Ultrahigh-frequency film bulk acoustic wave device and preparation method thereof

Abstract

The invention provides an ultrahigh-frequency film bulk acoustic wave device and a preparation method thereof, and the ultrahigh-frequency film bulk acoustic wave device achieves high-order mode excitation through a piezoelectric layer in a single polarization direction and a reverse electric field of an adjacent layer. According to the preparation of the ultrahigh-frequency film bulk acoustic wave device, only piezoelectric layers with identical polarization directions need to be prepared, a differential preparation process of piezoelectric films with multiple polarization directions does not need to be researched, developed and controlled, the complexity of the process steps is reduced, and the whole preparation process is based on mature semiconductor processes such as etching, deposition and sacrificial layer release. No special equipment or customization technology needs to be introduced, the threshold of technology research and development and production implementation is greatly reduced, through technology simplification, the manufacturing cost is reduced, and large-scale mass production can be achieved.

Description

Technical Field

[0001] This application relates to the field of MEMS device technology, and more specifically, to an ultra-high frequency thin-film bulk acoustic wave device and its fabrication method. Background Technology

[0002] The market demand for high-frequency thin-film bulk acoustic wave (TFT-AS) devices is growing rapidly. The frequency of TFT-AS devices is related to the thickness of the piezoelectric layer, and to ensure the quality of the piezoelectric layer, its thickness needs to be maintained at a certain level. To achieve higher frequencies, the electrode thickness is often reduced; however, excessively small electrode thickness leads to a dramatic increase in electrical losses, which severely degrades the quality factor of TFT-AS devices and significantly hinders their development. Furthermore, for high-frequency TFT-AS devices (e.g., 6 GHz and above), ensuring high device yield while maintaining the necessary performance parameters presents a significant challenge, requiring sufficiently thin electrodes.

[0003] Studies have shown that introducing layers with different polarization orientations into piezoelectric materials can effectively excite previously difficult-to-drive higher-order modes, thereby doubling the operating frequency of filters. The essence of this method is to alternately align the polarization orientations of different parts of the piezoelectric layer with the electric field direction of the electrical signal, either in the opposite or the same direction, thus exciting higher-order modes. Traditional methods involve preparing piezoelectric layers with different polarization orientations while maintaining a consistent electric field direction. This matches the strain distribution of even-order thickness modes with the polarization orientation, enhancing the electromechanical coupling effect and effectively exciting second, third, or higher-order modes to meet the operating requirements of high-frequency filters. Currently, this method requires complex processes such as polarization, bonding transfer, and piezoelectric layer deposition process control to prepare multi-polarization piezoelectric thin films, resulting in significant drawbacks such as high process difficulty, limited mass production, and high manufacturing costs. Summary of the Invention

[0004] The purpose of this application is to provide an ultra-high frequency thin-film bulk acoustic wave device and its fabrication method, in order to solve the problems of existing solutions that require complex processes such as polarization, bonding transfer, and piezoelectric layer deposition process control to prepare multi-polarization piezoelectric thin films, which have significant drawbacks such as high process difficulty, limited mass production, and high manufacturing cost.

[0005] The multilayer piezoelectric resonator arrangement proposed in patent CN 1293486A aims to reduce the resonator area. Each piezoelectric layer has a different polarization direction and electric field direction. However, its polarization and electric field arrangement differs significantly from that of this patent. In this patent, each piezoelectric layer has the same polarization direction, but the electric field directions between adjacent layers alternate. In contrast, the structure proposed in patent CN 1293486A involves not all piezoelectric layers having the same polarization direction, and the electric field directions between adjacent layers are sometimes alternating and sometimes non-alternating. Therefore, this patent is significantly different from patent number CN 1293486A. The structure of this patent can realize the higher-order modes of the resonator through electric field distribution under the condition of a piezoelectric layer polarization direction, without the need to reverse the polarization of the piezoelectric layer. Therefore, it has significant cost and mass production advantages. Only the arrangement of polarization and electric field combination described in this patent can achieve the function of exciting higher-order modes. Any other different structure cannot achieve this function.

[0006] This application provides a method for fabricating an ultra-high frequency thin-film bulk acoustic wave device, comprising: The surface of the substrate is etched to form a cavity structure; Deposit a sacrificial layer in a cavity structure; On the front side of the substrate, electrode material is deposited and etched to form a first electrode layer and a bottom electrode of the same layer; On the front side of the substrate, a piezoelectric material is deposited to obtain the first piezoelectric layer; On the first piezoelectric layer, electrode material is deposited and etched to form a second electrode layer; On the front side of the substrate, a second piezoelectric layer is obtained by depositing a piezoelectric material; wherein the polarization directions of the first piezoelectric layer and the second piezoelectric layer are the same; On the second piezoelectric layer, electrode material is deposited and etched to form the third electrode layer; On the front side of the substrate, the second piezoelectric layer and the first piezoelectric layer are etched until the first electrode layer and the bottom electrode are exposed. On the front side of the substrate, the second piezoelectric layer is etched until the second electrode layer is exposed; A first metal pad is formed by depositing metal material in a first coupling region on the front side of the substrate, and a second metal pad is formed by depositing metal material in a second coupling region on the front side of the substrate; wherein, the first coupling region is the coupling region between the second electrode layer and the bottom electrode, and the second coupling region is the coupling region between the third electrode layer and the first electrode layer; one of the first metal pad and the second metal pad is grounded, and the other is connected to an electrical signal; The sacrificial layer is removed to obtain a thin-film bulk acoustic wave device with a cavity.

[0007] In the above technical solution, the ultra-high frequency thin-film bulk acoustic wave device achieves high-order mode excitation through a piezoelectric layer with a single polarization direction and an opposing electric field in adjacent layers. The fabrication of the ultra-high frequency thin-film bulk acoustic wave device only requires the fabrication of piezoelectric layers with identical polarization directions, eliminating the need for developing and controlling differentiated fabrication processes for multi-polarization piezoelectric thin films. This reduces the complexity of the process steps. The entire fabrication process is based on mature semiconductor processes such as etching, deposition, and sacrificial layer release, without the need for special equipment or customized processes. This significantly lowers the barriers to technology development and production implementation, reduces manufacturing costs through process simplification, and enables large-scale mass production.

[0008] Specifically, a sacrificial layer release process is used to deposit multiple piezoelectric layers with identical polarization directions, each separated by upper and lower electrodes. To achieve the effect of alternating polarization directions and electric field directions, the electric field direction applied to each piezoelectric layer is opposite to that of the adjacent layers. This allows for the excitation of higher-order modes using only a piezoelectric film with one polarization direction and electric fields in different directions. This method avoids the complex processes of polarization, bonding transfer, and piezoelectric layer deposition process control to prepare multi-polarization piezoelectric films, resulting in lower process difficulty, limited scalability, and lower manufacturing costs.

[0009] In some alternative embodiments, the surface of the substrate is etched to form a cavity structure, including: A cavity structure is formed on the substrate using a dry etching process.

[0010] In the above technical solution, the substrate material can be one of silicon, silicon carbide, sapphire, or any combination thereof. First, the substrate is ultrasonically cleaned using an SPM solution. Then, a cavity structure is formed on the substrate using dry etching. The etching angle should be less than 70 degrees. The cross-section of the cavity can be one of trapezoidal, triangular, rectangular, or square, or any combination thereof. The lateral width of the cavity is 20-600 μm, and the depth of the cavity is 0.5 μm-5 μm.

[0011] In some alternative implementations, depositing a sacrificial layer in the cavity structure includes: A sacrificial material is deposited on a substrate using MOCVD or PECVD processes, and then partially removed from the substrate and the sacrificial material using chemical mechanical polishing to form a sacrificial layer.

[0012] In the above technical solution, the sacrificial material can be one of silicon, silicon oxide, doped silicon oxide, silicon nitride, doped silicon nitride, or any combination thereof. A sacrificial material layer with a thickness slightly greater than the cavity depth is deposited on the substrate obtained in the previous step using MOCVD or PECVD. Chemical mechanical polishing (CMP) is then used to partially remove the sacrificial material layer and the substrate, leaving a sacrificial layer with a thickness less than the cavity depth.

[0013] In some alternative embodiments, on the front side of the substrate, electrode material is deposited and etched to form a first electrode layer and a bottom electrode in the same layer, including: Electrode material is deposited on the front side of the substrate using magnetron sputtering or MOCVD, and then patterned using a dry etching process to form a first electrode layer and a bottom electrode that are in the same layer but isolated from each other.

[0014] In the above technical solution, the electrode material can be one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, and nickel, with a thickness of 50-2000 nm and a lateral width of 20-500 μm for the patterned first electrode layer. A certain thickness of electrode material is deposited on the substrate prepared in the previous step using magnetron sputtering or MOCVD, and then dry-etched to form the first electrode layer of the device. The etching process for the first electrode is as follows: RF power 500 / 60 W, chamber pressure 6 mT, SF6 / O2 etching gas flow rate 60 / 80 sccm, etching rate approximately 100 nm / min. To ensure the coverage of subsequent film layers, the etching angle should be ≤15°.

[0015] In some alternative embodiments, a first piezoelectric layer is formed by depositing a piezoelectric material on the front side of the substrate, comprising: The first piezoelectric layer is obtained by depositing piezoelectric material on the front side of the substrate using magnetron sputtering or MOCVD processes.

[0016] In the above technical solution, the piezoelectric material can be one or any combination of aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate (PZT), lithium niobate, etc., and the thickness of the first piezoelectric layer is 20-2000 nm. The first piezoelectric layer is obtained by depositing a certain thickness of piezoelectric material on the substrate prepared in the previous step using magnetron sputtering or MOCVD.

[0017] In some alternative embodiments, an electrode material is deposited on the first piezoelectric layer and etched to form a second electrode layer, including: Electrode material is deposited on the first piezoelectric layer using magnetron sputtering or MOCVD, and then patterned using a dry etching process to form the second electrode layer.

[0018] In the above technical solution, the electrode material can be one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, and nickel, with a thickness of 50-2000 nm and a lateral width of 20-500 μm for the patterned second electrode layer. A certain thickness of electrode material is deposited on the substrate prepared in the previous step using magnetron sputtering or MOCVD, and then dry-etched to form the second electrode layer of the device. The etching process for the second electrode is as follows: RF power 500 / 60 W, chamber pressure 6 mT, SF6 / O2 etching gas flow rate 60 / 80 sccm, etching rate approximately 100 nm / min. To ensure the coverage of subsequent film layers, the etching angle should be ≤15°.

[0019] In some alternative embodiments, a second piezoelectric layer is obtained by depositing a piezoelectric material on the front side of the substrate, comprising: A second piezoelectric layer is obtained by depositing piezoelectric material on the front side of the substrate using magnetron sputtering or MOCVD processes.

[0020] In the above technical solution, the piezoelectric material can be one or any combination of aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate (PZT), lithium niobate, etc., and the thickness of the second piezoelectric layer is 20-2000 nm. The second piezoelectric layer is obtained by depositing a certain thickness of piezoelectric material on the substrate prepared in the previous step using magnetron sputtering or MOCVD.

[0021] In some alternative embodiments, an electrode material is deposited and etched on the second piezoelectric layer to form a third electrode layer, including: Electrode material is deposited on the second piezoelectric layer using magnetron sputtering or MOCVD, and then patterned using a dry etching process to form the third electrode layer.

[0022] In the above technical solution, the electrode material can be one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, and nickel, with a thickness of 50-2000 nm and a lateral width of 20-500 μm for the patterned third electrode layer. A certain thickness of electrode material is deposited on the substrate prepared in the previous step using magnetron sputtering or MOCVD, and then dry-etched to form the third electrode layer of the device. The etching process for the third electrode is as follows: RF power 500 / 60 W, chamber pressure 6 mT, SF6 / O2 etching gas flow rate 60 / 80 sccm, etching rate approximately 100 nm / min. To ensure the coverage of subsequent film layers, the etching angle should be ≤15°.

[0023] In some alternative embodiments, on the front side of the substrate, the second piezoelectric layer and the first piezoelectric layer are etched until the first electrode layer and the bottom electrode are exposed, including: A dry etching process is used to etch the second piezoelectric layer and the first piezoelectric layer on the front side of the substrate.

[0024] In the above technical solution, dry etching is used to etch the second piezoelectric layer and the first piezoelectric layer of the substrate obtained in the previous step, so that the first electrode layer and the bottom electrode are exposed. The etching process is as follows: RF power 600 / 100W, chamber pressure 8Mt, etching gas Cl2 / Ar flow rate 120 / 40sccm, and etching rate of about 350nm / min.

[0025] In some alternative implementations, on the front side of the substrate, the second piezoelectric layer is etched until the second electrode layer is exposed, including: A dry etching process is used to etch the second piezoelectric layer on the front side of the substrate.

[0026] In the above technical solution, dry etching is used to etch the second piezoelectric layer of the substrate obtained in the previous step, so that the first electrode layer and the bottom electrode are exposed. The etching process is as follows: RF power 600 / 100W, chamber pressure 8Mt, etching gas Cl2 / Ar flow rate 120 / 40sccm, and etching rate of about 350nm / min.

[0027] In some alternative embodiments, a first metal pad is formed by depositing metal material in a first coupling region on the front side of the substrate, and a second metal pad is formed by depositing metal material in a second coupling region on the front side of the substrate, including: Metal materials are deposited on the first and second coupling regions on the front side of the substrate obtained in the previous step using thermal evaporation or magnetron sputtering processes, and then patterned using dry etching, wet etching, or stripping processes to obtain the first and second metal pads.

[0028] In the above technical solution, the metal material can be one of gold, platinum, copper, aluminum, silver, titanium, and nickel, or any combination thereof. The thickness of the first metal pad and the second metal pad is 0.4μm-10μm.

[0029] In some alternative embodiments, the sacrificial layer is removed to obtain a thin-film bulk acoustic wave device with a cavity, including: The substrate prepared in the previous step was soaked in a release solution made of hydrofluoric acid HF and buffer BOE.

[0030] This application provides an ultra-high frequency thin-film bulk acoustic wave device, which includes a resonant stacked structure and a cavity structure. The resonant stack structure is positioned above the cavity structure; The resonant stacked structure includes n piezoelectric layers and n+1 electrode layers, with the piezoelectric layers and electrode layers stacked alternately. The polarization directions of the n piezoelectric layers are consistent; The n+1 electrode layers are arranged from bottom to top as the first electrode layer, the second electrode layer, ..., the n+1th electrode layer; The resonant stacked structure also includes a bottom electrode, a first metal pad, and a second metal pad; wherein the bottom electrode and the first electrode layer are located on the same layer; The bottom electrode is coupled to all even-numbered electrode layers via a first metal pad, and the first electrode layer is coupled to all odd-numbered electrode layers via a second metal pad; one of the first metal pad and the second metal pad is grounded, and the other is connected to an electrical signal.

[0031] In the above technical solution, all piezoelectric layers have the same polarity, and the electric field directions of adjacent piezoelectric layers are opposite, thereby achieving an alternating distribution of polarity and electric field direction in the same or opposite direction, and realizing high-order mode excitation. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 A flowchart illustrating the fabrication steps of an ultra-high frequency thin-film bulk acoustic wave device provided in this application embodiment; Figure 2 A schematic diagram of the substrate obtained in step S1 of this application embodiment; Figure 3 A schematic diagram of the substrate obtained in step S2 of this application embodiment; Figure 4 A schematic diagram of the substrate obtained in step S3 of this application embodiment; Figure 5 A schematic diagram of the substrate obtained in step S4 of this application embodiment; Figure 6 A schematic diagram of the substrate obtained in step S5 of this application embodiment; Figure 7 A schematic diagram of the substrate obtained in step S6 of this application embodiment; Figure 8 A schematic diagram of the substrate obtained in step S7 of this application embodiment; Figure 9 A schematic diagram of the substrate obtained in step S8 of this application embodiment; Figure 10 A schematic diagram of the substrate obtained in step S9 of this application embodiment; Figure 11 A schematic diagram of the substrate obtained in step S10 of this application embodiment; Figure 12A schematic diagram of the double-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave device obtained in step S11 of this application embodiment; Figure 13 A schematic diagram of a three-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave device provided in another embodiment of this application; Figure 14 This is a comparison of impedance curves for single-layer piezoelectric thin-film bulk acoustic wave devices, double-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave devices, and triple-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave devices.

[0034] Icons: 100-Substrate, 101-Sacrificial layer, 102-First electrode layer, 103-First piezoelectric layer, 104-Second electrode layer, 105-Second piezoelectric layer, 106-Third electrode layer, 1071-First metal pad, 1072-Second metal pad, 108-Third piezoelectric layer, 109-Fourth electrode layer, 110-Bottom electrode. Detailed Implementation

[0035] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0036] Please refer to Figure 1 , Figure 1 A flowchart illustrating the fabrication steps of an ultra-high frequency thin-film bulk acoustic wave device provided in this application embodiment includes: Step S1: Etch the surface of the substrate 100 to form a cavity structure; Step S2: Deposit a sacrificial layer 101 in the cavity structure; Step S3: On the front side of the substrate, deposit electrode material and etch to form a first electrode layer 102 and a bottom electrode 110 of the same layer; Step S4: Deposit piezoelectric material on the front side of the substrate to obtain the first piezoelectric layer 103; Step S5: Deposit electrode material on the first piezoelectric layer 103 and etch to form the second electrode layer 104; Step S6: On the front side of the substrate, a piezoelectric material is deposited to obtain a second piezoelectric layer 105; wherein the polarization directions of the first piezoelectric layer 103 and the second piezoelectric layer 105 are the same. Step S7: Deposit electrode material on the second piezoelectric layer 105 and etch to form the third electrode layer 106; Step S8: On the front side of the substrate, etch the second piezoelectric layer 105 and the first piezoelectric layer 103 until the first electrode layer 102 and the bottom electrode 110 are exposed. Step S9: Etch the second piezoelectric layer 105 on the front side of the substrate until the second electrode layer 104 is exposed. Step S10: Deposit metal material in the first coupling region on the front side of the substrate to form a first metal pad 1071, and deposit metal material in the second coupling region on the front side of the substrate to form a second metal pad 1072; wherein, the first coupling region is the coupling region between the second electrode layer 104 and the bottom electrode 110, and the second coupling region is the coupling region between the third electrode layer 106 and the first electrode layer 102; one of the first metal pad 1071 and the second metal pad 1072 is grounded, and the other is connected to an electrical signal; Step S11: Remove the sacrificial layer 101 to obtain a thin-film bulk acoustic wave device with a cavity.

[0037] In this embodiment, the ultra-high frequency thin-film bulk acoustic wave device achieves high-order mode excitation through a piezoelectric layer with a single polarization direction and an opposing electric field in adjacent layers. The fabrication of the ultra-high frequency thin-film bulk acoustic wave device only requires the fabrication of piezoelectric layers with identical polarization directions, eliminating the need for developing and controlling differentiated fabrication processes for multi-polarization piezoelectric thin films. This reduces the complexity of the process steps. The entire fabrication process is based on mature semiconductor processes such as etching, deposition, and sacrificial layer 101 release, without the need for special equipment or customized processes. This significantly lowers the barriers to technology development and production implementation, reducing manufacturing costs through process simplification and enabling large-scale mass production.

[0038] Specifically, a sacrificial layer 101 release process is used to deposit multiple piezoelectric layers with identical polarization directions, each separated by upper and lower electrodes. To achieve the effect of alternating polarization directions and electric field directions, the electric field direction applied to each piezoelectric layer is opposite to that of the adjacent piezoelectric layer. This allows for the excitation of higher-order modes using only a piezoelectric film with one polarization direction and electric fields in different directions. This method avoids the complex processes of polarization, bonding transfer, and piezoelectric layer deposition process control to prepare multi-polarization piezoelectric films, resulting in lower process difficulty, limited scalability, and lower manufacturing costs.

[0039] Please refer to Figure 2 , Figure 2 A schematic diagram of the substrate obtained in step S1 of the embodiments of this application.

[0040] In some alternative embodiments, the surface of the substrate 100 is etched to form a cavity structure, including: A cavity structure is formed on substrate 100 using a dry etching process.

[0041] Dry etching is a process that removes materials through gas-phase chemical reactions or physical bombardment, without the use of liquid chemical reagents.

[0042] In this embodiment, the substrate 100 can be made of silicon, silicon carbide, sapphire, or any combination thereof. First, the substrate 100 is ultrasonically cleaned with SPM solution. Then, a cavity structure is formed on the substrate 100 using dry etching. The etching angle should be less than 70 degrees. The cross-section of the cavity can be trapezoidal, triangular, rectangular, or square, or any combination thereof. The lateral width of the cavity is 20-600 μm, and the depth of the cavity is 0.5 μm-5 μm.

[0043] Please refer to Figure 3 , Figure 3 A schematic diagram of the substrate obtained in step S2 of this application embodiment.

[0044] In some alternative embodiments, depositing a sacrificial layer 101 in the cavity structure includes: A sacrificial material is deposited on the substrate using MOCVD or PECVD processes, and a chemical mechanical polishing process is used to partially remove the sacrificial material and the substrate 100 to form a sacrificial layer 101.

[0045] Among them, MOCVD (Metal-Organic Chemical Vapor Deposition) is a chemical vapor deposition technology that deposits a thin film on the surface of a substrate 100 by decomposing a metal-organic compound precursor at high temperature.

[0046] PECVD (Plasma-Enhanced Chemical Vapor Deposition) is a chemical vapor deposition technique that uses plasma to activate reactive gases to achieve thin film deposition at low temperatures.

[0047] In this embodiment, the sacrificial material can be one or any combination of silicon, silicon oxide, doped silicon oxide, silicon nitride, doped silicon nitride, etc. A sacrificial material layer with a thickness slightly greater than the cavity depth is deposited on the substrate prepared in the previous step using MOCVD or PECVD. Chemical mechanical polishing (CMP) is then used to partially remove the sacrificial material layer and the substrate 100, leaving a sacrificial layer 101 with a thickness less than the cavity depth.

[0048] Please refer to Figure 4 , Figure 4 A schematic diagram of the substrate obtained in step S3 of this application embodiment.

[0049] In some alternative embodiments, on the front side of the substrate, electrode material is deposited and etched to form a first electrode layer 102 and a bottom electrode 110 in the same layer, including: Electrode material is deposited on the front side of the substrate using magnetron sputtering or MOCVD, and patterned using a dry etching process to form the first electrode layer 102 and the bottom electrode 110.

[0050] Among them, magnetron sputtering is a physical vapor deposition technology that uses high-energy ions to bombard a target material, causing the target material atoms to be sputtered and deposited onto the substrate 100.

[0051] In this embodiment, the electrode material can be one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, and nickel, with a thickness of 50-2000 nm. The lateral width of the patterned first electrode layer 102 is 20-500 μm. A certain thickness of electrode material is deposited on the substrate prepared in the previous step using magnetron sputtering or MOCVD, and then dry-etched to form the first electrode layer 102 of the device. The etching process for the first electrode is as follows: RF power 500 / 60 W, chamber pressure 6 mT, SF6 / O2 etching gas flow rate 60 / 80 sccm, etching rate approximately 100 nm / min. To ensure the coverage of subsequent film layers, the etching angle should be ≤15°.

[0052] Please refer to Figure 5 , Figure 5 A schematic diagram of the substrate obtained in step S4 of this application embodiment.

[0053] In some alternative embodiments, a first piezoelectric layer 103 is formed by depositing a piezoelectric material on the front side of the substrate, comprising: The first piezoelectric layer 103 is obtained by depositing piezoelectric material on the front side of the substrate using magnetron sputtering or MOCVD process.

[0054] In this embodiment, the piezoelectric material can be one or any combination of aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate (PZT), lithium niobate, etc., and the thickness of the first piezoelectric layer 103 is 20-2000 nm. The first piezoelectric layer 103 is obtained by depositing a certain thickness of piezoelectric material on the substrate prepared in the previous step using magnetron sputtering or MOCVD.

[0055] Please refer to Figure 6 , Figure 6 A schematic diagram of the substrate obtained in step S5 of this application embodiment.

[0056] In some alternative embodiments, depositing electrode material and etching to form a second electrode layer 104 on the first piezoelectric layer 103 includes: Electrode material is deposited on the first piezoelectric layer 103 using magnetron sputtering or MOCVD, and then patterned using a dry etching process to form the second electrode layer 104.

[0057] In this embodiment, the electrode material can be one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, and nickel, with a thickness of 50-2000 nm. The lateral width of the patterned second electrode layer 104 is 20-500 μm. A certain thickness of electrode material is deposited on the substrate prepared in the previous step using magnetron sputtering or MOCVD, and the second electrode layer 104 of the device is formed by dry etching. The etching process for the second electrode is as follows: RF power 500 / 60 W, chamber pressure 6 mT, SF6 / O2 etching gas flow rate 60 / 80 sccm, etching rate approximately 100 nm / min. To ensure the coverage of subsequent film layers, the etching angle should be ≤15°.

[0058] Please refer to Figure 7 , Figure 7 A schematic diagram of the substrate obtained in step S6 of this application embodiment.

[0059] In some alternative embodiments, a second piezoelectric layer 105 is formed by depositing a piezoelectric material on the front side of the substrate, comprising: A second piezoelectric layer 105 is obtained by depositing piezoelectric material on the front side of the substrate using magnetron sputtering or MOCVD processes.

[0060] In this embodiment, the piezoelectric material can be one or any combination of aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate (PZT), lithium niobate, etc., and the thickness of the second piezoelectric layer 105 is 20-2000 nm. The second piezoelectric layer 105 is obtained by depositing a certain thickness of piezoelectric material on the substrate prepared in the previous step using magnetron sputtering or MOCVD.

[0061] Please refer to Figure 8 , Figure 8 A schematic diagram of the substrate obtained in step S7 of this application embodiment.

[0062] In some alternative embodiments, an electrode material is deposited and etched on the second piezoelectric layer 105 to form a third electrode layer 106, including: Electrode material is deposited on the second piezoelectric layer 105 using magnetron sputtering or MOCVD, and then patterned using a dry etching process to form the third electrode layer 106.

[0063] In this embodiment, the electrode material can be one or any combination of molybdenum, gold, platinum, copper, aluminum, silver, titanium, tungsten, and nickel, with a thickness of 50-2000 nm. The lateral width of the patterned third electrode layer 106 is 20-500 μm. A certain thickness of electrode material is deposited on the substrate prepared in the previous step using magnetron sputtering or MOCVD, and then dry-etched to form the third electrode layer 106 of the device. The etching process for the third electrode is as follows: RF power 500 / 60 W, chamber pressure 6 mT, SF6 / O2 etching gas flow rate 60 / 80 sccm, etching rate approximately 100 nm / min. To ensure the coverage of subsequent film layers, the etching angle should be ≤15°.

[0064] Please refer to Figure 9 , Figure 9 A schematic diagram of the substrate obtained in step S8 of this application embodiment.

[0065] In some alternative embodiments, on the front side of the substrate, the second piezoelectric layer 105 and the first piezoelectric layer 103 are etched until the first electrode layer 102 and the bottom electrode 110 are exposed, including: A dry etching process is used to etch the second piezoelectric layer 105 and the first piezoelectric layer 103 on the front side of the substrate.

[0066] In this embodiment, dry etching is used to etch the second piezoelectric layer 105 and the first piezoelectric layer 103 of the substrate obtained in the previous step, so that the first electrode layer 102 and the bottom electrode 110 are exposed. The etching process is as follows: RF power 600 / 100W, chamber pressure 8Mt, etching gas Cl2 / Ar flow rate 120 / 40sccm, and etching rate of about 350nm / min.

[0067] Please refer to Figure 10 , Figure 10 A schematic diagram of the substrate obtained in step S9 of this application embodiment.

[0068] In some alternative embodiments, on the front side of the substrate, the second piezoelectric layer 105 is etched until the second electrode layer 104 is exposed, including: The second piezoelectric layer 105 is etched on the front side of the substrate using a dry etching process.

[0069] In this embodiment, dry etching is used to etch the second piezoelectric layer 105 of the substrate obtained in the previous step, so that the first electrode layer 102 and the bottom electrode 110 are exposed. The etching process is as follows: RF power 600 / 100W, chamber pressure 8Mt, etching gas Cl2 / Ar flow rate 120 / 40sccm, and etching rate of about 350nm / min.

[0070] Please refer to Figure 11 , Figure 11 A schematic diagram of the substrate obtained in step S10 of this application embodiment.

[0071] In some optional embodiments, a first metal pad 1071 is formed by depositing metal material in a first coupling region on the front side of the substrate, and a second metal pad 1072 is formed by depositing metal material in a second coupling region on the front side of the substrate, including: Metal materials are deposited on the first and second coupling regions on the front side of the substrate obtained in the previous step using thermal evaporation or magnetron sputtering processes, and then patterned using dry etching, wet etching, or stripping processes to obtain the first metal pad 1071 and the second metal pad 1072.

[0072] Thermal evaporation is a physical vapor deposition technique that uses a heating source material to evaporate the vapor, which then condenses on a substrate 100 to form a thin film.

[0073] In this embodiment, the metal material can be one or any combination of gold, platinum, copper, aluminum, silver, titanium, and nickel. The thickness of the first metal pad 1071 and the second metal pad 1072 is 0.4μm-10μm.

[0074] Please refer to Figure 12 , Figure 12 A schematic diagram of the double-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave device obtained in step S11 of the embodiments of this application.

[0075] In some alternative embodiments, the sacrificial layer 101 is removed to obtain a thin-film bulk acoustic wave device with a cavity, comprising: The substrate prepared in the previous step was soaked in a release solution made of hydrofluoric acid HF and buffer BOE.

[0076] In the fabrication of ultra-high frequency thin-film bulk acoustic wave devices, the release solution composed of hydrofluoric acid (HF) and buffered oxide etchant (BOE) is mainly used to remove the sacrificial layer 101 (such as silicon oxide or silicon nitride) to form the cavity structure of the device. The standard ratio of BOE (e.g., 6:1 BOE) or the HF concentration is adjusted according to the thickness of the sacrificial layer 101 material (such as SiO2 or Si3N4) and the required etching rate.

[0077] Please refer to Figure 13 , Figure 13This is a schematic diagram of a three-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave device according to another embodiment of this application. Compared with the two-layer structure, this device adds a third piezoelectric layer 108 and a fourth electrode layer 109. In this embodiment, the bottom electrode 110, the second electrode layer 104, and the fourth electrode layer 109 are all coupled to the first metal pad 1071, and the first electrode layer 102 and the third electrode layer 106 are both coupled to the second metal pad 1072.

[0078] Please refer to Figure 14 , Figure 14 The impedance curves of single-layer piezoelectric thin-film bulk acoustic wave devices, double-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave devices, and triple-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave devices are compared. It can be seen that, compared with single-layer piezoelectric thin-film bulk acoustic wave devices, double-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave devices and triple-layer piezoelectric ultra-high frequency thin-film bulk acoustic wave devices reach the peak resonance intensity at a higher frequency and can excite higher frequencies.

[0079] This application provides an ultra-high frequency thin-film bulk acoustic wave device, which includes a resonant stacked structure and a cavity structure. The resonant stack structure is positioned above the cavity structure; The resonant stacked structure includes n piezoelectric layers and n+1 electrode layers, with the piezoelectric layers and electrode layers stacked alternately. The polarization directions of the n piezoelectric layers are consistent; The n+1 electrode layers are arranged from bottom to top as the first electrode layer, the second electrode layer, ..., the n+1th electrode layer; The resonant stacked structure also includes a bottom electrode, a first metal pad, and a second metal pad; wherein the bottom electrode and the first electrode layer are located on the same layer; The bottom electrode is coupled to all even-numbered electrode layers via a first metal pad, and the first electrode layer is coupled to all odd-numbered electrode layers via a second metal pad; one of the first metal pad and the second metal pad is grounded, and the other is connected to an electrical signal.

[0080] In this embodiment, all piezoelectric layers have the same polarity, and adjacent piezoelectric layers are subjected to electric fields in opposite directions, thereby achieving an alternating distribution of polarity and electric field direction in the same or opposite directions, and realizing high-order mode excitation.

[0081] In the embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some communication interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.

[0082] Furthermore, the units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0083] Furthermore, the functional modules in the various embodiments of this application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0084] In this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, without necessarily requiring or implying any such actual relationship or order between these entities or operations.

[0085] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for fabricating an ultra-high frequency thin-film bulk acoustic wave device, characterized in that, include: The surface of the substrate is etched to form a cavity structure; Deposit a sacrificial layer in a cavity structure; On the front side of the substrate, electrode material is deposited and etched to form a first electrode layer and a bottom electrode of the same layer; On the front side of the substrate, a piezoelectric material is deposited to obtain the first piezoelectric layer; On the first piezoelectric layer, electrode material is deposited and etched to form a second electrode layer; On the front side of the substrate, a second piezoelectric layer is obtained by depositing a piezoelectric material; wherein the polarization directions of the first piezoelectric layer and the second piezoelectric layer are the same; On the second piezoelectric layer, electrode material is deposited and etched to form the third electrode layer; On the front side of the substrate, the second piezoelectric layer and the first piezoelectric layer are etched until the first electrode layer and the bottom electrode are exposed. On the front side of the substrate, the second piezoelectric layer is etched until the second electrode layer is exposed; A first metal pad is formed by depositing metal material in a first coupling region on the front side of the substrate, and a second metal pad is formed by depositing metal material in a second coupling region on the front side of the substrate; wherein, the first coupling region is the coupling region between the second electrode layer and the bottom electrode, and the second coupling region is the coupling region between the third electrode layer and the first electrode layer; one of the first metal pad and the second metal pad is grounded, and the other is connected to an electrical signal; The sacrificial layer is removed to obtain a thin-film bulk acoustic wave device with a cavity.

2. The method as described in claim 1, characterized in that, The surface of the etched substrate forms a cavity structure, including: A cavity structure is formed on the substrate using a dry etching process.

3. The method as described in claim 1, characterized in that, The deposition of a sacrificial layer in the cavity structure includes: A sacrificial material is deposited on a substrate using MOCVD or PECVD processes, and then partially removed from the substrate and the sacrificial material using chemical mechanical polishing to form a sacrificial layer.

4. The method as described in claim 1, characterized in that, The process of depositing electrode material and etching to form a first electrode layer and a bottom electrode on the front side of the substrate includes: Electrode material is deposited on the front side of the substrate using magnetron sputtering or MOCVD, and then patterned using a dry etching process to form a first electrode layer and a bottom electrode that are in the same layer but isolated from each other.

5. The method as described in claim 1, characterized in that, The first piezoelectric layer is obtained by depositing a piezoelectric material on the front side of the substrate, including: The first piezoelectric layer is obtained by depositing piezoelectric material on the front side of the substrate using magnetron sputtering or MOCVD processes.

6. The method as described in claim 1, characterized in that, The deposition of electrode material and etching to form a second electrode layer on the first piezoelectric layer includes: Electrode material is deposited on the first piezoelectric layer using magnetron sputtering or MOCVD, and then patterned using a dry etching process to form the second electrode layer.

7. The method as described in claim 1, characterized in that, The second piezoelectric layer is obtained by depositing a piezoelectric material on the front side of the substrate, including: A second piezoelectric layer is obtained by depositing piezoelectric material on the front side of the substrate using magnetron sputtering or MOCVD processes.

8. The method as described in claim 1, characterized in that, The deposition of electrode material and etching to form a third electrode layer on the second piezoelectric layer includes: Electrode material is deposited on the second piezoelectric layer using magnetron sputtering or MOCVD, and then patterned using a dry etching process to form the third electrode layer.

9. The method as described in claim 1, characterized in that, The process of etching the second piezoelectric layer and the first piezoelectric layer on the front side of the substrate until the first electrode layer and the bottom electrode are exposed includes: A dry etching process is used to etch the second piezoelectric layer and the first piezoelectric layer on the front side of the substrate.

10. The method as described in claim 1, characterized in that, The process of etching the second piezoelectric layer on the front side of the substrate until the second electrode layer is exposed includes: A dry etching process is used to etch the second piezoelectric layer on the front side of the substrate.

11. The method as described in claim 1, characterized in that, The deposition of metal material in a first coupling region on the front side of the substrate to form a first metal pad, and deposition of metal material in a second coupling region on the front side of the substrate to form a second metal pad, includes: Metal materials are deposited on the first and second coupling regions on the front side of the substrate using thermal evaporation or magnetron sputtering processes, and then patterned using dry etching, wet etching, or stripping processes to obtain the first and second metal pads.

12. The method as described in claim 1, characterized in that, The removal of the sacrificial layer to obtain a thin-film bulk acoustic wave device with a cavity includes: The substrate was soaked in a release solution prepared with hydrofluoric acid HF and buffer BOE.

13. An ultra-high frequency thin-film bulk acoustic wave device, characterized in that, Including resonant stacked structures and cavity structures; The resonant stack structure is disposed above the cavity structure; The resonant stacked structure includes n piezoelectric layers and n+1 electrode layers, with the piezoelectric layers and electrode layers stacked alternately. The polarization directions of the n piezoelectric layers are consistent; The n+1 electrode layers are arranged from bottom to top as the first electrode layer, the second electrode layer, ..., the n+1th electrode layer; The resonant stacked structure further includes a bottom electrode, a first metal pad, and a second metal pad; wherein the bottom electrode and the first electrode layer are located on the same layer; The bottom electrode is coupled to all even-numbered electrode layers via a first metal pad, and the first electrode layer is coupled to all odd-numbered electrode layers via a second metal pad; one of the first metal pad and the second metal pad is grounded, and the other is connected to an electrical signal.

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