A thin-film bulk acoustic resonator structure with dual stress modulation and its fabrication method

Abstract

The application discloses a thin film bulk acoustic resonator structure with double stress adjustment and a preparation method thereof. The thin film bulk acoustic resonator structure comprises a resonant structure and a capacitive stress regulation structure. The capacitive stress regulation structure comprises a first stress regulation structure and a second stress regulation structure. The first stress regulation structure and the second stress regulation structure are both parallel-plate capacitive structures. The resonant structure is located between the first stress regulation structure and the second stress regulation structure. In the application, the first top electrode in the first stress loading structure and the third bottom electrode in the second stress loading structure change the elastic stiffness coefficient of the piezoelectric layer under the driving of electrostatic force, and then change the resonant frequency of the resonator, thereby realizing temperature compensation. Meanwhile, the modulation signal and the excitation signal can be effectively separated, and the application has the characteristics of small size, low cost and low power consumption. The preparation method is simple and can be mass-produced.

Description

Technical Field

[0001] This invention relates to the field of radio frequency communication, and in particular to a thin-film bulk acoustic resonator structure and its fabrication method. Background Technology

[0002] With the continuous development of communication technology and the increasing number of communication frequency bands, radio frequency terminals are placing higher performance and smaller size requirements on radio frequency filters. Film Bulk Acoustic Resonators (FBARs) have advantages such as high resonant frequency, high quality factor, and small size. Filters made from FBARs have excellent performance and have gradually become one of the hot topics in radio frequency filter research.

[0003] The main structure of a FBAR (Bulk Flat Amplifier) ​​is a sandwich structure consisting of an upper metal electrode, a piezoelectric thin film, and a lower metal electrode. When a radio frequency (RF) signal is applied to the upper and lower electrodes of the FBAR, a longitudinal wave propagating along the thickness direction is excited in the piezoelectric thin film and reflected at the upper and lower interfaces of the sandwich structure. The acoustic loss is minimized when the longitudinal wave satisfies the standing wave oscillation condition within the sandwich structure. Then, the piezoelectric thin film converts the longitudinal wave into an electrical signal through the piezoelectric effect, achieving frequency selection of the electrical signal. Near the frequency that causes the bulk longitudinal wave to oscillate as a standing wave, if the phase of the electrical signal is consistent with the polarization phase of the piezoelectric thin film material, the FBAR produces series resonance with minimum impedance; the resonant frequency at this point is the series resonant frequency. If the phase of the electrical signal is opposite to the polarization phase of the piezoelectric thin film material, the FBAR produces parallel resonance with maximum impedance; the resonant frequency at this point is the parallel resonant frequency. The relative frequency gap between the two is usually represented by the effective electromechanical coupling coefficient; the larger the relative gap, the larger the effective electromechanical coupling coefficient.

[0004] In traditional FBAR devices, the negative temperature coefficient of sound in both piezoelectric and electrode materials causes the series and parallel resonant frequencies of the FBAR to decrease with increasing temperature. This leads to a shift in the passband of filters composed of FBARs with temperature variations. If a filter applied to a congested frequency band experiences a passband shift with temperature, it will struggle to effectively filter out interference signals from adjacent frequency bands, potentially causing device failure. Therefore, minimizing the temperature-induced resonant frequency drift of FBARs is crucial in FBAR filter applications.

[0005] In existing technologies, the following methods are mainly used to compensate for the temperature drift of the FBAR resonant frequency: 1. Adding a temperature compensation layer with a positive sound velocity temperature coefficient to the FBAR structure. However, this reduces the electromechanical coupling coefficient of the resonator, thus decreasing the bandwidth of the FBAR filter. 2. Adding a heating device, such as a resistance wire, to the FBAR structure. The heat generated by the resistance wire changes the elastic stiffness coefficient of the piezoelectric material, thereby achieving temperature compensation. However, this method is more suitable for low-temperature environments and consumes a lot of power. 3. Applying a DC bias to the upper and lower boundaries of the piezoelectric oscillator to compensate for the negative sound velocity temperature characteristics of the piezoelectric material, thus achieving temperature compensation. However, since the DC bias signal is directly applied to the working electrode, there is a problem of mutual interference between the excitation signal and the DC bias signal, and the frequency adjustment range is small. 4. Connecting a voltage-controlled capacitor in series with the FBAR. The capacitance of the voltage-controlled capacitor is controlled by the voltage output of the bridge circuit, and the voltage output of the bridge circuit changes with temperature. Temperature compensation can be achieved through proper design. However, this method cannot simultaneously adjust the series and parallel resonant frequencies of the FBAR. Therefore, it is necessary to propose a novel temperature-compensated thin-film bulk acoustic resonator to solve the above problems. Summary of the Invention

[0006] Objective of the invention: To address the aforementioned limitations of existing technologies, this invention proposes a thin-film bulk acoustic resonator (FBAR) structure with dual stress adjustment. This structure can simultaneously compensate for the temperature of the series and parallel resonant frequencies of the FBAR without causing a significant decrease in the effective electromechanical coupling coefficient. Furthermore, a simple manufacturing process suitable for large-scale fabrication is also proposed.

[0007] Technical solution: A thin-film bulk acoustic resonator structure with dual stress adjustment, comprising a resonant structure and a capacitive stress-adjusting structure; the capacitive stress-adjusting structure includes a first stress-adjusting structure and a second stress-adjusting structure; the resonant structure is located between the first stress-adjusting structure and the second stress-adjusting structure;

[0008] The first stress regulation structure includes, from bottom to top, a first substrate, a first bottom electrode, a first cavity, a first insulating layer, and a first top electrode; wherein, the first cavity is located in the first insulating layer and is disposed between the first bottom electrode and the first top electrode;

[0009] The second stress regulation structure includes, from bottom to top, a third bottom electrode, a second cavity, a fourth insulating layer, a fifth insulating layer, a third top electrode, and a second substrate; wherein, the second cavity is located between the fourth insulating layer and the fifth insulating layer, and is disposed between the third bottom electrode and the third top electrode;

[0010] The resonant structure includes, from bottom to top, a second insulating layer, a second bottom electrode, a piezoelectric layer, a second top electrode, and a third insulating layer;

[0011] The first cavity, the first top electrode, the second insulating layer, the second bottom electrode, the piezoelectric layer, the second top electrode, the third insulating layer, the third bottom electrode, and the second cavity overlap in the thickness direction to form the effective resonant region of the resonator.

[0012] Furthermore, the materials of the first top electrode, the second bottom electrode, the second top electrode, and the third bottom electrode are conductive materials with a longitudinal wave characteristic acoustic impedance greater than 50 megohms; the first insulating layer, the second insulating layer, the third insulating layer, the fourth insulating layer, and the fifth insulating layer are insulating materials with a longitudinal wave characteristic acoustic impedance less than 20 megohms.

[0013] Furthermore, the first bottom electrode and the third top electrode are made of doped silicon, the first top electrode, the second bottom electrode, the second top electrode and the third bottom electrode are made of tungsten or molybdenum, and the first insulating layer, the second insulating layer, the third insulating layer, the fourth insulating layer and the fifth insulating layer are made of silicon dioxide.

[0014] Furthermore, the thicknesses of the first bottom electrode, the first insulating layer, the first top electrode, the second insulating layer, and the second bottom electrode satisfy the Bragg reflection condition, and the thicknesses of the second top electrode, the third insulating layer, the third bottom electrode, the fourth insulating layer, the fifth insulating layer, and the third top electrode also satisfy the Bragg reflection condition.

[0015] Furthermore, the piezoelectric layer is made of aluminum nitride, and its c-axis is oriented in the thickness direction.

[0016] Furthermore, the thickness of the first cavity and the second cavity is between 0.1 μm and 1 μm.

[0017] Furthermore, by applying DC voltage signals to the first top electrode and the first bottom electrode in the first stress control structure and to the third bottom electrode and the third top electrode in the second stress control structure, tensile stress is generated on the first top electrode in the direction toward the first bottom electrode, and tensile stress is generated on the third bottom electrode in the direction toward the third top electrode. This generates tensile stress in the thickness direction in the piezoelectric layer, which counteracts the phenomenon that the elastic stiffness coefficient of the piezoelectric material decreases with increasing temperature, thus achieving temperature compensation.

[0018] The method for fabricating the thin-film bulk acoustic resonator structure includes:

[0019] Step 1: Ion implantation doping is performed on the upper surface of the first substrate, followed by high-temperature annealing of the first substrate to form the first bottom electrode; then, magnetron sputtering is performed on the upper surface of the first bottom electrode to prepare the first insulating layer.

[0020] Step 2: The first cavity sacrificial layer filling area is etched on the first insulating layer by photolithography. Then, the sacrificial layer material is deposited on the device surface by chemical vapor deposition. Then, the excess sacrificial layer material is removed by chemical mechanical polishing. The first cavity sacrificial layer is formed in the etched area of ​​the first insulating layer.

[0021] Step 3: Deposit the first top electrode, the second insulating layer, the second bottom electrode, the piezoelectric layer, the second top electrode, the third insulating layer, the third bottom electrode, and the fourth insulating layer sequentially on the first insulating layer and the first cavity sacrificial layer using a magnetron sputtering process.

[0022] Step 4: The lower half of the second cavity is etched on the fourth insulating layer using photolithography; then the first cavity sacrificial layer is released to form the first cavity;

[0023] Step 5: Ion implantation doping is performed on the upper surface of the second substrate, followed by high-temperature annealing of the second substrate to form the third top electrode; then, magnetron sputtering is performed on the upper surface of the third top electrode to prepare the fifth insulating layer, and photolithography is performed to etch the upper half of the second cavity.

[0024] Step 6: Invert the second substrate, align the fifth insulating layer with the fourth insulating layer on the first substrate, and perform a bonding process to complete the fabrication of the thin-film bulk acoustic resonator.

[0025] Beneficial effects: 1. This invention applies stress to the piezoelectric layer in the resonant structure through a capacitive stress loading structure to change the elastic stiffness coefficient of the piezoelectric material, thereby changing the longitudinal wave velocity of the piezoelectric material. Since the series and parallel resonant frequencies of the FBAR are positively correlated with the longitudinal wave velocity of the piezoelectric material, the effect of simultaneously adjusting the series and parallel resonant frequencies of the FBAR can be achieved.

[0026] 2. In this invention, a DC bias signal is applied to the first bottom electrode and the first top electrode, as well as the third bottom electrode and the third top electrode, and an RF AC signal is applied to the second bottom electrode and the second top electrode. No additional biaser is needed for signal superposition, thus achieving effective separation of the modulation signal and the excitation signal.

[0027] 3. The stress loading method used in this invention is to convert the DC bias signal into electrostatic force. This method generates very little leakage current, and therefore has very low power consumption.

[0028] 4. This invention does not design an additional temperature compensation layer structure in the resonant structure, so while achieving temperature compensation, it does not cause a reduction in the effective electromechanical coupling coefficient of FBAR. Attached Figure Description

[0029] Figure 1 This is a cross-sectional schematic diagram of the FBAR structure of the present invention;

[0030] Figures 2-7 This is a schematic diagram of the FBAR structure process flow of the present invention;

[0031] In the figure, the reference numerals are as follows: 1-First substrate; 2-First bottom electrode; 3-First insulating layer; 4-First cavity; 401-Sacrificial layer of the first cavity; 5-First top electrode; 6-Second insulating layer; 7-Second bottom electrode; 8-Piezoelectric layer; 9-Second top electrode; 10-Third insulating layer; 11-Third bottom electrode; 12-Fourth insulating layer; 13-Fifth insulating layer; 14-Second cavity; 1401-Lower half of the second cavity; 1402-Upper half of the second cavity; 15-Third top electrode; 16-Second substrate. Detailed Implementation

[0032] The invention will now be further explained with reference to the accompanying drawings.

[0033] like Figure 1 As shown, a thin-film bulk acoustic resonator structure with dual stress adjustment includes a resonant structure and a capacitive stress-adjusting structure. Both the first and second stress-adjusting structures are parallel-plate capacitive structures, with the resonant structure located between the first and second stress-adjusting structures.

[0034] The first stress control structure includes, from bottom to top, a first substrate 1, a first bottom electrode 2, a first cavity 4, a first insulating layer 3, and a first top electrode 5. The second stress control structure includes, from bottom to top, a third bottom electrode 11, a second cavity 14, a fourth insulating layer 12, a fifth insulating layer 13, a third top electrode 15, and a second substrate 16.

[0035] The resonant structure includes, from bottom to top, a second insulating layer 6, a second bottom electrode 7, a piezoelectric layer 8, a second top electrode 9, and a third insulating layer 10. A first cavity 4 is located within the first insulating layer 3 and is disposed between the first bottom electrode 2 and the first top electrode 5. A second cavity 14 is located between the fourth insulating layer 12 and the fifth insulating layer 13 and is disposed between the third bottom electrode 11 and the third top electrode 15. The overlapping region in the thickness direction of the first cavity 4, the first top electrode 5, the second insulating layer 6, the second bottom electrode 7, the piezoelectric layer 8, the second top electrode 9, the third insulating layer 10, the third bottom electrode 11, and the second cavity 14 constitutes the effective resonant region of the resonator. For ease of bonding during fabrication, the single insulating layer is divided into a fourth insulating layer 12 and a fifth insulating layer 13; depending on the manufacturing process, the fourth insulating layer 12 and the fifth insulating layer 13 can be fused into a single insulating layer.

[0036] The first substrate 1 and the second substrate 16 are made of single-crystal silicon. The first bottom electrode 2 and the third top electrode 15 are made of doped silicon. The first top electrode 5, the second bottom electrode 7, the second top electrode 9, and the third bottom electrode 11 are made of conductive materials with high acoustic impedance, such as tungsten (W) and molybdenum (Mo). The first insulating layer 3, the second insulating layer 6, the third insulating layer 10, the fourth insulating layer 12, and the fifth insulating layer 13 are made of silicon dioxide. Because the electrode layers have high acoustic impedance while the insulating layers have low acoustic impedance, the thicknesses of the electrode layers and the insulating layers can be rationally designed to form Bragg reflector layers, thereby reducing the leakage of bulk acoustic wave energy in the resonant structure and improving the quality factor of the resonator. Typically, the thicknesses of the electrode layers and the insulating layers are set to one-quarter of the wavelength of the bulk acoustic wave generated by the resonant structure.

[0037] The piezoelectric layer 8 is made of aluminum nitride, with its c-axis oriented along the thickness direction, making its elastic stiffness coefficient more significantly affected by tensile stress. The thicknesses of the first cavity 4 and the second cavity 14 respectively affect the magnitude of the electrostatic force in the first top electrode 5 and the third bottom electrode 11. Specifically, when the DC bias voltage applied between the first top electrode 5 and the first bottom electrode 2 is the same, the smaller the thickness of the first cavity 4, the greater the electrostatic force generated in the first top electrode 5, and the greater the impact on the elastic stiffness coefficient of the piezoelectric layer 8, resulting in a more significant temperature compensation effect. Similarly, when the DC bias voltage applied between the third bottom electrode 11 and the third top electrode 15 is the same, the smaller the thickness of the second cavity 14, the greater the electrostatic force generated in the third bottom electrode 11, and the greater the impact on the elastic stiffness coefficient of the piezoelectric layer 8, resulting in a more significant temperature compensation effect. However, if the thickness of the first cavity 4 or the second cavity 14 is too small, it can easily cause the first top electrode 5 and the first bottom electrode 2 to attract each other, or the third top electrode 15 and the third bottom electrode 11 to attract each other, which in turn leads to the failure of the first stress loading structure or the second stress loading structure, making it impossible to adjust the resonant frequency of the FBAR, i.e., frequency compensation cannot be achieved. Therefore, the thickness of the first cavity 4 and the second cavity 14 is set between 0.1 μm and 1 μm, preferably 0.5 μm.

[0038] The principle behind the temperature compensation achieved by the device structure of this invention is as follows: By applying DC voltage signals to the first top electrode and the first bottom electrode in the first stress-controlled structure, and to the third bottom electrode and the third top electrode in the second stress-controlled structure, tensile stress is generated on the first top electrode in the direction of the first bottom electrode, and tensile stress is generated on the third bottom electrode in the direction of the third top electrode, thereby generating tensile stress in the thickness direction of the piezoelectric layer. Since the elastic stiffness coefficient in the thickness direction of the piezoelectric material increases with the increase of the applied tensile stress, applying tensile stress to the piezoelectric material can counteract the phenomenon that the elastic stiffness coefficient of the piezoelectric material decreases with increasing temperature, thus achieving temperature compensation.

[0039] The fabrication method of the above-mentioned thin-film bulk acoustic resonator structure with dual stress adjustment includes the following steps:

[0040] Step 1: As Figure 2 As shown, ion implantation doping is performed on the upper surface of the first substrate 1 to a depth of 0.4 μm to 0.6 μm. The first substrate 1 is then subjected to high-temperature annealing to activate impurity ions and repair lattice damage caused by ion implantation, forming a first bottom electrode 2 on the upper surface of the first substrate 1. Subsequently, a first insulating layer 3 is fabricated on the upper surface of the first bottom electrode 2 using a magnetron sputtering process.

[0041] Step 2: As Figure 3 As shown, a photolithography process is performed on the first insulating layer 3 to etch the first cavity sacrificial layer 401 filling region. Subsequently, a chemical vapor deposition process is performed on the device surface to deposit the sacrificial layer material BPSG, and then the excess sacrificial layer material is removed by a chemical mechanical polishing process, forming the first cavity sacrificial layer 401 in the etched area of ​​the first insulating layer 3.

[0042] Step 3: As Figure 4 As shown, a first top electrode 5, a second insulating layer 6, a second bottom electrode 7, a piezoelectric layer 8, a second top electrode 9, a third insulating layer 10, a third bottom electrode 11, and a fourth insulating layer 12 are sequentially deposited on the first insulating layer 3 and the first cavity sacrificial layer 401 by magnetron sputtering. After each thin film is deposited, a chemical mechanical polishing process is performed to improve the surface roughness of the thin film.

[0043] Step 4: As Figure 5 As shown, the lower half region 1401 of the second cavity 14 is etched on the fourth insulating layer 12 by photolithography; then the first cavity sacrificial layer 401 is released to form the first cavity 4.

[0044] Step 5: As Figure 6 As shown, a second substrate 16 is prepared, and ion implantation doping is performed on the upper surface of the second substrate 16 to a depth of 0.4 μm to 0.6 μm. Then, the second substrate 16 is subjected to high-temperature annealing to activate impurity ions and repair lattice damage caused by ion implantation, forming a third top electrode 15 on the upper surface of the second substrate 16. Subsequently, a fifth insulating layer 13 is prepared on the upper surface of the third top electrode 15 by magnetron sputtering and patterned to etch out the upper half region 1402 of the second cavity 14.

[0045] Step 6: As Figure 7 As shown, the second substrate 16 is inverted, the fifth insulating layer 13 is aligned with the fourth insulating layer 12 on the first substrate 1, and a bonding process is performed to complete the fabrication of the thin-film bulk acoustic resonator.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A film bulk acoustic resonator with dual stress adjustment, characterized by, The resonant structure and the capacitive stress regulating structure are included; The capacitive stress regulating structure includes a first stress regulating structure and a second stress regulating structure; The resonant structure is located between the first stress regulating structure and the second stress regulating structure; The first stress regulating structure includes a first substrate (1) from bottom to top, a first bottom electrode (2), a first cavity (4), a first insulating layer (3), and a first top electrode (5); wherein the first cavity (4) is located in the first insulating layer (3) and is arranged between the first bottom electrode (2) and the first top electrode (5); The second stress regulating structure includes a third bottom electrode (11), a second cavity (14), a fourth insulating layer (12), a fifth insulating layer (13), a third top electrode (15), and a second substrate (16) from bottom to top; wherein the second cavity (14) is located in the fourth insulating layer (12) and the fifth insulating layer (13) and is arranged between the third bottom electrode (11) and the third top electrode (15); The resonant structure includes a second insulating layer (6), a second bottom electrode (7), a piezoelectric layer (8), a second top electrode (9), and a third insulating layer (10) from bottom to top; The overlapping area of the first cavity (4), the first top electrode (5), the second insulating layer (6), the second bottom electrode (7), the piezoelectric layer (8), the second top electrode (9), the third insulating layer (10), the third bottom electrode (11), and the second cavity (14) in the thickness direction constitutes an effective resonant area of the resonator.

2. The film bulk acoustic resonator with dual stress adjustment of claim 1, wherein, The materials of the first top electrode (5), the second bottom electrode (7), the second top electrode (9), and the third bottom electrode (11) are conductive materials with a longitudinal wave characteristic acoustic impedance greater than 50 megaohm; The first insulating layer (3), the second insulating layer (6), the third insulating layer (10), the fourth insulating layer (12), and the fifth insulating layer (13) are insulating materials with a longitudinal wave characteristic acoustic impedance less than 20 megaohm.

3. The film bulk acoustic resonator with dual stress adjustment of claim 2, wherein, The materials of the first bottom electrode (2) and the third top electrode (15) are doped silicon, the materials of the first top electrode (5), the second bottom electrode (7), the second top electrode (9), and the third bottom electrode (11) are tungsten or molybdenum, and the materials of the first insulating layer (3), the second insulating layer (6), the third insulating layer (10), the fourth insulating layer (12), and the fifth insulating layer (13) are silicon dioxide.

4. The film bulk acoustic resonator with dual stress adjustment of claim 2 or 3, wherein, The thicknesses of the first bottom electrode (2), the first insulating layer (3), the first top electrode (5), the second insulating layer (6), and the second bottom electrode (7) satisfy the Bragg reflection condition, and the thicknesses of the second top electrode (9), the third insulating layer (10), the third bottom electrode (11), the fourth insulating layer (12), the fifth insulating layer (13), and the third top electrode (15) satisfy the Bragg reflection condition.

5. The film bulk acoustic resonator with dual stress adjustment of claim 4, wherein, The material of the piezoelectric layer (8) is aluminum nitride, and the c-axis orientation is the thickness direction.

6. The film bulk acoustic resonator with dual stress adjustment of any one of claims 1-3, 5, wherein, The thicknesses of the first cavity (4) and the second cavity (14) are between 0.1 μm and 1 μm.

7. The film bulk acoustic resonator with dual stress adjustment of any one of claims 1-3, 5, wherein, By applying a direct current voltage signal on the first top electrode (5) and the first bottom electrode (2) in the first stress control structure and on the third bottom electrode (11) and the third top electrode (15) in the second stress control structure, a tensile stress in the direction of the first bottom electrode (2) is generated on the first top electrode (5) and a tensile stress in the direction of the third top electrode (15) is generated on the third bottom electrode (11), so that a tensile stress in the thickness direction is also generated in the piezoelectric layer (8), the phenomenon that the elastic stiffness coefficient of the piezoelectric material decreases with the increase of temperature is offset, and temperature compensation is achieved.

8. The method of claim 1-7, wherein the film bulk acoustic resonator is prepared by the steps of: forming a first electrode layer on a substrate; forming a piezoelectric layer on the first electrode layer; forming a second electrode layer on the piezoelectric layer; and forming a cavity in the second electrode layer. Comprise: Step 1: ion implantation doping is performed on the upper surface of the first substrate (1), and then high temperature annealing is performed on the first substrate (1) to form the first bottom electrode (2); then, a first insulating layer (3) is prepared on the upper surface of the first bottom electrode (2) by magnetron sputtering process; Step 2: a first cavity sacrificial layer (401) filling area is etched on the first insulating layer (3) by photolithography process, then a chemical vapor deposition process is performed on the surface of the device, the sacrificial layer material is deposited, and then the excess sacrificial layer material is removed by chemical mechanical polishing process, and the first cavity sacrificial layer (401) is formed in the etching area in the first insulating layer (3); Step 3: a first top electrode (5), a second insulating layer (6), a second bottom electrode (7), a piezoelectric layer (8), a second top electrode (9), a third insulating layer (10), a third bottom electrode (11) and a fourth insulating layer (12) are sequentially deposited on the first insulating layer (3) and the first cavity sacrificial layer (401) by magnetron sputtering process; Step 4: the lower half area (1401) of the second cavity (14) is etched on the fourth insulating layer (12) by photolithography process; then the first cavity sacrificial layer (401) is released to form the first cavity (4); Step 5: ion implantation doping is performed on the upper surface of the second substrate (16), and then high temperature annealing is performed on the second substrate (16) to form the third top electrode (15); then, a fifth insulating layer (13) is prepared on the upper surface of the third top electrode (15) by magnetron sputtering process, and a second cavity (14) upper half area (1402) is etched by photolithography process; Step 6: reverse the second substrate (16), align the fifth insulating layer (13) with the fourth insulating layer (12) on the first substrate (1), and perform bonding process to complete the preparation of the thin film bulk acoustic resonator.

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