Film bulk acoustic resonator and preparation method of transparent protective layer

Abstract

The invention belongs to the technical field of semiconductor materials and electronic communication devices, and discloses a film bulk acoustic resonator and a preparation method of a transparent protective layer, the film bulk acoustic resonator comprises a film bulk acoustic resonator semi-finished product, the uppermost layer of the film bulk acoustic resonator semi-finished product is a metal electrode, the top of the metal electrode is provided with the transparent protective layer, the transparent protective layer is SiO2, and the transparent protective layer is a transparent protective layer. The transparent protection layer is provided with openings according to the distribution of the electrodes and is used for limiting the positions of packaging and ball mounting, the transparent protection layer is arranged on the metal electrodes, the performance of the chip and electrode connection are not affected, meanwhile, the standardization and reliability of chip packaging connection can be improved, and the metal electrodes can be better protected from being damaged by collision, scratch, natural oxidation and the like.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor materials and electronic communication devices, and in particular to a method for preparing a thin film bulk acoustic wave resonator and a transparent protective layer. Background Art

[0002] Film bulk acoustic resonator (FBAR) is a new type of radio frequency device with an excellent quality factor Q value and the advantage of being integrated on an IC chip. It is also compatible with the complementary metal oxide semiconductor (CMOS) process, and can effectively avoid the problem that surface acoustic wave resonators and dielectric resonators are not compatible with the CMOS process.

[0003] The core structure of the film bulk acoustic wave resonator is a piezoelectric oscillation stack structure composed of an acoustic mirror-electrode-piezoelectric layer-electrode. Its working principle is that when an electrical signal passes through the electrodes at both ends, the inverse piezoelectric effect of the material will convert the electrical signal into mechanical vibration. The mechanical vibration propagates in the piezoelectric film in the form of sound waves. When the propagation distance of the sound wave in the piezoelectric film is exactly an odd multiple of half the wavelength, resonance will occur. The sound wave loss at the resonant frequency is the smallest, so that the sound signal of this frequency can pass through the piezoelectric film layer, while signals of other frequencies are blocked, so that only signals with specific frequencies are output at the output end to achieve the resonance function of the electrical signal.

[0004] At present, the metal electrodes used for wiring or ball planting in thin film bulk acoustic wave resonators are easily damaged by collision scratches and natural oxidation. At the same time, there are no restrictions on the position and size of the ball planting during packaging, which not only increases the packaging cost but also is not conducive to the standardization of the product. Summary of the invention

[0005] The purpose of the present application is to provide a thin film bulk acoustic wave resonator and a method for preparing a transparent protective layer, which can protect metal electrodes from collision scratches and natural oxidation, and improve the standardization and reliability of chip packaging connections.

[0006] In the first aspect, the present application provides a thin film bulk acoustic wave resonator, including a thin film bulk acoustic wave resonator semi-finished product, the top layer of the thin film bulk acoustic wave resonator semi-finished product is a metal electrode, and a transparent protective layer is provided on the top of the metal electrode; the transparent protective layer is SiO2; the transparent protective layer is provided with openings according to the electrode distribution, which is used to limit the position of the package planting ball.

[0007] The thin film bulk acoustic wave resonator provided in this application cleverly solves the problem of metal electrode being easily damaged and the uncertainty of the packaging ball position by adding a transparent protective layer on the metal electrode and setting a specific opening. This design not only protects the key metal electrode, but also improves the accuracy and controllability of the packaging process, thereby significantly improving the performance and reliability of the thin film bulk acoustic wave resonator.

[0008] Preferably, the thin film bulk acoustic wave resonator semi-finished product includes a substrate, an acoustic reflector, a bottom electrode, a piezoelectric film and a top electrode stacked in sequence from bottom to top; the acoustic reflector is located directly below the piezoelectric film, and an upper and lower electrode connecting layer is connected between the bottom electrode and the top electrode; a bonding layer surrounding the piezoelectric film and the top electrode is also provided at the top edge of the bottom electrode, the top cover of the bonding layer is connected with a WLP packaging layer, and the metal electrode electrically connected to the bonding layer is provided on the top of the WLP packaging layer.

[0009] The semi-finished film bulk acoustic wave resonator adopts a structure that is stacked from bottom to top, including key components such as substrate, acoustic reflector, bottom electrode, piezoelectric film and top electrode. The setting of the acoustic reflector helps to improve the resonance efficiency, and the upper and lower electrode connection layers ensure good connection between the electrodes. In addition, the design of the bonding layer, WLP packaging layer and metal electrode facilitates subsequent packaging and external connection. This structural design not only optimizes the performance of the resonator, but also improves the reliability and integration of the device. Preferably, the acoustic reflector is a cavity or a Bragg reflector layer.

[0010] By using a cavity or a Bragg reflector as an acoustic reflector, the performance of a thin film bulk acoustic resonator can be effectively improved. The cavity structure is simple and easy to make, while the Bragg reflector can provide better performance. These two structures provide different options for designers to choose the appropriate acoustic reflector structure according to specific application requirements.

[0011] Preferably, the piezoelectric film includes at least one of PZT, AlN, GaN, ZnO, CdS and LiNbO3.

[0012] By using at least one of PZT, AlN, GaN, ZnO, CdS and LiNbO3 as a piezoelectric film material in a thin film acoustic wave resonator, the problem of selecting piezoelectric film materials can be effectively solved. These materials have their own characteristics, for example, PZT has a high piezoelectric coefficient, AlN and GaN have good temperature stability and CMOS compatibility, ZnO and CdS have a high electromechanical coupling coefficient, and LiNbO3 has excellent piezoelectric properties and a high electromechanical coupling coefficient. By selecting the right material or material combination, the performance of the resonator can be optimized according to specific application requirements, such as improving the Q value, improving frequency stability, and enhancing the electroacoustic conversion efficiency, thereby realizing a high-performance and high-reliability thin film acoustic wave resonator.

[0013] Preferably, the upper and lower electrode connection layer is a conductive layer, and the top electrode, the bottom electrode and the upper and lower electrode connection layer include at least one of molybdenum, tungsten, gold, aluminum, silver and titanium.

[0014] By selecting appropriate conductive materials and structural designs, the problems of conductivity of the upper and lower electrode connection layers and electrode material selection are solved. Using a conductive layer as the upper and lower electrode connection layer can ensure the effective transmission of electrical signals between the top electrode and the bottom electrode. At the same time, by selecting metal materials such as molybdenum, tungsten, gold, aluminum, silver and titanium, the conductivity, stability and cost requirements in different application scenarios can be met. This design not only improves the performance of the thin film bulk acoustic wave resonator, but also increases its applicability and flexibility.

[0015] Preferably, the substrate is high-resistance silicon, lithium niobate or sapphire.

[0016] The choice of substrate material can meet the performance requirements of the FBAW resonator in different application scenarios. By selecting a suitable substrate material, the performance and reliability of the FBAW resonator can be effectively improved, and the technical problems of substrate material selection can be solved. The choice of this substrate material, combined with the structure of the entire FBAW resonator, can provide a good foundation for the upper acoustic reflector, electrode, piezoelectric film and other structures, thereby realizing a high-performance FBAW resonator.

[0017] Preferably, the thickness of the top electrode and the bottom electrode is 200 nm-300 nm, and the thickness of the upper and lower electrode connection layer is 1.4 μm.

[0018] The performance of the FBAW resonator can be optimized by setting the appropriate electrode thickness and connection layer thickness. The setting of the top and bottom electrode thickness can affect the resonant frequency and quality factor of the device, while the thickness of the upper and lower electrode connection layer affects the electrical performance and reliability of the device. Precise control of these thickness parameters can help optimize device performance and improve the working efficiency and stability of the resonator.

[0019] Preferably, the thickness of the metal electrode is 4200 nm, and the thickness of the transparent protective layer is 1000 nm.

[0020] These two specific thickness settings play a key role in solving the technical problems of setting the thickness of the metal electrode and the transparent protective layer in the thin film bulk acoustic wave resonator. The 4200nm thickness of the metal electrode is the result of optimization, which can ensure good electrical performance without being too thick to affect the overall size and performance of the device. The 1000nm thickness of the transparent protective layer is a balance between protection effect and transparency, which can provide sufficient protection without being too thick to affect visibility during the ball planting process.

[0021] In a second aspect, the present application provides a method for preparing a transparent protective layer of a thin film bulk acoustic wave resonator, which is used to prepare the transparent protective layer in the thin film bulk acoustic wave resonator described above, comprising the following steps: A1. Preparing a transparent protective layer on the surface of the metal electrode using plasma chemical vapor deposition; A2. Etching openings on the transparent protective layer by plasma etching for packaging ball implantation.

[0022] This preparation method effectively solves the problem of easy damage to the metal electrodes of the thin film acoustic wave resonator and the irregular position of the package ball by adding a transparent protective layer on the surface of the metal electrode and etching specific openings on the transparent protective layer. Plasma chemical vapor deposition technology can form a uniform and dense transparent protective layer on the surface of the metal electrode, effectively protecting the metal electrode from damage such as collision scratches and natural oxidation. At the same time, by accurately etching openings on the transparent protective layer through plasma etching technology, the position and size of the package ball can be accurately defined, which improves the standardization and consistency of the product and reduces the packaging cost. This method not only protects the metal electrode, but also optimizes the packaging process and improves the reliability and production efficiency of the thin film acoustic wave resonator.

[0023] Furthermore, the present application also proposes that before step A1, the substrate, the acoustic reflector, the bottom electrode, the piezoelectric film, the top electrode, the upper and lower electrode connecting layer, the bonding layer, the WLP packaging layer and the metal electrode are assembled to obtain the semi-finished film bulk acoustic wave resonator.

[0024] As can be seen from the above, the present application provides a method for preparing a thin film bulk acoustic wave resonator and its transparent protective layer, including a thin film bulk acoustic wave resonator semi-finished product, the top layer of the thin film bulk acoustic wave resonator semi-finished product is a metal electrode, and a transparent protective layer is provided on the top of the metal electrode; the transparent protective layer is SiO2; the transparent protective layer is provided with openings according to the electrode distribution, which are used to limit the position of the package planting ball. By providing a transparent protective layer on the top of the metal electrode, the metal electrode can be effectively protected from collision scratches and natural oxidation, thereby improving the performance and life of the resonator. At the same time, the openings provided on the transparent protective layer can limit the position of the package planting ball, reduce the packaging cost, and improve the standardization and reliability of the chip packaging connection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of the structure of a thin film bulk acoustic wave resonator provided in an embodiment of the present application.

[0026] Figure 2 This is a schematic diagram of the structure of a thin film bulk acoustic wave resonator provided in an embodiment of the present application when a transparent protective layer is not prepared.

[0027] Figure 3 This is a flow chart of a method for preparing a transparent protective layer provided in an embodiment of the present application.

[0028] Explanation of reference numerals: 1. Substrate; 2. Acoustic reflector; 3. Bottom electrode; 4. Piezoelectric film; 5. Top electrode; 6. Upper and lower electrode connection layer; 7. Bonding layer; 8. WLP packaging layer; 9. Metal electrode; 10. Transparent protective layer. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application claimed for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application.

[0030] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0031] As a new type of RF device, film bulk acoustic resonator (FBAR) has the advantages of high quality factor Q value and can be integrated into IC chip, which is compatible with CMOS process. However, in practical applications, FBAR faces serious technical challenges, mainly in the two aspects of metal electrode fragility and uncertain packaging ball position. These problems not only affect the performance and reliability of FBAR, but also increase the packaging cost and reduce the standardization of products. In the RF front-end module of 5G communication base station, FBAR plays an important role as a key filter component. Specifically, in a typical base station configuration, multiple FBAR devices are required to achieve signal filtering in different frequency bands. These FBAR devices are usually connected to external circuits through metal electrodes. During the production and installation process, metal electrodes are extremely vulnerable to damage due to the lack of effective protection. Specifically, during the packaging process, operators may accidentally scratch the electrode surface, or the electrode may be damaged by vibration during transportation. In addition, due to the non-fixed ball planting position, the ball planting position of each FBAR device may be slightly different, which makes it difficult to achieve automated packaging in large-scale production, thereby increasing production costs and time.

[0032] In film bulk acoustic resonator (FBAR), package ball planting refers to the placement of metal solder balls (usually tin balls) on specific pads during the packaging process to facilitate subsequent soldering connections. This process is an important step in the semiconductor packaging process, especially in flip chip ball grid array packaging (FCBGA). The purpose of ball planting is to ensure the electrical connection between the chip and the external circuit while providing mechanical support. In the process of package ball planting, two methods are usually used: solder paste plus solder balls or flux paste plus solder balls. Among them, in film bulk acoustic resonator, metal electrodes are vulnerable to collision, scratches and natural oxidation. Therefore, optimizing the location of package ball planting is crucial to ensure the reliability and performance of the device.

[0033] Please refer to Figure 1 , Figure 2 In a thin film bulk acoustic wave resonator provided in the present application, a transparent protective layer 10 is arranged on the top of the metal electrode 9 of the topmost layer of the semi-finished thin film bulk acoustic wave resonator. This transparent protective layer 10 can effectively prevent the metal electrode 9 from being damaged by collision scratches and natural oxidation. At the same time, openings are arranged on the transparent protective layer 10 according to the electrode distribution to accurately define the position of the package implant.

[0034] Among them, the semi-finished film bulk acoustic wave resonator refers to a film bulk acoustic wave resonator structure that has not yet completed the final packaging, and can be specifically implemented by a multilayer structure including a substrate 1, an acoustic reflector 2, a bottom electrode 3, a piezoelectric film 4 and a top electrode 5. The metal electrode 9 refers to a conductive layer arranged on the top layer of the semi-finished film bulk acoustic wave resonator, and can be specifically implemented by metal materials such as molybdenum, tungsten, gold, aluminum, silver and titanium. The transparent protective layer 10 refers to a transparent material layer covering the top of the metal electrode 9, and can be specifically implemented by SiO2 material. The opening refers to a specific area on the transparent protective layer 10 corresponding to the electrode, which is used to limit the position of the package planting ball, and can be specifically formed on the transparent protective layer 10 by an etching process.

[0035] The core innovation of the present application is to set a transparent protective layer 10 on top of the metal electrode 9 on the top layer of the semi-finished film bulk acoustic wave resonator, and to set openings on the transparent protective layer 10 according to the electrode distribution. This design can not only effectively protect the metal electrode 9 from the external environment, but also accurately define the position of the package planting ball, thereby improving the standardization and consistency of the package.

[0036] SiO2 material has excellent transparency, wear resistance and chemical stability, and can effectively prevent the metal electrode from physical damage and chemical erosion. First, SiO2 has extremely high chemical stability, is insoluble in water, and hardly reacts with other acids except hydrofluoric acid. This stability enables the SiO2 layer to effectively protect the metal electrode from chemical erosion in the environment and reduce the risk of natural oxidation. Secondly, as a hard protective film, the SiO2 layer can resist external physical damage, such as collisions and scratches, and protect the metal electrode from damage. The SiO2 film also has good insulation properties and can be used as a circuit isolation medium or insulating medium, which means that the SiO2 protective layer will not affect the electrical properties of the metal electrode and provide additional protection. In addition, the SiO2 film has a low refractive index and good light transmittance. In practical applications, the presence of the transparent protective layer 10 will not affect the electrical properties of the metal electrode. At the same time, due to the transparency of SiO2, the operator can clearly see the metal electrode 9 below, which is convenient for subsequent packaging and detection. The purpose of setting the opening is to protect the metal electrode 9 while still being able to perform ball planting operations at a specific position. The position and size of the opening correspond to the layout of the metal electrode 9. The precise positioning of these openings ensures that bump placement can only occur at the intended locations, improving package consistency and reliability.

[0037] In summary, the SiO2 protective layer not only provides physical and chemical protection for the metal electrode, but also controls the position and size of the ball planting through precise opening design, thereby improving the packaging quality and reliability of the thin film bulk acoustic wave resonator. Through this design, the present application effectively solves the problem of the metal electrode 9 being easily damaged and the uncertainty of the packaging ball planting position. The presence of the transparent protective layer 10 significantly improves the durability of the metal electrode 9, and the precisely set openings make automated packaging possible, thereby reducing production costs and improving production efficiency.

[0038] Furthermore, the semi-finished film bulk acoustic wave resonator includes a substrate 1, an acoustic reflector 2, a bottom electrode 3, a piezoelectric film 4 and a top electrode 5 stacked in sequence from bottom to top, the acoustic reflector 2 is located directly below the piezoelectric film 4, an upper and lower electrode connecting layer 6 is connected between the bottom electrode 3 and the top electrode 5, a bonding layer 7 surrounding the piezoelectric film 4 and the top electrode 5 is also provided on the top edge of the bottom electrode 3, a WLP packaging layer 8 is covered on the top of the bonding layer 7, a metal electrode 9 electrically connected to the bonding layer 7 is provided on the top of the WLP packaging layer 8, a transparent protective layer 10 is provided on the top of the metal electrode 9, which can protect the metal electrode from collision scratches and natural oxidation, thereby improving the standardization and reliability of the chip packaging connection.

[0039] The semi-finished film bulk acoustic wave resonator of the present application adopts a structural design that is stacked from bottom to top, including key components such as substrate 1, acoustic reflector 2, bottom electrode 3, piezoelectric film 4 and top electrode 5. This structural design not only optimizes the performance of the resonator, but also improves the reliability and integration of the device. Specifically, the substrate 1 serves as the basic supporting structure of the entire device, and materials such as high-resistance silicon, lithium niobate or sapphire can be selected. The acoustic reflector 2 is located directly below the piezoelectric film to reflect sound waves and improve the resonance efficiency. The bottom electrode 3 and the top electrode 5 form an electric field to excite the piezoelectric film to generate sound waves. Preferably, a bonding layer 7 surrounding the piezoelectric film 4 and the top electrode 5 is provided at the top edge of the bottom electrode 3 to provide support for subsequent packaging. The top cover of the bonding layer 7 is connected to a WLP packaging layer 8 to provide protection and packaging. A metal electrode 9 electrically connected to the bonding layer 7 is provided on the top of the WLP packaging layer 8 for external electrical connection.

[0040] This structural design achieves efficient sound wave propagation and electrical signal conversion through reasonable material selection and stacking arrangement. The setting of the acoustic reflector 2 effectively improves the resonance efficiency and reduces energy loss. The design of the upper and lower electrode connection layers 6 ensures good connection between the electrodes and improves the stability of the device. The design of the bonding layer 7, WLP packaging layer 8 and metal electrode 9 facilitates subsequent packaging and external connection, enhances the integration and reliability of the device, and lays the foundation for achieving high-performance resonance function.

[0041] The acoustic reflector 2 is a cavity or a Bragg reflector layer, and the Bragg reflector layer is formed by overlapping high and low acoustic impedances. Figure 1 In the embodiment, as a preferred embodiment, the acoustic reflector 2 is a cavity, which is opened at the top of the substrate 1 facing the piezoelectric film 4. The acoustic reflector 2 is an important component of the thin film bulk acoustic resonator, and is used to reflect sound waves and improve the resonance efficiency. The cavity structure realizes the reflection of sound waves by forming a cavity under the piezoelectric film. This structure can effectively isolate the sound waves from propagating to the substrate, thereby improving the quality factor of the resonator. Specifically, the cavity can be formed by first depositing a sacrificial layer on the substrate 1, then making a piezoelectric film and other structures thereon, and finally removing the sacrificial layer by etching. The thickness of the cavity is usually designed to be a quarter wavelength to achieve the best reflection effect.

[0042] The Bragg reflector is made of multiple layers of materials with different acoustic impedances stacked alternately. By carefully designing the thickness and acoustic impedance of each layer of material, efficient sound wave reflection can be achieved at a specific frequency. The Bragg reflector can provide a wider bandwidth and better temperature stability. For example, a Bragg reflector can be constructed using alternating high acoustic impedance materials and low acoustic impedance materials.

[0043] These two acoustic reflector structures play a key role in the thin film bulk acoustic wave resonator. The cavity structure effectively reduces the leakage of acoustic energy to the substrate by creating an acoustic isolation layer, thereby improving the quality factor of the resonator. The Bragg reflector forms an efficient acoustic wave reflection interface within a specific frequency range through the difference in acoustic impedance of multiple layers of materials. Both structures can significantly improve the performance of the resonator, but each has its own characteristics and applicable scenarios.

[0044] By using a cavity or a Bragg reflection layer as an acoustic reflector 2, the performance of the thin film bulk acoustic wave resonator is effectively improved. Compared with the traditional solid reflection layer, both structures can provide better sound wave isolation effect. The solid reflection layer can usually only provide limited sound wave reflection, resulting in part of the sound energy leaking to the substrate, reducing the quality factor of the resonator. The cavity structure proposed in the present application almost completely isolates the propagation of sound waves to the substrate, and the Bragg reflection layer achieves more efficient sound wave reflection through a multi-layer structure. This not only improves the quality factor of the resonator, but also improves its frequency response characteristics and temperature stability.

[0045] The piezoelectric film 4 is a thin film material having a piezoelectric effect, and includes at least one of PZT, AlN, GaN, ZnO, CdS and LiNbO3.

[0046] The piezoelectric film 4 is the core component of the thin film bulk acoustic wave resonator, and its material selection directly affects the performance of the resonator. By selecting at least one of PZT, AlN, GaN, ZnO, CdS and LiNbO3 as the material of the piezoelectric film 4, a variety of material selections can be achieved to meet the needs of different application scenarios. These materials have excellent piezoelectric properties and can improve the electroacoustic conversion efficiency of the resonator. By adjusting the material properties, the frequency response and temperature stability of the resonator can be optimized. Some materials have good CMOS process compatibility, which is conducive to device integration.

[0047] The material selection scheme for the piezoelectric film 4 proposed in this application has a variety of possible implementations. For example, a single material can be selected as the piezoelectric film 4, such as using only PZT or AlN. Another way is to use a composite structure of multiple materials, such as a PZT / AlN double-layer structure or an AlN / ZnO alternating multilayer structure. These different implementations can be selected and optimized according to specific application requirements. The selection of the piezoelectric film 4 material is closely related and interactive with other structural components of the resonator, such as the bottom electrode 3 and the top electrode 5. For example, when AlN is selected as the piezoelectric film, a good lattice match can be formed with the molybdenum electrode, thereby improving the film quality and device performance. When using PZT, compatibility with platinum electrodes may need to be considered. In addition, the thickness of the piezoelectric film 4 also needs to be coordinated with the electrode thickness to achieve the best resonance effect. Specifically, the thickness of the piezoelectric film 4 is 300nm-1200nm, and the preferred thickness needs to be selected according to the product frequency band.

[0048] The piezoelectric film 4 of the present application can effectively improve the performance of the resonator. PZT material has a high piezoelectric coefficient, which can significantly improve the electromechanical coupling coefficient of the device, thereby enhancing the signal conversion efficiency. AlN and GaN materials have good temperature stability, which can improve the frequency stability of the resonator under different temperature environments. ZnO and CdS materials have high electromechanical coupling coefficients, which can improve the bandwidth of the device. LiNbO3 has excellent piezoelectric properties and high electromechanical coupling coefficients, which can achieve high-performance resonators. By selecting suitable piezoelectric film 4 materials or material combinations, the performance of the resonator can be optimized according to specific application requirements. For example, for applications requiring high Q values, AlN materials can be selected; for applications requiring wide bandwidth, ZnO or PZT materials can be selected. This flexible material selection strategy enables thin film bulk acoustic wave resonators to adapt to different application scenarios, such as RF filters, sensors or resonators.

[0049] The top electrode 5 and the bottom electrode 3 include at least one of molybdenum, tungsten, gold, aluminum, silver and titanium. The upper and lower electrode connection layer 6 is a conductive layer, which includes at least one of molybdenum, tungsten, gold, aluminum, silver and titanium.

[0050] Using a conductive layer as the upper and lower electrode connection layer 6 can ensure the effective transmission of electrical signals between the top electrode 5 and the bottom electrode 3. At the same time, by selecting metal materials such as molybdenum, tungsten, gold, aluminum, silver and titanium, the conductivity, stability and cost requirements in different application scenarios can be met. This design not only improves the performance of the thin film bulk acoustic wave resonator, but also increases its applicability and flexibility.

[0051] Specifically, the present application uses a conductive layer as the upper and lower electrode connection layer 6, which can significantly improve the conductivity of the thin film bulk acoustic wave resonator. The design of the conductive layer ensures a good electrical connection between the top electrode 5 and the bottom electrode 3, thereby reducing the loss during signal transmission. This structural design helps to improve the overall performance and efficiency of the device.

[0052] Furthermore, the present application selects at least one of molybdenum, tungsten, gold, aluminum, silver and titanium as the material of the top electrode 5, the bottom electrode 3 and the upper and lower electrode connection layer 6. These metal materials have different properties and can be selected according to specific application requirements. For example, gold and silver have excellent conductivity and are suitable for scenes requiring high conductivity; molybdenum and tungsten have high melting points and good corrosion resistance, and are suitable for use in high temperature or corrosive environments; aluminum has light weight and cost advantages, and is suitable for large-scale production; titanium has good biocompatibility and is suitable for applications in the biomedical field.

[0053] Therefore, the technical solution of the present application can meet the needs of different application scenarios through the flexibility of material selection. For example, in scenarios where high conductivity is required, gold or silver can be selected as the electrode material; in cost-sensitive applications, aluminum can be selected as the electrode material; in environments that require high temperature resistance or corrosion resistance, molybdenum or tungsten can be selected as the electrode material. This diverse material selection provides greater flexibility and adaptability for the application of thin film bulk acoustic resonators.

[0054] Wherein, the substrate 1 is high-resistance silicon, lithium niobate or sapphire.

[0055] The substrate 1 of the thin film bulk acoustic wave resonator is the basis of the entire device and has an important influence on the performance of the device. Selecting high-resistance silicon, lithium niobate or sapphire as the material of the substrate 1 has the following effects: The high resistivity of the high-resistance silicon substrate effectively reduces parasitic capacitance and signal loss, thereby improving the device's quality factor Q. This feature is crucial to improving the frequency selectivity and signal processing capabilities of the thin film bulk acoustic wave resonator.

[0056] The excellent piezoelectric properties and high acoustic velocity characteristics of lithium niobate substrates directly improve the operating frequency and bandwidth of the device. This enables thin-film bulk acoustic wave resonators based on lithium niobate substrates to operate in a higher frequency range, meeting the needs of modern communication systems for high-frequency devices. At the same time, a wider bandwidth means that the device can process more information, improving the data transmission capacity of the communication system.

[0057] The high hardness and good thermal stability of the sapphire substrate significantly improve the reliability and durability of the device. This feature enables the thin film bulk acoustic wave resonator to work stably in harsher environments, extending the service life of the device and reducing the maintenance cost of the system. Especially in high-power application scenarios, the excellent heat dissipation performance of the sapphire substrate can effectively prevent the device from failing due to overheating.

[0058] The selection of these substrate 1 materials can meet the performance requirements of the thin film bulk acoustic wave resonator in different application scenarios. By selecting a suitable substrate 1 material, the performance and reliability of the thin film bulk acoustic wave resonator can be effectively improved. The selection of this substrate 1 material is matched with the structure of the entire thin film bulk acoustic wave resonator, which can provide a good foundation for the upper layer of the acoustic reflector 2, the metal electrode 9 and the piezoelectric film 4, thereby realizing a high-performance thin film bulk acoustic wave resonator.

[0059] The materials of these substrates 1 interact positively with other structural components of the thin film bulk acoustic wave resonator. For example, the combination of the high-resistance silicon substrate 1 and the acoustic reflector 2 can further improve the reflection efficiency of the acoustic wave energy and reduce energy loss. The matching of the lithium niobate substrate 1 and the piezoelectric film 4 can enhance the piezoelectric effect and improve the electroacoustic conversion efficiency of the device. The high thermal conductivity characteristics of the sapphire substrate 1 can improve the heat dissipation performance of the device and improve the stability of the device in high-power applications.

[0060] The substrate 1 material selection scheme proposed in this application provides greater room for improving the performance of the thin film bulk acoustic wave resonator, enabling the thin film bulk acoustic wave resonator to play a role in a wider range of application fields, such as 5G communications, satellite navigation, and high-temperature sensing.

[0061] The thickness of the top electrode 5 and the bottom electrode 3 is 200 nm-300 nm; the thickness of the upper and lower electrode connection layer 6 is 1.4 μm.

[0062] The thickness of the top electrode 5 and the bottom electrode 3 is set to 200nm-300nm. This thickness range can ensure that the electrodes have good electrical conductivity, and at the same time, it will not be too thick to affect the propagation of sound waves. The thickness of the upper and lower electrode connection layer 6 is set to 1.4μm. This thickness can ensure good electrical connection between the electrodes, and at the same time, it will not be too thick to affect the structural stability of the overall device. By setting the appropriate electrode thickness and connection layer thickness, the performance of the thin film bulk acoustic wave resonator can be optimized. The setting of the thickness of the top electrode 5 and the bottom electrode 3 can affect the resonant frequency and quality factor of the device, while the thickness of the upper and lower electrode connection layer 6 affects the electrical performance and reliability of the device. Precise control of these thickness parameters can help optimize device performance and improve the working efficiency and stability of the resonator.

[0063] In the present application, the thickness of the top electrode 5 and the bottom electrode 3 is set to 200nm-300nm. This thickness range can reduce the impact on the propagation of sound waves while ensuring the conductivity of the electrode. For example, if the electrode thickness is less than 200nm, it may cause the electrode resistance to increase, affecting the electrical performance of the device. If the thickness exceeds 300nm, the sound waves may be excessively attenuated, reducing the quality factor of the device. The thickness of the upper and lower electrode connecting layer 6 is set to 1.4μm to ensure that there is sufficient electrical connection between the electrodes, reduce parasitic resistance, and improve the electrical performance of the device. At the same time, the thickness of 1.4μm will not be too thick, avoiding adverse effects on the stability of the overall structure. The setting of these thickness parameters also takes into account the feasibility of the manufacturing process. The electrode thickness of 200nm-300nm and the connection layer thickness of 1.4μm are both within the precise control range of existing thin film deposition technology, and can be accurately deposited by methods such as magnetron sputtering.

[0064] Compared with the traditional structure, the design of the present application can reduce the influence of the electrode on the propagation of the sound wave while ensuring good conductivity, thereby improving the quality factor of the device. At the same time, the optimized thickness of the connection layer can ensure good electrical connection and improve the reliability and stability of the device.

[0065] The thickness of the metal electrode 9 is 4200 nm, and the thickness of the transparent protective layer 10 is 1000 nm.

[0066] This specific thickness setting plays a key role in solving the technical problem of thickness setting of metal electrode 9 and transparent protective layer 10 in thin film bulk acoustic wave resonator. The 4200nm thickness of metal electrode 9 can ensure good electrical performance without being too thick to affect the overall size and performance of the device. The 1000nm thickness of transparent protective layer 10 is a balance point found between protection effect and transparency, which can provide sufficient protection without being too thick to affect visibility during ball implantation.

[0067] The thickness settings of the metal electrode 9 and the transparent protective layer 10 produce a synergistic effect. The 4200nm thick metal electrode 9 provides sufficient conductivity and mechanical strength to ensure the effective transmission of electrical signals and the stability of the structure. The 1000nm thick transparent protective layer 10 provides sufficient protection without affecting the function of the metal electrode, preventing the metal electrode 9 from being corroded and damaged by the external environment. This combination not only solves the original technical problems, but also further optimizes the overall performance of the device, such as increasing the Q value or improving the frequency response characteristics.

[0068] refer to Figure 3 The present application provides a method for preparing a transparent protective layer of a thin film bulk acoustic wave resonator, comprising the following steps: A1. A transparent protective layer 10 is prepared on the surface of the metal electrode 9 by plasma chemical vapor deposition; A2. Etch openings in the transparent protective layer 10 by plasma etching for packaging ball implants.

[0069] Specifically, in the first step A1, a transparent protective layer 10 is prepared on the surface of the metal electrode 9 by plasma chemical vapor deposition technology. This method can achieve uniform and dense deposition of the protective layer. The protective layer material can be selected from SiO2, which has good transparency and chemical stability. During the deposition process, the thickness and quality of the protective layer can be controlled by adjusting parameters such as gas flow, power and temperature. In the second step A2, an opening is etched on the transparent protective layer by plasma etching technology. The purpose of this step is to provide a precise position for package ball planting. Plasma etching can achieve high-precision, high-aspect ratio microstructure processing. By adjusting the etching gas composition, power and time, the shape and size of the opening can be controlled. These two steps cooperate with each other to jointly solve the problem of standardization of the position of metal electrode 9 protection and package ball planting. The transparent protective layer prepared by plasma chemical vapor deposition can effectively prevent the metal electrode 9 from being eroded and mechanically damaged by the external environment, while not affecting the electrical properties of the electrode. The opening made by plasma etching provides precise position guidance for package ball planting, improving the consistency and reliability of packaging.

[0070] Plasma chemical vapor deposition technology can form a uniform, dense, transparent protective layer on the surface of the metal electrode 9, effectively preventing the metal electrode 9 from being damaged by collision scratches and natural oxidation. This protective layer not only improves the durability of the metal electrode 9, but also maintains its electrical properties, thereby extending the service life of the thin film bulk acoustic resonator. Then, openings are accurately etched on the transparent protective layer using plasma etching technology, which can accurately define the position and size of the package planting ball. This method significantly improves the standardization and consistency of the product, reduces the packaging cost, and also improves the packaging yield.

[0071] Furthermore, the preparation method of the present application is compatible with the existing thin film bulk acoustic wave resonator manufacturing process and can be directly integrated into the existing production line without significantly changing the existing process flow. This not only reduces the implementation cost, but also improves production efficiency. In the thin film bulk acoustic wave resonator prepared by this method, the surface of the metal electrode 9 is well protected by the SiO2 protective layer, which significantly improves the oxidation resistance and scratch resistance. At the same time, the precisely controlled opening position and size provide accurate positioning for the subsequent packaging ball planting, improving the consistency and reliability of the packaging.

[0072] Traditional methods usually rely solely on packaging to protect the metal electrode 9, while the present application provides more direct and effective protection by adding a transparent protective layer 10. In the prior art, the packaging ball planting position often relies on manual or simple mechanical positioning, with poor accuracy and consistency. The present application provides more accurate positioning for packaging ball planting by precisely etching openings in the protective layer. The plasma chemical vapor deposition and plasma etching technologies used in the present application are both mature processes commonly used in the semiconductor industry, which are easy to integrate with existing production lines and do not require the introduction of completely new equipment or processes. This protection method is not only suitable for thin film bulk acoustic wave resonators, but can also be extended to other microelectronic devices that require protection of metal electrodes, and has broad application prospects.

[0073] Before step A1, the substrate 1, the acoustic reflector 2, the bottom electrode 3, the piezoelectric film 4, the top electrode 5, the upper and lower electrode connecting layers 6, the bonding layer 7, the WLP packaging layer 8 and the metal electrode 9 are assembled to obtain a semi-finished film bulk acoustic wave resonator, and then a transparent protective layer 10 is prepared on the semi-finished film bulk acoustic wave resonator through steps A1 and A2.

[0074] The technical solution of the present application provides a standardized basis for the subsequent preparation of the protective layer by completing the basic structural assembly of the thin film bulk acoustic wave resonator before preparing the transparent protective layer 10. This method can ensure that the transparent protective layer 10 can better cover and protect the metal electrode 9, while providing a reliable basic structure for the subsequent etching opening. In this way, the problem of the metal electrode 9 being easily damaged can be effectively solved, and the foundation can be laid for the standardization of the packaging ball planting position.

[0075] Pre-assembly of the substrate 1, acoustic reflector 2, bottom electrode 3, piezoelectric film 4, top electrode 5, upper and lower electrode connection layer 6, bonding layer 7, WLP packaging layer 8 and metal electrode 9 is crucial for the performance of the final product. The accurate assembly process ensures good contact and electrical connection between the various layers, which is crucial for the uniform coverage of the subsequent transparent protective layer 10. At the same time, the complete semi-finished product structure provides a stable foundation for the transparent protective layer 10, which helps to improve the adhesion and durability of the protective layer.

[0076] Compared with the prior art, the top metal electrode 9 of the thin film bulk acoustic wave resonator of the present application is a key component for wiring or ball planting. A transparent protective layer 10 is arranged on the top of the metal electrode 9 to protect the metal electrode 9 from collision scratches and natural oxidation. The transparent protective layer 10 is made of SiO2 material, which has good transparency and protection. The transparent protective layer 10 is provided with openings according to the electrode distribution. This design can accurately define the position of the package ball planting. By setting openings at specific positions, it can be ensured that the ball planting can only be carried out at a predetermined position, thereby improving the standardization and consistency of the package. This not only helps to reduce the packaging cost, but also improves the overall quality and reliability of the product. By adding a transparent protective layer 10 to the metal electrode 9 and setting specific openings, the problem of the metal electrode 9 being easily damaged and the uncertainty of the package ball planting position is cleverly solved. This design not only protects the key metal electrode 9, but also improves the accuracy and controllability of the packaging process, thereby significantly improving the performance and reliability of the thin film bulk acoustic wave resonator.

[0077] In this document, relational terms such as first and second, etc. are used merely to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0078] The above description is only an embodiment of the present application and is not intended to limit the protection scope of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A thin film bulk acoustic wave resonator, comprising a thin film bulk acoustic wave resonator semi-finished product, wherein the top layer of the thin film bulk acoustic wave resonator semi-finished product is a metal electrode (9), characterized in that: A transparent protective layer (10) is provided on the top of the metal electrode (9); The transparent protective layer (10) is SiO2; The transparent protective layer (10) is provided with openings according to the electrode distribution, and is used to limit the position of the package implant ball.

2. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: The thin film bulk acoustic wave resonator semi-finished product comprises a substrate (1), an acoustic reflection mirror (2), a bottom electrode (3), a piezoelectric film (4) and a top electrode (5) which are stacked in sequence from bottom to top; The acoustic reflector (2) is located directly below the piezoelectric film (4), and an upper and lower electrode connection layer (6) is connected between the bottom electrode (3) and the top electrode (5); A bonding layer (7) surrounding the piezoelectric film (4) and the top electrode (5) is also provided at the top edge of the bottom electrode (3); a WLP packaging layer (8) is connected to the top of the bonding layer (7); and the metal electrode (9) electrically connected to the bonding layer (7) is provided on the top of the WLP packaging layer (8).

3. The thin film bulk acoustic wave resonator according to claim 2, characterized in that: The acoustic reflector (2) is a cavity or a Bragg reflector layer.

4. The thin film bulk acoustic wave resonator according to claim 2, characterized in that: The piezoelectric film (4) comprises at least one of PZT, AlN, GaN, ZnO, CdS and LiNbO3.

5. The thin film bulk acoustic wave resonator according to claim 2, characterized in that: The upper and lower electrode connection layer (6) is a conductive layer, and the top electrode (5), the bottom electrode (3) and the upper and lower electrode connection layer (6) include at least one of molybdenum, tungsten, gold, aluminum, silver and titanium.

6. The thin film bulk acoustic wave resonator according to claim 2, characterized in that: The substrate (1) is high-resistance silicon, lithium niobate or sapphire.

7. The thin film bulk acoustic wave resonator according to claim 2, characterized in that: The thickness of the top electrode (5) and the bottom electrode (3) is 200 nm-300 nm, and the thickness of the upper and lower electrode connection layer (6) is 1.4 μm.

8. The thin film bulk acoustic wave resonator according to claim 2, characterized in that: The thickness of the metal electrode (9) is 4200 nm, and the thickness of the transparent protective layer (10) is 1000 nm.

9. A method for preparing a transparent protective layer of a thin film bulk acoustic wave resonator, used for preparing the transparent protective layer in the thin film bulk acoustic wave resonator according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: A1. Preparing a layer of the transparent protective layer (10) on the surface of the metal electrode (9) by plasma chemical vapor deposition; A2. Etching openings on the transparent protective layer (10) by plasma etching for packaging ball implants.

10. The preparation method according to claim 9, characterized in that: Prior to step A1, the substrate (1), the acoustic reflector (2), the bottom electrode (3), the piezoelectric film (4), the top electrode (5), the upper and lower electrode connection layer (6), the bonding layer (7), the WLP packaging layer (8) and the metal electrode (9) are assembled to obtain the semi-finished film bulk acoustic wave resonator.

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