50b facing each other, and having piezoelectricity. A structural example of the piezoelectric substrate 50 will be described with reference to FIGS. 4A to 4C.

The multilayer substrate 40 is an example of the first substrate, and as shown in FIG. 2, includes main surfaces 40a and 40b facing each other, and includes a plurality of dielectric layers L1, L2, and L3. The multilayer substrate 40 is disposed such that the main surface 40a faces the main surface 50a. As the multilayer substrate 40, for example, a Low Temperature Co-Fired Ceramics (LTCC) substrate having a multilayer structure in the plurality of dielectric layers L1 to L3, a High Temperature Co-Fired Ceramics (HTCC) substrate, a component incorporated substrate, a substrate having a Redistribution Layer (RDL), or a printed substrate may be used.

The multilayer substrate 40 includes an electrode layer L41 which is a surface of the dielectric layer L1 on the side in the z-axis positive direction, an electrode layer L42 which is a surface of the dielectric layer L2 on the side in the z-axis positive direction, an electrode layer L43 which is a surface of the dielectric layer L3 on the side in the z-axis positive direction, and an electrode layer L44 which is a surface of the dielectric layer L3 on the side in the z-axis negative direction, from the main surface 40a toward the main surface 40b, and a conductor pattern including the planar electrode is provided on each of the electrode layers.

3. Basic Structure of Series Arm Resonator and Parallel Arm Resonator

Next, a basic structure of each of the series arm resonators and each of the parallel arm resonators which define the multiplexer 1 will be described. FIG. 4A is a plan view and a cross-sectional view which schematically show a first example of the acoustic wave resonator of the multiplexer 1 according to the present example embodiment. FIG. 4A shows a basic structure of an acoustic wave resonator of the multiplexer 1. An acoustic wave resonator 60 shown in FIG. 4A is provided to describe a typical structure of the acoustic wave resonator of the multiplexer 1, and the number, a length, and the like of electrode fingers of the electrode are not limited thereto.

The acoustic wave resonator 60 includes the piezoelectric substrate 50 and comb electrodes 60a and 60b. As shown in (a) of FIG. 4A, a pair of the comb electrodes 60a and 60b facing each other are provided on the piezoelectric substrate 50. The comb electrode 60a includes a plurality of electrode fingers 61a parallel or substantially parallel to each other and a busbar electrode 62a that connects one end of each of the plurality of electrode fingers 61a to each other. In addition, the comb electrode 60b includes a plurality of electrode fingers 61b parallel or substantially parallel to each other and a busbar electrode 62b that connects one end of each of in the plurality of electrode fingers 61b to each other. The plurality of electrode fingers 61a and 61b extend along a direction orthogonal or substantially orthogonal to an acoustic wave propagation direction (X-axis direction). The busbar electrode 62a and the busbar electrode 62b are disposed to face each other with the electrode fingers 61a and 61b interposed therebetween. The comb electrodes 60a and 60b define an IDT electrode 54.

Here, when the filter 20 according to the present example embodiment performs electromechanical conversion by using a surface acoustic wave, the IDT electrode 54 is a functional electrode. The acoustic wave resonator 60 may include reflectors at both ends of the IDT electrode 54 in the acoustic wave propagation direction (X-axis direction).

As shown in (b) of FIG. 4A, for example, the IDT electrode 54 has a multilayer structure including a close contact layer 540 and a main electrode layer 542.

The close contact layer 540 is a layer to improve close contact between the piezoelectric substrate 50 and the main electrode layer 542, and for example, Ti is used as a material thereof. As a material of the main electrode layer 542, for example, Al including about 1% Cu is used. A protection layer 55 covers the comb electrodes 60a and 60b. The protection layer 55 is a layer to protect the main electrode layer 542 from an outside environment, to adjust frequency temperature characteristics, and to improve humidity resistance, and for example, is a dielectric film including silicon dioxide as a main component.

Materials of the close contact layer 540, the main electrode layer 542, and the protection layer 55 are not limited to the above-described materials. Furthermore, the IDT electrode 54 may have another structure other than the above-described multilayer structure. For example, the IDT electrode 54 may be made of metal such as Ti, Al, Cu, Pt, Au, Ag, and Pd, or an alloy, or may include a plurality of multilayer bodies made of the metal or the alloy described above. In addition, the protection layer 55 does not need to be provided.

Next, a multilayer structure of the piezoelectric substrate 50 will be described.

As shown in (c) of FIG. 4A, the piezoelectric substrate 50 includes a high acoustic velocity support substrate 51, a low acoustic velocity film 52, and a piezoelectric film 53 laminated in this order.

For example, the piezoelectric film 53 is made of a θ° Y-cut X propagation LiTaO₃piezoelectric single crystal or piezoelectric ceramics (single crystal or ceramics through which the surface acoustic wave propagates in an X-axis direction, which is, for example, lithium tantalate single crystal or ceramics cut by a plane in which the X-axis is set as a central axis, and an axis rotated by θ° from the Y-axis is set as a normal line). A material and a cut-angle θ of the piezoelectric single crystal used as the piezoelectric film 53 are appropriately selected depending on required specifications of each filter.

The high acoustic velocity support substrate 51 supports the low acoustic velocity film 52, the piezoelectric film 53, and the IDT electrode 54. Furthermore, the high acoustic velocity support substrate 51 is a substrate in which the acoustic velocity of the bulk wave in the high acoustic velocity support substrate 51 is higher than the acoustic velocity of the acoustic wave of a surface acoustic wave or a boundary acoustic wave propagating through the piezoelectric film 53, and prevents a surface acoustic wave from leaking down from the high acoustic velocity support substrate 51 by confining the surface acoustic wave in a portion at which the piezoelectric film 53 and the low acoustic velocity film 52 are laminated. As a material of the high acoustic velocity support substrate 51, for example, a piezoelectric body such as aluminum nitride, lithium tantalate, lithium niobate, and crystal, ceramic such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, spinel, and sialon, a dielectric such as aluminum oxide, silicon oxynitride, diamond-like carbon (DLC), and diamond, or a semiconductor such as silicon, and alternatively, a material having the above-described materials as the main components can be used. The above-described spinel includes, for example, an aluminum compound including one or more elements selected from Mg, Fe, Zn, and Mn, and oxygen. Examples of the above-described spinel can include MgAl₂O₄, FeAl₂O₄, ZnAl₂O₄, and MnAl₂O₄.

The low acoustic velocity film 52 is a film in which the acoustic velocity of the bulk wave in the low acoustic velocity film 52 is lower than that of the bulk wave propagating through the piezoelectric film 53, and is disposed between the piezoelectric film 53 and the high acoustic velocity support substrate 51. This structure and a property that energy of an acoustic wave is concentrated on a medium having a low acoustic velocity reduce or prevent a possibility that surface acoustic wave energy leaks out from the IDT electrode 54. As a material of the low acoustic velocity film 52, for example, a dielectric such as a compound obtained by adding fluorine, carbon, or boron to glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, and silicon oxide, or a material having the above-described materials as the main components can be used.

According to the above-described multilayer structure of the piezoelectric substrate 50, a Q value in a resonant frequency and an anti-resonant frequency can be significantly increased, compared to a structure in the related art in which the piezoelectric substrate is used as a single layer. That is, since the acoustic wave resonator having a large Q value can be provided, a filter having a small insertion loss can be provided by using the acoustic wave resonator.

The high acoustic velocity support substrate 51 may have a structure in which a support substrate and a high acoustic velocity film having the higher acoustic velocity of the propagating bulk wave than that of the acoustic wave such as the surface acoustic wave or a boundary acoustic wave propagating through the piezoelectric film 53 are laminated. In this case, as a material of the high acoustic velocity film, the same material as the material of the high acoustic velocity support substrate 51 can be used. As a material of the support substrate, for example, a piezoelectric body such as aluminum nitride, lithium tantalate, lithium niobate, and crystal, ceramic such as alumina, sapphire, magnesia, silicon nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite, a dielectric such as diamond and glass, a semiconductor such as silicon and gallium nitride, or a resin, and alternatively, a material having the above-described materials as the main components can be used.

In the present specification, the “main component of the material” means a component in which a ratio occupied by the material exceeds 50% by weight. The main component may exist in any one state of single crystal, polycrystal, and amorphous, or in a mixed state thereof.

FIG. 4B is a cross-sectional view schematically showing a second example of an acoustic wave resonator of the multiplexer 1 according to the present example embodiment. In the acoustic wave resonator 60 shown in FIG. 4A, an example in which the IDT electrode 54 is provided on the piezoelectric substrate 50 including the piezoelectric film 53 has been described. However, as shown in FIG. 4B, the substrate on which the IDT electrode 54 is provided may be a piezoelectric single crystal substrate 57 including a single layer of the piezoelectric body layer.

For example, the piezoelectric single crystal substrate 57 includes a piezoelectric single crystal of LiNbO₃. The acoustic wave resonator according to the present example includes, for example, the piezoelectric single crystal substrate 57 of LiNbO₃, the IDT electrode 54, and the protection layer 58 provided on the piezoelectric single crystal substrate 57 and on the IDT electrode 54.

The multilayer structure, the material, the cut-angle, and a thickness of the piezoelectric film 53 and the piezoelectric single crystal substrate 57 may be appropriately changed depending on required bandpass characteristics of the multiplexer 1 and the like. The acoustic wave resonator including the LiTaO₃piezoelectric substrate or the like having another cut-angle other than the above-described cut-angle can achieve the same or substantially the same advantageous effects as those of the acoustic wave resonator 60 including the piezoelectric film 53 described above.

In addition, the piezoelectric substrate on which the IDT electrode 54 is provided may have a structure in which the support substrate, an energy confinement layer, and the piezoelectric film are laminated in this order. The IDT electrode 54 is provided on the piezoelectric film. As the piezoelectric film, for example, the LiTaO₃piezoelectric single crystal or the piezoelectric ceramics can be used. The support substrate supports the piezoelectric film, the energy confinement layer, and the IDT electrode 54.

The energy confinement layer includes one layer or a plurality of layers, and the velocity of the bulk acoustic wave propagating through the at least one layer is higher than the velocity of the acoustic wave propagating in the vicinity of the piezoelectric film. For example, the energy confinement layer may have a multilayer structure including the low acoustic velocity layer and the high acoustic velocity layer. The low acoustic velocity layer is a film in which the acoustic velocity of the bulk wave in the low acoustic velocity layer is lower than the acoustic velocity of the acoustic wave propagating through the piezoelectric film. The high acoustic velocity layer is a film in which the acoustic velocity of the bulk wave in the high acoustic velocity layer is higher than the acoustic velocity of the acoustic wave propagating through the piezoelectric film. The support substrate may be used as the high acoustic velocity layer.

In addition, the energy confinement layer may be an acoustic impedance layer having a configuration in which a low acoustic impedance layer having a relatively low acoustic impedance and a high acoustic impedance layer having a relatively high acoustic impedance are alternately laminated.

Here, electrode parameters of the IDT electrode defining the acoustic wave resonator 60 will be described.

A wavelength of the acoustic wave resonator is defined by a wavelength λ that is a repeating period in the plurality of electrode fingers 61a or 61b forming the IDT electrode 54 shown in (b) of FIG. 4A. In addition, an electrode finger pitch is ½ of the wavelength λ, and when a line width of the electrode fingers 61a and 61b defining each of the comb electrodes 60a and 60b is defined as W, and a space width between the electrode finger 61a and the electrode finger 61b which are adjacent to each other is defined as S, the electrode finger pitch is defined as (W+S).

In the IDT electrode 54, when an interval between the adjacent electrode fingers is not constant, the electrode finger pitch of the IDT electrode 54 is defined as an average electrode finger pitch of the IDT electrode 54. The average electrode finger pitch of the IDT electrode 54 is defined as Di/(Ni−1), when the total number of the electrode fingers 61a and 61b included in the IDT electrode 54 is defined as Ni, and when a distance between centers of the electrode finger located in one end and the electrode finger located in the other end of the IDT electrode 54 in the acoustic wave propagation direction is defined as Di.

In addition, FIG. 4C is a cross-sectional view schematically showing a third example of an acoustic wave resonator of the multiplexer 1 according to the present example embodiment. FIG. 4C shows a bulk acoustic wave resonator as the acoustic wave resonator of the multiplexer 1. As shown in the drawing, for example, the bulk acoustic wave resonator includes a support substrate 65, a lower electrode 66, a piezoelectric body layer 67, and an upper electrode 68 laminated in this order.

The support substrate 65 supports the lower electrode 66, the piezoelectric body layer 67, and the upper electrode 68, and is a silicon substrate, for example. In the support substrate 65, a cavity is provided in a region that comes into contact with the lower electrode 66. In this manner, the piezoelectric body layer 67 can freely vibrate.

The lower electrode 66 is an example of a third planar electrode, and is provided on one surface of the support substrate 65. The upper electrode 68 is an example of a fourth planar electrode, and is provided on one surface of the support substrate 65. As materials of the lower electrode 66 and the upper electrode 68, for example, Al including about 1% Cu is used.

The piezoelectric body layer 67 is an example of a piezoelectric thin film, and is provided between the lower electrode 66 and the upper electrode 68. For example, the piezoelectric body layer 67 includes at least one of zinc oxide (ZnO), aluminum nitride (AlN), lead zirconate titanate (PZT), potassium niobate (KN), lithium niobate (LN), lithium tantalate (LT), crystal, and lithium borate (LiBO) as the main component.

The bulk acoustic wave resonator having the above-described multilayer configuration induces the bulk acoustic wave inside the piezoelectric body layer 67, and generates resonance by applying electric energy between the lower electrode 66 and the upper electrode 68. The bulk acoustic wave generated by the bulk acoustic wave resonator propagates between the lower electrode 66 and the upper electrode 68 in a direction perpendicular or substantially perpendicular to a film surface of the piezoelectric body layer 67. That is, the bulk acoustic wave resonator is a resonator using the bulk acoustic wave.

Here, when the filter 20 according to the present example embodiment performs electromechanical conversion by using the bulk acoustic wave, the lower electrode 66, the piezoelectric body layer 67, and the upper electrode 68 are functional electrodes. In addition, the support substrate 65 may be a first substrate instead of the piezoelectric substrate 50.

4. Bonding Structure Between Filter Chip and Multilayer Substrate

Next, a bonding structure between the filter chip 2 and the multilayer substrate 40 will be described with reference to FIGS. 3 and 5 to 7B.

As shown in FIG. 3, in the filter chip 2, the parallel arm resonator p21 (first parallel arm resonator) includes a portion of the piezoelectric substrate 50 and an IDT electrode 54p. The IDT electrode 54p is an example of a second functional electrode, and is one of the IDT electrodes 54. In addition, the series arm resonator s21 (first series arm resonator) includes another portion of the piezoelectric substrate 50 and an IDT electrode 54s. The IDT electrode 54s is an example of the first functional electrode, and is one of the IDT electrodes 54.

The output terminal 101 and the input terminal 102 which are shown in FIG. 1 include the same or substantially the same planar electrode as the common terminal 100 on the main surface 50a. The bump electrode 70 is bonded to each of the common terminal 100, the input terminal 110, the output terminal 120, the terminals 111, 112, 113, 121, and 122. As shown in FIG. 3, the bump electrode 70 (121) is an example of the first bump electrode, and is connected to the IDT electrode 54p.

FIG. 5 is a plan view of each layer of the multilayer substrate 40 of the multiplexer 1 according to the present example embodiment. As shown in FIG. 5, the multilayer substrate 40 includes planar electrodes 410, 420, 430, 440, 441, 442, 443, and 444, and a plurality of via conductors 81. A circle (○) shown in (a) to (c) of FIG. 5 represents a via conductor 81 that penetrates from a surface on the main surface 40a side to a surface on the main surface 40b side in any of the dielectric layers L1 to L3.

An electrode layout of the electrode layer L41 provided on the surface of the dielectric layer L1 on the main surface 40a side is shown in (a) of FIG. 5. The bump electrode 70 provided in the filter chip 2 is bonded to the planar electrode of the electrode layer L41. The planar electrode 410 provided on the electrode layer L41 is an example of the first planar electrode, and is bonded to the bump electrodes 70 (121) and 70 (111). The planar electrode 410 to which the bump 70 (121) is connected is connected to the planar electrode 420 of the electrode layer L42 which is a lower layer of the electrode layer L41 by the plurality of via conductors 81.

An electrode layout of the electrode layer L42 provided on the surface of the dielectric layer L2 on the main surface 40a side is shown in (b) of FIG. 5. The planar electrode 420 is connected to the planar electrode 430 of the electrode layer L43 which is the lower layer of the electrode layer L42 by the plurality of via conductors 81.

An electrode layout of the electrode layer L43 provided on the surface of the dielectric layer L3 on the main surface 40a side is shown in (c) of FIG. 5. The planar electrode 430 is connected to the planar electrode 440 of the electrode layer L44 which is the lower layer of the electrode layer L43 by the plurality of via conductors 81.

An electrode layout of the electrode layer L44 provided on the surface of the dielectric layer L3 on the main surface 40b side is shown in (d) of FIG. 5. The planar electrode 440 provided on the electrode layer L44 is an example of a second planar electrode, is connected to the planar electrode 430 provided on the electrode layer L43 with the plurality of via conductors 81 interposed therebetween, and is connected to the ground. In addition, the planar electrode 441 provided on the electrode layer L44 is connected to the bump electrode 70 (100) of the electrode layer L41 with the electrode layers L42 and L43 interposed therebetween. In addition, the planar electrode 442 provided on the electrode layer L44 is connected to the bump electrode 70 (110) of the electrode layer L41 with the electrode layers L42 and L43 interposed therebetween. In addition, the planar electrode 443 provided on the electrode layer L44 is connected to the bump electrode 70 (120) of the electrode layer L41 with the electrode layers L42 and L43 interposed therebetween. In addition, the planar electrode 444 provided on the electrode layer L44 is connected to the bump electrode 70 (122) of the electrode layer L41 with the electrode layers L42 and L43 interposed therebetween. The planar electrodes 440, 441, 442, 443, and 444 provided on the electrode layer L44 are external connection terminals for connecting the multiplexer 1 to an external substrate disposed to face the main surface 40b.

The number of the via conductors 81 connecting the planar electrode 410 and the planar electrode 420 is largest in the numbers of the via conductors 81 connecting one planar electrode of the electrode layer L41 and one planar electrode of the electrode layer L42. In this manner, an inductor component between the planar electrode 410 and the planar electrode 420 can be reduced.

In addition, the number of the via conductors 81 connecting the planar electrode 420 and the planar electrode 430 is largest in the numbers of the via conductors 81 connecting one planar electrode of the electrode layer L42 and one planar electrode of the electrode layer L43. In this manner, the inductor component between the planar electrode 420 and the planar electrode 430 can be reduced.

In addition, the number of the via conductors 81 connecting the planar electrode 430 and the planar electrode 440 is largest in the numbers of the via conductors 81 connecting one planar electrode of the electrode layer L43 and one planar electrode of the electrode layer L44. In this manner, the inductor component between the planar electrode 430 and the planar electrode 440 can be reduced.

According to these configurations, the inductor component from the planar electrode 440 which is the external connection terminal to the bump 70 (121) can be reduced, and as a result, steepness of filter characteristics can be improved.

The planar electrode 410 bonded to the bump electrode 70 (121) does not need to be disposed on the electrode layer L41 which is an outermost layer of the multilayer substrate 40, and may be disposed on the first dielectric layer in the plurality of dielectric layers L1 to L3 in which the planar electrode is provided. The planar electrode 440 does not need to be disposed on the electrode layer L44 which is the outermost layer of the multilayer substrate 40, and may be disposed on the second dielectric layer on the main surface 40b side with respect to the first dielectric layer in the plurality of dielectric layers L1 to L3 in which the planar electrode is provided.

FIG. 6 is a plan view of each layer of the multilayer substrate 40 of a multiplexer according to a comparative example. The multiplexer according to the comparative example is different from the multiplexer 1 according to the example embodiment only in that the planar electrode 410 of the electrode layer L41 is replaced with a planar electrode 510.

An electrode layout of the electrode layer L41 is shown in (a) of FIG. 6. The bump electrode 70 provided in the filter chip 2 is bonded to the planar electrode of the electrode layer L41. The planar electrode 510 provided on the electrode layer L41 is bonded to the bump electrodes 70 (121) and 70 (111). Each electrode layout in (b) to (d) of FIG. 6 is the same or substantially the same as each electrode layout in (b) to (d) of FIG. 5.

FIG. 7A is an enlarged plan view of the electrode layer L41 of the multilayer substrate 40 according to the present example embodiment. In addition, FIG. 7B is an enlarged plan view of the electrode layer L41 of the multilayer substrate according to the comparative example. FIG. 7A is an enlarged plan view of a region VIIA in (a) of FIG. 5, and FIG. 7B is an enlarged plan view of a region VIIB in (a) of FIG. 6.

Here, as shown in FIG. 7A, in the filter 20 according to the present example embodiment, in a plan view of the main surface 40a, the bump electrode 70 (121) is located between two via conductors 81a and 81b in the plurality of via conductors 81 connected to the planar electrode 410. The bump electrode 70 (121) is connected between the parallel arm resonator p21 of the filter 20 and the ground. As shown in Table 1, the parallel arm resonator p21 has a highest resonant frequency in the plurality of parallel arm resonators of the filter 20. The plurality of parallel arm resonators of the filter 20 are parallel arm resonators that contribute to providing a pass band of the filter 20, and are specifically defined as parallel arm resonators in which the anti-resonant frequency is located inside the pass band of the filter 20.

In addition, the parallel arm resonator p21 has the highest resonant frequency in the plurality of parallel arm resonators of the filter 20, in other words, the parallel arm resonator p21 has a smallest electrode finger pitch of the IDT electrode in the plurality of parallel arm resonators of the filter 20.

In the ladder acoustic wave filter, when parasitic inductance is generated in a path that connects the parallel arm resonator and the ground, the resonant frequency of the parallel arm resonator varies. When the electrostatic capacitance of the parallel arm resonator is defined as Cp and the parasitic inductance is defined as Lp, the resonant frequency (=1/2π√(LpCp)) of the parallel arm resonator varies to a low frequency side as the parasitic inductance Lp increases, and an interval between the resonant frequency and the anti-resonant frequency is widened. In this manner, an attenuation slope on the low frequency side of the pass band is reduced, and an attenuation in the vicinity of the low frequency side of the pass band deteriorates. In particular, the parallel arm resonator having the highest resonant frequency in the plurality of parallel arm resonators of the acoustic wave filter determines the attenuation and the steepness in the vicinity of the low frequency side of the pass band. Therefore, when the resonant frequency of the parallel arm resonator having the highest resonant frequency varies to the low frequency side, attenuation characteristics in the vicinity of the low frequency side of the pass band of the acoustic wave filter greatly deteriorate. In the multiplexer 1 and the filter 20 according to the present example embodiment, an intentional inductor is not connected between the parallel arm resonator p21 having the highest resonant frequency in the plurality of parallel arm resonators and the ground. The intentional inductor includes a chip-shaped inductor and an inductor including a conductor coil provided on the electrode layer of the multilayer substrate.

In the multiplexer according to the comparative example, as shown in FIG. 7B, in a plan view of the main surface 40a, the bump electrode 70 (121) is not located between two via conductors 81 in the plurality of via conductors 81 connected to the planar electrode 510. Therefore, when a bonding position of the bump electrode 70 (121) deviates, a distance between the bump electrode 70 (121) and the via conductor 81 closest to the bump electrode 70 (121) varies. Therefore, the parasitic inductance generated between the bump electrode 70 (121) and the planar electrode 440 of the electrode layer L44 connected to the ground greatly varies.

In contrast, in a case of the multiplexer 1 according to the present example embodiment, as shown in FIG. 7A, the bump electrode 70 (121) is located between two via conductors 81a and 81b in the plurality of via conductors 81. Therefore, even when the bonding position of the bump electrode 70 (121) varies, the distance between the bump electrode 70 (121) and the via conductor 81b decreases when the distance between the bump electrode 70 (121) and the via conductor 81a increases. In this manner, variations in the parasitic inductance defined by parallel connection of the parasitic inductance generated in the path that connects the bump electrode 70 (121) and the via conductor 81a and the parasitic inductance generated in the path that connects the bump electrode 70 (121) and the via conductor 81b are reduced or prevented.

FIG. 8A is a graph showing isolation characteristics of the multiplexer 1 according to the present example embodiment. In addition, FIG. 8B is a graph showing isolation characteristics of the multiplexer according to the comparative example. The multiplexer according to the comparative example is different from the multiplexer 1 according to the present example embodiment only in that the planar electrode 410 of the filter 20 is replaced with the planar electrode 510.

Each of FIGS. 8A and 8B shows two types of waveform data (solid line and broken line). In both of FIGS. 8A and 8B, solid line waveform data is data when the position of the bump electrode 70 (121) deviates by about +30 μm in the y-axis positive direction with respect to broken line waveform data.

In the multiplexer 1 according to the present example embodiment, the isolation of the pass band of the filter 10 is, for example, about 58.5 dB when there is no positional deviation (broken line data in FIG. 8A), and is, for example, about 58.0 dB when there is positional deviation (solid line data in FIG. 8A). Therefore, the isolation shows a deterioration of, for example, about 0.5 dB.

On the other hand, in the multiplexer according to the comparative example, the isolation of the pass band of the filter 10 is, for example, about 58.4 dB when there is no positional deviation (broken line data in FIG. 8B), and is, for example, about 54.1 dB when there is positional deviation (solid line data in FIG. 8B). Therefore, the isolation shows a deterioration of, for example, about 4.3 dB.

As described above, in the multiplexer 1 according to the present example embodiment, compared to the multiplexer according to the comparative example, even when there is a deviation in the bonding position of the bump electrode to connect the parallel arm resonator having the highest resonant frequency to the ground when the filter chip 2 is face-down bonded to the multilayer substrate 40, variations in the parasitic inductance generated between the parallel arm resonator and the ground are reduced or prevented. Therefore, the isolation on the high frequency side of the pass band of the filter 10 can be improved. In other words, compared to the filter according to the comparative example, the filter 20 according to the present example embodiment can improve attenuation characteristics in the vicinity of the low frequency side of the pass band of the filter 20. Therefore, it is possible to provide the filter 20 and the multiplexer 1 in which the deterioration in the bandpass characteristics is reduced or prevented.

In addition, in the filter 20 according to the present example embodiment, as shown in FIG. 1, the parallel arm resonator p21 is connected to the path that connects the input terminal 102 and the series arm resonator s22 and to the terminal 121, and the parallel arm resonator p22 is connected to the path that connects the output terminal 120 and the series arm resonator s22 and to the terminal 121. That is, as shown in FIG. 3, the parallel arm resonators p21 and p22 are connected to the ground with the common bump electrode 70 (121) interposed therebetween.

As electrostatic capacitance Cp increases, in the resonant frequency (=1/2π√(LpCp)) of the parallel arm resonator, the resonant frequency is likely to vary even when parasitic inductance Lp slightly varies. Therefore, it is effective to reduce the electrostatic capacitance Cp to reduce or prevent the variations in the resonant frequency. However, it is necessary to reduce the number of the bump electrodes 70 connected to the ground to achieve a miniaturized filter chip, and the plurality of parallel arm resonators need to be connected to the common bump electrode 70. In this manner, in the multiplexer according to the related art (comparative example), synthetic electrostatic capacitance Cp of the parallel arm resonators p21 and p22 connected to one bump electrode 70 increases, and the resonant frequency greatly varies even when the parasitic inductance Lp slightly varies. Consequently, there is an issue in that both the miniaturized filter chip and the reduced or prevented characteristic variations cannot be achieved.

In contrast, according to the multiplexer 1 and the filter 20 in the present example embodiment, even when the synthetic electrostatic capacitance Cp of the parallel arm resonators p21 and p22 connected to one bump electrode 70 (121) increases, the variations in the parasitic inductance Lp due to the positional deviation of the bump electrode 70 (121) can be reduced or prevented. Therefore, it is possible to reduce or prevent the variations in the attenuation characteristics on the low frequency side with respect to the pass band of the filter 20 defined by the parallel arm resonator p21 having the highest resonant frequency in the plurality of parallel arm resonators. Therefore, it is possible to provide the miniaturized filter 20 and the multiplexer 1 in which the deterioration in the bandpass characteristics is reduced or prevented.

In addition, in the multiplexer 1 according to the present example embodiment, as shown in FIG. 7A, in a plan view of the main surface 40a, the bump electrode 70 (121) is located between two via conductors 81a and 81b in the plurality of via conductors 81 connected to the planar electrode 410, and is located between two via conductors 81c and 81d located on a virtual straight line intersecting a virtual line segment connecting the two via conductors 81a and 81b.

According to this configuration, the variations in the parasitic inductance can be reduced or prevented not only when the bonding position of the bump electrode 70 (121) deviates in a direction along the virtual line connecting the via conductors 81a and 81b in a plan view of the main surface 40a, but also when the bonding position deviates in a direction along the virtual line connecting the via conductors 81c and 81d.

In addition, as shown in FIG. 3, in the multiplexer 1 according to the present example embodiment, eight bump electrodes 70 are disposed on the main surface 50a. In the eight bump electrodes 70, the bump electrode 70 (113) (second bump electrode) and the bump electrode 70 (120) (third bump electrode) are disposed in both end portions of the outer edge of the piezoelectric substrate 50 in a plan view of the main surface 50a. In contrast, the bump electrode 70 (121) is located between the bump electrode 70 (113) and the bump electrode 70 (120) in a plan view of the main surface 50a. In other words, the bump electrode 70 (121) is disposed in a region excluding a corner portion of the piezoelectric substrate 50. Since a distance between the bump electrode disposed in the corner portion of the piezoelectric substrate 50 and the center of the piezoelectric substrate 50 is long, a position variation distance of the bump electrode increases compared to position variations in a rotation direction of the piezoelectric substrate 50. Therefore, the variations in the parasitic inductance increase. Therefore, the bump electrode 70 (121) connected to the parallel arm resonator p21 having the highest resonant frequency in the plurality of parallel arm resonators is disposed in the region excluding the corner portion of the piezoelectric substrate 50, that is, a region close to the center of the piezoelectric substrate 50. In this manner, it is possible to effectively reduce or prevent characteristic variations caused by not only the positional deviation in the x-axis and y-axis directions but also the positional deviation in the rotation direction.

In addition, in the filter 20 according to the present example embodiment, as shown in Table 1, the parallel arm resonator p21 has the smallest electrostatic capacitance in the plurality of parallel arm resonators.

The parallel arm resonator p21 having the highest resonant frequency in the plurality of parallel arm resonators has the highest impedance on the low frequency side inside the pass band. In the parallel arm resonator, as the impedance is higher, the insertion loss in the pass band can be reduced. Therefore, the impedance can be increased by reducing or minimizing the electrostatic capacitance of the parallel arm resonator p21, and the insertion loss in the pass band can be improved.

The electrostatic capacitance of the surface acoustic wave resonator is proportional to (number of pairs×cross width) of the IDT electrode. Therefore, as a method of specifying the parallel arm resonator having the smallest electrostatic capacitance in the plurality of parallel arm resonators, the magnitudes of (number of pairs×cross width) of the IDT electrodes may be compared.

In addition, in the filter 20 according to the present example embodiment, the parallel arm resonator p23 includes the piezoelectric substrate 50, the IDT electrode (third functional electrode: shown as p23 in FIG. 3) disposed on the main surface 50a, and the bump electrode 70 (122) (fourth bump electrode) connected to the IDT electrode. In addition, as shown in FIG. 5, the multilayer substrate 40 includes a planar electrode 411 (fifth planar electrode) disposed on the electrode layer L41 and bonded to the bump electrode 70 (122), the planar electrode 444 (sixth planar electrode) disposed on the electrode layer L44 and connected to the ground, and the inductor 33 (disposed on the electrode layer L42) connected between the planar electrode 411 and the planar electrode 444.

In the parallel arm resonator p23, the ground is isolated from the parallel arm resonator p21 having the highest resonant frequency inside the multiplexer 1, and the parallel arm resonator p23 is connected to the ground via the bump electrode 70 (122) different from the bump electrode 70 (121) and the inductor 33. Since the inductor 33 is connected to the parallel arm resonator p23, an interval between the resonant frequency and the anti-resonant frequency of the parallel arm resonator p23 is widened, and an attenuation pole due to the resonant frequency of the parallel arm resonator p23 can be located on the low frequency side inside the pass band of the filter 10. Therefore, it is possible to provide the filter 20 in which the attenuation characteristics are improved over a wide band on the low frequency side with respect to the pass band of the filter 20.

In addition, since the parallel arm resonator p24 is connected to the bump electrode 70 (122) together with the parallel arm resonator p23, the synthetic electrostatic capacitance of the parallel arm resonators p23 and p24 increases, and an inductance value for obtaining a predetermined resonant frequency can be reduced. In this manner, since a line width of the inductor 33 provided inside the multilayer substrate 40 can be increased, variations in the inductance value of the inductor 33 can be reduced or prevented. Therefore, it is possible to provide the small filter 20 in which the attenuation characteristics are improved and the small multiplexer 1 in which the isolation characteristics are improved.

5. Advantageous Effects

As described above, the filter 20 according to the present example embodiment includes the series arm resonator s21 disposed in the series arm path that connects the input terminal 102 and the output terminal 120, the plurality of parallel arm resonators p21 to p24 connected between the series arm path and the ground, the multilayer substrate 40 including the main surfaces 40a and 40b facing each other and the plurality of dielectric layers, the piezoelectric substrate 50 including the main surface 50a facing the main surface 40a, and the bump electrode 70 (121) disposed on the main surface 50a