Bulk acoustic wave filter and duplexer

Abstract

The present application discloses a bulk acoustic wave filter and a duplexer. The bulk acoustic wave filter comprises an input terminal, an output terminal, first-type resonators and second-type resonators; the first-type resonators are arranged in series between the input terminal and the output terminal; one end of each second-type resonator is connected between the input terminal and the output terminal and the other end thereof is grounded; a first resonator, a first sub-resonator, and a second sub-resonator each comprise a bottom electrode, a piezoelectric layer, a top electrode, and a boundary loop structure; along the thickness direction of the bulk acoustic wave filter, the boundary loop structure overlaps the edge of the top electrode; and the thickness of the boundary loop structure in the first resonator is different from the thickness of the boundary loop structure in the first sub-resonator, and is different from the thickness of the boundary loop structure in the second sub-resonator. By means of the technical means, by setting the thicknesses of boundary loop structures in different types of resonators, out-of-band rejection can be improved and the performance of bulk acoustic wave filters can be improved.

Description

Bulk acoustic wave filter and duplexer

[0001] Cross Reference to Related Applications

[0002] This application claims priority to the Chinese patent application No. 202411170045.3, filed on August 23, 2024, entitled "A bulk acoustic wave filter and duplexer", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of filter, in particular to a bulk acoustic wave filter and duplexer. BACKGROUND

[0004] Radio frequency front-end filters, duplexers and multiplexers based on thin film bulk acoustic wave devices are widely used in smart phones, communication terminals and communication base stations due to their small size, low insertion loss, fast roll-off and low power consumption.

[0005] A typical thin film bulk acoustic wave filter is composed of thin film bulk acoustic wave resonators in series and parallel. In the passband, the series thin film bulk acoustic wave resonators exhibit low resistance characteristics, and the parallel thin film bulk acoustic wave resonators exhibit high resistance characteristics, so the passband loss is small. Out of the passband, the series thin film bulk acoustic wave resonators exhibit high resistance characteristics, and the parallel thin film bulk acoustic wave resonators exhibit low resistance characteristics, achieving out-of-band rejection.

[0006] In order to improve the Q value of the resonator and thus improve the in-band insertion loss of the filter, a boundary ring structure is usually added at the edge of the active area of the series resonator and the parallel resonator. However, the resonator will resonate at the boundary ring structure, resulting in a parasitic peak in the impedance curve of the resonator at low frequencies, thereby deteriorating the out-of-band rejection of the filter.

[0007] SUMMARY

[0008] Embodiments of the present application provide a bulk acoustic wave filter and a duplexer to improve out-of-band rejection and improve the performance of the bulk acoustic wave filter.

[0009] In a first aspect, embodiments of the present application provide a bulk acoustic wave filter, comprising: an input terminal, an output terminal, a first type resonator and a second type resonator; the first type resonator comprises at least one first resonator, and the second type resonator comprises at least one first sub-resonator and at least one second sub-resonator;

[0010] The first type resonator is arranged in series between the input terminal and the output terminal; one end of the second type resonator is connected between the input terminal and the output terminal, and the other end of the second type resonator is grounded;

[0011] The first resonator, the first sub-resonator and the second sub-resonator each comprise a bottom electrode, a piezoelectric layer located on one side of the bottom electrode, a top electrode located on a side of the piezoelectric layer away from the bottom electrode, and a boundary ring structure located on a side of the top electrode away from the bottom electrode; the boundary ring structure overlaps with an edge of the top electrode in a thickness direction of the bulk acoustic wave filter;

[0012] The thickness of the boundary ring structure in the first resonator is different from the thickness of the boundary ring structure in the first sub-resonator, and the thickness of the boundary ring structure in the first resonator is different from the thickness of the boundary ring structure in the second sub-resonator.

[0013] Optionally, the boundary ring structure comprises a first boundary ring structure located on a side of the top electrode away from the bottom electrode in the first resonator, a second boundary ring structure located on a side of the top electrode away from the bottom electrode in the first sub-resonator, and a third boundary ring structure located on a side of the top electrode away from the bottom electrode in the second sub-resonator.

[0014] The thickness of the first boundary ring structure is d1, the thickness of the second boundary ring structure is d2, and the thickness of the third boundary ring structure is d3.

[0015] Wherein, d1>d2≥d3, or d1>d3≥d2.

[0016] Optionally, an air bridge and at least two support columns are comprised between the piezoelectric layer and the top electrode.

[0017] The support columns are supported between the piezoelectric layer and the top electrode.

[0018] Optionally, the distance between two adjacent support columns in the first resonator, the distance between two adjacent support columns in the first sub-resonator, and the distance between two adjacent support columns in the second sub-resonator are not equal.

[0019] Optionally, the bottom electrode comprises a first bottom side and a first side side.

[0020] The included angle between the first bottom side and the first side side is θ.

[0021] Wherein, 15°≤θ≤60°.

[0022] Optionally, the first resonator, the first sub-resonator and the second sub-resonator further comprise a substrate, an acoustic reflection layer and a seed layer.

[0023] The seed layer is located between the substrate and the bottom electrode.

[0024] The acoustic reflection layer is located between the substrate and the seed layer, and the bottom electrode, the acoustic reflection layer and the top electrode overlap along the thickness direction of the bulk acoustic wave filter.

[0025] Optionally, the acoustic reflection layer comprises a cavity.

[0026] Alternatively, the acoustic reflection layer comprises a Bragg reflection layer; the Bragg reflection layer comprises a first acoustic impedance layer and a second acoustic impedance layer, and the first acoustic impedance layer and the second acoustic impedance layer are arranged alternately along the thickness direction of the bulk acoustic wave filter.

[0027] The acoustic impedance of the first acoustic impedance layer is different from the acoustic impedance of the second acoustic impedance layer.

[0028] Optionally, the first sub-resonator further comprises a first mass loading layer located between the top electrode and the boundary ring structure.

[0029] The second sub-resonator further comprises a second mass loading layer located between the top electrode and the boundary ring structure.

[0030] The thickness of the first mass loading layer is smaller than the thickness of the second mass loading layer.

[0031] Optionally, the bulk acoustic wave filter further comprises an input matching inductor, an output matching inductor and a plurality of ground inductors.

[0032] The input matching inductor is connected in series between the input terminal and the output terminal, and is located on the side close to the input terminal.

[0033] The output matching inductor is connected in series between the input terminal and the output terminal, and is located on the side close to the output terminal.

[0034] One end of the ground inductor is connected to the second type resonator, and the other end of the ground inductor is grounded.

[0035] In a second aspect, the embodiments of the present application further provide a duplexer comprising the bulk acoustic wave filter according to any one of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0036] FIG. 1 is a structural schematic diagram of a bulk acoustic wave filter according to an embodiment of the present application;

[0037] FIG. 2 is a cross-sectional structural schematic diagram of a first resonator according to an embodiment of the present application;

[0038] FIG. 3 is a cross-sectional structural schematic diagram of a first sub-resonator according to an embodiment of the present application;

[0039] Fig. 4 is a schematic diagram of a cross-sectional structure of a second sub-resonator according to an embodiment of the present application;

[0040] Fig. 5 is a schematic diagram of an impedance curve of a bulk acoustic wave filter according to the prior art;

[0041] Fig. 6 is a schematic diagram of a response curve of a bulk acoustic wave filter according to the prior art;

[0042] Fig. 7 is a schematic diagram of an impedance curve of a bulk acoustic wave filter according to an embodiment of the present application;

[0043] Fig. 8 is a schematic diagram of a response curve of a bulk acoustic wave filter according to an embodiment of the present application;

[0044] Fig. 9 is a schematic diagram of a cross-sectional structure of a second first resonator according to an embodiment of the present application;

[0045] Fig. 10 is a schematic diagram of a cross-sectional structure of a third first resonator according to an embodiment of the present application. DETAILED DESCRIPTION

[0046] The present application will be further described below in conjunction with the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application. In addition, it should be noted that, for the convenience of description, only the parts related to the present application are shown in the drawings, rather than all the structures.

[0047] Fig. 1 is a structural schematic diagram of a bulk acoustic wave filter provided by an embodiment of the present application, Fig. 2 is a sectional structural schematic diagram of a first resonator provided by an embodiment of the present application, Fig. 3 is a sectional structural schematic diagram of a first sub-resonator provided by an embodiment of the present application, and Fig. 4 is a sectional structural schematic diagram of a second sub-resonator provided by an embodiment of the present application. As shown in Figs. 1-4, the bulk acoustic wave filter comprises: an input terminal 10, an output terminal 20, a first type resonator 30, and a second type resonator 40; the first type resonator 30 comprises at least one first resonator 301, and the second type resonator 40 comprises at least one first sub-resonator 401 and at least one second sub-resonator 402; the first type resonator 30 is arranged in series between the input terminal 10 and the output terminal 20; one end of the second type resonator 40 is connected between the input terminal 10 and the output terminal 20, and the other end of the second type resonator 40 is grounded; the first resonator 301, the first sub-resonator 401, and the second sub-resonator 402 each comprise a bottom electrode 104, a piezoelectric layer 105 located on one side of the bottom electrode 104, a top electrode 106 located on a side of the piezoelectric layer 105 away from the bottom electrode 104, and a boundary ring structure 109 located on a side of the top electrode 106 away from the bottom electrode 104; along a thickness direction (Z direction shown in Fig. 2) of the bulk acoustic wave filter, the boundary ring structure 109 overlaps with an edge of the top electrode 106; the thickness of the boundary ring structure 109 in the first resonator 301 is different from the thickness of the boundary ring structure 109 in the first sub-resonator 401, and the thickness of the boundary ring structure 109 in the first resonator 301 is different from the thickness of the boundary ring structure 109 in the second sub-resonator 402.

[0048] Specifically, the first type resonator 30 is arranged in series between the input terminal 10 and the output terminal 20, that is, the first type resonator 30 is a series resonator. One end of the second type resonator 40 is connected between the input terminal 10 and the output terminal 20, and the other end of the second type resonator 40 is grounded, that is, the second type resonator 40 is a parallel resonator. The first type resonator 30 comprises at least one first resonator 301, that is, the number of series resonators in the bulk acoustic wave filter can be one or more. The second type resonator 40 comprises at least one first sub-resonator 401 and at least one second sub-resonator 402, that is, the number of first sub-resonators 401 in the bulk acoustic wave filter can be one or more, and the number of second sub-resonators 402 can also be one or more.

[0049] Specifically, referring to FIG. 2, the first resonator 301, the first sub-resonator 401 and the second sub-resonator 402 each include a bottom electrode 104, a piezoelectric layer 105 located on one side of the bottom electrode 104, and a top electrode 106 located on a side of the piezoelectric layer 105 away from the bottom electrode 104. The overlapping region of the bottom electrode 104, the piezoelectric layer 105 and the top electrode 106 is the working area of the resonator, i.e. the effective resonant region, and the region outside the working area is the boundary region. When an electrical signal is applied to the top electrode 106 and the bottom electrode 104, acoustic waves will be excited in the piezoelectric layer 105. These acoustic waves mainly propagate in the vertical direction in the working area. In order to confine these vertically propagating acoustic waves between the top electrode 106 and the bottom electrode 104, the upward propagating acoustic waves are reflected back to the working area by the air-metal boundary at the top surface of the top electrode 106, and the downward propagating acoustic waves are reflected back to the effective resonant region by the acoustic reflection layer.

[0050] Specifically, the boundary ring structure 109 is located on a side of the top electrode 106 away from the bottom electrode 104, and along the thickness direction Z of the bulk acoustic wave filter, the boundary ring structure 109 overlaps with the edge of the top electrode 106, that is, the boundary ring structure 109 is arranged at the edge position of the top electrode 106, that is, the boundary ring structure 109 is arranged at the edge position of the working area. In this way, there is a difference in acoustic impedance between the working area and the boundary area during the transmission of the acoustic waves, that is, the acoustic waves that are about to leak can be reflected back to the working area, thereby reducing acoustic wave leakage and improving the Q value of the resonator.

[0051] As a comparative example, FIG. 5 is a schematic diagram of an impedance curve of a bulk acoustic wave filter in the prior art, and FIG. 6 is a schematic diagram of a response curve of a bulk acoustic wave filter in the prior art. As shown in FIGS. 5 and 6, when the thickness of the boundary ring structure 109 in the first resonator 301 is equal to the thickness of the boundary ring structure 109 in the first sub-resonator 401, and the thickness of the boundary ring structure 109 in the first resonator 301 is equal to the thickness of the boundary ring structure 109 in the second sub-resonator 402, that is, the thicknesses of the boundary ring structures of the three are equal, the resonator will resonate at the boundary ring structure, resulting in a parasitic peak in the impedance curve of the resonator at low frequencies. The resonant frequencies of the main resonances of the first resonator 301, the first sub-resonator 401 and the second sub-resonator 402 are fs1, fs2 and fs3 respectively, and the frequencies of the parasitic peaks are fs1_1, fs2_1 and fs3_1 respectively. In the prior art, since the first type resonator 30 and the second type resonator 40 are on the same wafer, the thicknesses of the boundary ring structures are generally the same. Therefore, when fs3 < fs2 < fs1, fs3_1 < fs2_1 < fs1_1. At this time, a parasitic peak will also be formed at the position of the resonator parasitic peak in the filter, and the existence of the parasitic peak seriously deteriorates the out-of-band rejection at this position. For example, the bulk acoustic wave filter shown in FIG. 6 has only -20 dB of rejection.

[0052] Fig. 7 is an impedance curve diagram of a bulk acoustic wave filter provided by an embodiment of the present application, and Fig. 8 is a response curve diagram of a bulk acoustic wave filter provided by an embodiment of the present application. As shown in Figs. 7 and 8, an embodiment of the present application sets the thickness of the inner boundary ring structure 109 of the first resonator 301 to be different from the thickness of the inner boundary ring structure 109 of the first sub-resonator 401, and the thickness of the inner boundary ring structure of the first resonator 301 is different from the thickness of the inner boundary ring structure 109 of the second sub-resonator 402. For example, the thickness of the inner boundary ring structure 109 of the first resonator 301 is greater than the thickness of the inner boundary ring structure 109 of the first sub-resonator 401, and the thickness of the inner boundary ring structure of the first sub-resonator 401 is equal to the thickness of the inner boundary ring structure 109 of the second sub-resonator 402. As shown in Fig. 7, the parasitic bee of the first resonator 301 is located between the parasitic bees of the first sub-resonator 401 and the second sub-resonator 402, i.e., fs3_1<fs1_1<fs2_1. At this time, the response curve of the bulk acoustic wave filter is as shown in Fig. 8, the suppression of the parasitic peak position is close to -40 dB, which is improved by nearly 20 dB compared with the prior art. It can be seen that, by setting the thickness of the inner boundary ring structure of different types of resonators, an embodiment of the present application can improve the out-of-band suppression and improve the performance of the bulk acoustic wave filter.

[0053] For example, the edge of the top electrode is a right angle, and the edge of the boundary ring structure can be flush with the edge of the top electrode, or the edge of the boundary ring structure can wrap the top electrode, so as to prevent the top electrode and the boundary ring structure from delaminating in the subsequent use process, thereby facilitating the stability and reliability of the resonator.

[0054] The bulk acoustic wave filter provided by an embodiment of the present application includes at least one first resonator of a first type of resonator, and at least one first sub-resonator and at least one second sub-resonator of a second type of resonator, and the boundary ring structure is arranged in each type of resonator, so that there is an acoustic impedance difference when the sound wave propagates in the working area and the boundary area, thereby reflecting the leaked sound wave back to the working area and improving the Q value of the resonator. Further, the thickness of the inner boundary ring structure of the first resonator is different from the thickness of the inner boundary ring structure of the first sub-resonator, and the thickness of the inner boundary ring structure of the first resonator is different from the thickness of the inner boundary ring structure of the second sub-resonator, so as to improve the out-of-band suppression and improve the performance of the bulk acoustic wave filter.

[0055] Optionally, with continuous reference to FIGS. 1-4, the boundary ring structure 109 includes a first boundary ring structure 1091 located on the side of the top electrode 106 away from the bottom electrode 104 in the first resonator 301, a second boundary ring structure 1092 located on the side of the top electrode 106 away from the bottom electrode 104 in the first sub-resonator 401, and a third boundary ring structure 1093 located on the side of the top electrode 106 away from the bottom electrode 104 in the second sub-resonator 402; the thickness of the first boundary ring structure 1091 is d1, the thickness of the second boundary ring structure 1092 is d2, and the thickness of the third boundary ring structure 1093 is d3; wherein d1>d2≥d3, or d1>d3≥d2.

[0056] Specifically, as a feasible implementation, d1>d2≥d3, that is, the thickness of the first boundary ring structure 1091 is greater than the thickness of the second boundary ring structure 1092, and the thickness of the second boundary ring structure 1092 is greater than or equal to the thickness of the third boundary ring structure 1093, which can improve the out-of-band rejection and improve the performance of the bulk acoustic wave filter.

[0057] As another feasible implementation, d1>d3≥d2, that is, the thickness of the first boundary ring structure 1091 is greater than the thickness of the third boundary ring structure 1093, and the thickness of the third boundary ring structure 1093 is greater than or equal to the thickness of the second boundary ring structure 1092, which can improve the out-of-band rejection and improve the performance of the bulk acoustic wave filter on the one hand, and can realize the diversification of the bulk acoustic wave filter on the other hand.

[0058] Optionally, FIG. 9 is a schematic diagram of the cross-sectional structure of a second first resonator provided by an embodiment of the present application, as shown in FIG. 9, the air bridge 108 and at least two support columns 130 are included between the piezoelectric layer 105 and the top electrode 106; the support column 130 is supported between the piezoelectric layer 105 and the top electrode 106.

[0059] Specifically, the air bridge 108 is included between the piezoelectric layer 105 and the top electrode 106, so that when the acoustic wave propagates in the vertical direction, it will be reflected at the position of the air bridge 108, which can further confine the acoustic wave in the piezoelectric layer 105, thereby reducing acoustic wave leakage and improving the performance of the bulk acoustic wave filter.

[0060] Further, the support column 130 is supported between the piezoelectric layer 105 and the top electrode 106, so that by setting the support column 130, on the one hand, the support effect on the top electrode 106 can be increased, thereby ensuring the stability of the resonator, and on the other hand, the reflection effect of the acoustic wave can be improved, which can better confine the acoustic wave in the working area and improve the Q value of the resonator.

[0061] It should be noted that FIG. 9 only shows the technical solution that two support columns 130 are arranged in the air bridge 108, and it can be understood that the number of support columns 130 is three or even more.

[0062] Optionally, still referring to FIG. 9, the distance between the two adjacent support columns 130 in the first resonator 301, the distance between the two adjacent support columns in the first sub-resonator, and the distance between the two adjacent support columns in the second sub-resonator are all different.

[0063] It should be noted that FIG. 9 only shows the technical solution that the support column 130 is arranged in the first resonator 301, and it can be understood that the support column 130 can be arranged in the air bridge of the first sub-resonator and the second sub-resonator.

[0064] Specifically, in the same resonator, the distance between the two adjacent support columns can be understood as the distance between the projections of the two support columns on the substrate. Further, the distance between the two adjacent support columns in the first resonator, the distance between the two adjacent support columns in the first sub-resonator, and the distance between the two adjacent support columns in the second sub-resonator are all different, which can improve the out-of-band rejection and improve the performance of the bulk acoustic wave filter.

[0065] Illustratively, when multiple support columns are arranged in the air bridge in the same resonator, the distance between the two adjacent support columns is different, so that the air bridge can reflect acoustic waves of multiple different wavelengths.

[0066] Optionally, still referring to FIG. 4, the bottom electrode 104 includes a first bottom edge 1041 and a first side edge 1042; the included angle between the first bottom edge 1041 and the first side edge 1042 is θ; wherein 15°≤θ≤60°.

[0067] Specifically, taking the second sub-resonator 402 as an example, the first bottom edge 1041 and the first side edge 1042 are not arranged perpendicularly, but have an inclination angle, which is conducive to the subsequent deposition of the piezoelectric layer 105, and thus the quality of the piezoelectric layer 105 at the inclination angle position can be improved.

[0068] Further, the included angle θ between the first bottom edge 1041 and the first side edge 1042 satisfies 15°≤θ≤60°, so that the included angle between the first bottom edge 1041 and the first side edge 1042 is moderate, which can ensure the deposition of the piezoelectric layer 105 on the one hand, and is conducive to the reflection of acoustic waves at the inclination angle position on the other hand.

[0069] Illustratively, when θ<15°, it means that the included angle between the first bottom edge 1041 and the first side edge 1042 is small, which is not conducive to the reflection of acoustic waves at the inclination angle position.

[0070] For example, when θ>60°, the angle between the first bottom side 1041 and the first side 1042 is large, which is not conducive to the deposition of the piezoelectric layer 105.

[0071] Optionally, continuing to refer to FIGS. 2-4, the first resonator 301, the first sub-resonator 401, and the second sub-resonator 402 further include: the substrate 101, the acoustic reflection layer 102, and the seed layer 103; the seed layer 103 is located between the substrate 101 and the bottom electrode 104; the acoustic reflection layer 102 is located between the substrate 101 and the seed layer 103, and the bottom electrode 104, the acoustic reflection layer 102, and the top electrode 106 overlap in the thickness direction Z of the bulk acoustic wave filter.

[0072] Specifically, the material of the substrate 101 can be Si, SOI, or sapphire. By arranging the seed layer 103 between the substrate 101 and the bottom electrode 104, the deposition of the bottom electrode 104 is facilitated.

[0073] Specifically, the acoustic reflection layer 102 is located between the substrate 101 and the seed layer 103, and the bottom electrode 104, the acoustic reflection layer 102, and the top electrode 106 overlap in the thickness direction Z of the bulk acoustic wave filter. In this way, when the acoustic wave propagates downward, it is reflected at the position of the acoustic reflection layer 102, thereby reducing acoustic wave leakage and improving the Q value of the resonator.

[0074] It should be noted that the top electrode 106 and the piezoelectric layer 105 can further include an air gap 107. In this way, when the acoustic wave propagates in the vertical direction, an acoustic impedance difference is generated between the piezoelectric layer 105 and the air gap 107, thereby confining the acoustic wave in the piezoelectric layer, reducing acoustic wave leakage, and improving the Q value of the resonator.

[0075] Optionally, FIG. 10 is a schematic diagram of a cross-sectional structure of a third first resonator provided by an embodiment of the present application. As shown in FIGS. 2 and 10, the acoustic reflection layer 102 includes a cavity 1021; or the acoustic reflection layer 102 includes a Bragg reflection layer 1022; the Bragg reflection layer 1022 includes a first acoustic impedance layer 10221 and a second acoustic impedance layer 10222, which are arranged alternately in the thickness direction Z of the bulk acoustic wave filter; and the acoustic impedance of the first acoustic impedance layer 10221 is different from the acoustic impedance of the second acoustic impedance layer 10222.

[0076] As a feasible implementation manner, continuing to refer to FIG. 2, the acoustic reflection layer 102 includes the cavity 1021. When the acoustic wave propagates downward, it is reflected at the junction between the cavity 1021 and the bottom electrode, thereby reducing acoustic wave leakage and improving the Q value of the resonator.

[0077] As another possible implementation, with continued reference to FIG. 10, the sound reflecting layer 102 includes a Bragg reflecting layer 1022. The Bragg reflecting layer 1022 is formed by alternately arranging a first sound impedance layer 10221 and a second sound impedance layer 10222. Since the sound impedance of the first sound impedance layer 10221 is different from the sound impedance of the second sound impedance layer 10222, the sound wave has a sound impedance difference when propagating in the Bragg reflecting layer 1022, thereby reflecting the downwardly leaking sound wave back to the working area, reducing the sound wave leakage, and improving the Q value of the resonator.

[0078] Optionally, with continued reference to FIGS. 3 and 4, the first sub-resonator 401 further includes a first mass loading layer 110 between the top electrode 106 and the boundary ring structure 109; and the second sub-resonator 402 further includes a second mass loading layer 120 between the top electrode 106 and the boundary ring structure 109; and the thickness of the first mass loading layer 110 is less than the thickness of the second mass loading layer 120.

[0079] Specifically, the first sub-resonator 401 and the second sub-resonator 402 are parallel resonators. By setting the thickness of the first mass loading layer 110 to be less than the thickness of the second mass loading layer 120, the out-of-band rejection of the left side stopband of the bulk acoustic wave filter can be improved, thereby improving the performance of the bulk acoustic wave filter.

[0080] Specifically, by changing the material and structure of the mass loading layer in the parallel resonator, the frequency of the resonator can be changed, thereby adjusting the passband bandwidth, flatness, return loss, and other performance parameters of the filter.

[0081] Optionally, with continued reference to FIG. 1, the bulk acoustic wave filter further includes an input matching inductor 50, an output matching inductor 60, and a plurality of ground inductors 70; the input matching inductor 50 is connected in series between the input terminal 10 and the output terminal 20, and is located on the side close to the input terminal 10; the output matching inductor 60 is connected in series between the input terminal 10 and the output terminal 20, and is located on the side close to the output terminal 20; and one end of the ground inductor 70 is connected to the second type resonator 40, and the other end of the ground inductor 70 is grounded.

[0082] Specifically, by setting the input matching inductor 50 and the output matching inductor 60, better matching can be achieved to block high-frequency signals, transmit low-frequency signals, suppress pulsating signals in the power supply, filter high-frequency noise, and achieve time delay effects. By setting the ground inductor, high-frequency noise can be suppressed to protect the circuit from interference.

[0083] In summary, the bulk acoustic wave filter provided by the embodiments of the present application can improve the out-of-band rejection and improve the performance of the bulk acoustic wave filter by setting the thickness of the inner boundary ring structure of the first resonator different from the thickness of the inner boundary ring structure of the first sub-resonator and the thickness of the inner boundary ring structure of the first resonator different from the thickness of the inner boundary ring structure of the second sub-resonator. In addition, the bulk acoustic wave filter provided by the embodiments of the present application can improve the out-of-band rejection and improve the performance of the bulk acoustic wave filter by setting the distance between the two adjacent support columns in the first resonator, the distance between the two adjacent support columns in the first sub-resonator, and the distance between the two adjacent support columns in the second sub-resonator all different.

[0084] Based on the same application concept, the embodiments of the present application also provide a duplexer, which includes the bulk acoustic wave filter described in the above embodiments, so the duplexer provided by the embodiments of the present application also has the game effects described in the above embodiments, which will not be described here.

[0085] It should be noted that the above are only the preferred embodiments of the present application and the technical principles applied. Those skilled in the art will understand that the present application is not limited to the specific embodiments described herein, and those skilled in the art can make various obvious changes, re-adjustments, mutual combinations and substitutions without departing from the protection scope of the present application. Therefore, although the present application has been described in more detail through the above embodiments, the present application is not limited to the above embodiments, and more other equivalent embodiments can be included without departing from the concept of the present application, and the scope of the present application is determined by the scope of the appended claims. Industrial applicability

[0086] The bulk acoustic wave filter of the present application can reflect the leaked acoustic wave back to the working area, improve the Q value of the resonator, and improve the out-of-band rejection and the performance of the bulk acoustic wave filter. The bulk acoustic wave filter of the present application can be applied to smart phones, communication terminals, and communication base stations.

Claims

1. A bulk acoustic wave filter, characterized by, The application relates to a bulk acoustic wave filter. The bulk acoustic wave filter comprises an input terminal, an output terminal, a first type resonator and a second type resonator; the first type resonator comprises at least one first resonator, and the second type resonator comprises at least one first sub-resonator and at least one second sub-resonator; The first type resonator is arranged in series between the input terminal and the output terminal; One end of the second type resonator is connected between the input terminal and the output terminal, and the other end of the second type resonator is grounded; The first resonator, the first sub-resonator and the second sub-resonator each comprise a bottom electrode, a piezoelectric layer located on one side of the bottom electrode, a top electrode located on a side of the piezoelectric layer away from the bottom electrode, and a boundary ring structure located on a side of the top electrode away from the bottom electrode; along the thickness direction of the bulk acoustic wave filter, the boundary ring structure overlaps with the edge of the top electrode; The thickness of the boundary ring structure in the first resonator is different from the thickness of the boundary ring structure in the first sub-resonator, and the thickness of the boundary ring structure in the first resonator is different from the thickness of the boundary ring structure in the second sub-resonator.

2. The bulk acoustic wave filter of claim 1, wherein, The boundary ring structure comprises a first boundary ring structure located on a side of the top electrode away from the bottom electrode in the first resonator, a second boundary ring structure located on a side of the top electrode away from the bottom electrode in the first sub-resonator, and a third boundary ring structure located on a side of the top electrode away from the bottom electrode in the second sub-resonator; The thickness of the first boundary ring structure is d1, the thickness of the second boundary ring structure is d2, and the thickness of the third boundary ring structure is d3; Wherein, d1>d2>=d3, or d1>d3>=d2.

3. The bulk acoustic wave filter of claim 1, wherein, The air bridge and the at least two support columns are arranged between the piezoelectric layer and the top electrode; The support columns are supported between the piezoelectric layer and the top electrode.

4. The bulk acoustic wave filter of claim 3, wherein, The distance between two adjacent support columns in the first resonator, the distance between two adjacent support columns in the first sub-resonator and the distance between two adjacent support columns in the second sub-resonator are all different.

5. The bulk acoustic wave filter of claim 1, wherein, The bottom electrode comprises a first bottom side and a first side side; The included angle between the first bottom side and the first side side is theta; Wherein, 15 DEG <= theta <= 60 DEG.

6. The bulk acoustic wave filter of claim 1, wherein, The first resonator, the first sub-resonator and the second sub-resonator further comprise a substrate, an acoustic reflection layer and a seed layer; The seed layer is located between the substrate and the bottom electrode; The acoustic reflection layer is located between the substrate and the seed layer, and along the thickness direction of the bulk acoustic wave filter, the bottom electrode, the acoustic reflection layer and the top electrode overlap.

7. The bulk acoustic wave filter of claim 6, wherein, The acoustic reflection layer comprises a cavity; Or, the acoustic reflection layer comprises a Bragg reflection layer; the Bragg reflection layer comprises a first acoustic impedance layer and a second acoustic impedance layer, and along the thickness direction of the bulk acoustic wave filter, the first acoustic impedance layer and the second acoustic impedance layer are arranged alternately in sequence; Wherein, the acoustic impedance of the first acoustic impedance layer is different from the acoustic impedance of the second acoustic impedance layer.

8. The bulk acoustic wave filter of claim 1, wherein, The first sub-resonator further includes a first mass load layer between the top electrode and the boundary ring structure; The second sub-resonator further includes a second mass load layer between the top electrode and the boundary ring structure; The first mass load layer has a thickness smaller than a thickness of the second mass load layer.

9. The bulk acoustic wave filter of claim 1, wherein, The bulk acoustic wave filter further includes an input matching inductor, an output matching inductor, and a plurality of ground inductors; The input matching inductor is connected in series between the input terminal and the output terminal, and is located on a side close to the input terminal; The output matching inductor is connected in series between the input terminal and the output terminal, and is located on a side close to the output terminal; One end of the ground inductor is connected to the second type resonator, and the other end of the ground inductor is grounded.

10. A diplexer, characterized by A bulk acoustic wave filter comprising any one of claims 1-9.

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