom electrode 122 an integral structure on a horizontal plane, without steps during deposition, resulting in better film quality for the first bottom electrode 121 and the second bottom electrode 122.

[0043] Optional, such as Figure 3 , Figure 4 , Figure 5 , Figure 6 and Figure 7 As shown, the shape of the central region 151 includes a circle, a polygon, or an irregular shape, or the central region 151 includes multiple sub-regions, which are arranged in sequence according to a closed figure.

[0044] Among them, such as Figure 3 The central region is 151 of a circle. Figure 4 The central region of the rectangle is 151. Figure 5 The central region of the pentagon is 151. Figure 6 Multiple circular regions are arranged to form a circle. Figure 7 A circle is formed by arranging multiple pentagonal regions.

[0045] When the central region 151 is a single, integrated area, it is easier to operate and achieves higher precision during the preparation process.

[0046] When the central region 151 is divided into multiple sub-regions, these sub-regions are distributed along a circular path, such as... Figure 6 and Figure 7 As shown; the first bottom electrode 121 and the second bottom electrode 122 are connected in each sub-region to form a local connection structure; the generated heat is dispersed in multiple sub-regions, with the same total heat power but significantly reduced local temperature rise; the separation electrode in the outer peripheral region 152 serves as a continuous heat conduction zone, conducting heat out of the effective resonant region 150.

[0047] As an feasible approach, such as Figure 8 As shown, outside the effective resonant region 150, a heat dissipation structure 160 is also provided between the first bottom electrode 121 and the second bottom electrode 122.

[0048] When heat is transferred to outside the effective resonant region 150, the heat on the second bottom electrode 122 is transferred to the substrate 110 through the heat dissipation structure 160, reducing the interfacial thermal resistance between the first bottom electrode 121 and the second bottom electrode 122 and improving the overall thermal conductivity.

[0049] The heat dissipation structure 160 can be made of polysilicon, which can increase heat dissipation and also electrically connect the first bottom electrode 121 and the second bottom electrode 122.

[0050] Optional, such as Figure 1 and Figure 2 As shown, outside the effective resonant region 150, a cavity structure 171 or an air wing 172 is also provided between the upper electrode and the piezoelectric layer 130.

[0051] Harmonics generated within the effective resonant region 150 are reflected at the boundary of the effective resonant region 150. To prevent sound waves from leaking from the upper electrode to outside the effective resonant region 150 at the boundary of the effective resonant region 150, this embodiment of the application provides a cavity structure 171 or an air wing 172 between the upper electrode and the piezoelectric layer 130 outside the effective resonant region 150. This separates the upper electrode from the piezoelectric layer 130. The acoustic impedance of air is much lower than that of metal and piezoelectric materials, forming a high acoustic reflection interface. Thus, when sound waves are transmitted within the piezoelectric layer 130 to the boundary of the effective resonant region 150, they are blocked by the cavity structure 171 or the air wing 172, thereby suppressing sound wave leakage and improving the Q value and filter selectivity.

[0052] In the fabrication of the bulk acoustic resonator 100, after the piezoelectric layer 130 is deposited, a sacrificial layer process and an etch-release technique are used. Specifically, as follows: Figure 19 As shown, a sacrificial block 183 is coated or deposited on the surface of the piezoelectric layer 130 outside the effective region, and then... Figure 22 As shown, an upper electrode layer 140 is deposited, making it suspended at the edge of the effective resonant region 150. Finally, the sacrificial block 183 is removed by etching, forming a local cavity structure 171 or an air wing 172. The material of the sacrificial block 183 can be silicon oxide, silicate glass, etc.

[0053] As an feasible approach, such as Figure 1 and Figure 2 As shown, a seed layer 173 is also provided between the substrate 110 and the first bottom electrode 121, and between the first bottom electrode 121 and the second bottom electrode 122.

[0054] Seed layer 173 optimizes the crystal orientation, adhesion, and interfacial thermal conductivity of the metal electrode. Specifically, a first bottom electrode 121 (e.g., Mo) is deposited on seed layer 173. Its crystal structure is induced by seed layer 173, forming a highly c-axis oriented thin film with uniform crystal phase and high quality. Depositing an intermediate seed layer 173 on the surface of the first bottom electrode 121 improves the interfacial bonding between the second bottom electrode 122 (e.g., W, Al) and the first bottom electrode 121; prevents intermetallic diffusion or reaction; and maintains good crystal orientation transfer. The second bottom electrode 122 grows under the guidance of seed layer 173, maintaining high crystal quality and low resistivity.

[0055] By setting the seed layer 173, the interface resistance can be reduced and the conductivity improved; the interface thermal resistance can be reduced, and heat can be more easily conducted downward or laterally through the bottom electrode; thus improving electrical and thermal performance.

[0056] The material of the seed layer 173 is not limited in this application embodiment; for example, it may be aluminum nitride.

[0057] In practical applications, to further improve the quality factor of the bulk acoustic resonator 100, a thickening layer 184 can be provided between the upper electrode layer 140 and the piezoelectric layer 130. The thickening layer 184 corresponds to the position of the cavity structure 171 or the air wing 172, such as... Figure 1 and Figure 2 As shown, by utilizing the gaps between the thickened layer 184 and the air wing 172, and between the thickened layer 184 and the cavity structure 171, the non-longitudinal electric field introduced by the lifting of the cavity structure 171 or the air wing 172 is effectively suppressed, thus avoiding the transverse sound waves excited by the non-longitudinal electric field inside the piezoelectric layer 130, thereby improving performance.

[0058] During the fabrication of the bulk acoustic resonator 100, after the sacrificial block 183 is fabricated, a layer of material can be deposited on the sacrificial block 183 and etched to form a thickening layer 184, wherein the thickening layer 184 is located on the sacrificial block 183. Specifically, the material of the thickening layer 184 can be a metal or a non-metallic material.

[0059] In addition, to protect the upper electrode layer 140, a passivation layer 185 is also provided on the upper electrode layer 140, such as... Figure 1 and Figure 2 As shown, the passivation layer 185 is used to protect the upper electrode layer 140 from corrosion by oxygen, moisture, etc. in the air. Specific materials can be aluminum nitride, silicon dioxide, silicon nitride, silicon carbide, or metal oxides or nitrides, etc.

[0060] To protect the lead-out electrodes, a protective layer 186 can be provided on the lead-out electrodes, such as... Figure 1 and Figure 2 As shown, a protective layer 186 is formed on the lead-out electrode. The material of the protective layer 186 can be the same as that of the passivation layer 185. The material can be aluminum nitride, silicon dioxide, silicon nitride, silicon carbide, or metal oxides or nitrides, etc.

[0061] To further verify the beneficial effects of the embodiments of this application, the applicant used a bulk acoustic wave resonator with a single-layer bottom electrode in the prior art as a comparative example, and simulated the performance of the bulk acoustic wave resonator with a two-layer bottom electrode in this application and the comparative example. The results are as follows. Figure 9 , Figure 10 and Figure 11 As shown, where, Figure 9 The resistance values ​​of both are given by... Figure 9 As can be seen, the resistance value decreased from 0.41 to 0.18, a reduction of more than 50%; Figure 10 The impedance curves of the two are shown below. Figure 10 It can be seen that the impedance decreases and the quality factor increases; Figure 11 The frequency shift between the two under the same applied power is given by... Figure 11It can be seen that the frequency offset of this application (not greater than 4MHz) is much smaller than that of the prior art (not greater than 12MHz), indicating that the heat dissipation effect of this application is significantly better than that of the prior art, the resonator has a smaller power temperature rise and higher stability.

[0062] A second aspect of this application provides a method for fabricating a bulk acoustic resonator 100, such as... Figure 12 As shown, it includes: S100: As Figure 13 and Figure 14 As shown, a substrate 110 is provided, a cavity 111 is formed on the substrate 110, and a sacrificial material 181 is filled in the cavity 111; A cavity 111 can be formed by etching from the upper surface of the substrate 110 downwards. The cavity 111 is then filled with a sacrificial material 181, which can be formed by deposition. It is understood that when the sacrificial material 181 is formed in the cavity 111 by deposition, the sacrificial material 181 will also cover the surface of the substrate 110. The sacrificial material 181 on the surface of the substrate 110 can be removed by chemical polishing.

[0063] The specific material of the sacrificial material 181 can be silicon dioxide, silicate glass, etc.

[0064] S200: such as Figure 15 , Figure 16 and Figure 17 As shown, a first bottom electrode 121 and a second bottom electrode 122 are formed on a substrate 110, wherein the first bottom electrode 121 and the second bottom electrode 122 are connected in a central region 151, and the first bottom electrode 121 and the second bottom electrode 122 are spaced apart in the stacking direction on the outer periphery of the central region 151. Corresponding to the structure, a seed layer 173 can be provided between the substrate 110 and the first bottom electrode 121 and between the first bottom electrode 121 and the second bottom electrode 122. Figure 15 A seed layer 173 and a first bottom electrode 121 are formed on the upper surface of the substrate 110. The seed layer 173 can be deposited. The edge of the first bottom electrode 121 has a certain angle with the horizontal surface, which is between 0 and 60°. The first bottom electrode 121 can be prepared by a process of deposition followed by etching. Figure 16 To form the sacrificial ring 182 on the first bottom electrode 121, a deposition-then-etching process can be used. Figure 17 For seeding layer 173 and second bottom electrode 122 on sacrificial ring 182, the first bottom electrode 121 and the second bottom electrode 122 are spaced apart in the stacking direction due to the arrangement of sacrificial ring 182.

[0065] S300: such as Figures 18 to 22As shown, a piezoelectric layer 130 and an upper electrode layer 140 are sequentially formed on the second bottom electrode 122. The area where the projection of the first bottom electrode 121, the second bottom electrode 122, the piezoelectric layer 130, and the cavity 111 overlaps on the substrate 110 is the effective resonant region 150. The effective resonant region 150 includes a central region 151 and the outer periphery of the central region 151. First, a piezoelectric layer 130 is formed on the second bottom electrode 122, such as Figure 18 As shown; then a sacrificial block 183 is formed on the piezoelectric layer 130 to form the cavity structure 171 and the air wing 172, as shown. Figure 19 As shown; etching the piezoelectric layer 130 exposes the upper electrode, forming a lead-out hole 188, as... Figure 20 As shown; then a thickened layer 184 is formed on the sacrificial block 183, as follows. Figure 21 As shown; finally, an upper electrode is formed on the thickened layer 184.

[0066] S400: such as Figure 25 The etching shown forms a release hole 187, and the sacrificial material 181 is released through the release hole 187 to form a cavity 111.

[0067] Prior to step S400, a passivation layer 185 may also be formed on the upper electrode layer 140, such as... Figure 23 As shown, a protective layer 186 is formed on the lead-out electrode or the lead-out hole 188, such as Figure 24 As shown.

[0068] The bulk acoustic wave resonator 100 prepared by the fabrication method has been described in detail in the foregoing embodiments, and will not be repeated here.

[0069] The above description is merely an optional embodiment of this application and is not intended to limit 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 protection scope of this application.

[0070] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not describe the various possible combinations separately.

Claims

1. A bulk acoustic resonator, characterized in that, The device includes a substrate, the upper surface of which is recessed to form a cavity. A first bottom electrode, a second bottom electrode, a piezoelectric layer, and an upper electrode layer are sequentially disposed on the substrate. The area where the first bottom electrode, the second bottom electrode, the piezoelectric layer, and the cavity overlap on the substrate is an effective resonant region. The effective resonant region includes a central region and an outer peripheral region surrounding the central region. Within the central region, the first bottom electrode and the second bottom electrode are connected. Within the outer peripheral region, the first bottom electrode and the second bottom electrode are spaced apart in the stacking direction.

2. The bulk acoustic resonator according to claim 1, characterized in that, An air cavity is formed between the first bottom electrode and the second bottom electrode within the outer peripheral region.

3. The bulk acoustic resonator according to claim 1, characterized in that, Within the central region, the second bottom electrode is recessed and connected to the first bottom electrode, and / or the first bottom electrode is convex and connected to the second bottom electrode.

4. The bulk acoustic resonator according to claim 1, characterized in that, Within the central region, either the first bottom electrode or the second bottom electrode is thickened to connect the first bottom electrode and the second bottom electrode.

5. The bulk acoustic resonator according to claim 1, characterized in that, Within the central region, a connecting electrode is disposed between the first bottom electrode and the second bottom electrode.

6. The bulk acoustic resonator according to claim 1, characterized in that, The shape of the central region may include a circle, a polygon, or an irregular shape; or, the central region may include multiple sub-regions, which are arranged sequentially in a closed pattern.

7. The bulk acoustic resonator according to claim 1, characterized in that, Outside the effective resonant region, a heat dissipation structure is also provided between the first bottom electrode and the second bottom electrode.

8. The bulk acoustic resonator according to claim 1, characterized in that, Outside the effective resonant region, a cavity structure or air wing is also provided between the upper electrode and the piezoelectric layer.

9. The bulk acoustic resonator according to claim 1, characterized in that, A seed layer is also provided between the substrate and the first bottom electrode, and between the first bottom electrode and the second bottom electrode.

10. A method for fabricating a bulk acoustic resonator, characterized in that, include: A substrate is provided, a cavity is formed on the substrate, and a sacrificial material is filled into the cavity; A first bottom electrode and a second bottom electrode are formed on the substrate, wherein the first bottom electrode and the second bottom electrode are connected in a central region, and the first bottom electrode and the second bottom electrode are spaced apart in a stacking direction on the outer periphery of the central region; A piezoelectric layer and an upper electrode layer are sequentially formed on the second bottom electrode. The area where the first bottom electrode, the second bottom electrode, the piezoelectric layer, and the cavity are projected and overlapped on the substrate is an effective resonant region. The effective resonant region includes the central region and the outer periphery of the central region. Etching forms a release hole, and sacrificial material is released through the release hole to form a cavity.

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