CN111327296A - Bulk acoustic wave filter element, method of forming the same, multiplexer, and communication apparatus - Google Patents
Bulk acoustic wave filter element, method of forming the same, multiplexer, and communication apparatus Download PDFInfo
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Abstract
The invention relates to the technical field of filters, in particular to a bulk acoustic wave filter element, a forming method thereof, a multiplexer and communication equipment, wherein the method comprises the following steps: arranging one part of resonators on an upper wafer, and arranging the other part of resonators on a lower wafer; the upper wafer and the lower wafer are arranged in an overlapping mode; and the butt joint pins of the upper wafer are bonded with the butt joint pins of the lower wafer, so that the resonators of the upper wafer and the lower wafer are connected to form the filter. According to the technical scheme of the invention, the resonators are respectively arranged on the upper wafer and the lower wafer, and the resonators on the upper wafer and the lower wafer are bonded through the butt-joint pins to form the filter, so that the planar area occupied by the resonators in the upper wafer and the lower wafer can be reduced, and the size of the filter can be further reduced.
Description
Technical Field
The present invention relates to the field of filter technology, and in particular, to a bulk acoustic wave filter device, a method for forming the same, a multiplexer, and a communication apparatus.
Background
Miniaturization and high performance of the bulk acoustic wave filter are the future development trend, and in the communication system, the bulk acoustic wave filter occupies a large part of the space, so the miniaturization and high performance of the bulk acoustic wave filter are important. The size of the bulk acoustic wave filter is mainly determined by the area occupied by the internal resonators, and the size of the individual resonators is difficult to further reduce under the limits of frequency and material requirements. When the resonator is fabricated on a silicon substrate, the area occupied by one filter element is also fixed. The used area of the resonator in the filter can be reduced as much as possible through the design of the resonator, but the performance of the filter is sacrificed by the method.
Currently, as shown in fig. 1, fig. 1 is a cross-sectional view of a conventional bulk acoustic wave filter, where one wafer 1 is used to manufacture a resonator, another wafer 2 is used to manufacture a VIA and a pin PAD, and the wafer 1 and the wafer 2 are connected by gold-gold bonding to form the filter. In the filter, the series resonators and the parallel resonators are both arranged on the wafer 1, and the plurality of parallel resonators occupy a certain planar area, and the area is fixed and unchangeable, so that the space occupied by the bulk acoustic wave filter as a whole is difficult to reduce.
Disclosure of Invention
Accordingly, it is a primary object of the present invention to provide a bulk acoustic wave filter device, a method of forming the same, a multiplexer, and a communication apparatus, which have a small size without affecting the performance of the filter.
To achieve the above object, according to a first aspect of the present invention, there is provided a method of forming a bulk acoustic wave filter element.
The method of forming a bulk acoustic wave filter element of the present invention includes: arranging one part of resonators on an upper wafer, and arranging the other part of resonators on a lower wafer; the upper wafer and the lower wafer are arranged in an overlapping mode; and the butt joint pins of the upper wafer are bonded with the butt joint pins of the lower wafer, so that the resonators of the upper wafer and the lower wafer are connected to form the filter.
Optionally, the series resonator of the filter is disposed on the upper wafer, and the parallel resonator is disposed on the lower wafer; or the series resonator of the filter is arranged on the lower wafer, and the parallel resonator is arranged on the upper wafer.
Optionally, for the piezoelectric layers of the series resonators and the parallel resonators, the piezoelectric layer thickness is increased and/or the piezoelectric layer dielectric constant is increased to increase the electromechanical coupling coefficient of the resonators in the filter.
Optionally, the method further comprises: reducing parasitic capacitance between resonators of the upper wafer and resonators of the lower wafer to increase an electromechanical coupling coefficient of resonators in the filter.
Optionally, before the docking pin of the upper wafer is bonded with the docking pin of the lower wafer, the electromechanical coupling coefficient of the resonator ranges from 6.5% to 9.5%; for said increasing the electromechanical coupling coefficient of the resonators in the filter, the range of the electromechanical coupling coefficient after the increasing is 6.5% to 9.5%.
Alternatively, the range is 7.5% to 8.5%.
Optionally, the spacing between the resonator of the upper wafer and the resonator of the lower wafer is between 1um and 50 um.
Optionally, the proportion of the electromechanical coupling coefficient of the resonator in the filter is increased by 1% to 0.02%.
Optionally, the method further comprises: the shape of the butt pin is adjusted according to the resonator, the shape of the pin, and the arrangement position of the two.
Optionally, the staggered area in the horizontal direction between the resonator pattern of the upper wafer and the resonator pattern of the lower wafer is adjusted to reduce the parasitic capacitance.
Optionally, the defined thickness of the docking pin is adjusted so as to adjust the spacing between the resonator of the upper wafer and the resonator of the lower wafer to reduce the parasitic capacitance.
Optionally, on the filter layout, the preceding stage circuit and the subsequent stage circuit of the serial branch circuit are arranged in a partitioned manner, and the preceding stage circuit and the subsequent stage circuit of the parallel branch circuit are arranged in a partitioned manner, and the preceding stage circuit on the upper wafer is arranged opposite to the preceding stage circuit on the lower wafer, and the subsequent stage circuit on the upper wafer is arranged opposite to the subsequent stage circuit on the lower wafer, so as to reduce the parasitic capacitance between the preceding stage and the subsequent stage.
Optionally, the method further comprises: and adjusting the electromechanical coupling coefficient of the series resonators to be smaller than that of the parallel resonators so as to improve the roll-off performance on the right side of the passband of the filter.
Optionally, the method further comprises: and adjusting the electromechanical coupling coefficient of the parallel resonators to be smaller than that of the series resonators so as to improve the roll-off performance on the left side of the filter passband.
Optionally, the step of adjusting the electromechanical coupling coefficient to be small includes: the thickness of the piezoelectric layer of the resonator is reduced.
Optionally, the step of adjusting the electromechanical coupling coefficient to be small includes: the dielectric constant of the piezoelectric layer of the resonator is reduced.
According to a second aspect of the present invention, there is provided a bulk acoustic wave filter element.
The bulk acoustic wave filter element comprises an upper wafer and a lower wafer which are vertically overlapped, wherein a resonator and a butt joint pin are respectively arranged on the upper wafer and the lower wafer; and the butt joint pins of the upper wafer are bonded with the butt joint pins of the lower wafer, so that the resonators of the upper wafer and the lower wafer are connected to form the filter.
Optionally, the series resonator of the filter is disposed on the upper wafer, and the parallel resonator is disposed on the lower wafer; or the series resonator of the filter is arranged on the lower wafer, and the parallel resonator is arranged on the upper wafer.
Optionally, there is a staggered area between the resonator pattern of the upper wafer and the resonator pattern of the lower wafer in the horizontal direction.
Optionally, on the filter layout, the front-stage circuit and the back-stage circuit of the serial branch are arranged in a partitioned manner, the front-stage circuit and the back-stage circuit of the parallel branch are arranged in a partitioned manner, the front-stage circuit on the upper wafer is arranged opposite to the back-stage circuit on the lower wafer, and the back-stage circuit on the upper wafer is arranged opposite to the front-stage circuit on the lower wafer.
Optionally, the thickness of the piezoelectric layer of the series resonator is different from the thickness of the piezoelectric layer of the parallel resonator.
Optionally, the dielectric constant of the piezoelectric layer of the series resonator is different from the dielectric constant of the piezoelectric layer of the parallel resonator.
Optionally, the pattern of the electrode edges, the interior, and/or the structural parameters are different between the series resonators and the parallel resonators.
Optionally, the spacing between the resonator of the upper wafer and the resonator of the lower wafer is between 1um and 50 um.
Optionally, the electromechanical coupling coefficient of the resonator is in a range of 6.5% to 9.5%.
Optionally, the electromechanical coupling coefficient of the resonator is in a range of 7.5% to 8.5%.
According to a third aspect of the present invention, there is provided a multiplexer comprising a plurality of bulk acoustic wave filter elements of the present invention.
According to a fourth aspect of the present invention, there is provided a communication device comprising the bulk acoustic wave filter element of the present invention.
According to the technical scheme of the invention, the resonators are respectively arranged on the upper wafer and the lower wafer, and the resonators on the upper wafer and the lower wafer are bonded through the butt-joint pins to form the filter, so that the planar area occupied by the resonators in the upper wafer and the lower wafer can be reduced, and the size of the filter can be further reduced. On one hand, the parasitic capacitance between the resonators in the upper wafer and the lower wafer caused by the method can influence the electromechanical coupling coefficient, so that the capacitance is restrained; on the other hand, the internal structure of the series resonators or the parallel resonators is adjusted to form structural difference, so that the roll-off performance of one side of the passband of the filter is improved.
Drawings
For purposes of illustration and not limitation, the present invention will now be described in accordance with its preferred embodiments, particularly with reference to the accompanying drawings, in which:
fig. 1 is a sectional view of a conventional filter;
fig. 2 is a sectional view of a bulk acoustic wave filter element provided by an embodiment of the present invention;
FIG. 3 illustrates a resonator arrangement according to an embodiment of the present invention;
FIG. 4 illustrates another resonator arrangement according to an embodiment of the present invention;
FIG. 5a is a schematic diagram of the arrangement of the components of the upper wafer;
FIG. 5b is a schematic diagram of the arrangement of the components of the lower wafer;
FIG. 6 is a schematic diagram of the capacitance generated between the resonators of the upper and lower wafers;
FIG. 7 is a simplified block diagram of a resonator;
FIG. 8 is an equivalent circuit diagram of the capacitor formed by the split resonator;
FIG. 9 is a schematic diagram illustrating the effect of reduced electromechanical coupling coefficients on filter performance;
FIG. 10 is a schematic diagram of the performance of the filter after the electromechanical coupling coefficients are restored to target values;
FIG. 11 is a schematic diagram of the interleaving of resonators on the upper and lower wafers;
FIG. 12 is a cross-sectional view of a filter modifying a piezoelectric material;
figure 13 is a cross-sectional view of a filter with a boss on a portion of the resonator;
fig. 14a and 14b are schematic diagrams illustrating performance improvement of the filter due to the difference of the electromechanical coupling coefficients of the partial resonators;
FIG. 15a is a schematic diagram of layout partitioning of an upper wafer;
FIG. 15b is a schematic view of a layout partition of a lower wafer;
fig. 16 is a schematic diagram of improvement of out-of-band suppression after a new layout arrangement mode is adopted.
Detailed Description
Fig. 2 is a cross-sectional view of a bulk acoustic wave filter element according to an embodiment of the present invention, in fig. 2, resonators are fabricated on both an upper wafer (wafer 1) and a lower wafer (wafer 2), and the wafer 1 and the wafer 2 are bonded by a butt pin PAD, thereby forming a filter. The resonator on the wafer 1 and the resonator on the wafer 2 need to meet a certain distance requirement to adjust the capacitance between the resonators, so that the equivalent kt of the resonators is adjusted, and certain performance requirements are further ensured. Specifically, this spacing D needs to satisfy 0< D ≦ 50um (microns), more specifically, D needs to satisfy 1um ≦ D ≦ 10 um.
Fig. 3 shows an arrangement of resonators according to an embodiment of the present invention, in fig. 3, the solid line is a series resonator, which may be disposed on wafer 1 or wafer 2, and conversely, the dashed parallel resonator is disposed on wafer 2 or wafer 1. Fig. 4 shows another resonator arrangement according to an embodiment of the present invention, in fig. 4, a solid line represents a part of the series resonators and a part of the parallel resonators, which may be arranged on the wafer 1 or the wafer 2, and a broken line represents another part of the series resonators and a part of the parallel resonators arranged on the wafer 2 or the wafer 1. The actual structure is not limited to the situation in the above figures, and some resonators in series and in parallel can be arbitrarily manufactured on one wafer, and the rest resonators can be manufactured on another wafer.
Fig. 5a is a schematic diagram of the arrangement of the components of the upper wafer, and fig. 5b is a schematic diagram of the arrangement of the components of the lower wafer, as shown in fig. 5a and 5b, the series resonators are fabricated on wafer 1, and the parallel resonators are fabricated on wafer 2; wherein, the wafer 1 and the wafer 2 both have input pins IN and output pins OUT, that is, the input pins and the output pins on the wafer 1 are connected to the wafer 2 through bonding wires, and then the VIA holes VIA are punched on the wafer 2 to PADs under the wafer 2 so as to connect with external circuits. The pair of ground pins G1, G2, G3 are directly connected to the PAD under wafer 2 VIA. B1, B2 and B3 are butt pins PAD connected in series and parallel, and the series and parallel resonators are connected through bonding wires. As can be seen from fig. 5a and 5B, the increased area of the docking pins PAD occupies a larger wafer area, so from the viewpoint of saving area, it is necessary to minimize the areas of B1, B2, and B3, because B1, B2, and B3 only have the function of electrical connection, and the functions of the electrical connection are different from those of IN, OUT, G1, G2, and G3 on which vias need to be formed, so that the reduced areas do not affect the reliability of the electrical connection, and generally, the areas of B1, B2, and B3 are 20% to 100% of the areas of other PADs (e.g., IN, OUT, G1-G3, etc.).
Meanwhile, the shapes of the B1, B2 and B3 as the ground pins PAD can be any shapes, and the shapes of the B1, B2 and B3 can be adjusted arbitrarily according to the shapes and the arrangement positions of the resonators and other layout structures (such as IN, OUT, G1-G3 and the like), so as to further reduce the area.
Fig. 6 is a schematic diagram of parasitic capacitance (hereinafter, referred to as capacitance) generated between the resonators of the upper wafer and the lower wafer, as shown in fig. 6, the resonators arranged after being split are oppositely arranged on the wafer 1 and the wafer 2, so that capacitance is generated on the resonators at that position, as shown in C1 and C2 in fig. 6. The size C of the capacitor is equal to epsilon S/d, wherein epsilon is the dielectric constant of the medium, and the medium in the structure is air and is a fixed value; s is the staggered area, and d is the distance between the upper electrode and the lower electrode. The size of the resulting capacitance is primarily related to the interleaving area S and the spacing d.
FIG. 7 is a simplified model diagram of a resonator, as shown in FIG. 7, the series resonator frequency of the resonator is determined by L and C1 in series, and the parallel resonator frequency is determined by L, C1, C2; the difference between the parallel resonance frequency Fp and the series resonance frequency Fs is proportional to the electromechanical coupling coefficient.
Fig. 8 is an equivalent circuit diagram when the split resonator forms a capacitor, as shown in fig. 8, C3 in the diagram is a capacitor generated by the split resonator being disposed opposite to each other, and it can be seen from the equivalent circuit diagram that the parallel capacitance increases, the influence on the series resonant frequency Fs is small, and the parallel resonant frequency Fp moves toward a low frequency, so that the difference between Fp and Fs decreases, and the electromechanical coupling coefficient of the resonator decreases; when the electromechanical coupling coefficient of the resonator is reduced, the bandwidth of the filter becomes narrow, resulting in degraded insertion loss on both sides of the filter passband. Fig. 9 is a schematic diagram illustrating the effect of the reduction of the electromechanical coupling coefficient on the performance of the filter. When the electromechanical coupling coefficient is reduced, the bandwidth of the filter passband becomes narrow, and the insertion loss on the left and right sides of the filter passband deteriorates. The solid line in the upper diagram is the case where the electromechanical coupling is not reduced, and the broken line is the case where the electromechanical coupling coefficient is reduced after being stacked in series-parallel.
Since the reduction of the electromechanical coupling coefficient is directly related to the capacitor C3, and the size of the capacitor C3 depends on the interleaving area and the spacing between the resonators on the wafer 1 and the wafer 2, the size of the capacitor C3 can be reduced by reducing the interleaving area S between the resonators or increasing the spacing d between the upper resonator and the lower resonator; on the other hand, the deterioration of insertion loss can be avoided by changing the piezoelectric layer material and the laminated structure of the resonator to improve the electromechanical coupling coefficient of the resonator. In particular, the thickness of the piezoelectric layer of the resonator can be increased and/or the dielectric constant of the piezoelectric layer of the resonator can be increased. Fig. 10 is a diagram illustrating the performance of the filter after the electromechanical coupling coefficient is restored to the target value. It can be seen that the passband can be restored to the original insertion loss level as long as the electromechanical coupling coefficient is increased. In the upper diagram, the solid line indicates the case where the electromechanical coupling is not reduced, and the broken line indicates the case where the electromechanical coupling coefficient is reduced and restored. When the upper and lower wafers are not stacked, the parasitic capacitance is not generated, and the initial range of the electromechanical coupling coefficient of the resonator is between 6.5% and 9.5%, preferably between 7.5% and 8.5%. The parasitic capacitance can cause the electromechanical coupling coefficient of the resonator to be reduced by 0.02% -1%. At this time, the electromechanical coupling coefficient is restored with the initial range as a target value in the above manner.
The staggered area is reduced by reducing the facing area of the upper resonator and the lower resonator as much as possible during layout, so as to reduce S, and the larger the staggered area S is, the more beneficial the reduction of the device area is, but the capacitance C3 is also increased correspondingly. In the case where the interleaving area S is zero, the capacitor C3 becomes considerably small, but the entire filter area is greatly increased at this time, which is not very advantageous in implementation. Fig. 11 is a schematic diagram of the staggered resonators on the upper wafer and the lower wafer, where 1 denotes the resonator on wafer 1, 2 denotes the resonator on wafer 2, and the area S of the staggered resonators 1 and 2 is the area that determines the capacitance, and the size of S can be adjusted by the arrangement of the resonators, so as to adjust the size of the capacitance C.
On the other hand, by increasing the metal thickness of the butt pin, the distance between the resonators facing up and down can be increased when the butt pin is bonded, so as to increase d.
Fig. 12 is a cross-sectional view of a filter with a changed piezoelectric material, and in fig. 12, the piezoelectric layers of the resonators on the wafer 1 and the wafer 2 are made of different materials, and the electromechanical coupling coefficient of the resonator itself can be improved on the original basis by changing the piezoelectric materials and the laminated structure, so as to compensate for the reduction of the electromechanical coupling coefficient by the capacitor. Methods of increasing the electromechanical coupling coefficient include adding a piezoelectric layer, increasing the dielectric constant of the piezoelectric layer, and changing electrode edges, internal patterns, and/or structural parameters of the resonator.
Due to the requirement of the roll-off of the filter, the electromechanical coupling coefficients of partial resonators are required to be small, the electromechanical coupling coefficients of the rest resonators are required to be large, and the adjustment of the electromechanical coupling coefficients of the partial resonators can be adjusted through the capacitor. Fig. 13 is a cross-sectional view of a filter with partial resonator-mounted bosses, as shown in fig. 13, where one of the resonators of wafer 1 is mounted on the boss, thereby reducing its spacing from the resonator on wafer 2. Fig. 14 is a schematic diagram of performance improvement of the filter due to the difference of the electromechanical coupling coefficients of the partial resonators. Wherein the electromechanical coupling coefficient of the series resonator decreases and the electromechanical coupling coefficient of the parallel resonator decreases. The solid line is a curve with no difference in electromechanical coupling coefficients, and the dotted line is a curve with difference. Where 14a is the pass band of the filter and 14b is the roll-off region to the right of the filter. It can be seen that the series electromechanical coupling coefficient of the filter is reduced, so that the roll-off on the right side becomes good, and the insertion loss on the left side also becomes good because the series electromechanical coupling coefficient of the filter is increased. Thus, the difference in the electromechanical coupling coefficient improves both the insertion loss and the roll-off.
Because the upper resonator and the lower resonator are opposite, the coupling is directly formed by the capacitor, the coupling between all nodes is larger than the coupling of a filter which is generally arranged, and the coupling brings serious deterioration of out-of-band rejection. Out-of-band rejection may be improved by determining the effect of coupling between various nodes on out-of-band rejection, and avoiding coupling of sensitive nodes. Generally, it is necessary to avoid coupling of the front stage and the rear stage of the filter. Fig. 15a is a layout partition diagram of an upper wafer, and fig. 15b is a layout partition diagram of a lower wafer; as shown in fig. 15a and 15b, the series resonators S1-S4 are on the wafer 1, the parallel resonators P1-P3 are on the wafer 2, the series resonators and the parallel resonators are respectively divided into two regions, i.e., regions 1, 2, 3, and 4, the series resonators S1 and S2 are front-stage circuits of the series arms, the series resonators S3 and S4 are rear-stage circuits of the series arms, the parallel resonators P1 and P2 are front-stage circuits of the parallel arms, and the parallel resonator P3 is rear-stage circuits of the parallel arms in the wafer 1. In layout arrangement, the resonators in the region 1 and the region 4 need to be prevented from being aligned, and the resonators in the region 2 and the region 3 need to be prevented from being aligned; the coupling generated by the front stage and the rear stage of the filter can cause the out-of-band rejection of the filter to be seriously degraded. Fig. 16 is a schematic diagram of improvement of out-of-band suppression after a new layout arrangement mode is adopted.
The present invention also provides a multiplexer, and the method and the product are extended to a duplexer or a multiplexer product made of any plurality of filters, including related devices. FIG. 16 is a schematic diagram of a multiplexer, wherein F1, F2, and Fn represent different frequencies, wherein n ≧ 2.
The present embodiment also provides a communication device including the bulk acoustic wave filter element described above, and since the volume of the bulk acoustic wave filter element is significantly reduced, the communication device can be reduced as well, which is advantageous for miniaturization of products.
The above-described embodiments should not be construed as limiting the scope of the invention. Those skilled in the art will appreciate that various modifications, combinations, sub-combinations, and substitutions can occur, depending on design requirements and other factors. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (28)
1. A method of forming a bulk acoustic wave filter element, comprising:
arranging one part of resonators on an upper wafer, and arranging the other part of resonators on a lower wafer; the upper wafer and the lower wafer are arranged in an overlapping mode;
and the butt joint pins of the upper wafer are bonded with the butt joint pins of the lower wafer, so that the resonators of the upper wafer and the lower wafer are connected to form the filter.
2. The method of claim 1,
the series resonator of the filter is arranged on the upper wafer, and the parallel resonator is arranged on the lower wafer; or the series resonator of the filter is arranged on the lower wafer, and the parallel resonator is arranged on the upper wafer.
3. Method according to claim 2, characterized in that for the piezoelectric layers of the series and parallel resonators the piezoelectric layer thickness is increased and/or the piezoelectric layer dielectric constant is increased to increase the electromechanical coupling coefficient of the resonators in the filter.
4. The method of claim 2, further comprising: reducing parasitic capacitance between resonators of the upper wafer and resonators of the lower wafer to increase an electromechanical coupling coefficient of resonators in the filter.
5. The method of claim 4,
before the butt joint pins of the upper wafer and the butt joint pins of the lower wafer are bonded, the electromechanical coupling coefficient of the resonator ranges from 6.5% to 9.5%;
for said increasing the electromechanical coupling coefficient of the resonators in the filter, the range of the electromechanical coupling coefficient after the increasing is 6.5% to 9.5%.
6. The method of claim 5, wherein the range is 7.5% to 8.5%.
7. The method of claim 3, wherein the spacing between the resonators of the upper wafer and the resonators of the lower wafer is between 1um and 50 um.
8. The method of claim 7, wherein the proportion of the electromechanical coupling coefficient of the resonators in the filter is increased by 1% to 0.02%.
9. The method of claim 3, further comprising: the shape of the butt pin is adjusted according to the resonator, the shape of the pin, and the arrangement position of the two.
10. The method of claim 3, wherein the staggered area in the horizontal direction between the resonator pattern of the upper wafer and the resonator pattern of the lower wafer is adjusted to reduce the parasitic capacitance.
11. The method of claim 3, wherein the defined thickness of the docking pin is adjusted to adjust a spacing between the resonator of the upper wafer and the resonator of the lower wafer to reduce the parasitic capacitance.
12. The method of claim 3,
on a filter layout, a preceding stage circuit and a subsequent stage circuit of a serial branch circuit are arranged in a partitioned manner, a preceding stage circuit and a subsequent stage circuit of a parallel branch circuit are arranged in a partitioned manner, the preceding stage circuit on an upper wafer is arranged opposite to the preceding stage circuit on a lower wafer, and the subsequent stage circuit on the upper wafer is arranged opposite to the subsequent stage circuit on the lower wafer, so that parasitic capacitance between the preceding stage circuit and the subsequent stage circuit is reduced.
13. The method of claim 3, further comprising: and adjusting the electromechanical coupling coefficient of the series resonators to be smaller than that of the parallel resonators so as to improve the roll-off performance on the right side of the passband of the filter.
14. The method of claim 3, further comprising: and adjusting the electromechanical coupling coefficient of the parallel resonators to be smaller than that of the series resonators so as to improve the roll-off performance on the left side of the filter passband.
15. The method of claim 12 or 13, wherein the step of adjusting the electromechanical coupling coefficient to be small comprises: the thickness of the piezoelectric layer of the resonator is reduced.
16. The method of claim 12 or 13, wherein the step of adjusting the electromechanical coupling coefficient to be small comprises: the dielectric constant of the piezoelectric layer of the resonator is reduced.
17. A bulk acoustic wave filter element characterized in that,
the bulk acoustic wave filter element comprises an upper wafer and a lower wafer which are vertically overlapped, and a resonator and a butt joint pin are respectively arranged on the upper wafer and the lower wafer;
and the butt joint pins of the upper wafer are bonded with the butt joint pins of the lower wafer, so that the resonators of the upper wafer and the lower wafer are connected to form the filter.
18. The bulk acoustic wave filter element according to claim 17,
the series resonator of the filter is arranged on the upper wafer, and the parallel resonator is arranged on the lower wafer; or the series resonator of the filter is arranged on the lower wafer, and the parallel resonator is arranged on the upper wafer.
19. The bulk acoustic wave filter element according to claim 18, wherein there are staggered areas in the horizontal direction between the resonator patterns of the upper wafer and the resonator patterns of the lower wafer.
20. The bulk acoustic wave filter element according to claim 18, wherein the front-stage circuit and the rear-stage circuit of the series arm are arranged in a divided manner, the front-stage circuit and the rear-stage circuit of the parallel arm are arranged in a divided manner, the front-stage circuit on the upper wafer is arranged to oppose the front-stage circuit on the lower wafer, and the rear-stage circuit on the upper wafer is arranged to oppose the rear-stage circuit on the lower wafer on the filter layout.
21. The bulk acoustic wave filter element according to claim 18, wherein the thickness of the piezoelectric layers of the series resonators is different from the thickness of the piezoelectric layers of the parallel resonators.
22. The bulk acoustic wave filter element according to claim 18, wherein the dielectric constant of the piezoelectric layers of the series resonators is different from the dielectric constant of the piezoelectric layers of the parallel resonators.
23. The bulk acoustic wave filter element according to claim 18, wherein an electrode edge, an internal pattern, and/or a structural parameter are different between the series resonators and the parallel resonators.
24. The bulk acoustic wave filter element according to claim 18, wherein the spacing between the resonators of the upper wafer and the resonators of the lower wafer is between 1um and 50 um.
25. The bulk acoustic wave filter element according to claim 18, wherein the electromechanical coupling coefficient of the resonator is in a range of 6.5% to 9.5%.
26. The bulk acoustic wave filter element according to claim 25, wherein the electromechanical coupling coefficient of the resonator is in a range of 7.5% to 8.5%.
27. A multiplexer comprising a plurality of bulk acoustic wave filter elements according to any one of claims 17 to 26.
28. A communication device comprising a bulk acoustic wave filter element according to any one of claims 17 to 26.
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