Bulk acoustic wave filter, and method for increasing bandwidth of bulk acoustic wave filter

Abstract

The present invention provides a bulk acoustic wave filter. The bulk acoustic wave filter comprises a plurality of resonance units which are connected, each resonance unit comprises a bulk acoustic wave resonator, and at least some of the resonance units in the bulk acoustic wave filter have more than two resonance modes, that is, the bulk acoustic wave filter is composed of bulk acoustic wave resonators having multiple resonance modes, so that the bulk acoustic wave filter having a large bandwidth can be implemented. The present invention further provides a method for increasing the bandwidth of a bulk acoustic wave filter. In the method for increasing the bandwidth of a bulk acoustic wave filter, the bandwidth of the bulk acoustic wave filter is increased in the manner of at least some of resonance units in the bulk acoustic wave filter having more than two resonance modes.

Description

Bulk Acoustic Filters and Methods to Increase Their Bandwidth Technical Field

[0001] This invention relates to the fields of semiconductors and microelectromechanical systems (MEMS), and particularly to a bulk acoustic wave filter and a method for increasing the bandwidth of the bulk acoustic wave filter. Background Technology

[0002] With the rapid development of mobile communication technology, the communication spectrum is constantly increasing and the communication frequency is constantly rising. These factors have placed higher demands on the radio frequency front-end devices in communication systems, and the technology is increasingly showing a trend towards higher frequency, larger bandwidth, and higher integration. Compared with traditional ceramic filters and surface acoustic wave (SAW) filters, bulk acoustic wave (BAW) filters have irreplaceable advantages in terms of operating frequency, quality factor (Q), and insertion loss.

[0003] The common BAW filter design structure is a trapezoidal structure. The main feature of this structure is that it is constructed using series and parallel bulk acoustic wave resonators, which has good power tolerance. Traditional bulk acoustic wave resonators use AlN as their piezoelectric material, and the electromechanical coupling coefficient of the resonators is usually below 4%. Consequently, the 3dB relative bandwidth of the filter can only reach 4%, which cannot meet the requirements of current broadband filters.

[0004] In existing technologies, the large bandwidth performance of bulk acoustic wave (BAW) filters is usually achieved by increasing the electromechanical coupling coefficient of the BAW resonator. For example, the electromechanical coupling coefficient of the BAW resonator is increased by using scandium-doped (Sc) AlN material as the piezoelectric material of the BAW resonator. However, the Sc doping method is difficult to implement due to process limitations. Summary of the Invention

[0005] One of the objectives of this invention is to provide a bulk acoustic wave filter and a method for increasing the bandwidth of the bulk acoustic wave filter, which can achieve the goal of increasing the bandwidth of the bulk acoustic wave filter.

[0006] To achieve the above objectives, one aspect of the present invention provides a bulk acoustic wave filter. The bulk acoustic wave filter includes a plurality of interconnected resonant units, each of the resonant units including a bulk acoustic wave resonator, wherein at least some of the resonant units have two or more resonant modes.

[0007] Optionally, at least a portion of the resonant unit further includes a first branch, the first branch including a capacitor and an inductor connected in series; in the resonant unit including the first branch, the first branch is connected in parallel with the bulk acoustic wave resonator, and the first branch is used to increase the resonant mode of the bulk acoustic wave resonator.

[0008] Optionally, the plurality of resonant units include series resonant units and parallel resonant units; at least some of the series resonant units include the first branch, or at least some of the parallel resonant units include the first branch, or at least some of the series resonant units and at least some of the parallel resonant units include the first branch.

[0009] Optionally, the series resonant unit includes a series resonator, and the series resonators of multiple series resonant units are connected in series between the input port and the output port of the bulk acoustic wave filter; the parallel resonant unit includes a parallel resonator, one end of which is connected between two adjacent series resonators, between the input port and the series resonator at the head, or between the output port and the series resonator at the tail, and the other end of which is grounded.

[0010] Optionally, each of the series resonant units has the same number of first branches, and all the first branches of the series resonant unit are connected in parallel with the series resonator of the series resonant unit.

[0011] Optionally, each of the parallel resonant units has the same number of first branches, and all the first branches of the parallel resonant unit are connected in parallel with the parallel resonator of the parallel resonant unit.

[0012] Optionally, the bulk acoustic resonator is connected in parallel with n of the first branches to increase n resonant modes, where n is an integer greater than or equal to 1; each resonant mode corresponds to a series resonant frequency and a parallel resonant frequency.

[0013] Optionally, one of the bulk acoustic resonators is connected in parallel with one of the first branches to add an additional resonant mode. The series resonant frequency corresponding to the additional resonant mode is fs, and the parallel resonant frequency corresponding to the additional resonant mode is fp. Wherein, Lse is the inductance value of the inductor, Cse is the capacitance value of the capacitor, and C0 is the static capacitance of the bulk acoustic resonator.

[0014] The present invention also provides a method for increasing the bandwidth of a bulk acoustic wave filter. The bulk acoustic wave filter includes a plurality of resonant units, each of which includes a bulk acoustic wave resonator. The method for increasing the bandwidth of the bulk acoustic wave filter includes employing at least some of the resonant units to have two or more resonant modes to increase the bandwidth of the bulk acoustic wave filter.

[0015] Optionally, a first branch is provided in at least a portion of the resonant unit, the first branch including a capacitor and an inductor connected in series; in the resonant unit including the first branch, the first branch is connected in parallel with the bulk acoustic wave resonator, and the first branch is used to increase the resonant mode of the bulk acoustic wave resonator.

[0016] Optionally, the plurality of resonant units include series resonant units and parallel resonant units; the method of setting a first branch in at least a portion of the resonant units includes: setting the first branch in at least a portion of the series resonant units, or setting the first branch in at least a portion of the parallel resonant units, or setting the first branch in at least a portion of the series resonant units and setting the first branch in at least a portion of the parallel resonant units.

[0017] Optionally, a method for giving the resonant unit more than two resonant modes includes increasing the resonant modes of the bulk acoustic wave resonator by adjusting at least one of the structure, position, shape, electrode thickness, piezoelectric material thickness, and piezoelectric material material of the bulk acoustic wave resonator.

[0018] Optionally, the bulk acoustic resonator includes a bottom electrode, a piezoelectric layer, and a top electrode stacked sequentially from bottom to top. By changing the material tangent of the piezoelectric layer, the bulk acoustic resonator can have more than two resonance modes.

[0019] In the bulk acoustic wave filter and the method for increasing the bandwidth of the bulk acoustic wave filter provided by the present invention, at least some of the resonant units in the bulk acoustic wave filter have two or more resonant modes, that is, the bulk acoustic wave filter is composed of bulk acoustic wave resonators with multiple resonant modes, thereby realizing a bulk acoustic wave filter with a large bandwidth.

[0020] Furthermore, the resonant modes of the bulk acoustic wave (SAW) resonator can be increased by setting a first branch in parallel with the SAW resonator in the bulk acoustic wave filter. This increases the bandwidth of the SAW filter without changing the original structure, position, shape, thickness, or material of the SAW resonator. The process is simple, and the first branch can be designed together with the SAW resonator, saving design resources. In addition, it avoids the need to use an external inductor to increase the electromechanical coupling coefficient and thus increase the filter bandwidth, thereby avoiding the problem of the SAW filter generating a new transmission zero or pole, which is beneficial to the design of the SAW filter.

[0021] Furthermore, the resonant modes of the bulk acoustic wave resonator can be increased by adjusting at least one of the following: structure, position, shape, electrode thickness, piezoelectric material thickness, and piezoelectric material material. This can increase the bandwidth of the bulk acoustic wave filter, reduce the number of bulk acoustic wave resonators required to fabricate a broadband bulk acoustic wave filter, and eliminate the need for external capacitors and inductors, thus simplifying the number of components within the bulk acoustic wave filter. Attached Figure Description

[0022] Figure 1 is a schematic diagram of a resonant unit of a bulk acoustic wave filter provided in an embodiment of the present invention.

[0023] Figure 2 is an impedance curve of a bulk acoustic resonator of a bulk acoustic filter provided in an embodiment of the present invention connected in parallel with a first branch.

[0024] Figure 3 is a circuit diagram of a bulk acoustic wave filter with a series resonator connected in parallel to the first branch according to an embodiment of the present invention.

[0025] Figure 4 shows the impedance curve of the resonant unit of the bulk acoustic wave filter shown in Figure 3.

[0026] Figure 5 is a circuit diagram of a bulk acoustic wave filter provided in an embodiment of the present invention, in which both the series resonator and the parallel resonator are connected in parallel to the first branch.

[0027] Figure 6 shows the impedance curve of the bulk acoustic wave filter shown in Figure 5.

[0028] Figure 7 is a circuit diagram of a sixth-order bulk acoustic filter provided in an embodiment of the present invention.

[0029] Figure 8 shows the passband response curve of the bulk acoustic wave filter shown in Figure 7 applied in the N77 frequency band.

[0030] Figure 9 is a schematic diagram of the structure of a bulk acoustic resonator provided in an embodiment of the present invention.

[0031] Figure 10 is an impedance curve of a bulk acoustic resonator provided in an embodiment of the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0033] This invention provides a bulk acoustic wave filter, which includes multiple resonant units connected in series. Each resonant unit includes a bulk acoustic wave resonator. At least some of the resonant units have two or more resonant modes, that is, at least some of the bulk acoustic wave resonators have two or more resonant modes. The bulk acoustic wave filter is composed of bulk acoustic wave resonators with multiple resonant modes, thereby realizing a bulk acoustic wave filter with a large bandwidth. Moreover, the bulk acoustic wave filter is easy to design and manufacture.

[0034] In this embodiment, at least a portion of the resonant unit of the bulk acoustic wave filter further includes a first branch. Figure 1 is a schematic diagram of a resonant unit of a bulk acoustic wave filter provided in an embodiment of the present invention. The resonant unit shown in Figure 1 is a resonant unit including a first branch. Referring to Figure 1, the resonant unit includes a bulk acoustic wave resonator Y and a first branch 3 connected in parallel with the bulk acoustic wave resonator Y. The first branch 3 includes a capacitor Cse and an inductor Lse connected in series. The first branch 3 is used to increase the resonant modes of the bulk acoustic wave resonator Y, so that the bulk acoustic wave resonator Y has two or more (i.e., multiple) resonant modes, that is, the resonant unit has two or more resonant modes.

[0035] It should be noted that when the bulk acoustic resonator Y is connected in parallel with a first branch 3, an additional resonant mode can be added. Each resonant mode corresponds to a series resonant frequency and a parallel resonant frequency.

[0036] Figure 2 is an impedance curve of a bulk acoustic wave resonator of a bulk acoustic wave filter provided in an embodiment of the present invention after being connected in parallel with a first branch. As shown in Figure 2, the bulk acoustic wave resonator Y connected in parallel with a first branch 3 has two resonance modes, with two series resonant frequencies and two parallel resonant frequencies.

[0037] Taking a bulk acoustic resonator Y connected in parallel with a first branch 3 as an example, the series resonant frequency corresponding to the additional resonant mode is fs, and the parallel resonant frequency corresponding to the additional resonant mode is fp. In the formula, Lse is the inductance of the inductor in the first branch, Cse is the capacitance of the capacitor in the first branch, and C0 is the static capacitance of the bulk acoustic resonator.

[0038] The bulk acoustic wave resonator Y of the bulk acoustic wave filter can also be connected in parallel with n first branches 3 to increase n resonant modes, where n is an integer greater than or equal to 1. The specific number of first branches 3 connected in parallel with the bulk acoustic wave resonator can be set according to the filter performance requirements, and this application does not limit it.

[0039] The bulk acoustic wave (BAW) filter in this embodiment can be a stepped filter. The multiple resonant units of the BAW filter can include series resonant units and parallel resonant units. The series resonant unit includes a series BAW resonator (hereinafter referred to as a series resonator). The series resonators of multiple series resonant units are connected in series between the input port and the output port of the BAW filter. The series resonator closer to the input port is the head series resonator, and the series resonator closer to the output port is the tail series resonator. The parallel resonant unit includes a parallel BAW resonator (hereinafter referred to as a parallel resonator). One end of the parallel resonator is connected between two adjacent series resonators, between the input port and the head series resonator, or between the output port and the tail series resonator. The other end of the parallel resonator is grounded. The BAW resonator Y in Figure 1 can be either a series resonator or a parallel resonator of the BAW filter.

[0040] For example, in the bulk acoustic wave filter, at least some of the series resonant units include the first branch, or at least some of the parallel resonant units include the first branch, or at least some of the series resonant units and at least some of the parallel resonant units include the first branch.

[0041] Figure 3 is a circuit diagram of a bulk acoustic wave filter with a series resonator connected in parallel to a first branch according to an embodiment of the present invention. Referring to Figure 3, the series resonant unit of the bulk acoustic wave filter includes a series resonator Y1 and a first branch 3. The series resonator Y1 is connected in series between the input port 1 and the output port 2 of the bulk acoustic wave filter, and the series resonator Y1 is connected in parallel with the first branch 3. The parallel resonant unit of the bulk acoustic wave filter includes a parallel resonator Y2. One end of the parallel resonator Y2 is connected between the series resonator Y1 and the output port 2, and the other end of the parallel resonator Y2 is grounded.

[0042] In other embodiments, one end of the parallel resonator Y2 can be connected between the series resonator Y1 and the input port 1, and the other end of the parallel resonator Y2 is grounded.

[0043] Figure 4 is an impedance curve of the resonant unit of the bulk acoustic wave filter shown in Figure 3. In this application, for ease of viewing, the vertical axis of all impedance curves is expressed in the form of relative impedance values.

[0044] Referring to Figures 3 and 4, after connecting a first branch 3, which includes a series inductor Lse and a capacitor Cse, in parallel to the series resonator Y1 of the series resonator unit of the bulk acoustic wave filter, the series resonator unit or series resonator has two resonant modes, corresponding to two series resonant frequencies and two parallel resonant frequencies. The parallel resonator unit has one resonant mode.

[0045] Figure 5 is a circuit diagram of a bulk acoustic wave filter provided in an embodiment of the present invention, in which both the series resonator and the parallel resonator are connected in parallel to the first branch. In one embodiment, as shown in Figure 5, both the series resonator Y1 and the parallel resonator Y2 of the bulk acoustic wave filter can have corresponding first branches 3 and are connected in parallel with their corresponding first branches 3.

[0046] Figure 6 shows the impedance curve of the bulk acoustic wave filter shown in Figure 5. Referring to Figure 6, after connecting the first branch 3 in parallel to both the series resonator Y1 of the series resonator unit and the parallel resonator Y2 of the parallel resonator unit of the bulk acoustic wave filter, both the series resonator unit and the parallel resonator unit have two resonance modes.

[0047] In another embodiment, only the parallel resonator Y2 of the bulk acoustic wave filter may have a corresponding first branch 3 and be connected in parallel with the corresponding first branch 3.

[0048] In this application, when a series resonant unit includes a first branch 3, the number of first branches 3 in each series resonant unit can be equal. Taking a series resonant unit having a series resonator Y1 as an example, each series resonator Y1 can correspond to an equal number of first branches 3 and be connected in parallel with the corresponding first branch 3.

[0049] When a parallel resonant unit includes a first branch 3, the number of first branches 3 in each parallel resonant unit can be equal. Taking a parallel resonant unit with a parallel resonator Y2 as an example, each parallel resonator Y2 corresponds to an equal number of first branches 3 and is connected in parallel with the corresponding first branch 3.

[0050] Among them, the inductance values ​​of inductors Lse in different first branches 3 can be the same or different, and the capacitance values ​​of capacitors Cse in different first branches 3 can be the same or different.

[0051] In some implementations, the number of first branches 3 in each series resonant unit may be unequal; the number of first branches 3 in each parallel resonant unit may also be unequal.

[0052] Figure 7 is a circuit diagram of a sixth-order bulk acoustic wave filter provided in an embodiment of the present invention. Referring to Figure 7, the bulk acoustic wave filter includes three series resonant units, each series resonant unit including a series resonator Y1, and three parallel resonant units, each parallel resonant unit including a parallel resonator Y2. The three series resonators Y1 are connected in series between the input port 1 and the output port 2 of the bulk acoustic wave filter. One end of two parallel resonators Y2 is connected between two adjacent series resonators Y1, and the other end is grounded. One end of one parallel resonator Y2 is connected between the series resonator Y1 and the output port 2, and the other end is grounded. In this bulk acoustic wave filter, each of the series resonators Y1 in the three series resonant units has a corresponding first branch 3 and is connected in parallel with the corresponding first branch 3.

[0053] Figure 8 shows the passband response curve of the bulk acoustic wave filter shown in Figure 7 applied to the N77 band. Referring to Figure 8, the insertion loss and suppression of the bulk acoustic wave filter both meet the requirements of 5G communication in the N77 band.

[0054] This application also provides a method for increasing the bandwidth of a bulk acoustic wave filter. As described above, the bulk acoustic wave filter includes a plurality of resonant units, each of which includes a bulk acoustic wave resonator. The method for increasing the bandwidth of the bulk acoustic wave filter includes employing at least some of the resonant units to have two or more resonant modes to increase the bandwidth of the bulk acoustic wave filter.

[0055] In one embodiment, a first branch is provided in at least a portion of the resonant unit, the first branch including a capacitor and an inductor connected in series; in the resonant unit including the first branch, the first branch is connected in parallel with the bulk acoustic wave resonator, the first branch being used to increase the resonant modes of the bulk acoustic wave resonator, such that the resonant unit has more than two resonant modes.

[0056] Referring to Figures 3, 5, and 7, the bulk acoustic wave filter can be a stepped filter. The multiple resonant units of the bulk acoustic wave filter can include at least one series resonant unit and at least one parallel resonant unit. The series resonant unit includes a series resonator Y1, and the parallel resonant unit includes a parallel resonator Y2.

[0057] The method of setting a first branch in at least a portion of the resonant units may include: setting the first branch in at least a portion of the series resonant units, or setting the first branch in at least a portion of the parallel resonant units, or setting the first branch in both at least a portion of the series resonant units and at least a portion of the parallel resonant units. That is, setting a first branch 3 in parallel with the series resonator Y1, or setting a first branch 3 in parallel with the parallel resonator Y2, or setting a first branch 3 in parallel with both the series resonator Y1 and the parallel resonator Y2.

[0058] The specific implementation method of setting a first branch in parallel with the bulk acoustic wave resonator in the bulk acoustic wave filter to increase the resonance mode of the bulk acoustic wave resonator can be referred to the above, and will not be repeated here.

[0059] In another embodiment, a method for enabling the resonant unit to have two or more resonant modes may include: increasing the number of resonant modes of the bulk acoustic wave resonator by adjusting at least one of the structure, position, shape, electrode thickness, piezoelectric material thickness, and piezoelectric material material of the bulk acoustic wave resonator. This increase in the number of resonant modes of the bulk acoustic wave resonator indicates an increase in the number of resonant modes of the resonant unit. This method allows the bulk acoustic wave resonator to have two or more resonant modes, thereby increasing the bandwidth of the bulk acoustic wave filter, reducing the number of bulk acoustic wave resonators required to fabricate a broadband bulk acoustic wave filter, and eliminating the need for external capacitors and inductors, thus simplifying the number of components within the bulk acoustic wave filter.

[0060] Figure 9 is a schematic diagram of a bulk acoustic wave resonator provided in an embodiment of the present invention. Referring to Figure 9, the bulk acoustic wave resonator includes a bottom electrode 11, a piezoelectric layer 12, and a top electrode 13 stacked sequentially from bottom to top. The overlapping area of ​​the bottom electrode 11, the piezoelectric layer 12, and the top electrode 13 in the thickness direction of the piezoelectric layer 12 is the effective area of ​​the bulk acoustic wave resonator.

[0061] For example, the bottom electrode 11 and the top electrode 13 can be made of the same material. The materials of the bottom electrode 11 and the top electrode 13 can be metals such as gold (Au), tungsten (W), molybdenum (Mo), platinum (Pt), ruthenium (Ru), iridium (Ir), titanium-tungsten (TiW), aluminum (Al), or titanium (Ti).

[0062] The material of the piezoelectric layer 12 can be aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO3), quartz, potassium niobate (KNbO3), or lithium tantalate (LiTaO3), etc.

[0063] For example, when the piezoelectric material is made into a thin sheet-like piezoelectric layer, the piezoelectric material can be cut from different tangential directions. By changing the material tangential direction of the piezoelectric layer 12, the bulk acoustic wave resonator can have more than two resonance modes. Figure 10 is an impedance curve of a bulk acoustic wave resonator provided in an embodiment of the present invention. As shown in Figure 10, by changing the material tangential direction of the piezoelectric layer 12, the bulk acoustic wave resonator has two resonance modes and does not require external capacitors, inductors, or other components.

[0064] In the bulk acoustic wave filter and the method for increasing the bandwidth of the bulk acoustic wave filter provided in this application, at least some of the resonant units in the bulk acoustic wave filter have two or more resonant modes, that is, the bulk acoustic wave filter is composed of bulk acoustic wave resonators with multiple resonant modes, thereby increasing the bandwidth of the bulk acoustic wave filter.

[0065] Furthermore, the resonant modes of the bulk acoustic wave (SAW) resonator can be increased by setting a first branch 3 in parallel with the SAW resonator in the bulk acoustic wave filter. This increases the resonant modes of the SAW resonator without changing its original structure, position, shape, thickness, or material, thus achieving the goal of increasing the bandwidth of the SAW filter. The manufacturing process is simple, and the first branch 3 can be designed together with the SAW resonator, eliminating the need for separate design and saving design resources. In addition, it avoids the need to use an external inductor to increase the electromechanical coupling coefficient and thus increase the filter bandwidth, thereby avoiding the problem of the SAW filter generating a new transmission zero or pole, which is beneficial to the design of the SAW filter.

[0066] It should be noted that this instruction manual uses a progressive approach, with later descriptions focusing on the differences from earlier descriptions. Similarities and similarities between different sections can be found by referring to each other.

[0067] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A bulk acoustic wave filter, characterized in that, It includes multiple interconnected resonant units, each of which includes a bulk acoustic resonator, wherein at least some of the resonant units have more than two resonant modes.

2. The bulk acoustic wave filter as described in claim 1, characterized in that, At least a portion of the resonant unit further includes a first branch, the first branch including a capacitor and an inductor connected in series; in the resonant unit including the first branch, the first branch is connected in parallel with the bulk acoustic wave resonator, the first branch being used to increase the resonant modes of the bulk acoustic wave resonator.

3. The bulk acoustic wave filter as described in claim 2, characterized in that, The plurality of resonant units include series resonant units and parallel resonant units; at least some of the series resonant units include the first branch, or at least some of the parallel resonant units include the first branch, or at least some of the series resonant units and at least some of the parallel resonant units include the first branch.

4. The bulk acoustic wave filter as described in claim 3, characterized in that, The series resonant unit includes a series resonator, and the series resonators of multiple series resonant units are connected in series between the input port and the output port of the bulk acoustic wave filter; the parallel resonant unit includes a parallel resonator, one end of which is connected between two adjacent series resonators, between the input port and the series resonator at the head, or between the output port and the series resonator at the tail, and the other end of which is grounded.

5. The bulk acoustic wave filter as described in claim 4, characterized in that, Each of the series resonant units has an equal number of first branches, and all the first branches of the series resonant unit are connected in parallel with the series resonator of the series resonant unit.

6. The bulk acoustic wave filter as described in claim 4, characterized in that, Each of the parallel resonant units has an equal number of first branches, and all the first branches of the parallel resonant unit are connected in parallel with the parallel resonator of the parallel resonant unit.

7. The bulk acoustic wave filter as described in claim 2, characterized in that, The bulk acoustic resonator is connected in parallel with n of the first branches to increase n resonant modes, where n is an integer greater than or equal to 1; each resonant mode corresponds to a series resonant frequency and a parallel resonant frequency.

8. The bulk acoustic wave filter as described in claim 2, characterized in that, When one of the bulk acoustic resonators is connected in parallel with one of the first branches, an additional resonant mode is added. The series resonant frequency corresponding to the additional resonant mode is fs, and the parallel resonant frequency corresponding to the additional resonant mode is fp. Wherein, Lse is the inductance value of the inductor, Cse is the capacitance value of the capacitor, and C0 is the static capacitance of the bulk acoustic resonator.

9. The bulk acoustic wave filter as described in claim 4, characterized in that, The number of first branches in each of the series resonant units is not equal.

10. The bulk acoustic wave filter as described in claim 4, characterized in that, The number of first branches in each of the parallel resonant units is not equal.

11. A method for increasing the bandwidth of a bulk acoustic wave filter, the bulk acoustic wave filter comprising a plurality of resonant units, each of the resonant units comprising a bulk acoustic wave resonator, characterized in that, The bandwidth of the bulk acoustic wave filter is increased by employing at least some of the resonant units having two or more resonant modes.

12. The method for increasing the bandwidth of a bulk acoustic wave filter as described in claim 11, characterized in that, A first branch is provided in at least a portion of the resonant unit, the first branch including a capacitor and an inductor connected in series; in the resonant unit including the first branch, the first branch is connected in parallel with the bulk acoustic resonator, the first branch being used to increase the resonant modes of the bulk acoustic resonator.

13. The method for increasing the bandwidth of a bulk acoustic wave filter as described in claim 12, characterized in that, The plurality of resonant units include series resonant units and parallel resonant units; the method of setting a first branch in at least a portion of the resonant units includes: setting the first branch in at least a portion of the series resonant units, or setting the first branch in at least a portion of the parallel resonant units, or setting the first branch in both at least a portion of the series resonant units and at least a portion of the parallel resonant units.

14. The method for increasing the bandwidth of a bulk acoustic wave filter as described in claim 11, characterized in that, A method for giving the resonant unit two or more resonant modes includes increasing the resonant modes of the bulk acoustic wave resonator by adjusting at least one of the structure, position, shape, electrode thickness, piezoelectric material thickness, and piezoelectric material material of the bulk acoustic wave resonator.

15. The method for increasing the bandwidth of a bulk acoustic wave filter as described in claim 11, characterized in that, The bulk acoustic wave resonator includes a bottom electrode, a piezoelectric layer, and a top electrode stacked sequentially from bottom to top. By changing the material tangent of the piezoelectric layer, the bulk acoustic wave resonator can have more than two resonance modes.

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