Film bulk acoustic resonator, filter and communication equipment

Abstract

The utility model discloses a film bulk acoustic resonator, a filter and a communication device, and the film bulk acoustic resonator comprises a carrier which comprises a first part and a second part; a cavity formed in the second portion of the carrier; a lower electrode formed on the carrier and covering the cavity; a piezoelectric layer formed on the lower electrode; an upper electrode formed on the piezoelectric layer; the capacitor is formed at the bottom of the cavity; the capacitor comprises a first electrode, a dielectric layer and a second electrode; a first electrode of the capacitor covers the bottom surface of the cavity, a dielectric layer is formed on the first electrode, and a second electrode is formed on the dielectric layer; the capacitor is used for adjusting the effective electromechanical coupling coefficient of the film bulk acoustic resonator.

Description

TECHNICAL FIELD

[0001] The utility model relates to the communication field, and specifically, relates to a film bulk acoustic resonator, filter and communication device. BACKGROUND

[0002] As the core device of the radio frequency front end, the filter has excellent performance, such as: low insertion loss, steep filter curve, high isolation, and smaller size, which is of great significance to the development of the new generation of communication standards, the miniaturization and multifunctionalization of personal mobile terminals. The new generation of bulk acoustic wave (BAW) technology is effectively solving the above two problems. The bulk acoustic wave filter prepared by using the bulk acoustic wave (BAW, Bulk Acoustic Wave) technology has a steeper filter curve, lower insertion loss and excellent out-of-band suppression capability.

[0003] The film bulk acoustic resonator (FBAR, Flim Bulk Acoustic Resonator) has the advantages of small size, high frequency, large power capacity, high sensitivity, etc., and plays an important role in the fields of communication, sensors, etc. In the field of radio frequency front end, it occupies an increasingly large share in the market of radio frequency filters, and has a great development advantage in the fields of biosensing, medical measurement, etc.

[0004] Under normal circumstances, the film bulk acoustic resonators on the entire filter will adopt the same thickness. The film bulk acoustic resonators with the same thickness can ensure the performance of the effective electromechanical coupling coefficient Kt2, frequency consistency, bandwidth and selectivity, insertion loss, etc. of the filter, which helps to improve the overall performance and reliability of the filter, and at the same time simplifies the manufacturing process of the filter. However, in some filters that require rapid roll-off on both sides of the passband, the structure of the film bulk acoustic resonator needs to be properly adjusted and optimized to meet the requirement of rapid roll-off on both sides of the passband. Therefore, it is desirable in the industry to provide a film bulk acoustic resonator that can improve the roll-off on both sides of the passband of the filter. SUMMARY

[0005] The utility model discloses in view of the above technical problem, designs a kind of film bulk acoustic resonator that can improve the roll-off on both sides of the passband of filter.

[0006] A brief summary of the utility model will be given in the following to provide a basic understanding of some aspects of the utility model. It should be understood that this summary is not an exhaustive summary of the utility model. It is not intended to determine the key or important parts of the utility model, nor is it intended to limit the scope of the utility model. Its purpose is only to give some concepts in a simplified form as a prelude to the more detailed description discussed later.

[0007] According to one aspect of the present application, a film bulk acoustic resonator comprises: a carrier, the carrier comprising a first portion and a second portion; a cavity formed in the second portion of the carrier; a lower electrode formed on the carrier and covering the cavity; a piezoelectric layer formed on the lower electrode; an upper electrode formed on the piezoelectric layer; a capacitor formed at the bottom of the cavity; the capacitor comprising a first electrode, a dielectric layer and a second electrode; the first electrode of the capacitor is covered on the bottom surface of the cavity, the dielectric layer is formed on the first electrode, and the second electrode is formed on the dielectric layer; and the capacitor is used to adjust the effective electromechanical coupling coefficient of the film bulk acoustic resonator.

[0008] Further, one end of the first electrode extends to the first portion of the carrier and is connected to the first lead-out line on the first surface of the carrier through a first conductive via; and the second electrode is electrically connected to the lower electrode through a conductive layer on the side wall of the cavity.

[0009] Further, one end of the first electrode extends to the first portion of the carrier and is connected to the second lead-out line at one end of the upper electrode through a second conductive via; and the second electrode is electrically connected to the lower electrode through a conductive layer on the side wall of the cavity.

[0010] Further, a mass loading layer is formed on the upper electrode or the lower electrode.

[0011] Further, the carrier comprises a substrate and a dielectric layer, and the cavity is formed in the substrate or the dielectric layer.

[0012] Further, the carrier comprises a substrate and a dielectric layer, and the cavity is formed in the substrate and the dielectric layer.

[0013] Further, the upper electrode and / or the lower electrode is formed in a circular shape, a regular pentagon shape or a polygonal shape with an internal angle greater than 90 degrees.

[0014] According to another aspect of the present application, a filter comprises: a first port, a second port and a filter network, the filter network being connected between the first port and the second port, the filter network comprising a plurality of series branches and a plurality of parallel branches, wherein each of the series branches and the parallel branches comprises at least one film bulk acoustic resonator; and some of the film bulk acoustic resonators in the filter network are the film bulk acoustic resonator as described above.

[0015] Further, the filter network comprises three series branches and four parallel branches, each of the series branches and the parallel branches comprises one film bulk acoustic resonator; the second series branch is provided with the film bulk acoustic resonator as described above, and the first parallel branch and the fourth parallel branch are provided with the film bulk acoustic resonator as described above.

[0016] According to the filter, the communication device is provided.

[0017] The scheme of the utility model can at least help to realize the following technical effects: the effective Kt2 of the partial resonator can be adjusted by the method of preparing the capacitor in the cavity, the rapid roll-off is obtained, the filter performance is improved, the increased metal connection can also play the role of rapid heat dissipation, and the power capacity is improved. BRIEF DESCRIPTION OF DRAWINGS

[0018] The specific content of the utility model will be described below with reference to the drawings, which will help to more easily understand the above and other purposes, characteristics and advantages of the utility model. The drawings are only used to show the principle of the utility model. In the drawings, the size and relative position of the unit are not necessarily drawn according to the proportion.

[0019] Figure 1 The structure schematic diagram of the film bulk acoustic resonator in the prior art is shown;

[0020] Figure 2 The frequency response curve contrast diagram before and after the series capacitor of the film bulk acoustic resonator is shown;

[0021] Figure 3 The structure schematic diagram of the film bulk acoustic resonator provided by the utility model embodiment one is shown;

[0022] Figure 4 The frequency response curve contrast diagram before and after the parallel capacitor of the film bulk acoustic resonator is shown;

[0023] Figure 5 The structure schematic diagram of the film bulk acoustic resonator provided by the utility model embodiment one is shown;

[0024] Figure 6 The specific circuit structure diagram of the filter is shown;

[0025] Figure 7 The frequency characteristics when the cavity of the partial film bulk acoustic resonator of the filter has the capacitor and does not have the capacitor are shown. DETAILED DESCRIPTION

[0026] In the following, the exemplary disclosure of the utility model will be described in conjunction with the drawings. In order to be clear and brief, all the features of realizing the utility model are not described in the specification. However, it should be understood that in the process of developing any such implementation of the utility model, many specific decisions of the utility model can be made in order to realize the specific goals of the developers, and these decisions can be changed with the different utility models.

[0027] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the device structure closely related to the solution according to the present invention is shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0028] It should be understood that the present invention is not limited to the described embodiments by reference to the accompanying drawings. Throughout this document, features may be substituted or borrowed between different embodiments where feasible, and one or more features may be omitted in one embodiment. It should be understood that the manufacturing steps of the present invention are exemplary in the embodiments, and the order of the steps may be adjusted.

[0029] Figure 1 A schematic diagram of a thin-film bulk acoustic resonator in the prior art is shown, wherein the same reference numerals denote the same components.

[0030] like Figure 1 As shown, the thin-film bulk acoustic resonator includes: a carrier 1000, in which a cavity 1100 is formed. Those skilled in the art will understand that the carrier 1000 may, exemplarily, be composed of a substrate, which may be a semiconductor-compatible material such as silicon (Si), gallium arsenide (GaAs), indium phosphide (InP), glass, sapphire, alumina, or SiC; or, the carrier 1000 may be a composite with a dielectric layer formed on the substrate, the dielectric layer being a single layer or multiple layers, and the dielectric layer material may, exemplarily, be silicon dioxide (SiO2), silicon nitride (Si3N4), silicon dioxide / silicon nitride / silicon dioxide (ONO), or alumina (Al2O3).

[0031] Furthermore, the cavity 1100 can be formed in the carrier 1000 by etching away a portion of the carrier 1000. When the carrier 1000 is a composite, the cavity 1100 can be formed in the substrate, in the dielectric layer, or simultaneously in the substrate and the dielectric layer.

[0032] A lower electrode 2000 is formed on the carrier 1000, completely covering the cavity 1100. The lower electrode 2000 can be a single layer or multiple layers, and can be formed of one or more conductive materials, such as various metals compatible with semiconductor processes, including copper (Cu), tungsten (W), molybdenum (Mo), iridium (Ir), aluminum (Al), platinum (Pt), ruthenium (Ru), niobium (Nb), or hafnium (Hf). It is understood that the electrode materials of the first part and the second part of the lower electrode 2000 may not be the same. Preferably, the material of the first part of the lower electrode 2000 is a metal with high electrical conductivity and thermal conductivity, such as copper (Cu), aluminum (Al), and tungsten (W).

[0033] A piezoelectric layer 3000 is formed on the lower electrode 2000. The piezoelectric layer 3000 can be formed from any piezoelectric material compatible with semiconductor processes, such as aluminum nitride (AlN), doped aluminum nitride, or zirconate titanate (PZT).

[0034] An upper electrode 4000 is formed on the piezoelectric layer 3000. The upper electrode 4000 can be formed of one or more conductive materials, such as various metals compatible with semiconductor processes, including tungsten, molybdenum, iridium, aluminum, platinum, ruthenium, niobium, or hafnium. The materials of the upper electrode 4000 and the lower electrode 2000 can be the same or different. A passivation layer can also be formed on the upper electrode 4000. The upper electrode 4000 and the lower electrode 2000 can be formed as circles, regular pentagons, or polygons with interior angles greater than 90 degrees.

[0035] In filters that require rapid roll-off on both sides of the passband, the structure of the thin-film bulk acoustic resonator needs to be appropriately adjusted and optimized to meet the requirements of rapid roll-off on both sides of the passband.

[0036] One solution is to combine thin-film bulk acoustic wave resonators with different resonant frequencies to achieve a steeper roll-off within a specific frequency band. Specifically, different resonant frequencies can be achieved by adding a mass loading layer 5000 to the thin-film bulk acoustic wave resonator. The mass loading layer can be positioned above the upper electrode 4000 or below the lower electrode 2000. The mass loading layer can be a single-layer or composite layer structure formed of one or more materials selected from gold, aluminum, molybdenum, tungsten, silicon nitride, or silicon dioxide.

[0037] However, simply setting a mass load layer of 5000 is insufficient to meet the requirement of rapid roll-off on both sides of the passband.

[0038] Example 1

[0039] Please see Figure 2 , Figure 2 This is a comparison of the frequency response curves of a thin-film bulk acoustic resonator before and after connecting a series capacitor. (See figure.) Figure 2 As shown, curve 1 is the frequency response curve of the thin-film bulk acoustic resonator before the series capacitor is connected, and curve 2 is the frequency response curve of the thin-film bulk acoustic resonator after the series capacitor is connected. Figure 2 As can be seen from the data, the series resonant frequency fs shifts to higher frequencies after a capacitor is connected in series with the resonator. Therefore, it can be concluded that connecting a capacitor in series with one end of a thin-film bulk acoustic wave resonator reduces the effective electromechanical coupling coefficient Kt2. Based on this, this invention provides a thin-film bulk acoustic wave resonator with a series capacitor.

[0040] Please see Figure 3 , Figure 3 This is a schematic diagram of a thin-film bulk acoustic resonator provided in Embodiment 1 of this utility model. The same reference numerals denote the same components.

[0041] like Figure 3 As shown, the thin-film bulk acoustic resonator includes: a carrier 1000, in which a cavity 1100 is formed. Those skilled in the art will understand that the carrier 1000 can, exemplarily, be composed of a substrate, which can be, for example, silicon (Si), gallium arsenide (GaAs), indium phosphide (InP), glass, sapphire, alumina, SiC, or other semiconductor-compatible materials; or the carrier 1000 can also be, for example... Figure 3 As shown, a composite material having a dielectric layer 1200 formed on a substrate is included. The dielectric layer 1200 can be a single layer or multiple layers, and the material of the dielectric layer 1200 can be, for example, silicon dioxide (SiO2), silicon nitride (Si3N4), silicon dioxide / silicon nitride / silicon dioxide (ONO), aluminum oxide (Al2O3), etc. The carrier 1000 has a first portion and a second portion.

[0042] Furthermore, the cavity 1100 can be formed in the second part of the carrier 1000 by etching away a portion of the carrier 1000. When the carrier 1000 is a composite, the cavity 1100 can be formed in the substrate, in the dielectric layer 1200, or simultaneously in the substrate and the dielectric layer 1200.

[0043] A capacitor is formed at the bottom of cavity 1100, such as Figure 2 As shown, the first electrode 6000 of the capacitor covers the bottom surface of the cavity, and one end of the first electrode extends to the first part of the carrier 1000 and is connected to the first lead line of the first surface of the carrier 1000 through the first conductive through hole.

[0044] A dielectric layer 6100 of the capacitor is formed on the first electrode 6000 of the capacitor, and a second electrode 6200 of the capacitor is formed on the dielectric layer 6100 of the capacitor.

[0045] A lower electrode 2000 is formed on the carrier 1000, completely covering the cavity 1100. The lower electrode 2000 can be a single layer or multiple layers, and can be formed of one or more conductive materials, such as various metals compatible with semiconductor processes, including copper (Cu), tungsten (W), molybdenum (Mo), iridium (Ir), aluminum (Al), platinum (Pt), ruthenium (Ru), niobium (Nb), or hafnium (Hf). The second electrode 6300 of the capacitor is electrically connected to the lower electrode 2000 through a conductive layer on the sidewall of the cavity 1100.

[0046] A piezoelectric layer 3000 is formed on the lower electrode 2000. The piezoelectric layer 3000 can be formed from any piezoelectric material compatible with semiconductor processes, such as aluminum nitride (AlN), doped aluminum nitride, or zirconate titanate (PZT).

[0047] An upper electrode 4000 is formed on the piezoelectric layer 3000. The upper electrode 4000 can be formed of one or more conductive materials, such as various metals compatible with semiconductor processes, including tungsten, molybdenum, iridium, aluminum, platinum, ruthenium, niobium, or hafnium. The materials of the upper electrode 4000 and the lower electrode 2000 can be the same or different. One end of the upper electrode 4000 has a lead. The upper electrode 4000 and the lower electrode 2000 can be formed as a circle, a regular pentagon, or a polygon with an interior angle greater than 90 degrees.

[0048] Furthermore, a mass loading layer 5000 can be formed on the upper electrode 4000. The mass loading layer can be a single-layer or composite layer structure formed of one or more materials selected from gold, aluminum, molybdenum, tungsten, silicon nitride, or silicon dioxide. By adding the mass loading layer, the requirement for rapid roll-off on both sides of the passband can be achieved in conjunction with the capacitance.

[0049] The thin-film bulk acoustic wave resonator provided in this embodiment adjusts the effective electromechanical coupling coefficient Kt2 of the thin-film bulk acoustic wave resonator by setting a series capacitor at the bottom of the cavity. For example, a rapid roll-off can be obtained by reducing the effective electromechanical coupling coefficient Kt2. The value of the series capacitor can be determined according to design requirements.

[0050] Example 2

[0051] Please see Figure 4 , Figure 4 This is a comparison of the frequency response curves of a thin-film bulk acoustic resonator before and after adding a parallel capacitor. (See figure.) Figure 4 As shown, curve 1 is the frequency response curve of the thin-film bulk acoustic wave resonator before the parallel capacitor is connected, and curve 3 is the frequency response curve of the thin-film bulk acoustic wave resonator after the parallel capacitor is connected. Figure 4 As can be seen from the data, the parallel resonant frequency fp of a thin-film bulk acoustic wave resonator shifts to a lower frequency after a capacitor is added in parallel. Therefore, it can be concluded that adding a capacitor in parallel across the thin-film bulk acoustic wave resonator reduces the effective electromechanical coupling coefficient Kt2.

[0052] The difference between Example 2 and Example 1 is only that the connection between the capacitor at the bottom of the cavity and the thin-film bulk acoustic resonator is changed from a series connection to a parallel connection.

[0053] Please see Figure 5 , Figure 5 This is a schematic diagram of a thin-film bulk acoustic resonator provided in Embodiment 1 of this utility model. The same reference numerals denote the same components.

[0054] like Figure 5As shown, the thin-film bulk acoustic resonator includes: a carrier 1000, in which a cavity 1100 is formed. A lower electrode 2000 is formed on the carrier 1000, completely covering the cavity 1100. A piezoelectric layer 3000 is formed on the lower electrode 2000, and an upper electrode 4000 is formed on the piezoelectric layer 3000.

[0055] In this embodiment, the arrangement of the carrier 1000, cavity 1100, lower electrode 2000, piezoelectric layer 3000 and upper electrode 4000 is the same as in Embodiment 1, and will not be repeated here.

[0056] Furthermore, a capacitor is formed at the bottom of cavity 1100, such as... Figure 4 As shown, the first electrode 6000 of the capacitor is formed on the bottom surface of the cavity, and one end of the first electrode 6000 extends to the first part of the carrier 1000 and is connected to the second lead of one end of the upper electrode 4000 through the second conductive through hole.

[0057] A dielectric layer 6100 of the capacitor is formed on the first electrode 6000, and a second electrode 6200 of the capacitor is formed on the dielectric layer 6100. The second electrode 6200 of the capacitor is electrically connected to the lower electrode 2000 through a conductive layer on the sidewall of the cavity 1100.

[0058] Furthermore, a mass load layer 5000 can be formed on the upper electrode 4000. The specific configuration of the mass load layer 5000 is the same as in Embodiment 1, and will not be repeated here. By adding the mass load layer, the requirement for rapid roll-off on both sides of the passband can be achieved in conjunction with the capacitor.

[0059] The thin-film bulk acoustic wave resonator provided in this embodiment adjusts the effective electromechanical coupling coefficient Kt2 of the thin-film bulk acoustic wave resonator by setting a parallel capacitor at the bottom of the cavity. For example, a rapid roll-off can be obtained by reducing the effective electromechanical coupling coefficient Kt2 of the thin-film bulk acoustic wave resonator. The capacitance value of the parallel capacitor can be determined according to design requirements.

[0060] The thin-film bulk acoustic wave resonator provided in this invention can be used to form a bulk acoustic wave filter. The filter provided in this invention includes a first port, a second port, and a filter network. The filter network is connected between the first port and the second port, and includes series branches and parallel branches, each of which includes at least one thin-film bulk acoustic wave resonator. When multiple thin-film bulk acoustic wave resonators are included in the series and parallel branches, the multiple bulk acoustic wave resonators are connected in series and / or parallel. When different resonant units have the same type of components, the parameter values ​​of the components can be equal or unequal. Capacitors can be connected in series or parallel to some of the thin-film bulk acoustic wave resonators in the filter, and the capacitors can be disposed in the cavity of the thin-film bulk acoustic wave resonator as described above.

[0061] For further details, please refer to Figure 6 , Figure 6 A specific circuit diagram of a filter is shown. For example... Figure 6 As shown, the filter includes a first port 100, a second port 200, and a filter network. The filter network is connected between the first port 100 and the second port 200. The filter network includes three series branches and four parallel branches. The first series branch has a thin-film bulk acoustic wave resonator s1; the second series branch has a thin-film bulk acoustic wave resonator s2 and a capacitor C1 connected in parallel with the thin-film bulk acoustic wave resonator s2; the third series branch has a thin-film bulk acoustic wave resonator s3. The first parallel branch has a thin-film bulk acoustic wave resonator p1 and a capacitor C2 connected in series with the thin-film bulk acoustic wave resonator p1. The second parallel branch has a thin-film bulk acoustic wave resonator p2. The third parallel branch has a thin-film bulk acoustic wave resonator p3. The fourth parallel branch has a thin-film bulk acoustic wave resonator p4 and a capacitor C3 connected in series with the thin-film bulk acoustic wave resonator p4. The thin-film bulk acoustic wave resonator s2 and the parallel capacitor C1 in the second series branch can be configured using the structure described in the second embodiment. The thin-film bulk acoustic wave resonator p1 and the series capacitor C2 in the first parallel branch can be configured using the structure described in the first embodiment. The thin-film bulk acoustic wave resonator p4 and the series capacitor C3 in the fourth parallel branch can be configured using the structure described in the first embodiment.

[0062] Please see Figure 7 , Figure 7 This diagram illustrates the frequency characteristics of a portion of the thin-film bulk acoustic resonator (BAS) of a filter with and without capacitance in the cavity. Solid lines represent portions of the BAS without capacitance, while dashed lines represent portions with capacitance. Figure 7 It is known that by preparing series or parallel capacitors in the cavity of some resonators in the filter, the effective Kt2 of some resonators can be reduced, and rapid roll-off can be achieved to reduce the effective electromechanical coupling coefficient Kt2 of some thin-film bulk acoustic resonators, thus achieving rapid roll-off.

[0063] The capacitors described above are fabricated in the cavities of a portion of the thin-film bulk acoustic resonator in the filter network. These capacitors are then connected in series or parallel with the thin-film bulk acoustic resonator, thereby reducing the effective Kt2 of the portion of the thin-film bulk acoustic resonator and enabling rapid roll-off.

[0064] The bulk acoustic wave filter provided by this utility model can be used in portable communication devices such as mobile phones, personal digital assistants (PDAs), personal wearable devices, and video game devices. The bulk acoustic wave filter can include any of the bulk acoustic wave resonators of this utility model.

[0065] The present invention has been described above with reference to specific embodiments. However, those skilled in the art should understand that these descriptions are exemplary and not intended to limit the scope of protection of the present invention. Those skilled in the art can make various modifications and variations to the present invention based on its spirit and principles, and these modifications and variations are also within the scope of the present invention.

Claims

1. A thin-film bulk acoustic resonator, characterized in that, include: A carrier, the carrier comprising a first part and a second part; A cavity, which is formed in the second part of the carrier; The lower electrode is formed on the carrier and covers the cavity; A piezoelectric layer is formed on the lower electrode; The upper electrode is formed on the piezoelectric layer; A capacitor is formed at the bottom of the cavity; the capacitor includes a first electrode, a dielectric layer, and a second electrode; the first electrode of the capacitor covers the bottom surface of the cavity, the dielectric layer is formed on the first electrode, and the second electrode is formed on the dielectric layer; the capacitor is used to adjust the effective electromechanical coupling coefficient of the thin-film bulk acoustic resonator.

2. The thin-film bulk acoustic resonator as described in claim 1, characterized in that: One end of the first electrode extends to the first part of the carrier and is connected to the first lead-out line on the first surface of the carrier through the first conductive through-hole; The second electrode is electrically connected to the lower electrode through a conductive layer on the cavity sidewall.

3. The thin-film bulk acoustic resonator as described in claim 1, characterized in that: One end of the first electrode extends to the first part of the carrier and is connected to the second lead-out line of one end of the upper electrode through the second conductive through hole; The second electrode is electrically connected to the lower electrode through a conductive layer on the cavity sidewall.

4. The thin-film bulk acoustic resonator according to any one of claims 1-3, characterized in that: A mass-loaded layer is formed on the upper or lower electrode.

5. The thin-film bulk acoustic resonator as described in claim 4, characterized in that: The carrier includes a substrate and a dielectric layer, and the cavity is formed in the substrate or the dielectric layer.

6. The thin-film bulk acoustic resonator as described in claim 4, characterized in that: The carrier includes a substrate and a dielectric layer, and the cavity is formed in both the substrate and the dielectric layer.

7. The thin-film bulk acoustic resonator as described in claim 5 or 6, characterized in that: The upper electrode and / or lower electrode are formed as a circle or a polygon with an interior angle greater than 90 degrees.

8. The thin-film bulk acoustic resonator as described in claim 5 or 6, characterized in that: The upper electrode and / or lower electrode are formed in the shape of a regular pentagon.

9. A filter, characterized in that, include: The system comprises a first port, a second port, and a filter network, with the filter network connected between the first port and the second port. The filter network includes multiple series branches and multiple parallel branches, with each series branch and parallel branch including at least one thin-film bulk acoustic resonator. The thin-film bulk acoustic resonators in the filter network are the thin-film bulk acoustic resonators as described in any one of claims 1-7.

10. The filter as described in claim 9, characterized in that, The filtering network includes three series branches and four parallel branches, each of which includes a thin-film bulk acoustic resonator; the second series branch is provided with a thin-film bulk acoustic resonator as described in claim 3, and the first and fourth parallel branches are provided with thin-film bulk acoustic resonators as described in claim 2.

11. A communication device, characterized in that, Includes the filter as described in claim 9 or 10.

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