JP2019004364A - Elastic wave filter and multiplexer - Google Patents

Abstract

To provide an elastic wave filter capable of improving an attenuation characteristics.SOLUTION: A ladder type elastic wave filter 10 includes three or more parallel arm circuits connected between a connection path connecting a first output terminal 20 and a second output terminal 21 and ground. The three or more parallel arm circuits each include a parallel arm resonator and an inductor connected in series. The parallel resonance is constituted of a substrate having a piezoelectric layer and an IDT electrode formed on the substrate, the three or more parallel arm circuits including the parallel arm resonators each with the IDT electrode. Repetition pitches P of a plurality of electrodes constituting the IDT electrode are different from each other, and an inductance value of an inductor L4 connected to a parallel arm resonator P4 having a repetition pitch largest among that of the parallel arm resonators included in the three or more parallel arm circuits.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an acoustic wave filter and a multiplexer.

  Recent mobile phones are required to simultaneously transmit and receive in a plurality of frequency bands and a plurality of wireless systems in one terminal, that is, to support so-called carrier aggregation (CA). In order to cope with this, a multiplexer (demultiplexer) for demultiplexing high-frequency signals having a plurality of radio carrier frequencies is arranged immediately below one antenna. The multiplexer is composed of a plurality of band pass filters. As the plurality of band pass filters, for example, an elastic wave filter composed of an elastic wave resonator having filter characteristics such as low loss in the pass band and steep pass characteristics around the pass band is used.

  Patent Document 1 discloses a technique related to such an acoustic wave filter (for example, a SAW (Surface Acoustic Wave) filter).

JP 2000-201053 A

  By the way, in the elastic wave resonator which comprises an elastic wave filter, unnecessary modes, such as a high-order mode, generate | occur | produce simultaneously simultaneously with the main mode for implement | achieving the filter characteristic mentioned above. When a higher-order mode is generated in the elastic wave resonator, the impedance characteristic of the elastic wave resonator is locally changed at a specific frequency in the attenuation band, spurious is generated, and the attenuation characteristic of the elastic wave filter is deteriorated. . Thereby, for example, when the frequency at which the spurious occurs and the pass band of another filter overlap, the pass characteristic in the pass band of the other filter may be deteriorated.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an elastic wave filter and a multiplexer that can improve attenuation characteristics.

  In order to achieve the above object, an elastic wave filter according to an aspect of the present invention is a ladder-type elastic wave filter between a path connecting a first input / output terminal and a second input / output terminal and a ground. Three or more parallel arm circuits connected to each other, each of the three or more parallel arm circuits having a parallel arm resonator and an inductor connected in series, wherein the parallel arm resonator includes a piezoelectric layer. The repetition pitch of the plurality of electrode fingers constituting each of the IDT electrodes of the parallel arm resonator included in the three or more parallel arm circuits is configured by a substrate having the IDT and an IDT electrode formed on the substrate. The inductance values of the inductors connected to the parallel arm resonator having the largest repetition pitch among the parallel arm resonators of the three or more parallel arm circuits, which are different from each other, The smallest in the inductance value of Kuta.

  The repetition pitch of the plurality of electrode fingers constituting the IDT electrode of the parallel arm resonator corresponds to the wavelength of the parallel arm resonator, and defines the low frequency side of the passband of the elastic wave filter. In addition, the inductor connected in series to the parallel arm resonator can move the resonance frequency of the parallel arm resonator to the low frequency side, and the bandwidth of the pass band can be adjusted. At this time, the frequency of the higher-order mode of the elastic wave filter is determined by the repetition pitch of the parallel arm resonator, and the inductor connected in series to the parallel arm resonator having a large repetition pitch is connected to the low-frequency side of the spurious due to the higher-order mode. This has a greater effect on the steepness of the slope of the slope. In other words, when the inductance value of the inductor connected in series with the parallel arm resonator having a large repetition pitch is large, the steepness of the attenuation slope on the low-frequency side of the spurious is low (in other words, the spurious tail is widened). In other words, the attenuation characteristic of the elastic wave filter is deteriorated. On the other hand, the inductance value of the inductor connected to the parallel arm resonator having the largest repetition pitch is the smallest among the inductance values of the inductors of three or more parallel arm circuits. The steepness of the attenuation slope can be increased.

  In addition, when the repetition pitch of the plurality of electrode fingers constituting each IDT electrode of the parallel arm resonators included in three or more parallel arm circuits is the same, the anti-resonance frequencies of the parallel arm resonators overlap, and accordingly The spurious is increased because the high-order mode frequencies are concentrated at one point. On the other hand, since the repetition pitches of the parallel arm resonators are different, it is difficult for the higher-order mode frequencies to concentrate on one point, and spurious can be reduced.

  Thus, since the spurious due to the higher order mode can be reduced and the steepness of the attenuation slope on the low frequency side of the spurious can be increased, the attenuation characteristic of the elastic wave filter can be improved.

  In the three or more parallel arm circuits, an inductor having a smaller inductance value may be connected to a parallel arm resonator having a larger repetition pitch.

  In parallel arm resonators having three or more parallel arm circuits, parallel arm resonators having a larger repetition pitch P are more likely to affect the steepness of the attenuation slope on the low-frequency side of the spurious due to higher-order modes. For example, the inductor connected to the parallel arm resonator having the second largest repetition pitch among the parallel arm resonators of three or more parallel arm circuits has a steepness of the attenuation slope on the low-frequency side of the spurious due to the higher order mode. It is easy to influence. However, since the inductance value of the inductor is smaller than the inductance value of the inductor connected to the third and subsequent parallel arm resonators, the effect on the steepness of the attenuation slope on the low frequency side of the spurious is low. Can be suppressed, and the attenuation characteristics of the elastic wave filter can be further improved.

Further, the elastic wave filter, Rayleigh waves propagating through the piezoelectric layer made of LiNbO _3, or may utilize a Love wave propagating through the piezoelectric layer made of LiNbO ₃ as a surface acoustic wave.

  Thereby, according to the elastic wave filter which concerns on 1 aspect of this invention, degradation of the attenuation | damping characteristic by the higher mode generated by a Rayleigh wave or a Love wave can be suppressed.

  The multiplexer according to one aspect of the present invention is connected to the elastic wave filter at the first input / output terminal that is a common connection point with the elastic wave filter, and has a frequency higher than the passband of the elastic wave filter. And a filter having a pass band.

  Thereby, the multiplexer which can improve the attenuation | damping property of an elastic wave filter can be provided. Specifically, the pass characteristics of a filter that is connected to the elastic wave filter at a common connection point and has a higher passband than the passband of the elastic wave filter by improving the attenuation characteristic of the elastic wave filter. Can be improved.

  According to the elastic wave filter and the multiplexer according to the present invention, the attenuation characteristic can be improved.

FIG. 1 is a configuration diagram illustrating an example of a multiplexer according to an embodiment. FIG. 2 is a plan view and a cross-sectional view schematically showing the resonator of the acoustic wave filter according to the embodiment. FIG. 3 is a diagram illustrating the pass characteristic of the elastic wave filter according to Comparative Example 1 and the pass characteristic of the elastic wave filter according to Comparative Example 2. FIG. 4 is a diagram illustrating the pass characteristic of the elastic wave filter according to the example, the pass characteristic of the elastic wave filter according to Comparative Example 1, and the pass characteristic of the elastic wave filter according to Comparative Example 3. FIG. 5 is an enlarged view of the vicinity of the attenuation slope on the low frequency side of the spurious shown in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that each of the embodiments described below shows a comprehensive or specific example. The numerical values, shapes, materials, constituent elements, arrangement of constituent elements, connection forms, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. Among the constituent elements in the following embodiments, constituent elements not described in the independent claims are described as optional constituent elements. In addition, the size of components shown in the drawings, or the ratio of the sizes is not necessarily strict. Moreover, in each figure, the same code | symbol is attached | subjected to the substantially same structure, The overlapping description may be abbreviate | omitted or simplified. In the following embodiments, “connected” includes not only the case of direct connection but also the case of electrical connection via other elements.

(Embodiment)
A multiplexer 1 according to an embodiment will be described with reference to FIGS.

[1. Basic configuration of multiplexer]
First, the configuration of the multiplexer 1 according to the first embodiment will be described with reference to FIG.

  FIG. 1 is a configuration diagram illustrating an example of a multiplexer 1 according to the first embodiment. FIG. 1 also shows an antenna element ANT and an inductor Lant connected to the common connection point N of the multiplexer 1. The antenna element ANT is a multiband antenna that transmits and receives a high-frequency signal and conforms to a communication standard such as LTE (Long Term Evolution).

  The multiplexer 1 is a demultiplexer / multiplexer including a plurality of filters having different passbands, and the terminals on the antenna ANT side of these filters are commonly connected to a first input / output terminal 20 that is a common connection point. . In the present embodiment, the multiplexer 1 is a quadplexer that includes four filters. As shown in FIG. 1, the multiplexer 1 includes an elastic wave filter 10 and filters 100 to 300. An RF signal processing circuit (RFIC: Radio Frequency Integrated Circuit) is provided on the opposite side of the multiplexer 1 from the antenna ANT (right side in FIG. 1) via, for example, a switch circuit or an amplifier circuit such as a power amplifier or a low noise amplifier. Is connected.

  The elastic wave filter 10 is a ladder-type elastic wave filter, and series arm resonators S1 to S4 connected in series to a path connecting the first input / output terminal 20 and the second input / output terminal 21, respectively, Parallel arm circuits 11 to 14 connected between the path and the ground are provided. The elastic wave filter 10 only needs to include three or more parallel arm circuits, and in this embodiment, includes four parallel arm circuits. The parallel arm circuit 11 includes a parallel arm resonator P1 and an inductor L1 connected in series. Similarly, the parallel arm circuit 12 has a parallel arm resonator P2 and an inductor L2 connected in series, and the parallel arm circuit 13 has a parallel arm resonator P3 and an inductor L3 connected in series. The parallel arm circuit 14 includes a parallel arm resonator P4 and an inductor L4 connected in series. The elastic wave filter 10 has such a ladder-type filter structure, so that the pass characteristic of the elastic wave filter 10 can be finely adjusted.

  The series arm resonators S1 to S4 and the parallel arm resonators P1 to P4 are, for example, SAW resonators, and include a substrate having a piezoelectric layer and an IDT electrode formed on the substrate. The structure of each resonator will be described in detail with reference to FIG.

  The elastic wave filter 10 is, for example, a bandpass filter (BPF), and is a filter having a transmission band (1710-1785 MHz) of LTE Band 3 as a pass band.

  The inductors L1 to L4 are connected in series to the parallel arm resonators P1 to P4, so that the passband of the acoustic wave filter 10 can be adjusted. Specifically, each inductor connected in series with each parallel arm resonator can move the resonance frequency of each parallel arm resonator to the lower side as the inductance value increases, and the bandwidth of the passband can be increased. Can be wide.

  The filter 100 is connected to other filters including the acoustic wave filter 10 at the first input / output terminal 20 which is a common connection point, and is provided in a path connecting the first input / output terminal 20 and the third input / output terminal 22. Yes. The filter 100 is a filter whose pass band is higher than the pass band of the elastic wave filter 10. The filter 100 is, for example, an elastic wave filter, but may be a filter composed of an LC resonance circuit. The filter 100 is, for example, a BPF, and is a filter having a reception band (2110-2170 MHz) of LTE Band 1 as a pass band.

  The filter 200 is connected to other filters including the acoustic wave filter 10 at the first input / output terminal 20 which is a common connection point, and is provided in a path connecting the first input / output terminal 20 and the fourth input / output terminal 23. Yes. The filter 200 is, for example, an elastic wave filter, but may be a filter configured by an LC resonance circuit. The filter 200 is, for example, a BPF and is a filter having a transmission band (1920-1980 MHz) of LTE Band 1 as a pass band.

  The filter 300 is connected to other filters including the acoustic wave filter 10 at the first input / output terminal 20 which is a common connection point, and is provided in a path connecting the first input / output terminal 20 and the fifth input / output terminal 24. Yes. The filter 300 is, for example, an elastic wave filter, but may be a filter configured by an LC resonance circuit. The filter 200 is, for example, a BPF, and is a filter that uses an LTE Band 3 reception band (1805 to 1880 MHz) as a pass band.

Acoustic wave filter 10, the Rayleigh wave propagating piezoelectric layer made of LiNbO _3, or, utilizing Love waves propagating through the piezoelectric layer made of LiNbO ₃ as a surface acoustic wave. When these surface acoustic waves are used, higher-order modes are also generated at the same time. By generating a higher-order mode in the elastic wave resonator, the impedance characteristic of the elastic wave resonator is locally changed at a specific frequency in the attenuation band of the elastic wave filter 10, and spurious is generated. The attenuation characteristics of the are deteriorated. Thereby, for example, when the frequency at which the spurious is generated overlaps with the pass band of a filter (for example, the filter 100) whose pass band is higher than the pass band of the elastic wave filter 10, the pass in the pass band of the filter is performed. Characteristics may deteriorate.

  The inductor Lant is connected between the first input / output terminal 20 and the ground. Thereby, impedance matching of the antenna element ANT, the elastic wave filter 10, and the filters 100 to 300 is performed.

[2. Basic structure of resonator]
Next, the basic structure of each resonator (series arm resonator and parallel arm resonator) constituting the acoustic wave filter 10 will be described.

  FIG. 2 is a plan view and a cross-sectional view schematically showing the resonator of the acoustic wave filter 10 according to the embodiment. In the figure, a schematic plan view and a schematic cross-sectional view showing the structure of the parallel arm resonator P1 among the plurality of resonators constituting the acoustic wave filter 10 are illustrated. The parallel arm resonator P1 shown in FIG. 2 is for explaining a typical structure of the plurality of resonators, and the number and length of electrode fingers constituting the electrode are as follows. It is not limited to.

  As shown in the plan view of FIG. 2, the parallel arm resonator P1 has a pair of comb-like electrodes 11a and 11b facing each other. Although not shown, the parallel arm resonator P1 further includes a reflector disposed adjacent to the pair of comb-like electrodes 11a and 11b in the propagation direction of the elastic wave. The pair of comb-like electrodes 11a and 11b constitutes an IDT electrode.

  The comb-teeth electrode 11a is arranged in a comb-teeth shape, and includes a plurality of electrode fingers 110a that are parallel to each other and a bus bar electrode 111a that connects one end of each of the plurality of electrode fingers 110a. The comb-like electrode 11b is arranged in a comb-teeth shape and includes a plurality of electrode fingers 110b parallel to each other and a bus bar electrode 111b that connects one end of each of the plurality of electrode fingers 110b. The plurality of electrode fingers 110a and 110b are formed to extend in a direction orthogonal to the elastic wave propagation direction.

  The comb-shaped electrodes 11a and 11b are not limited to the above configuration, and may include, for example, offset electrode fingers. The parallel arm resonator P1 may have a so-called inclined IDT in which the bus bar electrodes 111a and 111b are inclined with respect to the elastic wave propagation direction. Furthermore, the electrode fingers 110a and 110b may have so-called thinned electrodes thinned at a predetermined interval.

  Further, the IDT electrode composed of the plurality of electrode fingers 110a and 110b and the bus bar electrodes 111a and 111b has a laminated structure of the adhesion layer 51 and the main electrode layer 52 as shown in the sectional view of FIG. ing.

  The adhesion layer 51 is a layer for improving the adhesion between the piezoelectric substrate 50 and the main electrode layer 52, and, for example, Ti is used as a material. The main electrode layer 52 is made of, for example, Al containing 1% Cu. The protective layer 53 is formed so as to cover the IDT electrode. The protective layer 53 is a layer for the purpose of protecting the main electrode layer 52 from the external environment, adjusting frequency temperature characteristics, and improving moisture resistance, for example, a film containing silicon dioxide as a main component. .

  In addition, the material which comprises the contact | adherence layer 51, the main electrode layer 52, and the protective layer 53 is not limited to the material mentioned above. Furthermore, the IDT electrode does not have to have the above laminated structure. The IDT electrode may be composed of, for example, a metal or alloy such as Ti, Al, Cu, Pt, Au, Ag, or Pd, or may be composed of a plurality of laminates composed of the above metals or alloys. Also good. Further, the protective layer 53 may not be formed.

The piezoelectric substrate 50 is a piezoelectric substrate in which an IDT electrode and a reflector are arranged on the main surface, and is, for example, a substrate made of LiNbO ₃ .

  The wavelength of the acoustic wave resonator is defined by a wavelength λ which is a repetition period of the plurality of electrode fingers 110a or 110b constituting the IDT electrode shown in FIG. The electrode finger repetition pitch P is ½ of the wavelength λ, the line width of the electrode fingers 110a and 110b constituting the comb-shaped electrodes 11a and 11b is W, and the adjacent electrode fingers 110a and 110b When the space width between and is S, it is defined by (W + S).

  In the present embodiment, the repetition pitch P of the plurality of electrode fingers constituting each IDT electrode of the parallel arm resonators P1 to P4 included in the three or more parallel arm circuits (here, the parallel arm circuits 11 to 14) is: Different from each other. Further, the inductance value of the inductor connected to the parallel arm resonator having the largest repetition pitch P among the parallel arm resonators P1 to P4 included in the three or more parallel arm circuits (here, the parallel arm circuits 11 to 14) is: It is the smallest among the inductance values of the inductors L1 to L4 included in three or more parallel arm circuits. These will be described in detail with reference to FIGS.

[3. Passing characteristics of elastic wave filter]
Next, the pass characteristics of the elastic wave filter according to Comparative Examples 1 to 3 and the elastic wave filter 10 according to the example will be described. The circuit configurations of the acoustic wave filters of Comparative Examples 1 to 3 are the same as the circuit configuration of the acoustic wave filter 10 shown in FIG. 1, and the series arm resonators S1 to S4 and the parallel arm resonators P1 to P4 are respectively used. Inductors L1 to L4 are connected in series to the parallel arm resonators P1 to P4.

  Table 1 shows the repetition pitch of each resonator of Comparative Example 1 and the repetition pitch of each resonator of Comparative Example 2. In Comparative Examples 1 and 2, the inductance values of the inductors L1 to L4 are all the same value as 1.5 nH.

  As shown in Table 1, in Comparative Example 1, the repetitive pitch P of the plurality of electrode fingers constituting the IDT electrodes of the parallel arm resonators P1 to P4 is different from each other. On the other hand, in Comparative Example 2, the repetition pitch P of the plurality of electrode fingers constituting each IDT electrode of the parallel arm resonators P1 to P4 is the same. The pass characteristics of the elastic wave filter according to Comparative Example 1 and the pass characteristics of the elastic wave filter according to Comparative Example 2 will be described with reference to FIG.

  FIG. 3 is a diagram illustrating the pass characteristic of the elastic wave filter according to Comparative Example 1 and the pass characteristic of the elastic wave filter according to Comparative Example 2. As shown in FIG. 3, it can be seen that spurious due to the higher-order mode occurs in the vicinity of 2200-2300 MHz. As shown by the circled portions in FIG. 3, it can be seen that when the repetition pitch P of Comparative Example 2 is the same, the spurious is larger than when the Comparative Example 1 is different from each other. This is because when the repetition pitch P is the same, the anti-resonance frequencies of the parallel arm resonators P1 to P4 overlap, and accordingly, the higher-order mode frequencies are concentrated at one point, so that the spurious becomes large. . In Comparative Example 1, since the repetition pitches of the parallel arm resonators P1 to P4 are different from each other, it is difficult for the higher-order mode frequencies to concentrate on one point, and spurious can be reduced.

  As described above, the repetition pitch P of the plurality of electrode fingers constituting the IDT electrodes of the parallel arm resonators P1 to P4 of the parallel arm circuits 11 to 14 is different from each other, so that spurious due to the higher-order mode can be reduced. The attenuation characteristic of the elastic wave filter can be improved.

  The repetition pitch P is different from each other. For example, among the parallel arm resonators, the largest repetition pitch P differs by 0.3% or more with respect to the smallest repetition pitch P, and each parallel element is within the range. This means that the repetitive pitches P of the arm resonators are different from each other. Thereby, spurious can be reduced by 1.0 dB or more.

  Further, in order to explain the influence when the repetitive pitches P of the parallel arm resonators P1 to P4 are different from each other, in Comparative Example 1 and Comparative Example 2, the inductance values of the inductors L1 to L4 are set to the same value. On the other hand, in the present embodiment, the inductance value of the inductor connected in series to the parallel arm resonator having the largest repetition pitch P is made the smallest among the inductance values of the inductors L1 to L4 included in the parallel arm circuits 11 to 14. .

  Table 2 shows inductance values of the inductors L1 to L4 of the example, the comparative example 1, and the comparative example 3. In Example and Comparative Example 3, the repetition pitch P of each resonator is the same as that in Comparative Example 1 shown in Table 1. That is, also in Example and Comparative Example 3, the repetitive pitch P of the plurality of electrode fingers constituting the IDT electrodes of the parallel arm resonators P1 to P4 is different from each other.

  As shown in Table 2, in the embodiment, the parallel arm circuits 11 to 14 have the inductance value of the inductor L4 connected to the parallel arm resonator P4 having the largest repetition pitch P among the parallel arm resonators P1 to P4. It is the smallest among the inductance values of the inductors L1 to L4. As shown in the embodiment in Table 2, there may be a parallel arm resonator to which an inductor having the smallest inductance value is connected in addition to the parallel arm resonator P4 having the largest repetition pitch P. In the embodiment, the inductors L2 and L3 connected to the parallel arm resonators P2 and P3 also have the smallest inductance value. In Comparative Example 1, as described above, the inductance values of the inductors L1 to L4 are all the same value. In Comparative Example 3, the inductance value of the inductor L4 connected to the parallel arm resonator P4 having the largest repetition pitch P among the parallel arm resonators P1 to P4 is the inductance value of the inductor connected to another parallel arm resonator. Bigger than.

  The pass characteristics of the elastic wave filter 10 according to the example, the pass characteristics of the elastic wave filter according to the comparative example 1, and the pass characteristics of the elastic wave filter according to the comparative example 3 will be described with reference to FIGS. To do.

  FIG. 4 is a diagram illustrating the pass characteristic of the elastic wave filter 10 according to the example, the pass characteristic of the elastic wave filter according to Comparative Example 1, and the pass characteristic of the elastic wave filter according to Comparative Example 3. FIG. 5 is an enlarged view of the vicinity of the attenuation slope on the low frequency side of the spurious shown in FIG. As shown in FIGS. 4 and 5, the attenuation slope here is where the insertion loss increases as the frequency decreases around 2200 MHz.

  In Comparative Example 1, the inductance values of the inductors L1 to L4 are all the same value. On the other hand, in the embodiment, the inductance value of the inductor L1 is 2.5 nH, and the inductance values of the inductors L2 to L4 are 1.5 nH. In Comparative Example 3, the inductance value of the inductor L4 is 2.5 nH, and the inductance values of the inductors L1 to L3 are 1.5 nH. As shown by the circled portions in FIG. 5, the steepness of the attenuation slope is higher in the example than in the first comparative example (in other words, the spurious hem is narrower). On the other hand, in Comparative Example 3, the steepness of the attenuation slope is lower than that of Comparative Example 1 (in other words, the spurious tail is widened).

  This is because the frequency of the higher-order mode of the elastic wave filter is determined by the repetition pitch P, and the inductor connected in series to the parallel arm resonator having a larger repetition pitch P (that is, a larger wavelength) This is to have a greater influence on the steepness of the attenuation slope on the low frequency side. That is, as in Comparative Example 3, the inductance value of the inductor L4 connected in series to the parallel arm resonator P4 having a large repetition pitch P is equal to the inductors L1 to L3 connected in series to the other parallel arm resonators P1 to P3. When the value is larger than the inductance value, the steepness of the attenuation slope on the low-frequency side of the spurious becomes low (in other words, the skirt of the spurious spreads), and the attenuation characteristic of the elastic wave filter deteriorates. On the other hand, as in the embodiment, the inductance value of the inductor L4 connected to the parallel arm resonator P4 having the largest repetition pitch P is the inductance value of the inductors L1 to L4 included in the parallel arm circuits 11 to 14. As a result, the steepness of the attenuation slope on the low frequency side of the spurious can be increased.

  Thus, the inductance value of the inductor L4 connected to the parallel arm resonator P4 having the largest repetition pitch P among the parallel arm resonators P1 to P4 included in the parallel arm circuits 11 to 14 is equal to that of the parallel arm circuits 11 to 14. Since the steepness of the attenuation slope on the low frequency side of the spurious can be increased by being the smallest among the inductance values of the inductors L1 to L4, the attenuation characteristics of the acoustic wave filter can be improved.

  As described above, the repetition pitch P of the plurality of electrode fingers constituting the IDT electrodes of the parallel arm resonators P1 to P4 is different from each other, so that the first input / output terminal 20 which is a common connection point is connected to the elastic wave filter 10. Thus, it is possible to suppress the deterioration of the pass characteristics of the filter whose pass band is the frequency band in which spurious due to the higher-order mode of the elastic wave filter 10 is generated. The inductance value of the inductor L4 connected to the parallel arm resonator P4 having the largest repetition pitch P among the parallel arm resonators P1 to P4 is the inductance value of the inductors L1 to L4 included in the parallel arm circuits 11 to 14. And the first input / output terminal 20 is connected to the elastic wave filter 10 and passes through a filter whose pass band is a frequency band close to the low-side attenuation slope of the spurious due to the higher-order mode of the elastic wave filter 10. It can suppress that a characteristic deteriorates. For example, since the filter 100 uses the LTE Band 1 reception band (2110-2170 MHz) as the pass band, the steepness of the attenuation slope increases, so that the pass characteristic of the filter 100 can be prevented from deteriorating. In this way, it is possible to suppress deterioration of the pass characteristics of a filter that is connected to the elastic wave filter 10 at the first input / output terminal 20 that is a common connection point and has a pass band higher than the pass band of the elastic wave filter 10. it can. Further, for example, it is possible to suppress degradation of the quality of other communication around the frequency band in which the spurious is generated.

  In the parallel arm circuits 11 to 14, it is preferable that an inductor having a smaller inductance value is connected to a parallel arm resonator having a larger repetition pitch P. That is, in the acoustic wave filter 10, since the order in which the repetition pitch P is large is the order of the parallel arm resonators P4, P2, P3, and P1, it is preferable that the inductance value is small in the order of the inductors L4, L2, L3, and L1. . This is because the parallel arm resonator having a large repetition pitch P among the parallel arm circuits 11 to 14 is more likely to affect the steepness of the attenuation slope on the low frequency side of the spurious due to the higher order mode. For example, the inductor L2 connected to the parallel arm resonator P2 having the second largest repetition pitch P among the parallel arm resonators P1 to P4 affects the steepness of the attenuation slope on the low frequency side of the spurious due to the higher order mode. Easy to give. Therefore, the inductance value of the inductor L2 is smaller than the inductance values of the inductors L3 and L1 connected to the third and subsequent parallel arm resonators P3 and P1 with the repetition pitch P being larger than that of the spurious low frequency side. The steepness of the attenuation slope can be suppressed from being lowered, and the attenuation characteristic of the elastic wave filter can be further improved.

(Other embodiments)
As described above, the elastic wave filter and the multiplexer according to the embodiment of the present invention have been described with reference to the above embodiment. However, the present invention is not limited to the above embodiment. Another embodiment realized by combining arbitrary constituent elements in the above-described embodiment, and modifications obtained by applying various modifications conceivable by those skilled in the art to the above-described embodiment without departing from the gist of the present invention. Examples are also included in the present invention.

  For example, in the above-described embodiment, the acoustic wave filter 10 includes four series arm resonators S1 to S4, but may include one to three or five or more series arm resonators. In addition to the three or more parallel arm circuits, the elastic wave filter 10 may have a parallel arm to which a parallel arm resonator is connected without being connected to an inductor.

  Further, for example, the passbands of the acoustic wave filter 10 and the filters 100 to 300 are not limited to the above-described passbands.

  Further, for example, the multiplexer 1 is not limited to a quadplexer, and may be a duplexer or a triplexer including at least the elastic wave filter 10 and the filter 100.

  For example, the elastic wave filter 10 may not be applied to the multiplexer 1.

  For example, in the said embodiment, although the acoustic wave filter 10 utilized the Rayleigh wave or the Love wave as a surface acoustic wave, you may utilize a leaky wave. Even when the acoustic wave filter 10 uses a leaky wave, a higher-order mode is generated. However, according to the present invention, it is possible to suppress the deterioration of the attenuation characteristic due to the higher-order mode generated by the leaky wave.

When the acoustic wave filter 10 uses a leaky wave as a surface acoustic wave, the piezoelectric substrate 50 constituting each resonator has a stacked structure in which a high sound speed support substrate, a low sound speed film, and a piezoelectric film are stacked in this order. Have The piezoelectric film is, for example, a 50 ° Y-cut X-propagating LiTaO ₃ piezoelectric single crystal or a piezoelectric ceramic (a lithium tantalate single crystal cut along a plane whose normal is an axis rotated about 50 ° from the Y axis with the X axis as the central axis, Alternatively, it is made of ceramic and is made of a single crystal or ceramic in which surface acoustic waves propagate in the X-axis direction. The piezoelectric film has a thickness of 600 nm, for example. The high sound velocity support substrate is a substrate that supports the low sound velocity film, the piezoelectric film, and the IDT electrode. The high-sonic support substrate is a substrate in which the acoustic velocity of the bulk wave in the high-sonic support substrate is higher than that of the surface wave or boundary wave that propagates through the piezoelectric film. It functions in such a way that it is confined in the portion where the sonic film is laminated and does not leak below the high sonic support substrate. The high sound speed support substrate is, for example, a silicon substrate, and has a thickness of, for example, 200 μm. The low acoustic velocity film is a membrane in which the acoustic velocity of the bulk wave in the low acoustic velocity film is lower than the bulk wave propagating through the piezoelectric membrane, and is disposed between the piezoelectric membrane and the high acoustic velocity support substrate. Due to this structure and the property that energy is concentrated in a medium where acoustic waves are essentially low in sound velocity, leakage of surface acoustic wave energy to the outside of the IDT electrode is suppressed. The low acoustic velocity film is, for example, a film mainly composed of silicon dioxide and has a thickness of, for example, 670 nm. According to this laminated structure, the Q value at the resonance frequency and the anti-resonance frequency can be significantly increased as compared with the structure in which the piezoelectric substrate 50 is used as a single layer. That is, since a surface acoustic wave resonator having a high Q value can be configured, a filter with a small insertion loss can be configured using the surface acoustic wave resonator.

  Note that the high sound velocity support substrate has a structure in which a support substrate and a high sound velocity film in which the velocity of the bulk wave propagating is higher than that of the surface wave and boundary wave propagating in the piezoelectric film are stacked. It may be. In this case, the support substrate is a piezoelectric material such as sapphire, lithium tantalate, lithium niobate, crystal, alumina, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, etc. Various ceramics, dielectrics such as glass, semiconductors such as silicon and gallium nitride, resin substrates, and the like can be used. In addition, the high sound velocity film includes various materials such as aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, DLC film or diamond, a medium mainly composed of the above materials, and a medium mainly composed of a mixture of the above materials. High sound velocity material can be used.

  INDUSTRIAL APPLICABILITY The present invention can be widely used for communication devices such as mobile phones as elastic wave filters and multiplexers that can be applied to multiband systems.

DESCRIPTION OF SYMBOLS 1 Multiplexer 10 Elastic wave filter 11-14 Parallel arm circuit 11a, 11b Comb-shaped electrode 20 1st input / output terminal 21 2nd input / output terminal 22 3rd input / output terminal 23 4th input / output terminal 24 5th input / output terminal 50 Piezoelectric substrate 51 Adhesive layer 52 Main electrode layer 53 Protective layer 100, 200, 300 Filter 110a, 110b Electrode finger 111a, 111b Bus bar electrode P1-P4 Parallel arm resonator S1-S4 Series arm resonator L1-L4, Lant inductor ANT antenna element

Claims (4)

A ladder-type elastic wave filter,
3 or more parallel arm circuits connected between the path connecting the first input / output terminal and the second input / output terminal and the ground,
Each of the three or more parallel arm circuits has a parallel arm resonator and an inductor connected in series,
The parallel arm resonator includes a substrate having a piezoelectric layer and an IDT electrode formed on the substrate.
The repetition pitch of the plurality of electrode fingers constituting each of the IDT electrodes of the parallel arm resonators of the three or more parallel arm circuits is different from each other,
Among the parallel arm resonators included in the three or more parallel arm circuits, the inductance value of the inductor connected to the parallel arm resonator having the largest repetition pitch is the inductance value of the inductor included in the three or more parallel arm circuits. The smallest of the
Elastic wave filter. In the three or more parallel arm circuits, an inductor having a smaller inductance value is connected to a parallel arm resonator having a larger repetition pitch.
The elastic wave filter according to claim 1. The elastic wave filter, Rayleigh waves propagating through the piezoelectric layer made of LiNbO _3, or, utilizing Love waves propagating through the piezoelectric layer made of LiNbO ₃ as a surface acoustic wave,
The elastic wave filter according to claim 1 or 2. The elastic wave filter according to any one of claims 1 to 3,
A filter connected to the elastic wave filter at the first input / output terminal that is a common connection point, and having a pass band higher than the pass band of the elastic wave filter,
Multiplexer.

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