Bulk acoustic wave filter, design method, manufacturing method and communication device

Abstract

The present invention provides a bulk acoustic wave filter, a design method, a manufacturing method and a communication device, comprising: using a series thin film bulk acoustic wave resonator and a parallel thin film bulk acoustic wave resonator to build a bulk acoustic wave filter with a ladder topology structure, the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator both include a functional layer and a frame structure with a protrusion, wherein the functional layer includes a lower electrode, a piezoelectric layer, and an upper electrode; simulating to obtain a frequency response curve of the bulk acoustic wave filter, identifying the frequency range of a parasitic passband caused by the protrusions of the frame structure in the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator at a low frequency of the passband of the bulk acoustic wave filter; designing the parasitic resonance frequency of the series thin film bulk acoustic wave resonator to be lower than the parasitic resonance frequency of the parallel thin film bulk acoustic wave resonator at the frequency range corresponding to the parasitic passband, thereby forming a parasitic stopband replacing the parasitic passband at the frequency range of the parasitic passband.

Description

Technical Field

[0001] The present disclosure relates to a communication device and a design method, and more specifically, to a bulk acoustic wave filter, a design method, a manufacturing method and a communication device. Background Art

[0002] Bulk Acoustic Wave (BAW) filters have been widely used in RF front-end modules due to their advantages such as high frequency selectivity, high Q value, small size and low insertion loss. Film BAW resonator is an important component of BAW filters. The film BAW resonator usually includes an acoustic wave reflection area formed in a substrate, a lower electrode layer formed on the substrate to completely cover the acoustic wave reflection area, a piezoelectric layer formed on the lower electrode layer, and an upper electrode layer arranged on the piezoelectric layer. Due to the existence of the transverse mode, a part of the transverse wave will leak out from the edge of the electrode, which reduces the acoustic wave energy in the film BAW resonator, thereby reducing the Q value of the film BAW resonator.

[0003] In order to reduce the leakage of sound waves at the edge of the electrode, a frame structure with protrusions is usually provided at the edge of the upper electrode layer to improve the Q value of the thin film bulk acoustic wave resonator.

[0004] However, the FBAR with a raised frame will form a parasitic resonance on the left side of its resonant frequency, that is, at a low position. Therefore, when a filter is formed by using the FBAR with a raised frame, a parasitic passband caused by the raised frame exists at the low frequency of the passband, which affects the filter's out-of-band suppression. A parasitic passband refers to an unintended passband that appears in the filter's stopband.

[0005] In response to the above technical problems, the present disclosure designs a novel bulk acoustic wave filter, which can better solve the harmful effects of the "parasitic passband", avoid the degradation of the out-of-band suppression of the bulk acoustic wave filter, improve the performance of the filter, and further improve the performance of the communication equipment. Summary of the invention

[0006] A brief overview of the disclosure will be given below in order to provide a basic understanding of certain aspects of the disclosure. It should be understood that this overview is not an exhaustive overview of the disclosure. It is not intended to identify key or important parts of the disclosure, nor is it intended to limit the scope of the disclosure. Its purpose is simply to give certain concepts in a simplified form as a prelude to a more detailed description discussed later.

[0007] According to one aspect of the present disclosure, a design method for a bulk acoustic wave filter is provided, comprising: step one, using a series thin film bulk acoustic wave resonator and a parallel thin film bulk acoustic wave resonator to build a bulk acoustic wave filter with a ladder topology structure, the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator both include a functional layer and a frame structure with a protruding structure, wherein the functional layer includes a lower electrode, a piezoelectric layer, and an upper electrode; step two, using a simulation tool to model and simulate the bulk acoustic wave filter; step three, simulating to obtain a frequency response curve of the bulk acoustic wave filter, and identifying the frequency range of a parasitic passband caused by the frame structure with a protruding structure in the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator at a low frequency of the passband of the bulk acoustic wave filter; step four, designing the parasitic resonance frequency of the series thin film bulk acoustic wave resonator to be lower than the parasitic resonance frequency of the parallel thin film bulk acoustic wave resonator, thereby forming a parasitic stopband that replaces the parasitic passband at the frequency range of the parasitic passband.

[0008] Furthermore, in step 4, the sum of the thickness of each functional layer in the series film bulk acoustic wave resonator and the longitudinal sound velocity ratio of the corresponding functional layer material is added to the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal sound velocity ratio of the protruding material in the frame structure.

[0009] The value is set to be smaller than the sum of the thickness of each functional layer in the parallel thin film bulk acoustic wave resonator and the ratio of the longitudinal sound velocity of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the ratio of the longitudinal sound velocity of the protruding material in the frame structure.

[0010]

[0011] Furthermore, a ladder-type bulk acoustic wave filter is constructed by using a series-connected thin film bulk acoustic wave resonator and a parallel-connected thin film bulk acoustic wave resonator, so that the series-connected thin film bulk acoustic wave resonator Smaller than the parallel FBAW Among them, VE1 and HE1 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the series film bulk acoustic resonator, VP1 and HP1 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the series film bulk acoustic resonator, VE2 and HE2 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the series film bulk acoustic resonator, VE3 and HE3 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the parallel film bulk acoustic resonator, VP2 and HP2 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the parallel film bulk acoustic resonator, VE4 and HE4 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the parallel film bulk acoustic resonator; VF1 and HF1 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the series film bulk acoustic resonator, VF2 and HF2 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the parallel film bulk acoustic resonator.

[0012] Furthermore, in step four, the parameters of the thickness and material type of the frame structure in the series film bulk acoustic wave resonator and the frame structure in the parallel film bulk acoustic wave resonator are first adjusted to determine whether the sum of the thickness of each functional layer in the series film bulk acoustic wave resonator and the longitudinal wave sound velocity ratio of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal wave sound velocity ratio of the protruding material in the frame structure is less than the sum of the thickness of each functional layer in the parallel film bulk acoustic wave resonator and the longitudinal wave sound velocity ratio of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal wave sound velocity ratio of the protruding material in the frame structure; when the judgment result is yes, the adjustment is terminated; when the judgment result is no, the material and thickness parameters of the functional layers of the series film bulk acoustic wave resonator and the parallel film bulk acoustic wave resonator continue to be comprehensively adjusted until the judgment result is yes.

[0013] According to another aspect of the present disclosure, a method for preparing a bulk acoustic wave filter is provided, comprising: providing a substrate, forming an acoustic wave reflection area in or on the substrate; forming at least one series thin film bulk acoustic wave resonator and at least one parallel thin film bulk acoustic wave resonator on the substrate formed with the acoustic wave reflection area, the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator both comprising a functional layer and a frame structure with a protruding structure, wherein the functional layer comprises a lower electrode, a piezoelectric layer, and an upper electrode; forming a metal connection, constructing the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator into the bulk acoustic wave filter with a ladder topology structure; setting the parasitic resonance frequency of the series thin film bulk acoustic wave resonator to be lower than the parasitic resonance frequency of the parallel thin film bulk acoustic wave resonator, so as to form a parasitic stopband at the low frequency of the passband of the bulk acoustic wave filter to replace the parasitic passband caused by the frame structure with the protruding structure in the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator.

[0014] Furthermore, the sum of the thickness of each functional layer in the series film bulk acoustic resonator and the longitudinal sound velocity ratio of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal sound velocity ratio of the protruding material in the frame structure is added.

[0015] The value is set to be smaller than the sum of the thickness of each functional layer in the parallel thin film bulk acoustic wave resonator and the ratio of the longitudinal sound velocity of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the ratio of the longitudinal sound velocity of the protruding material in the frame structure.

[0016]

[0017] Further, a series resonant film bulk acoustic wave resonator and a parallel film bulk acoustic wave resonator are connected to form a ladder-type bulk acoustic wave filter, and the series film bulk acoustic wave resonator Smaller than the parallel FBAW Among them, VE1 and HE1 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the series film bulk acoustic resonator, VP1 and HP1 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the series film bulk acoustic resonator, VE2 and HE2 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the series film bulk acoustic resonator, VE3 and HE3 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the parallel film bulk acoustic resonator, VP2 and HP2 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the parallel film bulk acoustic resonator, VE4 and HE4 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the parallel film bulk acoustic resonator; VF1 and HF1 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the series film bulk acoustic resonator, VF2 and HF2 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the parallel film bulk acoustic resonator.

[0018] According to another aspect of the present disclosure, a bulk acoustic wave filter is provided, comprising: a bulk acoustic wave filter of a ladder-shaped topology structure constructed by at least one series resonant thin film bulk acoustic wave resonator and one parallel thin film bulk acoustic wave resonator; the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator both comprise a frame structure having a protruding structure and a functional layer comprising a lower electrode, a piezoelectric layer, and an upper electrode; the parasitic resonance frequency of the series thin film bulk acoustic wave resonator is lower than the parasitic resonance frequency of the parallel thin film bulk acoustic wave resonator; the bulk acoustic wave filter has a parasitic stopband at a low frequency of the passband to replace the parasitic passband caused by the frame structure having a protruding structure in the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator.

[0019] Furthermore, the sum of the thickness of each functional layer in the series film bulk acoustic resonator and the longitudinal sound velocity ratio of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal sound velocity ratio of the protruding material in the frame structure is added.

[0020] The value is set to be smaller than the sum of the thickness of each functional layer in the parallel thin film bulk acoustic wave resonator and the ratio of the longitudinal sound velocity of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the ratio of the longitudinal sound velocity of the protruding material in the frame structure.

[0021] Furthermore, the BAW filter is a ladder-type BAW filter, in which a thin film BAW resonator is connected in series. Smaller than the parallel FBAW Among them, VE1 and HE1 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the series film bulk acoustic resonator, VP1 and HP1 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the series film bulk acoustic resonator, VE2 and HE2 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the series film bulk acoustic resonator, VE3 and HE3 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the parallel film bulk acoustic resonator, VP2 and HP2 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the parallel film bulk acoustic resonator, VE4 and HE4 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the parallel film bulk acoustic resonator; VF1 and HF1 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the series film bulk acoustic resonator, VF2 and HF2 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the parallel film bulk acoustic resonator.

[0022] According to yet another aspect of the present disclosure, a communication device is provided, comprising any one of the filters described above.

[0023] The scheme disclosed in the present invention can help achieve at least one of the following effects: optimizing the geometry, material selection and coupling parameters of the thin film bulk acoustic wave resonator to reduce unexpected vibration modes, eliminate or weaken parasitic passbands, improve the noise suppression capability of the filter, and improve the performance of the filter and communication equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The specific contents of the present disclosure are described below with reference to the accompanying drawings, which will help to more easily understand the above and other purposes, features and advantages of the present disclosure. The accompanying drawings are only for illustrating the principles of the present disclosure. The sizes and relative positions of the units in the accompanying drawings need not be drawn to scale.

[0025] Figure 1 A schematic diagram of the basic structure of a bulk acoustic wave filter with a ladder topology structure disclosed in the present invention;

[0026] Figure 2 It is a schematic diagram of the working principle of a ladder-type bulk acoustic wave filter;

[0027] Figure 3 It is a basic structural diagram of a thin film bulk acoustic resonator with a frame structure;

[0028] Figure 4 is an impedance frequency characteristic curve diagram of a thin film bulk acoustic resonator with a frame structure;

[0029] Figure 5 Impedance frequency characteristic curve of a bulk acoustic wave filter constructed for a thin film bulk acoustic wave resonator with a frame structure;

[0030] Figure 6 It is a schematic diagram of the basic structure of the series-connected thin film bulk acoustic resonator in the present disclosure;

[0031] Figure 7 is a schematic diagram of the basic structure of the parallel thin film bulk acoustic resonator in the present disclosure;

[0032] Figure 8 Frequency response diagram of the bulk acoustic wave filter provided for the present disclosure. DETAILED DESCRIPTION

[0033] Below, exemplary disclosures of the present disclosure will be described in conjunction with the accompanying drawings. For the sake of clarity and conciseness, not all features of implementing the present disclosure are described in the specification. However, it should be understood that many decisions specific to the present disclosure may be made in the process of developing any such implementation of the present disclosure in order to achieve the developer's specific goals, and these decisions may vary from one disclosure to another.

[0034] It should also be noted that, in order to avoid obscuring the present disclosure due to unnecessary details, only device structures closely related to the solutions according to the present disclosure are shown in the drawings, while other details that are not closely related to the present disclosure are omitted.

[0035] It should be understood that the present disclosure is not limited to the described implementation forms due to the following description with reference to the accompanying drawings. Herein, where feasible, features between different embodiments may be replaced or borrowed, and one or more features may be omitted in one embodiment.

[0036] Figure 1 The basic structure of the BAW filter of the ladder topology structure of the present disclosure is shown. The BAW filter of the ladder topology structure adopts a film bulk acoustic wave resonator (FBAR) array to achieve high performance of the required filtering characteristics. It utilizes the cascade and interaction between the film bulk acoustic wave resonators to achieve a steep filter roll-off and good out-of-band suppression. In the ladder structure, the film bulk acoustic wave resonators are arranged in an orderly manner, and the frequency of each film bulk acoustic wave resonator and the coupling strength of the film bulk acoustic wave resonator are optimized to form a continuous frequency response curve, similar to the shape of a ladder, which allows a flat response in the passband, a fast roll-off at the edge of the passband, and a high suppression ratio in the stopband.

[0037] Figure 1 The ladder-type BAW filter shown in FIG. 1 is composed of a series FBAW resonator and a parallel FBAW resonator. The series FBAW resonator in the ladder-type BAW filter provides the low-pass characteristic of the filter, while the parallel FBAW resonator in the ladder-type BAW filter defines the high-pass characteristic. By carefully designing the parameters of the FBAW resonator, such as frequency, quality factor (Q value), and coupling strength, the passband, stopband, and roll-off characteristics of the filter can be controlled.

[0038] Combine the following Figure 2 Explain in detail the working principle of a first-order ladder-type bulk acoustic wave filter.

[0039] like Figure 2 As shown in the figure, the frequency corresponding to the minimum impedance point of the series film bulk acoustic wave resonator should be basically the same as the frequency corresponding to the maximum impedance point of the parallel film bulk acoustic wave resonator. Figure 2 When the BAW filter is operated at the frequency point a, the impedance of the parallel-connected FBAW resonator is at a minimum value, and the signal is almost completely short-circuited to the ground, so the transmission zero of the filter appears at the frequency point a. Figure 2 When working at the frequency of point b, the impedance of the parallel film bulk acoustic wave resonator is extremely large and is regarded as an open circuit, and the impedance of the series film bulk acoustic wave resonator is extremely small and is regarded as a short circuit. At this time, the signal can pass through the filter almost losslessly, and the filter passband appears near the frequency of point b. Figure 2 As shown in the figure, when the impedance of the series FBAW resonator is at the maximum value when working at the frequency of point c, the signal can hardly pass through, so the transmission zero of the filter appears again, and the resonant characteristics of the series FBAW resonator and the parallel FBAW resonator form the bandpass characteristics of the BAW filter. The passband of the BAW filter is the frequency range in which the signal can pass without significant attenuation. In the ladder-type BAW filter, the passband is defined by the series and parallel configuration of the FBAW resonator and the coupling relationship between them. During the design, the center frequency of the FBAW resonator is set within the passband range, while the width and shape of the passband depend on the Q value of the FBAW resonator, the coupling coefficient and the cascade structure of the entire filter. By optimizing these parameters, a filter with high selectivity, flat passband response and low insertion loss can be achieved ideally.

[0040] See also Figure 3 , Figure 3 The basic structure of the thin film bulk acoustic wave resonator in the present disclosure is shown in FIG. Figure 3 As shown, an acoustic wave reflection region 101 composed of a structure such as an air cavity or a Bragg reflection layer is formed in the substrate 100. The substrate can be silicon (Si), gallium arsenide (GaAs), indium phosphide (InP), glass, sapphire, aluminum oxide, or the like. 、 The Bragg reflector layer is formed by stacking films with different acoustic impedances. More preferably, the Bragg reflector layer is formed by stacking films with different acoustic impedances and the thickness of the films is controlled to be 1 / 4 of the wavelength.

[0041] A lower electrode layer 200 is formed on the substrate 100 to completely cover the acoustic wave reflection area. The lower electrode layer 200 can be a single layer or multiple layers. A piezoelectric layer 300 is formed on the lower electrode layer 200, and an upper electrode layer 400 is arranged on the piezoelectric layer 300. The upper electrode layer 400 can be a single layer or multiple layers. The upper / lower electrode layer can be formed of one or more conductive materials, such as various metals compatible with semiconductor processes including tungsten (W), molybdenum (Mo), iridium (Ir), aluminum (Al), platinum (Pt), ruthenium (Ru), niobium (Nb) or hafnium (Hf). The materials of the upper electrode and the lower electrode can be the same or different. The piezoelectric layer 300 can be formed of any piezoelectric material compatible with semiconductor processes, such as aluminum nitride (AlN), doped aluminum nitride or zirconate titanate (PZT). The functional layers of the thin film bulk acoustic wave resonator include the upper electrode layer 400 above the acoustic wave reflection area 101, the piezoelectric layer 300 and the lower electrode layer 100.

[0042] The overlapping area between the upper electrode layer 400, the piezoelectric layer 300 and the lower electrode layer 100 above any acoustic wave reflection area 101 is defined as the active area of ​​the FBAR, and the other areas outside the active area are defined as the peripheral area of ​​the FBAR. Figure 3 The frame structure 500 with protrusions shown is conducive to reflecting transverse waves by setting the frame structure 500 with protrusions on the upper electrode layer 400, weakening or reducing the adverse effects such as energy attenuation caused by the transverse mode between the active area and the peripheral area. It can be understood that the frame structure 500 with protrusions can be formed integrally with the upper electrode layer 400 by etching the upper electrode layer 400, or the frame structure 500 with protrusions can also be a separate frame structure additionally arranged on the upper electrode layer 400. It can be further understood that a recessed structure can also be formed by etching in the upper electrode layer 400, or a recessed structure can be formed by etching in a separate frame structure, and the present disclosure does not make further limitations on it.

[0043] It should be noted that Figure 3 The figure only illustrates the basic structure of the film bulk acoustic wave resonator, and does not mean any specific limitation on the structure of the film bulk acoustic wave resonator in the present disclosure. Those skilled in the art know that the film bulk acoustic wave resonator may also have other functional layers such as a mass load layer, a passivation layer, a seed layer, etc.

[0044] right Figure 3 The impedance frequency characteristics of the thin film bulk acoustic wave resonator shown in the figure can be tested to obtain Figure 4 The impedance frequency characteristic curve of the thin film bulk acoustic wave resonator is shown in FIG. Figure 4 As shown, a film bulk acoustic wave resonator with a frame structure having a protruding structure will form a parasitic resonator at the resonant frequency of the film bulk acoustic wave resonator. Figure 4As shown in the box. Therefore, when a thin film bulk acoustic wave resonator with a frame structure having a convex structure is constructed as shown in the figure below, Figure 1 The ladder topology of the BAW filter shown may result in the inability to obtain Figure 2 The ideal impedance frequency characteristic curve is as follows: Figure 5 The impedance frequency characteristic curve of the bulk acoustic wave filter is shown in FIG. Figure 5 As shown in the box, there is a parasitic passband at the low frequency of the BAW filter's passband, which affects the out-of-band suppression of the FBAW filter.

[0045] To solve the above problems, the basic structure of the BAW filter was optimized. The optimization design includes using the difference in parasitic resonance frequency between the series FBAW resonator and the parallel FBAW resonator to design the parasitic resonance frequency of the series FBAW resonator to be lower than the parasitic resonance frequency of the parallel FBAW resonator, thereby forming a parasitic stopband and avoiding the degradation of out-of-band suppression.

[0046] The specific design method includes: step 100, using a series thin film bulk acoustic wave resonator and a parallel thin film bulk acoustic wave resonator to build a bulk acoustic wave filter with a ladder topology structure, the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator both include a functional layer and a frame structure with a specific raised structure, wherein the functional layer includes a lower electrode, a piezoelectric layer, and an upper electrode; step 200, using advanced simulation tools to accurately model and simulate the bulk acoustic wave filter; step 300, obtaining a frequency curve of the bulk acoustic wave filter, and identifying the frequency range of the parasitic passband caused by the raised frame structure in the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator at the low frequency of the bulk acoustic wave filter passband; step 400, designing the parasitic resonance frequency of the series thin film bulk acoustic wave resonator to be lower than the parasitic resonance frequency of the parallel thin film bulk acoustic wave resonator at the frequency range corresponding to the parasitic passband, thereby forming a parasitic stopband that replaces the parasitic passband.

[0047] In a specific embodiment, in step 400, the parasitic resonant frequency of the series film bulk acoustic resonator is designed to be lower than the parasitic resonant frequency of the parallel film bulk acoustic resonator by adjusting the material and thickness of the protruding structure in the functional layer and the frame structure in the series film bulk acoustic resonator and the material and thickness of the protruding structure in the functional layer and the frame structure in the parallel film bulk acoustic resonator, thereby forming a parasitic stopband that replaces the parasitic passband.

[0048] More specifically, in step 400, the sum of the thickness of each functional layer in the series film bulk acoustic wave resonator and the longitudinal sound velocity ratio of the corresponding functional layer material is added to the inverse of the sum of the thickness of the protruding structure in the frame structure and the longitudinal sound velocity ratio of the protruding material in the frame structure.

[0049] The value is set to be smaller than the sum of the thickness of each functional layer in the parallel thin film bulk acoustic wave resonator and the ratio of the longitudinal sound velocity of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the ratio of the longitudinal sound velocity of the protruding material in the frame structure.

[0050]

[0051] In the design method disclosed in the present invention,

[0052] Set to less than

[0053] The design process can be carried out as described: first, the parameters of the thickness and material type of the frame structure in the series film bulk acoustic wave resonator and the frame structure in the parallel film bulk acoustic wave resonator are adjusted to determine whether the sum of the ratio of the thickness of each functional layer in the series film bulk acoustic wave resonator to the longitudinal wave sound velocity of the corresponding functional layer material plus the inverse of the sum of the ratio of the thickness of the protruding structure in the frame structure to the longitudinal wave sound velocity of the protruding material in the frame structure is less than the sum of the thickness of each functional layer in the parallel film bulk acoustic wave resonator to the longitudinal wave sound velocity ratio of the corresponding functional layer plus the inverse of the sum of the ratio of the thickness of the protruding structure in the frame structure to the longitudinal wave sound velocity of the protruding material in the frame structure; when the judgment result is yes, the adjustment is terminated; when the judgment result is no, the material and thickness parameters of the functional layers of the series film bulk acoustic wave resonator and the parallel film bulk acoustic wave resonator continue to be comprehensively adjusted until the judgment result is yes.

[0054] It can be seen that in the present disclosure, the position of the parasitic resonant frequency of the series film bulk acoustic resonator and the position of the parasitic resonant frequency of the parallel film bulk acoustic resonator can be controlled by adjusting the geometric dimensions and material properties of the protrusions of the frames of the series film bulk acoustic resonator and the parallel film bulk acoustic resonator, or controlling the geometric dimensions and material properties of the protrusions and functional layers of the frames, so as to form a parasitic stopband at the frequency corresponding to the parasitic passband, thereby avoiding the degradation of out-of-band suppression, wherein the functional layer of the film bulk acoustic resonator includes at least upper and lower electrode layers and a piezoelectric layer.

[0055] The design method of the present disclosure is further specifically described below by taking a bulk acoustic wave filter with a ladder topology structure as a specific example.

[0056] by Figure 3 The thin film bulk acoustic wave resonator with a raised frame structure shown in FIG. Figure 1The first-order ladder-type BAW filter of the series film bulk acoustic wave resonator and the parallel film bulk acoustic wave resonator is accurately modeled and simulated; the frequency response curve of the BAW filter is obtained, and the frequency range of the parasitic passband can be identified from the frequency response curve of the BAW filter. Then the material and thickness of each functional layer and frame of the series film bulk acoustic wave resonator and the parallel film bulk acoustic wave resonator are designed.

[0057] Specifically, Figure 6 As shown, the functional layers of the series thin film bulk acoustic wave resonator in the present disclosure include a first lower electrode layer E1, the material and thickness of the first lower electrode layer E1 are selected, the thickness is set to HE1, and the longitudinal wave sound velocity corresponding to the material is set to VE1; a first piezoelectric layer P1, the material and thickness of the first piezoelectric layer P1 are selected, the thickness is set to HP1, and the longitudinal wave sound velocity corresponding to the material is set to VP1; and a first upper electrode layer E2, the material and thickness of the first upper electrode layer E2 are selected, the thickness is set to HE2, and the longitudinal wave sound velocity corresponding to the material is set to VE2; a first frame structure F1 on the first upper electrode layer E2, the thickness of the protrusion in the first frame structure F1 is set to HF1, and the longitudinal wave sound velocity corresponding to the material is set to VF1.

[0058] like Figure 7 As shown, the functional layers of the parallel thin film bulk acoustic resonator in the present disclosure include a second lower electrode layer E3, the material and thickness of the second lower electrode layer E3 are selected, the thickness is set to HE3, and the longitudinal wave sound velocity corresponding to the material is set to VE3; a second piezoelectric layer P2, the material and thickness of the second piezoelectric layer P2 are selected, the thickness is set to HP2, and the longitudinal wave sound velocity corresponding to the material is set to VP2; and a second upper electrode E4, the material and thickness of the second upper electrode layer E4 are selected, the thickness is set to HE4, and the longitudinal wave sound velocity corresponding to the material is set to VE4; a second frame structure F2 on the second upper electrode layer E4, the thickness of the protrusion in the second frame structure F2 is set to HF2, and the longitudinal wave sound velocity corresponding to the material is set to VF2.

[0059] The parameters of the series film bulk acoustic wave resonator can be adjusted Smaller than the parallel FBAW Thus, when a parasitic stopband can be generated at the low frequency of the passband to replace the parasitic passband caused by the raised frame structure in the series FBAW resonator and the parallel FBAW resonator, the corresponding parameter debugging process can be ended.

[0060] Similarly, in the parameter debugging, the longitudinal wave sound velocity corresponding to the protruding material in the first frame F1 can be set to VF1 and its thickness HF1, and the longitudinal wave sound velocity corresponding to the protruding material in the second frame F2 can be set to VF2 and its thickness HF2 to determine the series connection of the thin film bulk acoustic resonator. Is it smaller than the parallel film bulk acoustic wave resonator? If the judgment result is yes, the parameter debugging is terminated; if it is not satisfied, the longitudinal wave sound velocity and thickness corresponding to each functional layer of the series film bulk acoustic resonator and the longitudinal wave sound velocity and thickness corresponding to each functional layer of the parallel film bulk acoustic resonator are comprehensively debugged until the judgment result is yes and the debugging is terminated.

[0061] by Figure 6-Figure 7 The FBAW resonator shown in Figure 1 is constructed as Figure 1 The trapezoidal BAW filter is then tested and the following is obtained: Figure 8 The frequency response diagram of the bulk acoustic wave filter provided by the present disclosure is shown in FIG. Figure 8 It can be found that, as shown in the box, there is a parasitic stopband replacing the parasitic passband at the low frequency of the passband, and there is no parasitic passband, which avoids the degradation of out-of-band suppression.

[0062] Those skilled in the art will understand that, although the design method and specific structure of the present invention are described in the present disclosure using a single-order bulk acoustic wave filter, the scope of protection of the present disclosure is not limited thereto, and the order of the bulk acoustic wave filter may be multiple orders, and the functional layer of the thin film bulk acoustic wave resonator may also cover other layers except the upper and lower electrodes and the piezoelectric layer, and the present disclosure does not impose any specific restrictions on this.

[0063] In another specific embodiment of the present disclosure, a bulk acoustic wave filter and a corresponding preparation method thereof are provided.

[0064] A substrate is provided, and after a thin film bulk acoustic wave resonator is formed on the substrate according to the aforementioned manufacturing method, a metal connection is then formed, and the series resonant thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator are constructed into a bulk acoustic wave filter with a ladder topology structure through the metal connection.

[0065] The geometric dimensions, material types and coupling strengths of the functional layers and frame structures of the series resonant thin film bulk acoustic wave resonator and the functional layers and frame structures with protrusions of the parallel thin film bulk acoustic wave resonator are prepared according to the parameters in the above-mentioned design method, so that the parasitic resonance frequency of the series thin film bulk acoustic wave resonator is set to be lower than the parasitic resonance frequency of the parallel thin film bulk acoustic wave resonator; so as to form a parasitic stopband at the low frequency of the passband of the bulk acoustic wave filter to replace the parasitic passband caused by the frame structures with protrusions in the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator.

[0066] Furthermore, the BAW filter provided by the present disclosure can be used in the field of portable communication devices such as mobile phones, personal digital assistants (PDAs), and electronic game devices, and the BAW filter can include any one of the thin film BAW resonators in the above-mentioned embodiments.

[0067] The present disclosure is described above in conjunction with specific implementation schemes, but it should be clear to those skilled in the art that these descriptions are exemplary and are not intended to limit the scope of protection of the present disclosure. Those skilled in the art can make various variations and modifications to the present disclosure based on the spirit and principles of the present disclosure, and these variations and modifications are also within the scope of the present disclosure.

Claims

1. A method for designing a bulk acoustic wave filter, characterized in that: include: Step 1: constructing a bulk acoustic wave filter with a ladder topology structure by using a series thin film bulk acoustic wave resonator and a parallel thin film bulk acoustic wave resonator, wherein the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator both include a functional layer and a frame structure with a protruding structure, wherein the functional layer includes a lower electrode, a piezoelectric layer, and an upper electrode; Step 2: Modeling and simulating the BAW filter using simulation tools; Step 3: Simulate and obtain a frequency response curve of the BAW filter, and identify the frequency range of the parasitic passband at the low frequency of the BAW filter passband caused by the frame structure with a protruding structure in the series film BAW resonator and the parallel film BAW resonator; Step 4: designing the parasitic resonance frequency of the series film bulk acoustic wave resonator to be lower than the parasitic resonance frequency of the parallel film bulk acoustic wave resonator, thereby forming a parasitic stopband replacing the parasitic passband at the frequency range of the parasitic passband; In step 4, the sum of the thickness of each functional layer in the series film bulk acoustic wave resonator and the longitudinal sound velocity ratio of the corresponding functional layer material is added to the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal sound velocity ratio of the protruding material in the frame structure. The value is set to be smaller than the sum of the thickness of each functional layer in the parallel thin film bulk acoustic wave resonator and the ratio of the longitudinal sound velocity of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the ratio of the longitudinal sound velocity of the protruding material in the frame structure.

2. The design method according to claim 1, characterized in that: A ladder-type bulk acoustic wave filter is constructed by using a series-connected film bulk acoustic wave resonator and a parallel-connected film bulk acoustic wave resonator. Smaller than the parallel FBAW Among them, VE1 and HE1 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the series film bulk acoustic resonator, VP1 and HP1 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the series film bulk acoustic resonator, VE2 and HE2 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the series film bulk acoustic resonator, VE3 and HE3 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the parallel film bulk acoustic resonator, VP2 and HP2 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the parallel film bulk acoustic resonator, VE4 and HE4 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the parallel film bulk acoustic resonator; VF1 and HF1 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the series film bulk acoustic resonator, VF2 and HF2 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the parallel film bulk acoustic resonator.

3. The design method according to claim 1 or 2, characterized in that: In step 4, the parameters of the thickness and material type of the frame structure in the series film bulk acoustic wave resonator and the frame structure in the parallel film bulk acoustic wave resonator are first adjusted to determine whether the sum of the ratio of the thickness of each functional layer in the series film bulk acoustic wave resonator to the longitudinal wave sound velocity of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal wave sound velocity ratio of the protruding material in the frame structure is less than the sum of the ratio of the thickness of each functional layer in the parallel film bulk acoustic wave resonator to the longitudinal wave sound velocity ratio of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal wave sound velocity ratio of the protruding material in the frame structure; When the judgment result is yes, the adjustment is ended, and when the judgment result is no, the material and thickness parameters of the functional layers of the series FBAR and the parallel FBAR continue to be comprehensively adjusted until the judgment result is yes.

4. A method for preparing a bulk acoustic wave filter, characterized in that ,include: Providing a substrate, and forming an acoustic wave reflecting area in or on the substrate; At least one series thin film bulk acoustic wave resonator and at least one parallel thin film bulk acoustic wave resonator are formed on the substrate where the acoustic wave reflection area is formed, wherein the series thin film bulk acoustic wave resonator and the parallel thin film bulk acoustic wave resonator both include a functional layer and a frame structure with a protruding structure, wherein the functional layer includes a lower electrode, a piezoelectric layer, and an upper electrode; Forming metal connections to construct the bulk acoustic wave filter of the ladder topology structure by connecting the series-connected FBAW resonators and the parallel-connected FBAW resonators; The parasitic resonance frequency of the series film bulk acoustic wave resonator is set to be lower than the parasitic resonance frequency of the parallel film bulk acoustic wave resonator, so as to form a parasitic stop band at a low frequency of the pass band of the bulk acoustic wave filter to replace the parasitic pass band caused by the frame structure having the protruding structure in the series film bulk acoustic wave resonator and the parallel film bulk acoustic wave resonator; The sum of the thickness of each functional layer in the series film bulk acoustic wave resonator and the longitudinal sound velocity ratio of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal sound velocity ratio of the protruding material in the frame structure The value is set to be smaller than the sum of the thickness of each functional layer in the parallel thin film bulk acoustic wave resonator and the ratio of the longitudinal sound velocity of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the ratio of the longitudinal sound velocity of the protruding material in the frame structure.

5. The method for preparing a bulk acoustic wave filter according to claim 4, characterized in that: A series resonant film bulk acoustic wave resonator and a parallel film bulk acoustic wave resonator are connected to form a ladder-type bulk acoustic wave filter. Smaller than the parallel FBAW Among them, VE1 and HE1 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the series film bulk acoustic resonator, VP1 and HP1 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the series film bulk acoustic resonator, VE2 and HE2 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the series film bulk acoustic resonator, VE3 and HE3 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the parallel film bulk acoustic resonator, VP2 and HP2 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the parallel film bulk acoustic resonator, VE4 and HE4 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the parallel film bulk acoustic resonator; VF1 and HF1 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the series film bulk acoustic resonator, VF2 and HF2 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the parallel film bulk acoustic resonator.

6. A bulk acoustic wave filter, characterized in that: include: A bulk acoustic wave filter having a ladder topology structure constructed by at least one series resonant film bulk acoustic wave resonator and one parallel film bulk acoustic wave resonator; The series film bulk acoustic wave resonator and the parallel film bulk acoustic wave resonator both include a frame structure with a protruding structure and a functional layer including a lower electrode, a piezoelectric layer, and an upper electrode; The parasitic resonance frequency of the series film bulk acoustic wave resonator is lower than that of the parallel film bulk acoustic wave resonator; The BAW filter has a parasitic stopband at a low frequency of the passband to replace the parasitic passband caused by the frame structure with a protruding structure in the series-connected FBAW resonator and the parallel-connected FBAW resonator. The sum of the thickness of each functional layer in the series film bulk acoustic wave resonator and the longitudinal sound velocity ratio of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the longitudinal sound velocity ratio of the protruding material in the frame structure The value is set to be smaller than the sum of the thickness of each functional layer in the parallel thin film bulk acoustic wave resonator and the ratio of the longitudinal sound velocity of the corresponding functional layer material plus the reciprocal of the sum of the thickness of the protruding structure in the frame structure and the ratio of the longitudinal sound velocity of the protruding material in the frame structure.

7. The bulk acoustic wave filter according to claim 6, wherein: The BAW filter is a ladder-type BAW filter, which is a series-connected thin-film BAW resonator. Smaller than the parallel FBAW Among them, VE1 and HE1 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the series film bulk acoustic resonator, VP1 and HP1 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the series film bulk acoustic resonator, VE2 and HE2 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the series film bulk acoustic resonator, VE3 and HE3 are the longitudinal wave sound velocity and thickness corresponding to the lower electrode layer in the parallel film bulk acoustic resonator, VP2 and HP2 are the longitudinal wave sound velocity and thickness corresponding to the piezoelectric layer in the parallel film bulk acoustic resonator, VE4 and HE4 are the longitudinal wave sound velocity and thickness corresponding to the upper electrode layer in the parallel film bulk acoustic resonator; VF1 and HF1 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the series film bulk acoustic resonator, VF2 and HF2 are the longitudinal wave sound velocity and thickness corresponding to the protruding structure in the frame structure of the parallel film bulk acoustic resonator.

8. A communication device comprising the bulk acoustic wave filter according to any one of claims 6 to 7.

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