Bulk acoustic wave filter and duplexer

Abstract

The invention discloses a bulk acoustic wave filter and a duplexer. 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 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; each of the first resonator, the first sub-resonator and the second sub-resonator comprises a bottom electrode, a piezoelectric layer, a top electrode and a boundary ring structure; along the thickness direction of the bulk acoustic wave filter, the boundary ring structure is overlapped with the edge of the top electrode; the thickness of the first resonator inner boundary ring structure is different from the thickness of the first sub-resonator inner boundary ring structure, and is different from the thickness of the second sub-resonator inner boundary ring structure. By adopting the technical means, through setting the thicknesses of the inner boundary ring structures of the resonators of different types, the out-of-band rejection can be improved, and the performance of the bulk acoustic wave filter can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a bulk acoustic wave filter and a duplexer. Background Art

[0002] RF 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.

[0003] A typical FBAW filter is composed of FBAW resonators in series and parallel. In the passband, the series FBAW resonator exhibits low impedance characteristics, while the parallel FBAW resonator exhibits high impedance characteristics, so the passband loss is small. Outside the passband, the series FBAW resonator exhibits high impedance characteristics, while the parallel FBAW resonator exhibits low impedance characteristics, achieving out-of-band suppression.

[0004] 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 to the edge of the series resonator and the parallel resonator. However, the resonator will resonate at the boundary ring structure, causing the impedance curve of the resonator to produce parasitic peaks at low frequencies, thereby deteriorating the out-of-band suppression of the filter. Summary of the invention

[0005] The embodiments of the present invention provide a bulk acoustic wave filter and a duplexer to improve out-of-band suppression and enhance the performance of the bulk acoustic wave filter.

[0006] In a first aspect, an embodiment of the present invention provides 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;

[0007] 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;

[0008] The first resonator, the first sub-resonator and the second sub-resonator each include 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 BAW filter, the boundary ring structure overlaps with an edge of the top electrode;

[0009] 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.

[0010] Optionally, the boundary ring structure includes 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;

[0011] 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;

[0012] Among them, d1>d2≥d3, or d1>d3≥d2.

[0013] Optionally, an air bridge and at least two support pillars are included between the piezoelectric layer and the top electrode;

[0014] The support column is supported between the piezoelectric layer and the top electrode.

[0015] Optionally, a distance between two adjacent support pillars in the first resonator, a distance between two adjacent support pillars in the first sub-resonator, and a distance between two adjacent support pillars in the second sub-resonator are not equal.

[0016] Optionally, the bottom electrode includes a first bottom edge and a first side edge;

[0017] The angle between the first bottom edge and the first side edge is θ;

[0018] Among them, 15°≤θ≤60°.

[0019] Optionally, the first resonator, the first sub-resonator and the second sub-resonator further include: a substrate, an acoustic reflection layer and a seed layer;

[0020] The seed layer is located between the substrate and the bottom electrode;

[0021] The acoustic reflection layer is located between the substrate and the seed layer, and along the thickness direction of the BAW filter, the bottom electrode, the acoustic reflection layer and the top electrode overlap.

[0022] Optionally, the sound reflection layer includes a cavity;

[0023] 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 along the thickness direction of the bulk acoustic wave filter, the first acoustic impedance layer and the second acoustic impedance layer are alternately arranged in sequence;

[0024] The acoustic impedance of the first acoustic impedance layer is different from the acoustic impedance of the second acoustic impedance layer.

[0025] Optionally, the first sub-resonator further comprises a first mass loading layer located between the top electrode and the boundary ring structure;

[0026] The second sub-resonator further includes a second mass loading layer between the top electrode and the boundary ring structure;

[0027] The thickness of the first mass loading layer is smaller than the thickness of the second mass loading layer.

[0028] Optionally, the BAW filter further includes: an input matching inductor, an output matching inductor, and a plurality of ground inductors;

[0029] The input matching inductor is arranged in series between the input terminal and the output terminal and is located on a side close to the input terminal;

[0030] The output matching inductor is arranged in series between the input terminal and the output terminal and is located on a side close to the output terminal;

[0031] One end of the ground inductor is connected to the second type resonator, and the other end of the ground inductor is grounded.

[0032] In a second aspect, an embodiment of the present invention further provides a duplexer, comprising a bulk acoustic wave filter as described in any one of the first aspects.

[0033] The technical solution provided by the embodiment of the present invention is that the bulk acoustic wave filter includes a first type of resonator and a second type of resonator. The first type of resonator is arranged in series between the input terminal and the output terminal, that is, the first type of resonator is a series resonator, one end of the second type of resonator is connected between the input terminal and the output terminal, and the other end of the second type of resonator is grounded, that is, the second type of resonator is a parallel resonator. The first type of resonator includes at least one first resonator, and the second type of resonator includes at least one first sub-resonator and at least one second sub-resonator, and by setting a boundary ring structure in each resonator, there is an acoustic impedance difference when the sound wave propagates in the working area and the boundary area, and then the leaked sound wave is reflected back to the working area, thereby improving the Q value of the resonator. Furthermore, the thickness of the boundary ring structure inside the first resonator is different from the thickness of the boundary ring structure inside the first sub-resonator, and the thickness of the boundary ring structure inside the first resonator is different from the thickness of the boundary ring structure inside the second sub-resonator, so that the out-of-band suppression can be improved and the performance of the bulk acoustic wave filter can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of the structure of a bulk acoustic wave filter provided by an embodiment of the present invention;

[0035] Figure 2 A schematic cross-sectional structure diagram of a first resonator provided by an embodiment of the present invention;

[0036] Figure 3 A schematic cross-sectional structure diagram of a first sub-resonator provided by an embodiment of the present invention;

[0037] Figure 4 A schematic cross-sectional structure diagram of a second sub-resonator provided by an embodiment of the present invention;

[0038] Figure 5 It is a schematic diagram of an impedance curve of a bulk acoustic wave filter in the prior art;

[0039] Figure 6 It is a schematic diagram of a response curve of a bulk acoustic wave filter in the prior art;

[0040] Figure 7 A schematic diagram of an impedance curve of a bulk acoustic wave filter provided by an embodiment of the present invention;

[0041] Figure 8 A schematic diagram of a response curve of a bulk acoustic wave filter provided by an embodiment of the present invention;

[0042] Fig. 9 A schematic cross-sectional structure diagram of a second first resonator provided by an embodiment of the present invention;

[0043] Fig.10A schematic cross-sectional structure diagram of a third first resonator provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0044] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0045] Figure 1 A schematic diagram of the structure of a bulk acoustic wave filter provided by an embodiment of the present invention, Figure 2 A schematic cross-sectional structure diagram of a first resonator provided in an embodiment of the present invention, Figure 3 A schematic cross-sectional structure diagram of a first sub-resonator provided in an embodiment of the present invention, Figure 4 A schematic cross-sectional structure diagram of a second sub-resonator provided by an embodiment of the present invention, such as Figure 1-Figure 4 As shown, the BAW 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, 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 all 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 the thickness direction of the BAW filter (such as Figure 2 The boundary ring structure 109 overlaps the edge of the top electrode 106 (Z direction shown in FIG). 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 in the first resonator 301 is different from the thickness of the boundary ring structure 109 in the second sub-resonator 402.

[0046] 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 includes 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 includes 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.

[0047] Specifically, refer to Figure 2 , the first resonator 301, the first sub-resonator 401 and the second sub-resonator 402 all 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 the side of the piezoelectric layer 105 away from the bottom electrode 104. The overlapping area of ​​the bottom electrode 104, the piezoelectric layer 105 and the top electrode 106 is the working area of ​​the resonator, that is, the effective resonance area, and the area outside the working area is the boundary area. When an electrical signal is applied to the top electrode 106 and the bottom electrode 104, sound waves are excited in the piezoelectric layer 105. These sound waves mainly propagate in the working area in the vertical direction. In order to limit these sound waves propagating in the vertical direction between the top electrode 106 and the bottom electrode 104, the sound waves propagating upward are reflected back to the working area through the air-metal boundary at the top surface of the top electrode 106, and the sound waves propagating downward are returned to the effective resonance area through the sound reflection layer.

[0048] Specifically, the boundary ring structure 109 is located on the 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 set at the edge of the top electrode 106, that is, the boundary ring structure 109 is set at the edge of the working area, so that during the transmission of the sound wave, there is an acoustic impedance difference between the working area and the boundary area, that is, the sound wave that is about to leak can be reflected back to the working area, thereby reducing the leakage of the sound wave and improving the Q value of the resonator.

[0049] As a comparative example, Figure 5 is a schematic diagram of an impedance curve of a bulk acoustic wave filter in the prior art, Figure 6 FIG. 1 is a schematic diagram of a response curve of a bulk acoustic wave filter in the prior art, such as Figure 5 and Figure 6As shown, when the thickness of the inner boundary ring structure 109 of the first resonator 301 is equal to the thickness of the inner boundary ring structure 109 of the first sub-resonator 401, and the inner boundary ring structure 109 of the first resonator 301 is equal to the thickness of the inner boundary ring structure 109 of the second sub-resonator 402, that is, when the thicknesses of the boundary ring structures of all three are equal, resonance will occur at the boundary ring structure of the resonator, resulting in a parasitic peak in the impedance curve of the resonator at low frequencies. Among them, the resonance 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 of resonator 30 and the second type of resonator 40 are on the same wafer, the thicknesses of their boundary ring structures are generally the same. Therefore, when fs3 < fs2 < fs1, fs3_1 < fs2_1 < fs1_1. At this time, the filter will also form a parasitic peak at the position of the parasitic peak of the resonator. The existence of the parasitic peak seriously deteriorates the out-of-band rejection here. Exemplarily, Figure 6 the suppression of the bulk acoustic wave filter shown in it is only -20 dB.

[0050] Figure 7 FIG. is a schematic diagram of the impedance curve of a bulk acoustic wave filter provided by an embodiment of the present invention. Figure 8 FIG. is a schematic diagram of the response curve of a bulk acoustic wave filter provided by an embodiment of the present invention. As Figure 7 and Figure 8 shown, in the embodiment of the present invention, the thickness of the inner boundary ring structure 109 of the first resonator 301 is set 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. Exemplarily, taking the thickness of the inner boundary ring structure 109 of the first resonator 301 being 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 being equal to the thickness of the inner boundary ring structure 109 of the second sub-resonator 402 as an example for illustration, as Figure 7 shown, the parasitic peak of the first resonator 301 is at a position between the parasitic peaks of the first sub-resonator 401 and the second sub-resonator 402, that is, fs3_1 < fs1_1 < fs2_1. At this time, the response curve of the bulk acoustic wave filter is as Figure 8 shown, the suppression at the parasitic peak position is close to -40 dB. Compared with the prior art, it is increased by nearly 20 dB. Thus, it can be seen that by setting the thicknesses of the inner boundary ring structures of different types of resonators in the embodiment of the present invention, the out-of-band rejection can be improved and the performance of the bulk acoustic wave filter can be enhanced.

[0051] Exemplarily, 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 to prevent delamination of the top electrode and the boundary ring structure during subsequent use, thereby helping to ensure the stability and reliability of the resonator.

[0052] In the BAW filter provided by the embodiment of the present invention, the first type of resonator includes at least one first resonator, the second type of resonator includes at least one first sub-resonator and at least one second sub-resonator, and a boundary ring structure is set in each resonator, so that when the sound wave propagates in the working area and the boundary area, there is a difference in acoustic impedance, and then the leaked sound wave is reflected back to the working area, thereby improving the Q value of the resonator. Furthermore, the thickness of the boundary ring structure inside the first resonator is different from the thickness of the boundary ring structure inside the first sub-resonator, and the thickness of the boundary ring structure inside the first resonator is different from the thickness of the boundary ring structure inside the second sub-resonator, so that the out-of-band suppression can be improved and the performance of the BAW filter can be improved.

[0053] Optional, continue to refer to Figure 1-Figure 4 The boundary ring structure 109 includes a first boundary ring structure 1091 located at a side of the top electrode 106 away from the bottom electrode 104 in the first resonator 301, a second boundary ring structure 1092 located at a 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 at a 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.

[0054] 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 out-of-band suppression and improve the performance of the bulk acoustic wave filter.

[0055] 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. This can improve out-of-band suppression and the performance of the bulk acoustic wave filter on the one hand, and can achieve diversified settings for the bulk acoustic wave filter on the other hand.

[0056] Optional, Fig. 9 A schematic cross-sectional structure diagram of a second first resonator provided in an embodiment of the present invention, as shown in FIG. Fig. 9As shown, an air bridge 108 and at least two support pillars 130 are included between the piezoelectric layer 105 and the top electrode 106 ; the support pillars 130 are supported between the piezoelectric layer 105 and the top electrode 106 .

[0057] Specifically, an air bridge 108 is included between the piezoelectric layer 105 and the top electrode 106, so that when the sound wave propagates in the vertical direction, it will be reflected at the position of the air bridge 108, which can further confine the sound wave to the piezoelectric layer 105, thereby reducing sound wave leakage and improving the performance of the bulk acoustic wave filter.

[0058] Furthermore, the support column 130 is supported between the piezoelectric layer 105 and the top electrode 106. 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. On the other hand, the reflection effect on the sound waves can be improved, the sound waves can be better confined to the working area, and the Q value of the resonator can be improved.

[0059] It should be noted that Fig. 9 Only the technical solution of two support columns 130 being provided in the air bridge 108 is shown. It is understandable that the number of the support columns 130 can be three or even more.

[0060] Optional, continue to refer to Fig. 9 , the distance between two adjacent support pillars 130 in the first resonator 301, the distance between two adjacent support pillars in the first sub-resonator, and the distance between two adjacent support pillars in the second sub-resonator are not equal.

[0061] It should be noted that Fig. 9 Only the technical solution of providing the support column 130 in the first resonator 301 is shown. It can be understood that the support column 130 can be provided in the air bridges of the first sub-resonator and the second sub-resonator.

[0062] Specifically, in the same resonator, the distance between two adjacent support pillars can be understood as the distance between the projections of the two support pillars on the substrate. Furthermore, the distance between two adjacent support pillars in the first resonator, the distance between two adjacent support pillars in the first sub-resonator, and the distance between two adjacent support pillars in the second sub-resonator are not equal, which can improve out-of-band suppression and improve the performance of the BAW filter.

[0063] Exemplarily, when a plurality of support columns are disposed in the air bridge in the same resonator, the distances between two adjacent support columns are different, so that the air bridge can reflect sound waves of multiple different wavelengths.

[0064] Optional, continue to refer to Figure 4The bottom electrode 104 includes a first bottom edge 1041 and a first side edge 1042 ; the angle between the first bottom edge 1041 and the first side edge 1042 is θ; wherein 15°≤θ≤60°.

[0065] Specifically, taking the second sub-resonator 402 as an example, the first bottom edge 1041 and the first side edge 1042 are not arranged vertically but have an inclination angle, which is beneficial to the subsequent deposition of the piezoelectric layer 105 and can improve the quality of the piezoelectric layer 105 at the inclination position.

[0066] Furthermore, the angle θ between the first bottom edge 1041 and the first side edge 1042 satisfies 15°≤θ≤60°, so that the 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 realizing sound wave reflection at the inclined position on the other hand.

[0067] Exemplarily, when θ<15°, it indicates that the angle between the first bottom edge 1041 and the first side edge 1042 is relatively small, which is not conducive to achieving sound wave reflection at the inclined position.

[0068] Exemplarily, when θ>60°, it indicates that the angle between the first bottom edge 1041 and the first side edge 1042 is relatively large, which is not conducive to the deposition of the piezoelectric layer 105 .

[0069] Optional, continue to refer to Figure 2-Figure 4 The first resonator 301, the first sub-resonator 401 and the second sub-resonator 402 further include: a substrate 101, an acoustic reflection layer 102 and a 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 along the thickness direction Z of the bulk acoustic wave filter, the bottom electrode 104, the acoustic reflection layer 102 and the top electrode 106 overlap.

[0070] Specifically, the material of the substrate 101 may be Si, SOI or sapphire. The seed layer 103 is provided between the substrate 101 and the bottom electrode 104, which is beneficial to the deposition of the bottom electrode 104.

[0071] Specifically, the acoustic reflection layer 102 is located between the substrate 101 and the seed layer 103, and along the thickness direction Z of the bulk acoustic wave filter, the bottom electrode 104, the acoustic reflection layer 102 and the top electrode 106 overlap, so that when the sound wave propagates downward, it will be reflected at the position of the acoustic reflection layer 102, thereby reducing sound wave leakage and improving the Q value of the resonator.

[0072] It should be noted that an air gap 107 may also be included between the top electrode 106 and the piezoelectric layer 105. When the sound wave propagates in the vertical direction, an acoustic impedance difference will be generated between the piezoelectric layer 105 and the air gap 107, thereby confining the sound wave to the piezoelectric layer, reducing sound wave leakage and improving the Q value of the resonator.

[0073] Optional, Fig.10 A schematic cross-sectional structure diagram of a third first resonator provided in an embodiment of the present invention, as shown in FIG. Figure 2 and Fig.10 As shown, the sound reflection layer 102 includes a cavity 1021; or, the sound 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, and along the thickness direction Z of the bulk acoustic wave filter, the first acoustic impedance layer 10221 and the second acoustic impedance layer 10222 are alternately arranged in sequence; wherein the acoustic impedance of the first acoustic impedance layer 10221 is different from the acoustic impedance of the second acoustic impedance layer 10222.

[0074] As a feasible implementation method, continue to refer to Figure 2 The sound reflection layer 102 includes a cavity 1021. When the sound wave propagates downward, it will be reflected at the junction of the cavity 1021 and the bottom electrode, thereby reducing the leakage of the sound wave and improving the Q value of the resonator.

[0075] As another possible implementation, continue to refer to Fig.10 The acoustic reflection layer 102 includes a Bragg reflection layer 1022. The Bragg reflection layer 1022 is formed by alternating the first acoustic impedance layer 10221 and the second acoustic impedance layer 10222 in sequence. Since the acoustic impedance of the first acoustic impedance layer 10221 is different from the acoustic impedance of the second acoustic impedance layer 10222, the acoustic wave has an acoustic impedance difference when propagating in the Bragg reflection layer 1022, and can reflect the downward leaked sound wave back to the working area, reduce the leakage of the sound wave, and improve the Q value of the resonator.

[0076] Optional, continue to refer to Figure 3 and Figure 4 The first sub-resonator 401 further includes a first mass load layer 110 located between the top electrode 106 and the boundary ring structure 109 ; the second sub-resonator 402 further includes a second mass load layer 120 located between the top electrode 106 and the boundary ring structure 109 ; the thickness of the first mass load layer 110 is less than the thickness of the second mass load layer 120 .

[0077] Specifically, the first sub-resonator 401 and the second sub-resonator 402 are both parallel resonators. By setting the thickness of the first mass load layer 110 to be smaller than the thickness of the second mass load layer 120, the out-of-band suppression of the left bandgap of the BAW filter can be improved, thereby improving the performance of the BAW filter.

[0078] Specifically, by changing the material and structure of the mass load layer in the parallel resonator, the frequency of the resonator can be changed, thereby adjusting the performance parameters of the filter such as the passband bandwidth, flatness, and return loss.

[0079] Optional, continue to refer to Figure 1 The BAW 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 arranged in series between the input terminal 10 and the output terminal 20, and is located on a side close to the input terminal 10; the output matching inductor 60 is arranged in series between the input terminal 10 and the output terminal 20, and is located on a side close to the output terminal 20; 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.

[0080] 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 delay the effect. By setting the ground inductor, high-frequency noise can be suppressed to protect the circuit from interference.

[0081] In summary, the BAW filter provided by the embodiment of the present invention can improve out-of-band suppression and improve the performance of the BAW filter by setting the thickness of the inner boundary ring structure of the first resonator to be 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 to be different from the thickness of the inner boundary ring structure of the second sub-resonator. In addition, by setting 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 to be unequal, it is possible to improve out-of-band suppression and improve the performance of the BAW filter.

[0082] Based on the same inventive concept, an embodiment of the present invention further provides a duplexer, which includes the bulk acoustic wave filter described in the above embodiment. Therefore, the duplexer provided by the embodiment of the present invention also has the gaming effect described in the above embodiment, which will not be repeated here.

[0083] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, combinations and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A bulk acoustic wave filter, characterized in that: include: An input terminal, an output terminal, a first type resonator, and a second type resonator; the first type resonator includes at least one first resonator, and the second type resonator includes 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 include 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 BAW filter, the boundary ring structure overlaps with an 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 according to claim 1, characterized in that The boundary ring structure includes 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; Among them, d1>d2≥d3, or d1>d3≥d2.

3. The bulk acoustic wave filter according to claim 1, wherein: An air bridge and at least two support pillars are included between the piezoelectric layer and the top electrode; The support column is supported between the piezoelectric layer and the top electrode.

4. The bulk acoustic wave filter according to claim 3, characterized in that The distance between two adjacent support pillars in the first resonator, the distance between two adjacent support pillars in the first sub-resonator, and the distance between two adjacent support pillars in the second sub-resonator are all unequal.

5. The bulk acoustic wave filter according to claim 1, wherein: The bottom electrode comprises a first bottom edge and a first side edge; The angle between the first bottom edge and the first side edge is θ; Among them, 15°≤θ≤60°.

6. The bulk acoustic wave filter according to claim 1, wherein: The first resonator, the first sub-resonator and the second sub-resonator further include: 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 BAW filter, the bottom electrode, the acoustic reflection layer and the top electrode overlap.

7. The bulk acoustic wave filter according to claim 6, characterized in that The sound reflecting layer includes a cavity; 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 along the thickness direction of the bulk acoustic wave filter, the first acoustic impedance layer and the second acoustic impedance layer are alternately arranged in sequence; 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 according to claim 1, wherein: The first sub-resonator further includes a first mass loading layer between the top electrode and the boundary ring structure; The second sub-resonator further includes a second mass loading layer between the top electrode and the boundary ring structure; The thickness of the first mass loading layer is smaller than the thickness of the second mass loading layer.

9. The bulk acoustic wave filter according to claim 1, wherein: The BAW filter further includes: an input matching inductor, an output matching inductor and a plurality of ground inductors; The input matching inductor is arranged 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 arranged 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 duplexer, characterized in that: Comprising a bulk acoustic wave filter as claimed in any one of claims 1 to 9.

Images