A thin film bulk acoustic wave resonator and a filter using the same

Abstract

The present application provides a thin film bulk acoustic wave resonator and a filter using the same, the thin film bulk acoustic wave resonator includes a substrate and a device structure, the device structure is arranged on the substrate; a reflector is arranged on one side of the substrate connected to the device structure; the device structure includes a first electrode layer, a piezoelectric film layer and a second electrode layer, the first electrode layer, the piezoelectric film layer and the second electrode layer are stacked and connected in sequence; a first acoustic impedance tuning structure is arranged on the second electrode layer, the first acoustic impedance tuning structure includes a first internal resonance region and a first external resonance region, the first external resonance region and the first internal resonance region have different acoustic impedances; the first internal resonance region is arranged in the region corresponding to the reflector on the second electrode layer. By adjusting the duty ratio and period of the first external resonance region and the first internal resonance region, a multi-layer transverse acoustic wave reflection interface can be formed, the acoustic wave energy is limited from leaking from the edge of the resonator, and the quality factor Q value of the resonator is improved.

Description

Technical Field

[0001] The present application relates to the technical field of acoustic wave resonators, and in particular to a thin film bulk acoustic wave resonator and a filter using the same. Background Art

[0002] With the development of multifunctional technology of wireless terminals, the requirements of miniaturization, low power consumption, low cost and high performance are put forward for frequency devices. Compared with the filters of traditional technology, the Film Bulk Acoustic Resonator (FBAR) has become the focus of attention of 5G technology with its advantages in high-frequency applications. FBAR has the advantages of low insertion loss and high rectangular coefficient, so it is widely used in today's wireless communication systems. FBAR resonator is also sensitive to the frequency of external environmental factors, and can respond to the changes of external conditions according to the changes of its frequency. It can be used as a sensor in the fields of biochemistry, medical diagnosis and environmental monitoring. FBAR is a technology that uses longitudinal body acoustic waves for resonance. The inverse piezoelectric effect of piezoelectric film converts electrical energy into longitudinal acoustic waves for resonance. The resonator can only pass waves of specific frequencies. Because the propagation speed of sound waves is about 5 orders of magnitude smaller than that of electromagnetic waves, the size of FBAR working under the same frequency conditions is much smaller than that of dielectric ceramic devices.

[0003] FBAR is an important component that determines the quality of RF signals entering and exiting the filter. The various indicators of the resonator determine the performance of the filter: the electromechanical coupling coefficient is determined by the bandwidth of the filter, the resonant frequency is determined by the attenuation point of the filter, and the quality factor Q is determined by the insertion loss of the filter. Resonators with different Q values ​​will cause the insertion loss of the filter to vary greatly. Therefore, how to improve the Q value of the film bulk acoustic wave resonator is an extremely important issue in the design of high-performance filters in the industry. The Q value is defined as the ratio of the total energy stored in the system to the energy lost by the resonator through various paths in each cycle. The specific calculation is the ratio of the product of the angular frequency and the total energy stored in the system to the energy lost by the resonator system through various paths in each cycle; a resonator with a high Q value indicates that it has low energy loss; a filter composed of a high Q value resonator has low insertion loss, steep stopband attenuation, good filter effect, and high rectangular coefficient; a sensor composed of a high Q value resonator has higher detection accuracy.

[0004] In the prior art, the main working mode of FBAR is longitudinal acoustic wave. When the main mode is generated, a transverse mode is generated. The leakage of the transverse mode seriously affects the quality factor Q of the parallel resonance point, thereby affecting the device performance. Summary of the invention

[0005] The present application aims to solve the technical problem in the prior art that the sound waves of a thin film bulk acoustic wave resonator are easily leaked, thereby affecting the quality factor Q value of the resonator.

[0006] In order to solve the above technical problems, the embodiment of the present application discloses a thin film bulk acoustic wave resonator, comprising a substrate and a device structure, wherein the device structure is arranged on the substrate;

[0007] A reflector is provided on one side of the substrate connected to the device structure; the reflector is a cavity structure or a Bragg reflector;

[0008] The device structure comprises a first electrode layer, a piezoelectric film layer and a second electrode layer, wherein the first electrode layer, the piezoelectric film layer and the second electrode layer are sequentially stacked and connected;

[0009] A first acoustic impedance tuning structure is disposed on the second electrode layer, the first acoustic impedance tuning structure includes a first internal resonance region and a first external resonance region, and the first external resonance region and the first internal resonance region have different duty ratios;

[0010] The first internal resonance region is disposed in a region on the second electrode layer corresponding to the reflector.

[0011] Further, the first external resonance region includes at least two first units, and each first unit in the first external resonance region has a corresponding period and duty cycle;

[0012] The first internal resonant region includes at least two second units, each second unit in the first internal resonant region has a corresponding period and duty cycle;

[0013] The period and duty cycle corresponding to each first unit in the first external resonance region are the same;

[0014] The period and duty cycle corresponding to each second unit in the first internal resonance region are the same;

[0015] The duty cycle corresponding to the second unit is different from the duty cycle corresponding to the first unit; and the period corresponding to the second unit is the same as the period corresponding to the first unit.

[0016] Furthermore, the device structure further comprises a supporting layer, the supporting layer comprises a corresponding first surface and a second surface, the first surface of the supporting layer is connected to the substrate in a stacking manner, and the second surface of the supporting layer is connected to the first electrode layer in a stacking manner.

[0017] Furthermore, it also includes a second acoustic impedance tuning structure; the second acoustic impedance tuning structure is arranged on the first surface of the support layer, the surface of the first electrode layer connected to the support layer, or the surface of the piezoelectric film layer connected to the first electrode layer;

[0018] The second acoustic impedance tuning structure includes a second inner resonant region and a second outer resonant region;

[0019] The second inner resonant region and the second outer resonant region have different duty cycles;

[0020] The second internal resonance region is located in a region on the first surface of the support layer corresponding to the reflector.

[0021] Furthermore, the second acoustic impedance tuning structure has the same structure as the first acoustic impedance tuning structure and corresponds to the position of the first acoustic impedance tuning structure.

[0022] Furthermore, the second acoustic impedance tuning structure and the first acoustic impedance tuning structure are asymmetric structures;

[0023] The alignment difference between the second acoustic impedance tuning structure and the first acoustic impedance tuning structure is a positive integer multiple of a period corresponding to one of the units in the first external resonance region.

[0024] Further, the first external resonance region includes at least two first units, each of which has a corresponding period and duty cycle; the first internal resonance region includes at least two second units, each of which has a corresponding period and duty cycle;

[0025] The period corresponding to each first unit in the first external resonance region and each second unit in the first internal resonance region is the same;

[0026] The duty ratio of each second unit in the first internal resonance region is the same, and the duty ratio corresponding to the outermost first unit in the first external resonance region to the outermost second unit in the first internal resonance region changes gradually;

[0027] Further, the first external resonance region includes at least two first units, each of which has a corresponding period and duty cycle; the first internal resonance region includes at least two second units, each of which has a corresponding period and duty cycle;

[0028] The duty ratios corresponding to each first unit in the first external resonant region and each second unit in the first internal resonant region are the same;

[0029] The period corresponding to each second unit in the first internal resonance region is the same;

[0030] The period corresponding to the outermost first unit in the first external resonance region to the outermost second unit in the first internal resonance region is gradually changing; or; the period corresponding to each first unit in the first external resonance region is the same, and the period corresponding to any first unit and any second unit is different.

[0031] Further, the first acoustic impedance tuning structure is a sub-wavelength acoustic microstructure;

[0032] The first acoustic impedance tuning structure is formed by providing a concave-convex structure on the second electrode layer.

[0033] A second aspect of the present application discloses a filter, comprising the thin film bulk acoustic wave resonator.

[0034] By adopting the above technical solution, the present application has the following beneficial effects:

[0035] The thin film bulk acoustic wave resonator provided in the present application is provided with a first acoustic impedance tuning structure on the second electrode layer. The acoustic impedance tuning structure can form a multi-layer lateral acoustic wave reflection interface by adjusting the duty ratio and period of the first external resonance region and the first internal resonance region, thereby limiting the leakage of acoustic wave energy from the edge of the resonator and improving the quality factor Q value of the resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 This is a schematic structural diagram of a thin film bulk acoustic resonator according to Embodiment 1 of the present application;

[0038] Figure 2 A top view of a first acoustic impedance tuning structure of a thin film bulk acoustic wave resonator according to an embodiment of the present application;

[0039] Figure 3 This is a schematic diagram of the structure of a filter in Example 1 of the present application.

[0040] Figure 4 This is a schematic structural diagram of a thin film bulk acoustic wave resonator according to the second embodiment of the present application;

[0041] Figure 5This is a comparison diagram of the impedance response characteristics of the thin film bulk acoustic wave resonator of Example 1 and Example 2 of the present application;

[0042] Figure 6 This is a schematic structural diagram of a thin film bulk acoustic wave resonator according to the third embodiment of the present application;

[0043] Figure 7 This is a schematic structural diagram of a thin film bulk acoustic wave resonator according to the third embodiment of the present application;

[0044] Figure 8 This is a schematic structural diagram of a thin film bulk acoustic wave resonator according to the fourth embodiment of the present application;

[0045] Fig. 9 A schematic diagram of the suppression of transverse acoustic wave spurious modes by a thin film bulk acoustic wave resonator according to an embodiment of the present application.

[0046] The following is a supplementary description of the attached drawings:

[0047] 1-substrate; 2-reflector; 3-first electrode layer; 4-piezoelectric film layer; 5-second electrode layer; 6-first acoustic impedance tuning structure; 61-first external resonance region; 62-first internal resonance region; 7-support layer; 8-second acoustic impedance tuning structure. DETAILED DESCRIPTION

[0048] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0049] The term "one embodiment" or "embodiment" as referred to herein refers to a specific feature, structure or characteristic that may be included in at least one implementation of the present application. In the description of the embodiments of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "top", "bottom", etc. is based on the orientation or positional relationship shown in the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more at least two of the features. Moreover, the terms "first", "second", etc. are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here can be implemented in an order other than those illustrated or described here.

[0050] Embodiment 1:

[0051] See also Figure 1 , Figure 1 This is a schematic diagram of the structure of a thin film bulk acoustic resonator according to an embodiment of the present application. Figure 1 The thin film bulk acoustic wave resonator comprises a substrate 1 and a device structure, wherein the device structure is arranged on the substrate 1;

[0052] A reflector 2 is provided on one side of the substrate 1 connected to the device structure; the reflector 2 may be a cavity structure or a Bragg reflector (DBR).

[0053] The device structure comprises a first electrode layer 3, a piezoelectric film layer 4 and a second electrode layer 5, wherein the first electrode layer 3, the piezoelectric film layer 4 and the second electrode layer 5 are sequentially stacked and connected;

[0054] In the embodiment of the present application, the device structure may further include a seed layer or a support layer 7; taking the support layer 7 as an example, the support layer 7 includes a corresponding first surface and a second surface, the first surface of the support layer 7 is stacked and connected with the substrate 1, and the second surface of the support layer 7 is stacked and connected with the first electrode layer 3. That is, the support layer 7, the first electrode layer 3, the piezoelectric film layer 4 and the second electrode layer 5 are stacked and connected in sequence from bottom to top.

[0055] A first acoustic impedance tuning structure 6 is provided on the second electrode layer 5. In the embodiment of the present application, the first acoustic impedance tuning structure 6 is a sub-wavelength acoustic microstructure;

[0056] The first acoustic impedance tuning structure 6 includes a first internal resonance region 62 and a first external resonance region 61 (i.e., forming a main resonator and a sub-resonator); the first external resonance region 61 and the first internal resonance region 62 have different acoustic impedances; in the embodiment of the present application, the duty cycle is defined as: the ratio between the width W of the graphic area within one period and the period T (the total width of the graphic area and the non-graphic area). Figure 1 As shown in ( Figure 1 The first external resonance region 61 shown in the figure is taken as an example including three first units; the first external resonance region in other embodiments described below is also taken as an example of three first units), if W1 is the width of the graphic area of ​​a unit in the first external resonance region 61 (i.e. Figure 1 The total width of a protrusion and a depression in the first external resonance region 61 is T1 (i.e. Figure 1 The duty cycle of the first external resonant region 61 is the ratio of W1 to the period T; if W2 is the pattern width of a unit in the first internal resonant region 62, the period of a unit in the first internal resonant region 62 is T2, and the duty cycle of the first internal resonant region 62 is the ratio of W2 to T2.

[0057] In the embodiment of the present application, the first external resonance region 61 includes at least two first units ( Figure 1 The first external resonance region 61 shown in the figure includes three first units; the first external resonance region in other embodiments described below also takes three first units as an example), and each first unit in the first external resonance region 61 has a corresponding period and duty cycle;

[0058] The period corresponding to each first unit in the first external resonance region 61 is the same;

[0059] The duty ratios corresponding to each first unit in the first outer resonant region 61 are the same.

[0060] In the embodiment of the present application, the first internal resonance region 62 includes at least two second units, and each second unit in the first internal resonance region 62 has a corresponding period and duty cycle;

[0061] The period and duty cycle corresponding to each second unit in the first internal resonance region 62 are the same;

[0062] The duty cycle corresponding to the second unit is different from the duty cycle corresponding to the first unit; that is, the duty cycle change form from the first external resonance region to the first internal resonance region is a sudden change.

[0063] The period corresponding to the second unit is the same as the period corresponding to the first unit.

[0064] The first acoustic impedance tuning structure 6 is formed by providing a concave-convex structure on the second electrode layer 3. The concave-convex structure can be a pattern of various patterns; Figure 2 2a and 2b are schematic top views of the first acoustic impedance tuning structure 6, i.e., the acoustic microstructure, of the embodiment of the present application, and each ring of the same shape represents the boundary line of the acoustic microstructure; wherein, Figure 2 The acoustic microstructure of a is uniformly distributed. Figure 2 The acoustic microstructure in b is non-uniformly distributed; Figure 2 c and Figure 2 d are schematic diagrams of specific rectangular and circular distributions, respectively; there is no parallel relationship between the boundary and the microstructure, the number of complete figures contained between each ring is the number of units in the area, each unit has a protruding figure, and the width of the protruding figure is determined according to the period and duty cycle. Figure 2 e is another schematic diagram of rectangular distribution, in which the rectangles are parallel to the border. All possible surface structures are not limited to those shown in the figure, and may also be other shapes with the same arrangement rules, such as ellipse, triangle or polygon. It should be noted that the accompanying drawings are only illustrative representations of possible surface distribution structures and are not necessarily drawn to actual scale.

[0065] exist Figure 1 In the embodiment, the first acoustic impedance tuning structure 6 is designed to adjust the duty cycle inside and outside the thin film bulk acoustic wave resonator. During the adjustment process, the period T of each unit in the internal resonance area and the external resonance area is kept consistent. When the units in the first internal resonance area 62 of the thin film bulk acoustic wave resonator and the units in the first external resonance area 61 have different duty cycles, they have different resonance frequencies. Since the acoustic microstructure is sub-wavelength, the periodically distributed concave-convex structure cannot be identified for the longitudinally propagating sound waves, which is equivalent to a horizontal plane. Different duty cycles make the height of the equivalent plane different, thus forming resonators with different frequencies, namely the main resonator and the sub-resonator, and the acoustic impedance of the interface becomes discontinuous. For the laterally propagating sound waves, reflections will be formed at the interfaces where the acoustic impedance is discontinuous, and continuous reflections will be formed between adjacent microstructures, so that the resonator of this embodiment can obtain a higher Q value than the resonator of the prior art. The acoustic subwavelength can be expressed as the lateral width W of the microstructure needs to be smaller than the wavelength of the longitudinal sound wave propagation, and further can be smaller than half of the longitudinal wave wavelength. The longitudinal wave wavelength can be calculated from the equivalent film thickness of the resonator.

[0066] In the embodiment of the present application, the thickness of the first acoustic impedance tuning structure 6 needs to be optimized according to the resonant frequency and duty cycle of the main resonator, and may range from 0.1 to 1 μm.

[0067] In the first acoustic impedance tuning structure 6 in the embodiment of the present application, the period T of each unit of the first internal resonance region 62 and each unit of the first external resonance region 61 is consistent. In this embodiment, the period T is designed to be an odd multiple of one quarter of the wavelength of the transverse acoustic wave under the specified frequency condition, and the range can be between 0.5 and 5 μm; in the first embodiment of the present application, the duty cycle and period of each second unit in the first internal resonance region 62 are the same, and the duty cycle and period of each first unit in the first external resonance region 61 are the same, the first unit and the second unit have the same period, and the duty cycle is different; wherein, the duty cycle of the first internal resonance region 62 and the first external resonance region 61 can be changed and combined between 0.1 and 0.9 according to actual needs. The greater the difference between the duty cycle of the internal resonator and the duty cycle of the external resonator, the greater the difference in the acoustic impedance between the two, the better the sound wave reflection effect, and the higher Q value can be obtained compared with the resonator of the prior art.

[0068] In the embodiment of the present application, the lateral edge of the external resonator may exceed the area on the second device layer corresponding to the reflector 2 (taking the reflector 2 as an air cavity as an example), or may be located inside the area on the second electrode layer 5 corresponding to the cavity; however, it must be ensured that the first internal resonance area is completely located inside the cavity to form an effective resonance area to avoid parasitic effects that deteriorate the performance of the acoustic wave resonator.

[0069] In the embodiment of the present application, the substrate 1 can be a high-resistance silicon substrate 1 (resistivity 1k-100kΩ·cm), gallium arsenide or sapphire, etc.; the first acoustic impedance tuning structure 6 and the second electrode layer 5 can be the same metal material, or different metal materials, the metal material of the second electrode layer 5 can be molybdenum (Mo), aluminum (Al), platinum (Pt), tungsten (W), gold (Au), etc.; the material of the first electrode layer 3 can be molybdenum (Mo), aluminum (Al), platinum (Pt), tungsten (W), gold (Au), etc.; the piezoelectric film layer 4 can be selected from materials or doped materials such as aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), etc., for example, the piezoelectric film layer 4 used in the embodiment of the present application is aluminum nitride (AlN), or it can be aluminum nitride AlN doped with rare earth elements (such as scandium (Sc), etc.).

[0070] In the embodiment of the present application, the second electrode layer 5 may be covered with a passivation layer film for protecting the electrode from oxidation.

[0071] The thin film bulk acoustic wave resonator provided by the present application is provided with a first acoustic impedance tuning structure 6 on the second electrode layer 5, and the acoustic impedance tuning structure is a subwavelength acoustic microstructure; by adjusting the duty cycle and period of the first external resonance region 61 and the first internal resonance region 62, the acoustic impedances of the first external resonance region 61 and the first internal resonance region are different, the degree of mismatch is improved, and a multi-layer lateral sound wave reflection interface can be formed, thereby limiting the leakage of sound wave energy from the edge of the resonator and improving the quality factor Q value of the resonator.

[0072] In the embodiment of the present application, the photolithography patterning of the first acoustic impedance tuning structure 6 can be performed simultaneously with the film layer in the resonator itself, without the need for additional process steps.

[0073] In the embodiment of the present application, by reasonably designing the first acoustic impedance tuning structure 6, the acoustic impedance tuning of the main resonator and the sub-resonator can be achieved through a single photolithography technology, thereby achieving a good acoustic wave reflection effect. Its manufacturing method is completely based on mature MEMS semiconductor process technology, and can be repeatedly mass-produced through existing equipment without the need to introduce other traditional processes, greatly reducing costs.

[0074] In the prior art, the frequency adjustment (high frequency or low frequency) of the sub-resonator requires different processes. High-frequency adjustment requires etching of both ends, and the etching depth must be strictly controlled; low-frequency adjustment may require a lift-off process or etching; if different frequency modulation methods are used in the same group of filters, the process steps will be increased. In the embodiment of the present application, whether the frequency of the sub-resonator (first external resonance area 61) is adjusted to be higher or lower than that of the main resonator (first internal resonance area 62), it is only necessary to adjust the duty cycle of the microstructure pattern in a photolithography plate, which can effectively reduce the complexity of the process preparation, thereby reducing the manufacturing cost.

[0075] The embodiment of the present application also provides a filter, including the above-mentioned thin film bulk acoustic wave resonator; Figure 3 Schematic diagram of the structure of a filter according to an embodiment of the present application, which includes a series branch and four parallel branches, and the series branch includes five thin film bulk acoustic wave resonators, such as Figure 2As shown, a first film bulk acoustic wave resonator 101, a second film bulk acoustic wave resonator 102, a third film bulk acoustic wave resonator 103, a fourth film bulk acoustic wave resonator 104 and a fifth film bulk acoustic wave resonator 105, a parallel film bulk acoustic wave resonator 201, 202, 203 and 204 connected in parallel are provided at the node between each adjacent two series resonators, and a grounding inductor is arranged between each parallel film bulk acoustic wave resonator and the grounding node to form a transmission zero point to adjust the out-of-band suppression strength of the filter; the film bulk acoustic wave resonator provided in the embodiment of the present application, wherein each resonator can be a film bulk acoustic wave resonator based on an acoustic microstructure proposed in the present invention, the number and structure of the series resonators and the parallel resonators are not limited to the structure shown in the figure, and the number can be increased or decreased or the structure can be designed according to the filter design index.

[0076] The acoustic impedance tuning structure mentioned in the embodiments of the present application can also be applied to solid-state mounted resonators (SMRs) and other similar resonators.

[0077] Embodiment 2:

[0078] The second embodiment of the present application is substantially the same as the first embodiment, the difference being that:

[0079] like Figure 4 As shown, the period corresponding to each first unit in the first external resonance region 61 and each second unit in the first internal resonance region 62 is the same;

[0080] The duty cycle of each second unit in the first internal resonance region 62 is the same, and the duty cycle corresponding to the outermost first unit in the first external resonance region 61 to the outermost second unit in the first internal resonance region 62 is gradually changed; that is, the duty cycle of each first unit in the first external resonance region 61 is not the same, but gradually changes from the edge of the first external resonance region 61 to the center, and the gradual change can be implemented to extend to the first internal resonance region; the width of the gradual change buffer region is Figure 4 The widths of the three units of the first outer resonance region 61 are designed according to actual needs, and the design range may be between 1 and 10 μm.

[0081] In the second embodiment of the present application, Figure 4As shown, the graphic area of ​​each first unit has a different width; for example, taking the first external resonance area 61 including three first units as an example, the graphic area widths of the three first units are the first width w1, the second width w2 and the third width w3 from the outside to the inside; their corresponding duty cycles are η3, η4 and η5 respectively; the graphic area width of any second unit of the first internal resonance area 62 is the fourth width w4, and its corresponding duty cycle is η2; wherein η3, η4, η5 and η2 may also be a gradual change rule; in the embodiment of the present application, the duty cycle gradual change rule from the edge to the center may be a linear gradual change of a linear function y=kx; or a nonlinear gradual change of a quadratic function y=-ax 2 +b, the function coefficient needs to be determined based on the frequency change caused by the actual duty cycle change. The effective coefficients can be (k=0.1, a=0.033, b=0.933); in addition, it can also be a step function with gradual change y=step(Δx=N*C), where N and c are positive integers. Figure 4 The schematic diagram in FIG. 1 only shows a linearly gradient first acoustic impedance tuning structure 6 ; in the embodiment of the present application, the gradient rule may also be a function type of other rules.

[0082] Compared with the film bulk acoustic wave resonator provided in Example 1, Example 2 of the present application has a gradual buffer area, which makes the acoustic impedance mismatch between the main resonator and the sub-resonator present a gradual process, reducing the probability of scattering of the transverse acoustic wave mode at the acoustic impedance mutation interface; therefore, the Q value of the film bulk acoustic wave resonator of Example 2 is slightly higher than the Q value of the film bulk acoustic wave resonator of Example 1.

[0083] Figure 5 : is a graph comparing the impedance response characteristics of a film bulk acoustic wave resonator with a sudden change in the duty cycle of an acoustic microstructure and a film bulk acoustic wave resonator with a gradual change in the duty cycle; wherein the solid line represents the resonator of the prior art, the dotted line represents the resonator of the acoustic microstructure with a gradual change in the duty cycle, and the dashed line represents the resonator of the acoustic microstructure with a sudden change in the duty cycle; Figure 5 As shown, the thin film bulk acoustic wave resonator formed by changing the duty cycle of the acoustic microstructure in the embodiment of the present application has a parallel resonance point impedance value Rp that is higher than the resonator in the prior art, and a higher impedance value Rp is equivalent to a higher Q value.

[0084] Embodiment three:

[0085] The third embodiment of the present application is substantially the same as the first embodiment, except that:

[0086] The duty cycle corresponding to each first unit in the first external resonance region 61 is the same; the duty cycle corresponding to each second unit in the first internal resonance region 62 is the same; wherein the duty cycle corresponding to the first unit and the second unit is the same; that is, the duty cycle corresponding to each unit of the first acoustic impedance tuning structure is the same; and the period corresponding to each second unit in the first internal resonance region (62) is the same;

[0087] like Figure 6 As shown, in an implementable solution, the period corresponding to each first unit in the first external resonance region 61 is the same, and the period corresponding to any first unit and any second unit is different; that is, the period from the first external resonance region to the first internal resonance region changes suddenly.

[0088] like Figure 7 As shown, in another feasible scheme, the period corresponding to the outermost first unit in the first external resonance region (61) to the outermost second unit in the first internal resonance region 62 is gradually changed; the period change gradient is designed according to the filter passband frequency range, so as to suppress the entire passband spurious mode. The gradual change law can be the same as the linear gradual change of the first function, the nonlinear gradual change of the quadratic function and the step function mentioned in the second embodiment, or it can be different. It should be noted that the filter provided in the implementation of the present application adopts the thin film bulk acoustic wave resonator provided in the present application; the period change gradient of the first acoustic impedance tuning structure 6 of the resonator is designed according to the filter passband frequency range, so as to suppress the entire passband spurious mode.

[0089] The filter provided in the embodiment of the present application performs periodic gradual change processing on the series resonator and the parallel resonator respectively: the change range of the series resonator is between the passband center and the right attenuation point, and the specific function expression can be y=6.97*(x / 10 3 ) 2 +0.707, x is a positive integer; the parallel resonator changes between the passband center and the left attenuation point, and the specific function expression can be y = -7.09*(x / 10 3 ) 2 +0.7195, x is a positive integer; when x is equal to zero, y at this time represents the period size at the center frequency, and the number of points is counted based on the frequency step. The function expression is not limited to the given formula, and the specific function coefficients need to be determined according to the actual filter passband frequency, but should not exceed the protection scope of the present invention.

[0090] The periodic gradient makes the acoustic microstructure unevenly arranged from the edge to the center. There is an additional buffer area with acoustic impedance change between the main resonator and the sub-resonator, which reduces the probability of scattering of transverse sound waves at the interface with sudden acoustic impedance change. In addition, this embodiment can effectively deal with the passband spurious mode of the filter while improving the Q value of the thin film bulk acoustic wave resonator.

[0091] Embodiment 4:

[0092] The fourth embodiment of the present application is substantially the same as the first embodiment, except that:

[0093] like Figure 8 As shown, the film bulk acoustic wave resonator provided in the fourth embodiment of the present application includes a second acoustic impedance tuning structure; the second acoustic impedance tuning structure can be located in other film layers of the film bulk acoustic wave resonator, for example, the second acoustic impedance tuning structure 8 can be arranged on the first surface of the support layer 7, on the surface of the first electrode layer 3 connected to the support layer, or on the surface of the piezoelectric film layer 4 connected to the first electrode layer 3;

[0094] The following description will be made by taking the second acoustic impedance tuning structure 8 being arranged on the first surface of the supporting layer 7 as an example. Figure 8 As shown, the second acoustic impedance tuning structure 8 includes a second inner resonant region and a second outer resonant region with different duty ratios;

[0095] The second internal resonance region is located in the region of the first surface of the support layer 7 corresponding to the reflector 2 .

[0096] In the embodiment of the present application, the second acoustic impedance tuning structure 8 is completely located inside the cavity of the reflector 2;

[0097] In an embodiment of the present application, an implementable solution is that the second acoustic impedance tuning structure 8 has the same structure as the first acoustic impedance tuning structure 6, and corresponds to the position of the first acoustic impedance tuning structure 6. That is, the second acoustic impedance tuning structure 8 has the same distribution, duty cycle, period, etc. as the second internal resonance region and the second external resonance region of the first acoustic impedance tuning structure 6, and the positions correspond, and the two ends are aligned.

[0098] In another feasible solution, the second acoustic impedance tuning structure 8 is not aligned with the first acoustic impedance tuning structure 6 at both ends, and the alignment difference δL between the second acoustic impedance tuning structure 8 and the first acoustic impedance tuning structure 6 is a positive integer multiple of the period T corresponding to one of the units in the first external resonance region 61.

[0099] The alignment difference needs to be designed as an integer multiple of the period because the reflection efficiency of a non-integer multiple period will be reduced. The specific multiple needs to take into account the actual size of the resonator; the same beneficial technical effect can also be achieved by increasing the number of units △k in the internal resonance area of ​​the first acoustic impedance tuning structure 6 or the second acoustic impedance tuning structure 8, and the effective area of ​​the resonator does not change.

[0100] The film bulk acoustic wave resonator with a double-layer acoustic microstructure provided in the embodiment of the present application further improves the difference between the equivalent acoustic impedance of the main resonator and the sub-resonator, is more conducive to sound wave reflection, and limits the leakage of sound wave energy at the edge of the resonator, thereby improving the Q value of the film bulk acoustic wave resonator.

[0101] It should be noted that the combination of the two acoustic impedance tuning structures of the FBAW resonator in the embodiment of the present application can be any combination of the structures of duty cycle mutation, gradual change and gradual function form, periodic mutation, etc. in embodiments one to three.

[0102] Fig. 9 This is a schematic diagram of the suppression of transverse acoustic wave spurious modes by a thin film bulk acoustic wave resonator. Fig. 9 As shown, the solid line is a resonator based on the prior art, the dotted line is a resonator with a sudden duty cycle acoustic microstructure on both the upper and lower surfaces, and the dotted line is a schematic diagram of the suppression of transverse acoustic wave spurious modes by a resonator with a sudden duty cycle acoustic microstructure on the upper surface and a gradual duty cycle acoustic microstructure on the lower surface; it can be seen from the figure that the thin film bulk acoustic wave resonators of the above three schemes can effectively suppress the spurious modes of transverse acoustic waves and flatten the jitter of the impedance curve; thereby effectively improving the passband flatness of the filter.

[0103] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A thin film bulk acoustic resonator, characterized in that: It comprises a substrate (1) and a device structure, wherein the device structure is arranged on the substrate (1); A reflector (2) is provided on one side of the substrate (1) connected to the device structure; the reflector (2) is a cavity structure or a Bragg reflector; The device structure comprises a first electrode layer (3), a piezoelectric film layer (4) and a second electrode layer (5), wherein the first electrode layer (3), the piezoelectric film layer (4) and the second electrode layer (5) are sequentially stacked and connected; The device structure further comprises a supporting layer (7), the supporting layer (7) comprising a first surface and a second surface corresponding to each other, the first surface of the supporting layer (7) being connected in a stacked manner to the substrate (1), and the second surface of the supporting layer (7) being connected in a stacked manner to the first electrode layer (3); A first acoustic impedance tuning structure (6) is provided on the second electrode layer (5), the first acoustic impedance tuning structure (6) comprising a first external resonance region (61) and a first internal resonance region (62), the first external resonance region (61) and the first internal resonance region (62) having different acoustic impedances; The first internal resonance region (62) is arranged in a region on the second electrode layer (5) corresponding to the reflector (2); The device structure further comprises a second acoustic impedance tuning structure (8); the second acoustic impedance tuning structure (8) is arranged on a first surface of the support layer (7), a surface of the first electrode layer (3) connected to the support layer (7), or a surface of the piezoelectric film layer (4) connected to the first electrode layer (3); the second acoustic impedance tuning structure (8) comprises a second internal resonance region and a second external resonance region; the second internal resonance region and the second external resonance region have different acoustic impedances; The second internal resonance region is located in a region corresponding to the reflector (2) on the first surface of the support layer (7), on the surface of the first electrode layer (3) connected to the support layer (7), or on the surface of the piezoelectric film layer (4) connected to the first electrode layer (3).

2. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: The first external resonance region (61) includes at least two first units, and each first unit in the first external resonance region (61) has a corresponding period and duty cycle; The first internal resonance region (62) includes at least two second units, and each second unit in the first internal resonance region (62) has a corresponding period and duty cycle; The period and duty cycle corresponding to each first unit in the first external resonance region (61) are the same; The period and duty cycle corresponding to each second unit in the first internal resonance region (62) are the same; The duty cycle corresponding to the second unit is different from the duty cycle corresponding to the first unit; and the period corresponding to the second unit is the same as the period corresponding to the first unit.

3. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: The second acoustic impedance tuning structure (8) has the same structure as the first acoustic impedance tuning structure (6), and corresponds to the position of the first acoustic impedance tuning structure (6).

4. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: The alignment difference between the second acoustic impedance tuning structure (8) and the first acoustic impedance tuning structure (6) is a positive integer multiple of the corresponding period of one unit in the first external resonance region (61).

5. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: The first external resonance region (61) includes at least two first units, each of which has a corresponding period and duty cycle; the first internal resonance region (62) includes at least two second units, each of which has a corresponding period and duty cycle; The periods corresponding to each first unit in the first external resonance region (61) and each second unit in the first internal resonance region (62) are the same; The duty cycle of each second unit in the first internal resonance region (62) is the same, and the duty cycle corresponding to the outermost first unit in the first external resonance region (61) to the outermost second unit in the first internal resonance region (62) changes gradually.

6. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: The first external resonance region (61) includes at least two first units, each of which has a corresponding period and duty cycle; the first internal resonance region (62) includes at least two second units, each of which has a corresponding period and duty cycle; The duty ratios corresponding to each first unit in the first external resonance region (61) and each second unit in the first internal resonance region (62) are the same; The periods corresponding to each second unit in the first internal resonance region (62) are the same; The period corresponding to the outermost first unit in the first external resonance region (61) to the outermost second unit in the first internal resonance region (62) is gradually changing; or; the period corresponding to each first unit in the first external resonance region (61) is the same, and the period corresponding to any first unit and any second unit is different.

7. The thin film bulk acoustic wave resonator according to claim 1, characterized in that: The first acoustic impedance tuning structure (6) is a sub-wavelength acoustic microstructure; The first acoustic impedance tuning structure (6) is formed by providing a concave-convex structure on the second electrode layer (5).

8. A filter, characterized in that: The invention comprises the thin film bulk acoustic wave resonator as described in any one of claims 1 to 7.

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