WO2021045031A1 - Acoustic wave filter - Google Patents

Abstract

An acoustic filter (1) is provided with a series arm resonator (s1 and s2) and a parallel arm resonator (p1 and p2), each formed from an acoustic resonator that has an IDT electrode, wherein: the IDT electrode has a pair of comb-shaped electrodes, each of which comprises a plurality of electrode fingers and a busbar electrode; and when an electrode finger among the plurality of electrode fingers that is not connected to either busbar electrode constituting the pair of comb-shaped electrodes is defined as a floating thinned-out electrode, and an electrode finger among the plurality of electrode fingers that is connected to the same busbar electrode as the electrode fingers on both sides of said electrode finger is defined as a polarity-reversed thinned-out electrode, the series arm resonator (s1) has the IDT electrode that includes the floating thinned-out electrode, and the parallel arm resonator (p1) has the IDT electrode that includes the polarity-reversed thinned-out electrode.

Description

SAW filter

The present invention relates to an elastic wave filter.

An elastic wave filter has been put into practical use as a band filter used in high-frequency circuits such as communication equipment. From the viewpoint of effectively utilizing frequency resources for wireless communication, many frequency bands are allocated as communication bands for mobile phones and the like, so that the intervals between adjacent frequency bands are narrowed. In view of the allocation status of this frequency band, the rate of change of the insertion loss from the pass band to the attenuation band at the end of the pass band (hereinafter referred to as steepness) is an important performance index in the SAW filter.

Patent Document 1 describes an IDT (InterDigital Transducer) that constitutes at least one of a series arm resonator and a parallel arm resonator in a ladder type elastic wave filter having a plurality of series arm resonators and a plurality of parallel arm resonators. A configuration in which the electrodes include thinning electrodes is disclosed. According to this configuration, the steepness in the pass band can be improved.

International Publication No. 2017/131170

However, due to the electrode finger structure of the thinning electrode, the variation mode of the resonance bandwidth (frequency difference between the resonance frequency and the anti-resonance frequency) of the elastic wave resonator including the thinning electrode, and the resonance Q value at the resonance point and the anti-resonance point can be changed. different. Therefore, when an elastic wave filter is formed by using a thinning electrode as a part of the IDT electrode, it is difficult to achieve both steepness in the pass band and low loss in the pass band.

Therefore, the present invention has been made to solve the above problems, and an object of the present invention is to provide an elastic wave filter having improved steepness while ensuring low loss in a pass band.

In order to achieve the above object, the elastic wave filter according to one aspect of the present invention is a path connecting the first input / output terminal and the second input / output terminal with the first input / output terminal and the second input / output terminal. It comprises one or more series arm resonators arranged above and one or more parallel arm resonators arranged between a node and ground on the path, said one or more series arm resonators and said. Each of the one or more parallel arm resonators includes an elastic wave resonator having an IDT (InterDigital Transferr) electrode formed on a substrate having piezoelectricity, and the IDT electrode is oriented in a direction intersecting the elastic wave propagation direction. The plurality of electrodes have a pair of comb-shaped electrodes composed of a plurality of electrode fingers stretched and arranged in parallel with each other and a bus bar electrode connecting one ends of the electrode fingers constituting the plurality of electrode fingers. Of the fingers, an electrode finger that is not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes is defined as a floating thinning electrode, and among the plurality of electrode fingers, the bus bar electrodes to which the electrode fingers on both sides are connected are defined. When the electrode finger connected to the same bus bar electrode as the above is defined as a polarity reversal thinning electrode, at least one of the one or more series arm resonators has an IDT electrode including the floating thinning electrode, and the above 1 At least one of the above parallel arm resonators has an IDT electrode including the polarity reversal thinning electrode.

According to the present invention, it is possible to provide an elastic wave filter having improved steepness while ensuring low loss in the pass band.

FIG. 1 is a circuit configuration diagram of an elastic wave filter according to an embodiment. FIG. 2A is a plan view and a cross-sectional view schematically showing an example of an elastic wave resonator according to the embodiment. FIG. 2B is a cross-sectional view schematically showing an elastic wave resonator according to the first modification of the embodiment. FIG. 3 is a circuit configuration diagram for explaining the basic operating principle of the ladder type elastic wave filter and a graph showing frequency characteristics. FIG. 4 is a graph showing the passage characteristics of the elastic wave filter and the impedance characteristics of the series arm resonator according to the embodiment. FIG. 5A is a schematic plan view showing the configuration of an IDT electrode including a floating thinning electrode in an elastic wave filter. FIG. 5B is a schematic plan view showing the configuration of an IDT electrode including a polarity reversal thinning electrode in an elastic wave filter. FIG. 5C is a schematic plan view showing the configuration of an IDT electrode including a filled thinning electrode in an elastic wave filter. FIG. 6A is a graph showing the impedance and Q value of an elastic wave resonator including a floating thinning electrode when the thinning rate is changed. FIG. 6B is a graph showing the impedance and Q value of an elastic wave resonator including a polarity reversal thinning electrode when the thinning rate is changed. FIG. 6C is a graph showing the impedance and Q value of an elastic wave resonator including a filled thinning electrode when the thinning rate is changed. FIG. 7 is a graph showing the reflection loss at the resonance point and the antiresonance point when the specific band of the elastic wave resonator is changed. FIG. 8 is a circuit configuration diagram of an elastic wave filter according to an embodiment. FIG. 9 is a graph comparing the insertion loss in the pass band of the elastic wave filter according to the example, the comparative example 1 and the comparative example 2.

Hereinafter, embodiments of the present invention will be described in detail with reference to Examples and Modifications. It should be noted that all of the embodiments described below show comprehensive or specific examples. Numerical values, shapes, materials, components, arrangement of components, connection modes, etc. shown in the following embodiments are examples, and are not intended to limit the present invention. Among the components in the following embodiments, the components not described in the independent claims are described as arbitrary components. Also, the sizes or ratios of the components shown in the drawings are not always exact.

(Embodiment)
[1 Circuit configuration of elastic wave filter 1]
FIG. 1 is a circuit configuration diagram of an elastic wave filter 1 according to an embodiment. As shown in the figure, the elastic wave filter 1 includes series arm resonators s1 and s2, parallel arm resonators p1 and p2, and input / output terminals 110 and 120.

Each of the series arm resonators s1 and s2 is arranged on a path connecting the input / output terminal 110 (first input / output terminal) and the input / output terminal 120 (second input / output terminal), and is connected in series with each other. Further, each of the parallel arm resonators p1 and p2 is arranged between the node on the path and the ground.

The number of series arm resonators may be 1 or more. Further, the number of parallel arm resonators arranged may be 1 or more.

Further, circuit elements such as an inductor and a capacitor, a vertically coupled resonator, and the like are inserted between the series arm resonators s1 and s2, the parallel arm resonators p1 and p2, the input / output terminals 110 and 120, and the ground. You may be.

With the above configuration, the elastic wave filter 1 constitutes a ladder type bandpass filter.

Below, the basic structures of the series arm resonator and the parallel arm resonator constituting the elastic wave filter 1 will be described.

[2 Structure of elastic wave resonator]
FIG. 2A is a schematic view schematically showing an example of an elastic wave resonator according to an embodiment. FIG. 2A is a plan view, and FIGS. It is a sectional view. FIG. 2A illustrates an elastic wave resonator 100 having a basic structure of a series arm resonator and a parallel arm resonator constituting the elastic wave filter 1. The elastic wave resonator 100 shown in FIG. 2A is for explaining a typical structure of the elastic wave resonator, and the number and length of the electrode fingers constituting the electrode are described in this. Not limited.

The elastic wave resonator 100 is composed of a substrate 5 having piezoelectricity and comb-shaped electrodes 100a and 100b.

As shown in FIG. 2A (a), a pair of comb-shaped electrodes 100a and 100b facing each other are formed on the substrate 5. The comb-shaped electrode 100a is composed of a plurality of electrode fingers 150a parallel to each other and a bus bar electrode 160a connecting the plurality of electrode fingers 150a. Further, the comb-shaped electrode 100b is composed of a plurality of electrode fingers 150b parallel to each other and a bus bar electrode 160b connecting the plurality of electrode fingers 150b. The plurality of electrode fingers 150a and 150b are formed along a direction orthogonal to the elastic wave propagation direction (X-axis direction).

Further, the IDT (InterDigital Transducer) electrode 54 composed of the plurality of electrode fingers 150a and 150b and the bus bar electrodes 160a and 160b has the adhesion layer 540 and the main electrode layer 542 as shown in FIG. 2A (b). It has a laminated structure of.

The adhesion layer 540 is a layer for improving the adhesion between the substrate 5 and the main electrode layer 542, and Ti is used as the material, for example. The film thickness of the adhesion layer 540 is, for example, 12 nm.

For the main electrode layer 542, for example, Al containing 1% Cu is used as the material. The film thickness of the main electrode layer 542 is, for example, 162 nm.

The protective layer 55 is formed so as to cover the comb-shaped electrodes 100a and 100b. The protective layer 55 is a layer for the purpose of protecting the main electrode layer 542 from the external environment, adjusting the frequency temperature characteristics, improving the moisture resistance, and the like. For example, a dielectric film containing silicon dioxide as a main component. Is. The thickness of the protective layer 55 is, for example, 25 nm.

The materials constituting the adhesion layer 540, the main electrode layer 542, and the protective layer 55 are not limited to the above-mentioned materials. Further, the IDT electrode 54 does not have to have the above-mentioned laminated structure. The IDT electrode 54 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. You may. Further, the protective layer 55 may not be formed.

Next, the laminated structure of the substrate 5 will be described.

As shown in FIG. 2A (c), the substrate 5 includes a hypersonic support substrate 51, a low sound velocity film 52, and a piezoelectric film 53, and the high sound velocity support substrate 51, the low sound velocity film 52, and the piezoelectric film 53 are provided. It has a structure laminated in this order.

The piezoelectric film 53 is a 50 ° Y-cut X-propagation LiTaO ₃ piezoelectric single crystal or a piezoelectric ceramic (a lithium tantalate single crystal cut along a plane whose normal axis is an axis rotated 50 ° from the Y axis with the X axis as the central axis, or It is made of ceramics (single crystal or ceramics in which surface acoustic waves propagate in the X-axis direction). The piezoelectric film 53 has, for example, a thickness of 600 nm. The material and cut angle of the piezoelectric single crystal used as the piezoelectric film 53 are appropriately selected according to the required specifications of each filter.

The hypersonic support substrate 51 is a substrate that supports the hypersonic film 52, the piezoelectric film 53, and the IDT electrode 54. The high sound velocity support substrate 51 is a substrate in which the sound velocity of the bulk wave in the high sound velocity support substrate 51 is higher than that of elastic waves such as surface waves and boundary waves propagating through the piezoelectric film 53, and the elastic surface waves are generated. It is confined in the portion where the piezoelectric film 53 and the low sound velocity film 52 are laminated, and functions so as not to leak below the high sound velocity support substrate 51. The hypersonic support substrate 51 is, for example, a silicon substrate and has a thickness of, for example, 200 μm.

The low sound velocity film 52 is a film in which the sound velocity of the bulk wave in the low sound velocity film 52 is lower than that of the bulk wave propagating in the piezoelectric film 53, and is arranged between the piezoelectric film 53 and the high sound velocity support substrate 51. To. Due to this structure and the property that the energy is concentrated in the medium in which the surface acoustic wave is essentially low sound velocity, the leakage of the surface acoustic wave energy to the outside of the IDT electrode is suppressed. The bass sound film 52 is, for example, a film containing silicon dioxide as a main component, and has a thickness of, for example, 670 nm.

According to the laminated structure of the substrate 5, the Q values at the resonance frequency and the antiresonance frequency can be significantly increased as compared with the conventional structure in which the piezoelectric substrate is used as a single layer. That is, since an elastic wave resonator having a high Q value can be constructed, it is possible to construct a filter having a small insertion loss by using the elastic wave resonator.

Further, when a thinning electrode is applied to the elastic wave resonator as described later in order to improve the steepness of the passband end of the elastic wave filter 1, the Q value of the elastic wave resonator becomes equivalently small. A case is assumed. On the other hand, according to the laminated structure of the substrate, the Q value of the elastic wave resonator 100 can be maintained at a high value. Therefore, it is possible to form the elastic wave filter 1 in which the low loss in the pass band is maintained.

The high sound velocity support substrate 51 has a structure in which a support substrate and a high sound velocity film in which the sound velocity of the bulk wave propagating is higher than that of elastic waves such as surface waves and boundary waves propagating in the piezoelectric film 53 are laminated. May have. In this case, the support substrate is provided with piezoelectric materials such as sapphire, lithium tantalate, lithium niobate, and crystal, alumina, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cozilite, mulite, steatite, and fol. Various ceramics such as sterite, dielectrics such as glass, semiconductors such as silicon and gallium nitride, and resin substrates can be used. Further, the treble velocity film includes aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon nitride, DLC film, diamond, a medium containing these materials as a main component, and a medium containing a mixture of these materials as a main component. Etc., various high-pitched sound velocity materials can be used.

Further, FIG. 2B is a cross-sectional view schematically showing an elastic wave resonator according to the first modification of the embodiment. In the elastic wave resonator 100 shown in FIG. 2A, an example in which the IDT electrode 54 is formed on the substrate 5 having the piezoelectric film 53 is shown, but the substrate on which the IDT electrode 54 is formed is shown in FIG. 2B. As described above, the piezoelectric single crystal substrate 57 made of a single layer of the piezoelectric layer may be used. The piezoelectric single crystal substrate 57 is composed of, for example, a piezoelectric single crystal of _{LiNbO 3.} The elastic wave resonator 100 according to this modification is _{composed of a piezoelectric single crystal substrate 57 of LiNbO 3} , an IDT electrode 54, and a protective layer 55 formed on the piezoelectric single crystal substrate 57 and the IDT electrode 54. ing.

The laminated structure, material, cut angle, and thickness of the piezoelectric film 53 and the piezoelectric single crystal substrate 57 described above may be appropriately changed according to the required passing characteristics of the elastic wave filter device and the like. _{Even an elastic wave resonator 100 using a LiTaO 3} piezoelectric substrate or the like having a cut angle other than the above-mentioned cut angle can exhibit the same effect as the elastic wave resonator 100 using the above-mentioned piezoelectric film 53. ..

Further, the substrate on which the IDT electrode 54 is formed may have a structure in which a support substrate, an energy confinement layer, and a piezoelectric film are laminated in this order. The IDT electrode 54 is formed on the piezoelectric film. Piezoelectric film, for example, LiTaO ₃ piezoelectric single crystal or piezoelectric ceramics are used. The support substrate is a substrate that supports the piezoelectric film, the energy confinement layer, and the IDT electrode 54.

The energy confinement layer is composed of one layer or a plurality of layers, and the velocity of the elastic bulk wave propagating in at least one of the layers is higher than the velocity of the elastic wave propagating in the vicinity of the piezoelectric film. For example, it may have a laminated structure of a low sound velocity layer and a high sound velocity layer. The low sound velocity layer is a film in which the sound velocity of the bulk wave in the low sound velocity layer is lower than the sound velocity of the elastic wave propagating in the piezoelectric film. The hypersonic layer is a film in which the sound velocity of the bulk wave in the hypersonic layer is higher than the sound velocity of the elastic wave propagating in the piezoelectric film. The support substrate may be a hypersonic layer.

Further, 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, an example (example) of the electrode parameters of the IDT electrode constituting the elastic wave resonator 100 will be described.

The wavelength of the elastic wave resonator is defined by the wavelength λ which is the repeating period of the plurality of electrode fingers 150a or 150b constituting the IDT electrode 54 shown in FIG. 2A (b). The electrode pitch is 1/2 of the wavelength λ, the line width of the electrode fingers 150a and 150b constituting the comb-shaped electrodes 100a and 100b is W, and the space width between the adjacent electrode fingers 150a and the electrode fingers 150b. Is defined as (W + S). Further, as shown in FIG. 2A (a), the crossing width L of the pair of comb-shaped electrodes 100a and 100b overlaps when viewed from the elastic wave propagation direction (X-axis direction) of the electrode finger 150a and the electrode finger 150b. The length of the electrode finger to be used. Further, the electrode duty of each elastic wave resonator is the line width occupancy of the plurality of electrode fingers 150a and 150b, and the ratio of the line width to the added value of the line width and the space width of the plurality of electrode fingers 150a and 150b. And is defined by W / (W + S). Further, the heights of the comb-shaped electrodes 100a and 100b are set to h. Hereinafter, parameters related to the shape of the IDT electrode of the elastic wave resonator, such as the wavelength λ, the crossover width L, the electrode duty, and the height h of the IDT electrode 54, are defined as electrode parameters.

[3 Operating principle of elastic wave filter]
Next, the operating principle of the ladder type elastic wave filter according to the present embodiment will be described.

FIG. 3 is a circuit configuration diagram for explaining the basic operating principle of the ladder type elastic wave filter and a graph showing frequency characteristics.

The elastic wave filter shown in FIG. 3A is a basic ladder type filter composed of one series arm resonator 16 and one parallel arm resonator 26. As shown in FIG. 3B, the parallel arm resonator 26 has a resonance frequency frp and an antiresonance frequency fap (> frp) in the resonance characteristics. Further, the series arm resonator 16 has a resonance frequency frs and an antiresonance frequency fas (> frs> frp) in the resonance characteristics.

In constructing a band path filter using a ladder type elastic wave resonator, generally, the anti-resonance frequency fap of the parallel arm resonator 26 and the resonance frequency frs of the series arm resonator 16 are brought close to each other. As a result, the vicinity of the resonance frequency frp where the impedance of the parallel arm resonator 26 approaches 0 becomes the low frequency side blocking region. Further, when the frequency is increased more than this, the impedance of the parallel arm resonator 26 becomes high in the vicinity of the antiresonance frequency fap, and the impedance of the series arm resonator 16 approaches 0 in the vicinity of the resonance frequency frs. As a result, in the vicinity of the anti-resonance frequency fap to the resonance frequency frs, a signal passing region is provided in the signal path from the input / output terminal 110 to the input / output terminal 120. This makes it possible to form a pass band that reflects the electrode parameters of the elastic wave resonator and the electromechanical coupling coefficient. Further, when the frequency becomes high and becomes near the anti-resonance frequency fas, the impedance of the series arm resonator 16 becomes high and becomes a high frequency side blocking region.

In a surface acoustic wave filter having the above operating principle, when a high frequency signal is input from the input / output terminal 110, a potential difference is generated between the input / output terminal 110 and the reference terminal, which distorts the piezoelectric layer and causes an elastic surface. Waves are generated. Here, by making the wavelength λ of the IDT electrode 54 substantially the same as the wavelength of the pass band, only the high frequency signal having the frequency component to be passed passes through the elastic wave filter.

The number of stages of the resonance stage composed of the parallel arm resonator and the series arm resonator is appropriately optimized according to the required specifications. Generally, when the elastic wave filter is configured by a plurality of resonance stages, the anti-resonance frequency fap of the plurality of parallel arm resonators and the resonance frequency frs of the plurality of series arm resonators are set in or near the passing band. Deploy. Further, the resonance frequency frp of the plurality of parallel arm resonators is arranged in the low frequency side blocking region, and the antiresonance frequency fas of the plurality of series arm resonators is arranged in the high frequency side blocking region.

According to the above operating principle of the ladder type elastic wave filter, the steepness of the low frequency side end of the pass band in the pass characteristic is the frequency difference between the resonance frequency frp and the anti-resonance frequency fap of one or more parallel arm resonators. It strongly depends on (resonance bandwidth). That is, the smaller the resonance bandwidth of one or more parallel arm resonators, the larger the slope of the straight line connecting the resonance frequency frp and the anti-resonance frequency fap (relative to the horizontal line), so that the low frequency of the pass band in the pass characteristics The steepness of the side end becomes high. Further, the steepness of the high frequency side end of the pass band in the pass characteristic strongly depends on the frequency difference (resonance bandwidth) between the resonance frequency frs and the anti-resonance frequency fas of one or more series arm resonators. That is, the smaller the resonance bandwidth of one or more series arm resonators, the larger the slope of the straight line connecting the resonance frequency frs and the anti-resonance frequency fas (with respect to the horizontal line). The steepness of the edge is high.

Further, the insertion loss of the low frequency side end portion in the pass band strongly depends on the Q value in the vicinity of the resonance frequency frp of one or more parallel arm resonators. Further, the insertion loss at the high frequency side end in the pass band strongly depends on the Q value in the vicinity of the antiresonance frequency fas of one or more series arm resonators. That is, the higher the Q value at the resonance frequency frp of one or more parallel arm resonators, the smaller the insertion loss at the low frequency side end in the pass band, and the higher the Q value at the resonance frequency fas of one or more series arm resonators. The higher the value, the smaller the insertion loss at the high frequency side end in the pass band.

That is, the higher the Q value at the resonance frequency frp of one or more parallel arm resonators and the higher the Q value at the anti-resonance frequency fas of one or more series arm resonators, the more the pass band shoulder drop (both ends of the pass band). Increase in the insertion loss of the part) is suppressed.

According to the operating principle of the basic elastic wave filter described above, the insertion loss and steepness of both ends of the pass band of the elastic wave filter 1 according to the present embodiment are determined by the series arm resonators s1, s2 and the parallel arm resonators. It is determined by adjusting the resonance frequency, anti-resonance frequency, resonance bandwidth, and Q value of p1 and p2, respectively.

[4 Resonance characteristics and passage characteristics of the elastic wave filter 1 according to the embodiment]
FIG. 4 is a graph showing the passing characteristics of the elastic wave filter 1 and the impedance characteristics of the series arm resonators s1 and s2 according to the embodiment. Note that FIG. 4 does not show the impedance characteristics of the parallel arm resonators p1 and p2.

In the elastic wave filter 1 according to the present embodiment, the resonance frequency frp1 of the parallel arm resonator p1 and the resonance frequency frp2 of the parallel arm resonator p2, which have the minimum impedance, are located in the low frequency side blocking region. Further, the anti-resonance frequency fap1 of the parallel arm resonator p1 having the maximum impedance and the anti-resonance frequency fap2 of the parallel arm resonator p2, and the resonance frequency frs1 and the series arm resonator of the series arm resonator s1 having the minimum impedance. The resonance frequency frs2 of s2 is located in the signal passing region of the passing band. Further, the anti-resonance frequency fas1 of the series arm resonator s1 and the anti-resonance frequency fas2 of the series arm resonator s2, which maximize the impedance, are located in the high frequency side blocking region.

Here, the anti-resonance frequency fas1 of the series arm resonator s1 is lower than the anti-resonance frequency fas2 of the series arm resonator s2. That is, among the one or more series arm resonators constituting the elastic wave filter 1, the series arm resonator s1 (first series arm resonator) has the lowest antiresonance frequency fas. Further, the series arm resonator s1 has an IDT electrode including a floating thinning electrode.

On the other hand, of the one or more series arm resonators constituting the elastic wave filter 1, the series arm resonator s2 has an IDT electrode including a polarity reversal thinning electrode.

The above-mentioned "one or more series arm resonators constituting the elastic wave filter 1" is a series arm resonator for forming a pass band of the elastic wave filter 1, and is an attenuation pole in a band away from the pass band. Does not include a series arm resonator that is placed only to form a. Specifically, the one or more series arm resonators constituting the elastic wave filter 1 are limited to the series arm resonators whose resonance frequency frs is located in or near the pass band of the elastic wave filter 1.

Although not shown, the resonance frequency frp1 of the parallel arm resonator p1 is higher than the resonance frequency frp2 of the parallel arm resonator p2. That is, among the one or more parallel arm resonators constituting the elastic wave filter 1, the parallel arm resonator p1 (first parallel arm resonator) has the highest resonance frequency frp. Further, the parallel arm resonator p1 has an IDT electrode including a polarity reversal thinning electrode.

On the other hand, the parallel arm resonator p2 of the one or more parallel arm resonators constituting the elastic wave filter 1 has an IDT electrode including a floating thinning electrode.

The above-mentioned "one or more parallel arm resonators constituting the elastic wave filter 1" is a parallel arm resonator for forming a pass band of the elastic wave filter 1, and is an attenuation pole in a band away from the pass band. Does not include parallel arm resonators arranged only to form. Specifically, the one or more parallel arm resonators constituting the elastic wave filter 1 are limited to parallel arm resonators whose anti-resonance frequency fap is located in or near the pass band of the elastic wave filter 1.

Further, the electrode finger configurations of the thinning electrodes exemplified by the floating thinning electrode and the polarity reversal thinning electrode will be described later with reference to FIGS. 5A to 5C, and the resonance characteristics of the thinning electrode will be described with reference to FIGS. 6A to 6C. To do.

In a ladder type elastic wave filter composed of one or more series arm resonators and one or more parallel arm resonators, in order to improve the steepness at the end of the passband and the insertion loss at the inner end of the passband. A so-called thinning electrode is applied to the IDT electrode constituting each resonator in order to reduce the problem (suppress the shoulder drop in the pass band).

In the elastic wave filter 1 according to the present embodiment, the steepness of the high frequency side end of the passband is greatly affected by the resonance characteristics of the series arm resonators s1 and s2 in the vicinity of the antiresonance frequency fas. When a thinning electrode is applied to the IDT electrodes of the series arm resonators s1 and s2 in order to improve the steepness at the end of the passing band, the resonance bandwidth and the resonance point and the anti-resonance point are affected by the electrode finger structure of the thinning electrode. The mode of change of the resonance Q value in is different. In both the floating thinning electrode and the polarity reversal thinning electrode, the resonance bandwidth (specific band) becomes narrower as the thinning ratio increases. Further, in the floating thinning electrode, the Q value decrease at the resonance point is large as the thinning rate increases, but the Q value decrease at the antiresonance point is small. On the other hand, in the polarity reversal thinning electrode, the decrease in the Q value at the antiresonance point is large as the thinning rate increases, but the decrease in the Q value at the resonance point is small.

According to the above configuration, a floating thinning electrode having a small decrease in Q value at the antiresonance point is applied to the IDT electrode of the series arm resonator s1 having the lowest antiresonance frequency fas among the series arm resonators s1 and s2. As a result, the steepness on the high frequency side of the pass band is improved mainly by the resonance characteristics near the antiresonance point of the series arm resonator s1, and the insertion loss at the high frequency side end in the pass band is mainly caused by the series arm resonator s1. It is improved by the Q value characteristic near the anti-resonance point. Further, a polarity reversal thinning electrode having a small decrease in Q value at the resonance point is applied to the series arm resonator s2. This makes it possible to suppress the deterioration of the insertion loss near the center in the pass band. That is, all the series arm resonators other than the series arm resonator s1 among one or more series arm resonators may have an IDT electrode including a polarity reversal thinning electrode.

Further, among the parallel arm resonators p1 and p2, a polarity reversal thinning electrode having a small decrease in Q value at the resonance point is applied to the IDT electrode of the parallel arm resonator p1 having the highest resonance frequency frp. As a result, the steepness on the low frequency side of the pass band is improved mainly by the resonance characteristics near the resonance point of the parallel arm resonator p1, and the insertion loss at the low frequency side end in the pass band is mainly increased by the parallel arm resonator p1. It is improved by the Q value characteristic near the resonance point of. Further, a floating thinning electrode having a small decrease in Q value at the antiresonance point is applied to the parallel arm resonator p2. This makes it possible to suppress the deterioration of the insertion loss near the center in the pass band. That is, all the parallel arm resonators other than the parallel arm resonator p1 among one or more parallel arm resonators may have an IDT electrode including a floating thinning electrode.

Therefore, it is possible to improve the steepness of the end of the pass band while reducing the insertion loss in the pass band of the elastic wave filter 1.

As the elastic wave filter according to the second modification of the present embodiment, the anti-resonance frequency fas1 of the series arm resonator s1 including the floating thinning electrode is not the lowest among the one or more series arm resonators s1 and s2. You may. As a result, as compared with the conventional example in which none of the one or more series arm resonators s1 and s2 includes the floating thinning electrode, the series arm resonator s1 includes the floating thinning electrode, so that the passband is steeper on the high frequency side. It is possible to improve the property and improve the insertion loss of the high frequency side end portion in the pass band. That is, at least one of the one or more series arm resonators may have an IDT electrode including a floating thinning electrode.

Further, the resonance frequency frp1 of the parallel arm resonator p1 including the polarity reversal thinning electrode does not have to be the highest among the one or more parallel arm resonators p1 and p2. Also in this case, as compared with the conventional example in which none of the one or more parallel arm resonators p1 and p2 includes the polarity reversal thinning electrode, the parallel arm resonator p1 includes the polarity reversal thinning electrode, so that the passband has a low frequency. The steepness of the side can be improved, and the insertion loss of the low frequency side end portion in the pass band can be improved. That is, at least one of the one or more parallel arm resonators may have an IDT electrode including a polarity reversal thinning electrode.

Further, all of one or more series arm resonators s1 and s2 may include a floating thinning electrode. As a result, as compared with the conventional example in which none of the one or more series arm resonators s1 and s2 includes the floating thinning electrode, the series arm resonators s1 and s2 include the floating thinning electrode, so that the passband high frequency side The steepness of the is improved, and the insertion loss at the high frequency side end in the pass band can be improved. Further, all of one or more parallel arm resonators p1 and p2 may include a polarity reversal thinning electrode. Also in this case, as compared with the conventional example in which none of the one or more parallel arm resonators p1 and p2 includes the polarity reversal thinning electrode, the parallel arm resonators p1 and p2 include the polarity reversal thinning electrode, so that the pass band The steepness on the low frequency side can be improved, and the insertion loss at the low frequency side end in the pass band can be improved.

Further, the series arm resonator s1 does not have to include the floating thinning electrode, and the series arm resonator s2 does not have to include the thinning electrode. As a result, as compared with the conventional example in which none of the one or more series arm resonators s1 and s2 includes the floating thinning electrode, the series arm resonator s1 includes the floating thinning electrode, so that the passband is steeper on the high frequency side. It is possible to improve the property and improve the insertion loss of the high frequency side end portion in the pass band. That is, one of the one or more series arm resonators has an IDT electrode including a floating thinning electrode, and the other series arm resonators do not have to include the thinning electrode.

Further, the parallel arm resonator p1 does not have to include the polarity reversal thinning electrode, and the parallel arm resonator p2 does not have to include the thinning electrode. Also in this case, as compared with the conventional example in which none of the one or more parallel arm resonators p1 and p2 includes the polarity reversal thinning electrode, the parallel arm resonator p1 includes the polarity reversal thinning electrode, so that the passband has a low frequency. The steepness of the side can be improved, and the insertion loss of the low frequency side end portion in the pass band can be improved. That is, one of the one or more parallel arm resonators has an IDT electrode including a polarity reversal thinning electrode, and the other parallel arm resonators do not have to include the thinning electrode.

In the following, the structures of the thinned-out electrodes of the series arm resonators s1 and s2 and the parallel arm resonators p1 and p2 will be illustrated.

[5 Electrode finger structure of thinned electrodes]
Hereinafter, the electrode finger structure of the IDT electrode including the thinned electrode will be illustrated with reference to FIGS. 5A to 5C.

FIG. 5A is a schematic plan view showing the configuration of the IDT electrode including the floating thinning electrode. FIG. 5B is a schematic plan view showing the configuration of the IDT electrode including the polarity reversal thinning electrode. FIG. 5C is a schematic plan view showing the configuration of the IDT electrode including the filled thinning electrode.

FIG. 5A exemplifies a planar drawing showing the IDT electrode structure of the elastic wave resonator 101 including the floating thinning electrode. The elastic wave resonator 101 shown in FIG. 5A is for explaining a typical structure of a floating thinned-out electrode, and the number and length of electrode fingers constituting the electrode are limited thereto. Not done.

The elastic wave resonator 101 is composed of a substrate 5 having piezoelectricity, comb-shaped electrodes 101a and 101b formed on the substrate 5, and a reflector 141.

As shown in FIG. 5A, the comb-shaped electrode 101a is composed of a plurality of electrode fingers 151a parallel to each other and a bus bar electrode 161a connecting one ends of the plurality of electrode fingers 151a. Further, the comb-shaped electrode 101b is composed of a plurality of electrode fingers 151b parallel to each other and a bus bar electrode 161b connecting one ends of the plurality of electrode fingers 151b to each other. The plurality of electrode fingers 151a and 151b are formed along a direction orthogonal to the surface acoustic wave propagation direction (X-axis direction). The comb-shaped electrodes 101a and 101b are arranged so that the plurality of electrode fingers 151a and 151b are opposed to each other so as to be interleaved with each other. That is, the IDT electrode of the elastic wave resonator 101 has a pair of comb-shaped electrodes 101a and 101b.

The comb-shaped electrode 101a has dummy electrodes arranged so as to face each other in the longitudinal direction of the plurality of electrode fingers 151b, but the dummy electrodes may not be present. Further, the comb-shaped electrode 101b has dummy electrodes arranged so as to face each other in the longitudinal direction of the plurality of electrode fingers 151a, but the dummy electrodes may not be present. Further, the comb-shaped electrodes 101a and 101b may be so-called inclined IDT electrodes in which the extending direction of the bus bar electrode is inclined with respect to the surface acoustic wave propagation direction, and also have a so-called piston structure. May be good.

The reflector 141 is composed of a plurality of electrode fingers parallel to each other and a bus bar electrode connecting the plurality of electrode fingers, and is arranged at both ends of the pair of comb-shaped electrodes 101a and 101b.

As shown in FIG. 2A (b), the IDT electrode composed of the pair of comb-shaped electrodes 101a and 101b has a laminated structure of the adhesion layer 540 and the main electrode layer 542. Not limited.

Here, the electrode fingers 152 are discretely formed on the IDT electrode of the elastic wave resonator 101. The electrode finger 152 is a floating thinning electrode that is not connected to any of the bus bar electrodes 161a and 161b and is arranged parallel to and at the same pitch as the plurality of electrode fingers 151a and 151b. Further, a plurality of electrode fingers 151a and 151b are arranged between two adjacent electrode fingers 152. That is, the pitch of the electrode fingers 152 is larger than the pitch of the plurality of electrode fingers 151a and 151b.

Here, the thinning rate of the IDT electrode having the floating thinning electrode is defined. The thinning ratio of the IDT electrodes in the elastic wave resonator 101 is such that the number of electrode fingers 152 in the IDT electrode is M, the adjacent pair of electrode fingers 151a and 151b is a pair of electrode fingers, and the electrode fingers 152 are not applied. When the number of pairs of IDT electrodes is N when only the electrode fingers 151a and 151b are repeated, it is represented by the following equation 1.

Thinning rate = M / {2 (NM) + 1} (Equation 1)

FIG. 5B illustrates a planar diagram showing the IDT electrode structure of the elastic wave resonator 201 including the polarity reversal thinning electrode. The elastic wave resonator 201 shown in FIG. 5B is for explaining a typical structure of a polarity reversal thinning electrode, and the number and length of electrode fingers constituting the electrode are included in this. Not limited.

The elastic wave resonator 201 is composed of a piezoelectric substrate 5, comb-shaped electrodes 201a and 201b formed on the substrate 5, and a reflector 241.

As shown in FIG. 5B, the comb-shaped electrode 201a is composed of a plurality of electrode fingers 251a parallel to each other and a bus bar electrode 261a connecting one ends of the plurality of electrode fingers 251a. Further, the comb-shaped electrode 201b is composed of a plurality of electrode fingers 251b parallel to each other and a bus bar electrode 261b connecting one ends of the plurality of electrode fingers 251b to each other. The plurality of electrode fingers 251a and 251b are formed along a direction orthogonal to the surface acoustic wave propagation direction (X-axis direction). The comb-shaped electrodes 201a and 201b are arranged so that the plurality of electrode fingers 251a and 251b are opposed to each other so as to be interleaved with each other. That is, the IDT electrode of the elastic wave resonator 201 has a pair of comb-shaped electrodes 201a and 201b.

The comb-shaped electrode 201a has dummy electrodes arranged so as to face each other in the longitudinal direction of the plurality of electrode fingers 251b, but the dummy electrodes may not be present. Further, the comb-shaped electrode 201b has dummy electrodes arranged so as to face each other in the longitudinal direction of the plurality of electrode fingers 251a, but the dummy electrodes may not be present. Further, the comb-shaped electrodes 201a and 201b may be so-called inclined IDT electrodes in which the extending direction of the bus bar electrode is inclined with respect to the surface acoustic wave propagation direction, and also have a so-called piston structure. May be good.

The reflector 241 is composed of a plurality of electrode fingers parallel to each other and a bus bar electrode connecting the plurality of electrode fingers, and is arranged at both ends of the pair of comb-shaped electrodes 201a and 201b.

As shown in FIG. 2A (b), the IDT electrode composed of the pair of comb-shaped electrodes 201a and 201b has a laminated structure of the adhesion layer 540 and the main electrode layer 542. Not limited.

Here, the electrode fingers 252 are discretely formed on the IDT electrode of the elastic wave resonator 201. The electrode finger 252 is a polarity reversal thinning electrode connected to the same bus bar electrode to which the electrode fingers on both sides are connected among all the electrode fingers constituting the pair of comb-shaped electrodes 201a and 201b. Further, a plurality of electrode fingers 251a and 251b are arranged between two adjacent electrode fingers 252. That is, the pitch of the electrode fingers 252 is larger than the pitch of the plurality of electrode fingers 251a and 251b.

Here, the thinning rate of the IDT electrode having the polarity reversal thinning electrode is defined. The thinning ratio of the IDT electrodes in the elastic wave resonator 201 is such that the number of electrode fingers 252 in the IDT electrode is M, a pair of adjacent electrode fingers 251a and 251b are used as a pair of electrode fingers, and the electrode fingers 252 are not applied. When the number of pairs of IDT electrodes is N in the case where only the electrode fingers 251a and 251b are repeated, it is represented by the above formula 1.

FIG. 5C exemplifies a planar drawing showing the IDT electrode structure of the elastic wave resonator 301 including the filled thinning electrode. The elastic wave resonator 301 shown in FIG. 5C is for explaining a typical structure of a filled thinning electrode, and the number and length of electrode fingers constituting the electrode are limited thereto. Not done.

The elastic wave resonator 301 is composed of a piezoelectric substrate 5, comb-shaped electrodes 301a and 301b formed on the substrate 5, and a reflector 341.

As shown in FIG. 5C, the comb-shaped electrode 301a is composed of a plurality of electrode fingers 351a parallel to each other and a bus bar electrode 361a connecting one ends of the plurality of electrode fingers 351a. Further, the comb-shaped electrode 301b is composed of a plurality of electrode fingers 351b parallel to each other and a bus bar electrode 361b connecting one ends of the plurality of electrode fingers 351b to each other. The plurality of electrode fingers 351a and 351b are formed along a direction orthogonal to the surface acoustic wave propagation direction (X-axis direction). The comb-shaped electrodes 301a and 301b are arranged so that the plurality of electrode fingers 351a and 351b are opposed to each other so as to be interleaved with each other. That is, the IDT electrode of the elastic wave resonator 301 has a pair of comb-shaped electrodes 301a and 301b.

The comb-shaped electrode 301a has dummy electrodes arranged so as to face each other in the longitudinal direction of the plurality of electrode fingers 351b, but the dummy electrodes may not be present. Further, the comb-shaped electrode 301b has dummy electrodes arranged so as to face each other in the longitudinal direction of the plurality of electrode fingers 351a, but the dummy electrodes may not be present. Further, the comb-shaped electrodes 301a and 301b may be so-called inclined IDT electrodes in which the extending direction of the bus bar electrode is inclined with respect to the surface acoustic wave propagation direction, and also have a so-called piston structure. May be good.

The reflector 341 is composed of a plurality of electrode fingers parallel to each other and a bus bar electrode connecting the plurality of electrode fingers, and is arranged at both ends of the pair of comb-shaped electrodes 301a and 301b.

As shown in FIG. 2A (b), the IDT electrode composed of the pair of comb-shaped electrodes 301a and 301b has a laminated structure of the adhesion layer 540 and the main electrode layer 542. Not limited.

Here, electrode fingers 352 are discretely formed on the IDT electrode of the elastic wave resonator 301. The electrode finger 352 is an electrode finger having the maximum electrode finger width in the IDT electrode of the elastic wave resonator 301, and has an electrode finger width that is at least twice the average electrode finger width in the electrode fingers excluding the electrode finger 352. It is a filled thinning electrode. In other words, in the electrode finger 352, the space between the adjacent electrode fingers 351a and 351b and the adjacent electrode fingers 351a and 351b is combined into one electrode finger, and any one of the bus bar electrodes 361a and 361b. It is a filled thinning electrode which is connected to and has a wider electrode finger width than a plurality of electrode fingers 351a and 351b. Further, a plurality of electrode fingers 351a and 351b are arranged between two adjacent electrode fingers 352. That is, the pitch of the electrode fingers 352 is larger than the pitch of the plurality of electrode fingers 351a and 351b.

Here, the thinning rate of the IDT electrode having the filled thinning electrode is defined. The thinning ratio of the IDT electrodes in the elastic wave resonator 301 is such that the number of electrode fingers 352 in the IDT electrode is M, a pair of adjacent electrode fingers 351a and 351b are used as a pair of electrode fingers, and the electrode fingers 352 are not applied. When the logarithm of the IDT electrode is N in the case where only the electrode fingers 351a and 351b are repeated, it is represented by the above formula 1.

[Resonance characteristics of elastic wave resonators with 6 thinned electrodes]
FIG. 6A shows the impedance ((a) of FIG. 6A) and Q of the elastic wave resonator including the floating thinning electrode when the thinning rate is changed (thinning rate: 0%, 4%, 7%, 14%). It is a graph which shows the value ((b) of FIG. 6A). FIG. 6B shows the impedance ((a) of FIG. 6B) of the elastic wave resonator including the polarity reversal thinning electrode when the thinning rate is changed (thinning rate: 0%, 4%, 7%, 14%). It is a graph which shows the Q value ((b) of FIG. 6B). FIG. 6C shows the impedance ((a) of FIG. 6C) and Q of the elastic wave resonator including the filled thinning electrode when the thinning rate is changed (thinning rate: 0%, 4%, 7%, 14%). It is a graph which shows the value ((b) of FIG. 6C).

As shown in FIG. 6A (a), the impedance showing the resonance characteristic of the elastic wave resonator 101 has a minimum value approaching 0 at the resonance frequency fr and a maximum value approaching infinity at the antiresonance frequency fa. Here, as the thinning rate of the floating thinning electrode increases, the resonance frequency fr shifts to the high frequency side. On the other hand, the anti-resonance frequency fa does not change due to the change in the thinning rate of the floating thinning electrode. Therefore, as the thinning ratio of the floating thinning electrode increases, the resonance bandwidth, which is the frequency difference between the resonance frequency fr and the antiresonance frequency fa, becomes narrower.

On the other hand, as shown in FIG. 6A (b), the Q value of the elastic wave resonator 101 decreases as the thinning ratio of the floating thinning electrode increases, but the decrease in the Q value near the anti-resonance frequency fa is relatively large. It is small, and the decrease in Q value near the resonance frequency fr is relatively large.

Further, as shown in FIG. 6B (a), the impedance showing the resonance characteristic of the elastic wave resonator 201 has a minimum value approaching 0 at the resonance frequency fr and a maximum value approaching infinity at the antiresonance frequency fa. .. Here, the resonance frequency fr does not change substantially due to the change in the thinning rate of the polarity reversal thinning electrode. On the other hand, as the thinning rate of the polarity reversal thinning electrode increases, the antiresonance frequency fa shifts to the low frequency side. Therefore, as the thinning ratio of the polarity reversal thinning electrode increases, the resonance bandwidth, which is the frequency difference between the resonance frequency fr and the antiresonance frequency fa, becomes narrower.

On the other hand, as shown in FIG. 6B (b), the Q value of the elastic wave resonator 201 decreases as the thinning ratio of the polarity reversal thinning electrode increases, but the decrease in the Q value near the resonance frequency fr is relatively large. It is small, and the decrease in Q value near the anti-resonance frequency fa is relatively large.

Further, as shown in FIG. 6C (a), the impedance showing the resonance characteristic of the elastic wave resonator 301 has a minimum value approaching 0 at the resonance frequency fr and a maximum value approaching infinity at the antiresonance frequency fa. .. Here, as the thinning rate of the filled thinning electrode increases, the resonance frequency fr shifts to the high frequency side. On the other hand, as the thinning rate of the filled thinning electrode increases, the antiresonance frequency fa shifts to the low frequency side. Therefore, as the thinning ratio of the filled thinning electrode increases, the resonance bandwidth, which is the frequency difference between the resonance frequency fr and the antiresonance frequency fa, becomes narrower.

On the other hand, as shown in FIG. 6C (b), the Q value of the elastic wave resonator 301 decreases as the thinning ratio of the filled thinning electrode increases, and the decrease in the Q value near the resonance frequency fr is relatively large. The decrease in the Q value near the anti-resonance frequency fa is also relatively large.

As described above, when the electrode finger structure of the thinning electrode is different, the resonance bandwidth and the change mode of the Q value at the resonance frequency fr and the antiresonance frequency fa are different.

FIG. 7 is a graph showing the reflection loss at the resonance point ((a) in FIG. 7) and the antiresonance point ((b) in FIG. 7) when the specific band of the elastic wave resonator is changed. The vertical axis in FIG. 7A shows the reflection loss of the elastic wave resonator at the antiresonance point, and the vertical axis in FIG. 7B shows the reflection loss of the elastic wave resonator at the resonance point. .. Further, although the horizontal axis in FIGS. 7A and 7 indicates the specific band (resonance bandwidth divided by the resonance frequency), it can be converted into a thinning rate. In this case, the larger the specific band, the smaller the thinning rate.

From (a) of FIG. 7, the smaller the specific band (the larger the thinning ratio), the larger the reflection loss at the antiresonance point of the elastic wave resonator including the polarity reversal thinning electrode and the elastic wave resonator including the filled thinning electrode. Become. On the other hand, the reflection loss at the antiresonance point of the elastic wave resonator including the floating thinning electrode does not change even if the specific band becomes small (the thinning ratio becomes large).

Further, from FIG. 7B, the smaller the specific band (the larger the thinning rate), the larger the reflection loss at the resonance point of the elastic wave resonator including the floating thinning electrode, the polarity reversal thinning electrode, or the filled thinning electrode. Become. However, the reflection loss at the resonance point of the elastic wave resonator including the polarity reversal thinning electrode is smaller than the reflection loss at the resonance point of the elastic wave resonator including the floating thinning electrode or the filled thinning electrode.

From (a) and (b) of FIG. 7, in the elastic wave filter 1 according to the present embodiment, the resonance bandwidth is narrowed by applying the floating thinning electrode to the series arm resonator s1, and the passband high frequency side is narrowed. It is possible to improve the steepness of the end portion and reduce the reflection loss near the anti-resonance point to reduce the insertion loss of the high frequency side end portion in the pass band. Further, by applying the polarity reversal thinning electrode to the series arm resonator s2, it is possible to reduce the reflection loss near the resonance point and reduce the insertion loss near the center of the pass band.

Further, from (a) and (b) of FIG. 7, in the elastic wave filter 1 according to the present embodiment, the resonance bandwidth is narrowed and passed by applying the polarity reversal thinning electrode to the parallel arm resonator p1. It is possible to improve the steepness of the low frequency side end of the band and reduce the reflection loss near the resonance point to reduce the insertion loss of the low frequency side end in the pass band. Further, by applying the floating thinning electrode to the parallel arm resonator p2, it is possible to reduce the reflection loss near the antiresonance point and reduce the insertion loss near the center of the pass band.

That is, according to the elastic wave filter 1 according to the present embodiment, it is possible to provide an elastic wave filter having improved steepness while suppressing shoulder drop at both ends in the pass band (ensuring low loss). It becomes.

[7 Circuit configuration, passage characteristics, and resonance characteristics of the elastic wave filter 1A according to the embodiment]
FIG. 8 is a circuit configuration diagram of the elastic wave filter 1A according to the embodiment. The elastic wave filter 1A according to the embodiment is an example of the elastic wave filter 1 according to the embodiment, and has a series arm resonator and a parallel arm resonator as compared with the elastic wave filter 1 according to the embodiment. The numbers are different.

As shown in FIG. 8, the elastic wave filter 1A includes series arm resonators 11, 12, 13, 14 and 15, parallel arm resonators 21, 22, 23 and 24, and input / output terminals 110 and 120. Be prepared.

Each of the series arm resonators 11, 12, 13, 14 and 15 is an elastic wave resonator arranged on a path connecting the input / output terminal 110 and the input / output terminal 120 and connected in series with each other. Further, each of the parallel arm resonators 21 to 24 is an elastic wave resonator arranged between the node on the path and the ground.

With the above configuration, the elastic wave filter 1A constitutes a ladder type bandpass filter.

Each of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 24 may be composed of a plurality of divided resonators.

The split resonator is arranged for the purpose of improving the power resistance of the SAW filter 1A and suppressing intermodulation distortion. By configuring one elastic wave resonator having a capacitive impedance with two divided resonators connected in series, a large area of the IDT electrode can be secured. As a result, the current densities of the two split resonators can be reduced with respect to the current densities of the one elastic wave resonator, so that the power resistance of the elastic wave filter 1A can be improved and the intermodulation distortion can be suppressed. ..

Further, the mode of ground connection of the parallel arm resonators 21 to 24 is appropriately determined according to the required damping characteristics.

Table 1 shows the thinned electrode configurations of the elastic wave filters according to Examples, Comparative Example 1 and Comparative Example 2. The elastic wave filters according to Comparative Example 1 and Comparative Example 2 each have the same circuit configuration as the circuit configuration of the elastic wave filter 1A shown in FIG. 8, but the elastic wave filter 1A according to the embodiment has the same circuit configuration. The electrode finger configuration of the thinned-out electrode is different from that of the thinned-out electrode.

As shown in Table 1, in the elastic wave filter 1A according to the embodiment, all of the series arm resonators 11 to 15 include a floating thinning electrode, and all of the parallel arm resonators 21 to 24 include a polarity reversal thinning electrode. There is.

Further, in the elastic wave filter according to Comparative Example 1, all of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 24 include polarity reversal thinning electrodes. Further, in the elastic wave filter according to Comparative Example 2, all of the series arm resonators 11 to 15 and the parallel arm resonators 21 to 24 include a floating thinning electrode.

The thinning rate of each resonator including the thinning electrode shown in Table 1 is 7%.

FIG. 9 is a graph comparing the insertion loss in the pass band of the elastic wave filter according to Example, Comparative Example 1 and Comparative Example 2.

As shown in FIG. 9A, the elastic wave filter 1A according to the present embodiment has a high frequency side end (Hch) inserted in the pass band as compared with the elastic wave filter according to Comparative Example 1. The loss is reduced. Further, as shown in FIG. 9B, the elastic wave filter 1A according to the present embodiment has a low frequency side end portion (L-ch) in the pass band as compared with the elastic wave filter according to the comparative example 2. ) Insertion loss is reduced.

This is because the elastic wave filter 1A according to the present embodiment uses a floating thinning electrode as the series arm resonators 11 to 15 having a small reflection loss near the anti-resonance point as compared with the elastic wave filter according to the comparative example 1. , It is understood that the insertion loss at the high frequency side end in the pass band has been improved.

Further, in the elastic wave filter 1A according to the present embodiment, a polarity reversal thinning electrode having a small reflection loss near the resonance point is applied as the parallel arm resonators 21 to 24 as compared with the elastic wave filter according to the comparative example 2. Therefore, it is understood that the insertion loss at the low frequency side end in the pass band has been improved.

According to the elastic wave filter 1A according to the present embodiment, a floating thinning electrode having a small decrease in the Q value of the anti-resonance point is applied as the series arm resonators 11 to 15, and the Q value of the resonance point is applied as the parallel arm resonators 21 to 24. A polarity reversal thinning electrode with a small decrease is applied. As a result, the steepness on the high frequency side of the passband and the insertion loss at the high frequency side end in the passband are improved by the resonance characteristics near the anti-resonance points of the series arm resonators 11 to 15, and the steepness on the low frequency side of the passband is improved. It is possible to improve the property and the insertion loss of the low frequency side end portion in the pass band by the resonance characteristics in the vicinity of the resonance points of the parallel arm resonators 21 to 24. Therefore, it is possible to improve the steepness of the end of the pass band while reducing the insertion loss in the pass band of the SAW filter 1A.

In the elastic wave filter 1A, the series arm resonator having the lowest antiresonance frequency among the series arm resonators 11 to 15 may have the largest thinning rate. This makes it possible to effectively improve the steepness on the high frequency side of the pass band.

Further, in the series arm resonators 11 to 15, the higher the anti-resonance frequency of the series arm resonator, the smaller the thinning rate may be. As a result, the series arm resonator having a large thinning rate can effectively improve the steepness on the high frequency side of the pass band, and the series arm resonator having a small thinning rate can suppress the deterioration of the insertion loss near the center of the pass band.

Further, in the elastic wave filter 1A, the parallel arm resonator having the highest resonance frequency among the parallel arm resonators 21 to 24 may have the largest thinning rate. This makes it possible to effectively improve the steepness on the low frequency side of the pass band.

Further, the lower the resonance frequency of the parallel arm resonators 21 to 24, the smaller the thinning rate may be. As a result, the parallel arm resonator with a large thinning rate can effectively improve the steepness on the low frequency side of the passband, and the parallel arm resonator with a small thinning rate can suppress the deterioration of the insertion loss near the center of the passband. ..

In an elastic wave resonator including a floating thinning electrode or a polarity reversal thinning electrode, the resonance bandwidth (specific band), which is the difference between the resonance frequency and the anti-resonance frequency, becomes smaller as the thinning ratio increases, and as the thinning ratio increases. The Q value at the resonance point and the anti-resonance point decreases. From this point of view, the larger the thinning ratio of the series arm resonator, the smaller the resonance bandwidth of the series arm resonator, so that the steepness of the high frequency side end of the passing band can be improved, and the thinning ratio of the series arm resonator can be improved. The smaller the value, the more the Q value decrease at the resonance point of the series arm resonator can be suppressed, so that the deterioration of the insertion loss in the passing band can be suppressed. Further, the larger the thinning ratio of the parallel arm resonator is, the smaller the resonance bandwidth of the parallel arm resonator can be, so that the steepness of the low frequency side end of the passing band can be improved, and the thinning ratio of the parallel arm resonator can be improved. The smaller the value, the more the Q value decrease at the anti-resonance point of the parallel arm resonator can be suppressed, so that the deterioration of the insertion loss in the passing band can be suppressed. Therefore, it is possible to improve the steepness of the end of the pass band while reducing the insertion loss in the pass band of the SAW filter 1A.

[8 effects, etc.]
The elastic wave filter 1 according to the present embodiment is arranged between one or more series arm resonators s1 and s2 arranged on the path connecting the input / output terminals 110 and 120, and the node and the ground on the path. The series arm resonators s1 and s2 and the parallel arm resonators p1 and p2 are provided with one or more parallel arm resonators p1 and p2, and the parallel arm resonators p1 and p2 have an IDT electrode formed on a piezoelectric substrate. Including children. The IDT electrode has a pair of comb-shaped electrodes composed of a plurality of electrode fingers and a bus bar electrode, and among the plurality of electrode fingers, an electrode finger not connected to any of the bus bar electrodes constituting the pair of comb-shaped electrodes. It is defined as a floating thinning electrode, and among all the electrode fingers constituting the pair of comb-shaped electrodes, the electrode finger connected to the same bus bar electrode as the bus bar electrode to which the electrode fingers on both sides are connected is defined as the polarity reversal thinning electrode. At this time, at least one of the series arm resonators s1 and s2 has an IDT electrode including a floating thinning electrode, and at least one of the parallel arm resonators p1 and p2 has an IDT electrode including a polarity reversal thinning electrode. ..

According to this, a floating thinning electrode having a small decrease in Q value at the antiresonance point is applied to the IDT electrode of at least one series arm resonator s1 of one or more series arm resonators. As a result, the steepness on the high frequency side of the pass band is improved mainly by the resonance characteristics near the antiresonance point of the series arm resonator s1, and the insertion loss at the high frequency side end in the pass band is mainly caused by the series arm resonator s1. It is improved by the Q value characteristic near the anti-resonance point. Further, a polarity reversal thinning electrode having a small decrease in Q value at the resonance point is applied to the IDT electrode of at least one parallel arm resonator p1 of one or more parallel arm resonators. As a result, the steepness on the low frequency side of the pass band is improved mainly by the resonance characteristics near the resonance point of the parallel arm resonator p1, and the insertion loss at the low frequency side end in the pass band is mainly increased by the parallel arm resonator p1. It is improved by the Q value characteristic near the resonance point of. Therefore, it is possible to improve the steepness of the end of the pass band while reducing the insertion loss in the pass band of the SAW filter 1.

Further, the first series arm resonator having the lowest antiresonance frequency among one or more series arm resonators may have an IDT electrode including a floating thinning electrode.

According to this, the first series arm resonator having the lowest antiresonance frequency among one or more series arm resonators reduces the insertion loss at the high frequency side end in the pass band and steepness on the high frequency side in the pass band. It has the strongest effect on sex. Therefore, the insertion loss of the high frequency side end portion in the pass band of the elastic wave filter 1 can be effectively reduced, and the steepness on the high frequency side of the pass band can be effectively improved.

Further, the first series arm resonator may have the largest thinning rate among one or more series arm resonators.

This makes it possible to effectively improve the steepness on the high frequency side of the pass band.

Further, among one or more series arm resonators, the higher the anti-resonance frequency of the series arm resonator, the smaller the thinning rate may be.

As a result, the series arm resonator with a large thinning rate can effectively improve the steepness on the high frequency side of the pass band, and the series arm resonator with a small thinning rate can suppress the deterioration of the insertion loss near the center of the pass band.

Further, all the series arm resonators other than the first series arm resonator among one or more series arm resonators may have an IDT electrode including a polarity reversal thinning electrode.

According to this, as all the series arm resonators except the first series arm resonator, the polarity reversal thinning electrode having a small decrease in Q value near the resonance point is applied, so that the insertion loss near the center in the pass band deteriorates. Can be suppressed.

Further, all the series arm resonators may have an IDT electrode including a floating thinning electrode.

As a result, as compared with the conventional example in which none of the one or more series arm resonators includes the floating thinning electrode, all the series arm resonators include the floating thinning electrode, so that the steepness on the high frequency side of the pass band is improved. It is possible to improve the insertion loss of the high frequency side end portion in the pass band.

Further, the first parallel arm resonator having the highest resonance frequency among one or more parallel arm resonators may have an IDT electrode including a polarity reversal thinning electrode.

According to this, the first parallel arm resonator having the highest resonance frequency among one or more parallel arm resonators reduces the insertion loss at the low frequency side end in the pass band and reduces the insertion loss on the low frequency side of the pass band. It has the strongest effect on steepness. Therefore, the insertion loss of the low frequency side end portion in the pass band of the elastic wave filter 1 can be effectively reduced, and the steepness on the low frequency side of the pass band can be effectively improved.

Further, the first parallel arm resonator may have the largest thinning rate among one or more parallel arm resonators.

This makes it possible to effectively improve the steepness on the low frequency side of the pass band.

Further, among one or more parallel arm resonators, the lower the resonance frequency of the parallel arm resonators, the smaller the thinning rate may be.

As a result, the parallel arm resonator with a large thinning rate can effectively improve the steepness on the low frequency side of the passband, and the parallel arm resonator with a small thinning rate can suppress the deterioration of the insertion loss near the center of the passband. ..

Further, all the parallel arm resonators other than the first parallel arm resonator among one or more parallel arm resonators may have an IDT electrode including a floating thinning electrode.

According to this, as all the parallel arm resonators except the first parallel arm resonator, a floating thinning electrode having a small decrease in Q value near the antiresonance point is applied, so that the insertion loss near the center in the pass band deteriorates. Can be suppressed.

Further, all parallel arm resonators may have an IDT electrode including a polarity reversal thinning electrode.

As a result, as compared with the conventional example in which none of the one or more parallel arm resonators includes the polarity reversal thinning electrode, all the parallel arm resonators include the polarity reversal thinning electrode, so that the pass band is steeper on the low frequency side. It is possible to improve the property and improve the insertion loss of the low frequency side end portion in the pass band.

(Other variants, etc.)
Although the elastic wave filter according to the above embodiment has been described with reference to examples and modifications, the elastic wave filter of the present invention is not limited to the above examples and modifications. Other embodiments realized by combining arbitrary components in the above-described embodiment and the modified example, and various modifications that can be conceived by those skilled in the art without departing from the gist of the present invention are applied to the above-described embodiment and the modified example. The present invention also includes the modified examples obtained above, and various devices incorporating the elastic wave filters according to the above-described embodiment and the modified examples.

The surface acoustic wave resonator constituting the surface acoustic wave filter 1 according to the above embodiment may be, for example, the surface acoustic wave (SAW: Surface Acoustic Wave) resonator described above, or BAW (Bulk Acoustic). Wave) It may be a resonator. The SAW includes not only surface waves but also boundary waves.

The present invention can be widely used in communication devices such as mobile phones as a highly steep elastic wave filter applicable to multi-band and multi-mode frequency standards.

1,1A Elastic wave filter 5 Substrate 11, 12, 13, 14, 15, 16, s1, s2 Series arm resonator 21, 22, 23, 24, 26, p1, p2 Parallel arm resonator 51 High-pitched sound support substrate 52 Bass velocity film 53 Piezoelectric film 54 IDT electrode 55 Protective layer 57 Piezoelectric single crystal substrate 100, 101, 201, 301 Elastic wave resonator 100a, 100b, 101a, 101b, 201a, 201b, 301a, 301b Comb electrode 110, 120 Input / output Terminals 150a, 150b, 151a, 151b, 152, 251a, 251b, 252, 351a, 351b, 352 Electrode fingers 160a, 160b, 161a, 161b, 261a, 261b, 361a, 361b Bus bar electrode 540 Adhesion layer 542 Main electrode layer

Claims (11)

1. The first input / output terminal and the second input / output terminal,
   One or more series arm resonators arranged on the path connecting the first input / output terminal and the second input / output terminal, and
   It comprises one or more parallel arm resonators arranged between a node on the path and ground.
   Each of the one or more series arm resonators and the one or more parallel arm resonators includes an elastic wave resonator having an IDT (InterDigital Transducer) electrode formed on a substrate having piezoelectricity.
   The IDT electrode is formed by a plurality of electrode fingers extending in a direction intersecting the elastic wave propagation direction and arranged in parallel with each other, and a bus bar electrode connecting one end of the electrode fingers constituting the plurality of electrode fingers. It has a pair of configured comb-shaped electrodes and
   Of the plurality of electrode fingers, an electrode finger that is not connected to any of the busbar electrodes constituting the pair of comb-shaped electrodes is defined as a floating thinning electrode.
   When the electrode finger connected to the same busbar electrode as the busbar electrode to which the electrode fingers on both sides are connected is defined as the polarity reversal thinning electrode among the plurality of electrode fingers.
   At least one of the one or more series arm resonators has an IDT electrode including the floating thinning electrode.
   At least one of the one or more parallel arm resonators has an IDT electrode including the polarity reversal thinning electrode.
   Elastic wave filter.
2. The first series arm resonator having the lowest antiresonance frequency among the one or more series arm resonators has an IDT electrode including the floating thinning electrode.
   The elastic wave filter according to claim 1.
3. The first series arm resonator has the largest thinning rate among the one or more series arm resonators.
   The elastic wave filter according to claim 2.
4. Among the one or more series arm resonators, the higher the antiresonance frequency of the series arm resonator, the smaller the thinning rate.
   The elastic wave filter according to claim 2 or 3.
5. Among the one or more series arm resonators, all the series arm resonators except the first series arm resonator have an IDT electrode including the polarity reversal thinning electrode.
   The elastic wave filter according to any one of claims 2 to 4.
6. All the series arm resonators among the one or more series arm resonators have an IDT electrode including the floating thinning electrode.
   The elastic wave filter according to any one of claims 2 to 4.
7. The first parallel arm resonator having the highest resonance frequency among the one or more parallel arm resonators has an IDT electrode including the polarity reversal thinning electrode.
   The elastic wave filter according to any one of claims 1 to 6.
8. The first parallel arm resonator has the largest thinning rate among the one or more parallel arm resonators.
   The elastic wave filter according to claim 7.
9. Among the one or more parallel arm resonators, the lower the resonance frequency of the parallel arm resonator, the smaller the thinning rate.
   The elastic wave filter according to claim 7 or 8.
10. Among the one or more parallel arm resonators, all the parallel arm resonators except the first parallel arm resonator have an IDT electrode including the floating thinning electrode.
    The elastic wave filter according to any one of claims 7 to 9.
11. All the parallel arm resonators among the one or more parallel arm resonators have an IDT electrode including the polarity reversal thinning electrode.
    The elastic wave filter according to any one of claims 7 to 9.

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