WO2011040332A1 - Acoustic wave filter device and branching filter provided with same - Google Patents

Abstract

Disclosed is an acoustic wave filter device having a passband and an attenuation band positioned on the high-range side of the passband, the attenuation amount in the attenuation band of which is increased without significant increase in the size of the acoustic wave filter device. Also disclosed is a branching filter provided with the same. The acoustic wave filter device (1) is provided with an input terminal (11); an output terminal (12); a first resonator (S1) provided between the input terminal (11) and the output terminal (12); and a second resonator (P3) that is connected between the ground potential and a connection node, where the connection node is between the input terminal (11) or the output terminal (12) and the first resonator (S1). The value of the resonance frequency (fFrh) of a response other than the response contributing to the formation of the passband of the second resonator (P3), minus the center frequency (fc) of the passband, normalized by the center frequency of the passband ((fFrh - fc) / fc), is in the range of 0.073 to 0.250.

Description

Elastic wave filter device and duplexer including the same

The present invention relates to an elastic wave filter device, and more particularly, to an elastic wave filter device having a pass band and an attenuation band located on the high side of the pass band, and a duplexer including the same.

Conventionally, a duplexer using an elastic wave filter device as a band filter such as a reception filter or a transmission filter is known. The bandpass filter that forms part of the duplexer is required to have a large attenuation outside the passband in order to achieve high isolation characteristics of the duplexer. In particular, in a high frequency band for wireless communication, a band in which a transmission band and a reception band are very close is used. For example, with respect to a transmission filter, an attenuation amount in an attenuation band on the high band side of the pass band Is strongly demanded.

As a technique for ensuring a sufficiently large attenuation amount in the attenuation band, for example, Patent Document 1 below describes a technique in which a series resonator is connected in series to a ladder filter.

JP 7-154200 A

For example, as described in Patent Document 1 below, when a series resonator is further connected in series to a ladder-type filter, the configuration of the filter device is complicated and the filter device is complicated because the series resonator must be provided separately. There was a problem of increasing the size.

The present invention has been made in view of such a point, and an object of the present invention is to provide an acoustic wave filter device having a pass band and an attenuation band located on the high frequency side of the pass band, and a duplexer including the same. The object is to increase the attenuation in the attenuation band without increasing the size of the elastic wave filter device.

An elastic wave filter device according to the present invention includes an input terminal, an output terminal, a first resonator, and a second resonator. The first resonator is provided between the input terminal and the output terminal. The second resonator is connected between a connection point between the input terminal or the output terminal and the first resonator and the ground potential. In the acoustic wave filter device according to the present invention, the first and second resonators form a pass band and an attenuation band on the high band side of the pass band. The second resonator has a response other than the response contributing to the formation of the passband. A value (f _Frh −f _c ) _obtained by subtracting the center frequency (f _c ) of the pass band from the resonance frequency (f _Frh ) of the response other than the response contributing to the formation of the pass band of the second resonator The value ((f _Frh −f _c ) / f _c ) normalized by the center frequency is in the range of 0.073 to 0.250. In the present invention, the response of the resonator means a response that appears on the impedance characteristics in detail.

In a specific aspect of the present invention, in the series arm that connects the input terminal and the output terminal, a first resonator is provided so as to constitute a series arm resonator, and the second resonator is: A parallel arm resonator disposed on the parallel arm connected between the series arm and the ground potential is provided. That is, in a specific aspect of the present invention, the elastic wave filter device is a ladder-type elastic wave filter device.

In another specific aspect of the present invention, the first resonator constitutes a longitudinally coupled resonator type acoustic wave filter portion connected between the input terminal and the output terminal, and the second resonator Is connected between a connection point between the input terminal or the output terminal and the longitudinally coupled resonator type acoustic wave filter unit and the ground potential. That is, in another specific aspect of the present invention, the elastic wave filter device is an elastic wave filter device having a longitudinally coupled resonator type elastic wave filter unit and a second resonator as a parallel trap.

In another specific aspect of the present invention, each of the first and second resonators includes a piezoelectric substrate, a first dielectric layer formed on the piezoelectric substrate, a piezoelectric substrate, and a first dielectric. A boundary acoustic wave resonator having an IDT electrode formed at a boundary with a body layer.

In still another specific aspect of the present invention, each of the first and second resonators is formed on the first dielectric layer and has a higher sound velocity than the first dielectric layer. The boundary acoustic wave resonator further includes two dielectric layers.

In still another specific aspect of the present invention, the first resonator is provided in the series arm connecting the input terminal and the output terminal so as to constitute the series arm resonator connected in series with each other. The second resonator is provided so as to constitute a parallel arm resonator disposed in a parallel arm connected between the series arm and the ground potential, and the IDT electrode is formed of Al or Al. As a main conductive film, the film thickness of the main conductive film normalized by the wavelength determined by the electrode finger pitch of the IDT electrode of the first resonator is 10% to It is in the range of 30%. According to this configuration, the attenuation amount of the attenuation band can be further increased.

In still another specific aspect of the present invention, the first arm is provided in the series arm connecting the input terminal and the output terminal so as to constitute the series arm resonator connected in series with each other. The second resonator is provided so as to constitute a parallel arm resonator disposed in a parallel arm connected between the series arm and the ground potential, and the first dielectric layer is The thickness of the first dielectric layer made of silicon oxide and normalized by the wavelength determined by the electrode finger pitch of the IDT electrode of the first resonator is in the range of 40% to 70%. According to this configuration, the attenuation amount of the attenuation band can be further increased.

In another specific aspect of the present invention, the response other than the response contributing to the formation of the passband of the second resonator is a higher-order mode of the response contributing to the formation of the passband.

In still another specific aspect of the present invention, the response other than the response contributing to the formation of the passband of the second resonator is a response different in type from the response contributing to the formation of the passband. is there.

The duplexer according to the present invention includes the elastic wave filter according to the present invention.

In the present invention, other than the response contributing to the formation of the passband of the second resonator connected between the connection point between the input terminal or the output terminal and the first resonator and the ground potential. the resonance frequency _{(f Frh)} from the passband center frequency _{(f c)} the value obtained by subtracting the normalized value of _(f Frh -f _c) at the center frequency of the passband of the response _((f Frh _-f c) / f _c ) is in the range of 0.073 to 0.250. Therefore, since a separate resonator for increasing the attenuation in the attenuation band is not required, the attenuation in the attenuation band can be increased without increasing the size of the elastic wave filter device. Therefore, high isolation characteristics can be realized by using the acoustic wave filter device of the present invention in a duplexer.

FIG. 1 is a schematic configuration diagram of a boundary acoustic wave filter device according to a first embodiment. FIG. 2 is a schematic cross-sectional view of the acoustic wave resonator according to the first embodiment. FIG. 3 is a schematic cross-sectional view in which a part of the acoustic wave resonator according to the first embodiment is enlarged. FIG. 4 is a schematic plan view for explaining the electrode structure of the acoustic wave resonator according to the first embodiment. FIG. 5 is a graph showing filter characteristics of the boundary acoustic wave filter device according to the first embodiment and impedance characteristics of the parallel arm resonator and the series arm resonator. Figure 6 is a graph showing the relationship between the attenuation in _{(f Frh -f c) / f} c and 1880MHz in the first embodiment. FIG. 7 is a schematic configuration diagram of the duplexer according to the first embodiment. FIG. 8 is a schematic configuration diagram of a reception filter of the duplexer in the first embodiment. FIG. 9 is a graph showing impedance characteristics of the parallel arm resonator at various second main conductive film thicknesses. FIG. 10 is a graph showing filter characteristics of the boundary acoustic wave filter device at various thicknesses of the second main conductive film. FIG. 11 is an enlarged graph of a part of the graph shown in FIG. FIG. 12 is a graph showing the isolation characteristics of the duplexer at various thicknesses of the second main conductive film. FIG. 13 is a graph showing impedance characteristics of the second resonator at various thicknesses of the first dielectric layer. FIG. 14 is a graph showing filter characteristics of the boundary acoustic wave filter device at various thicknesses of the first dielectric layer. FIG. 15 is an enlarged graph of a part of the graph shown in FIG. FIG. 16 is a graph showing the isolation characteristics of the duplexer at various thicknesses of the first dielectric layer. FIG. 17 is a schematic configuration diagram of an acoustic wave resonator according to the second embodiment.

Hereinafter, examples of preferable embodiments in which the present invention is implemented will be described.

(First embodiment)
FIG. 1 is a schematic configuration diagram of a boundary acoustic wave filter device according to this embodiment.

The boundary acoustic wave filter device 1 shown in FIG. 1 is a ladder-type boundary acoustic wave filter device 1. The boundary acoustic wave filter device 1 includes an input terminal 11 and an output terminal 12. Between the input terminal 11 and the output terminal 12, series arm resonators S11, S12, S21 to S23, S31, and S32 are provided as first resonators. Specifically, the input terminal 11 and the output terminal 12 are connected by a series arm 13. The first to third series arm resonators S 1 to S 3 are connected to each other in series at the series arm 13. In the present embodiment, the first series arm resonator S1 is composed of two series arm resonators S11 and S12 connected in series with each other. The second series arm resonator S2 includes three series arm resonators S21 to S23 connected in series with each other. The third series arm resonator S3 includes two series arm resonators S31 and S32 connected in series with each other.

Three parallel arms 14a to 14c are connected between the serial arm 13 and the ground electrodes 15a and 15b connected to the ground potential. Specifically, the first parallel arm 14a is connected between the connection point 13a between the first series arm resonator S1 and the second series arm resonator S2 and the ground electrode 15a. The first parallel arm 14a is provided with a first parallel arm resonator P1. The first parallel arm resonator P1 is composed of two parallel arm resonators P11 and P12 connected in series with each other. A first inductor L1 is provided between the first parallel arm resonator P1 and the ground electrode 15a.

The second parallel arm 14b is connected between the connection point 13b between the second series arm resonator S2 and the third series arm resonator S3 and the ground electrode 15b. The second parallel arm 14b is provided with a second parallel arm resonator P2. The second parallel arm resonator P2 includes two parallel arm resonators P21 and P22 connected in series.

A third parallel arm 14c is connected between the connection point 13c between the third series arm resonator S3 and the output terminal 12 and the ground electrode 15b. The third parallel arm 14c is provided with a third parallel arm resonator P3. The third parallel arm resonator P3 includes two parallel arm resonators P31 and P32 connected in series with each other.

A second inductor L2 is provided between the connection point between the second parallel arm resonator P2 and the third series arm resonator S3 and the ground electrode 15b.

In the following description, the series arm resonators S11, S12, S21 to S23, S31, and S32 may be collectively referred to as the series arm resonator S. Further, the parallel arm resonators P11, P12, P21, P22, P31, and P32 may be collectively referred to as a parallel arm resonator P. Further, the series arm resonator S and the parallel arm resonator P may be collectively referred to as “resonator 29”.

In this embodiment, the boundary acoustic wave filter device 1 is a filter device using a boundary acoustic wave, and the resonator 29 is a boundary acoustic wave resonator. Specifically, in this embodiment, the resonator 29 is a so-called three-medium type boundary acoustic wave resonator. More specifically, as shown in FIGS. 2 to 4, the resonator 29 includes a piezoelectric substrate 20 and first and second dielectric layers 21 and 22.

The piezoelectric substrate 20 is not particularly limited as long as the substrate expressing a piezoelectric effect, for example, can be constituted by a substrate such as LiTaO ₃ substrate or a LiNbO ₃ substrate.

The first dielectric layer 21 is formed on the piezoelectric substrate 20. An IDT electrode 30 and first and second grating reflectors 33 and 34 are formed at the boundary between the first dielectric layer 21 and the piezoelectric substrate 20. A second dielectric layer 22 is formed on the surface of the first dielectric layer 21 opposite to the piezoelectric substrate 20.

Since the second dielectric layer 22 has a sound velocity faster than that of the first dielectric layer 21, the elastic wave excited in the IDT electrode 30 is confined in the first dielectric layer 21, 1 propagates through the dielectric layer 21.

The material of the first and second dielectric layers 21 and 22 is not particularly limited as long as the sound speed of the second dielectric layer 22 is higher than the sound speed of the first dielectric layer 21. For example, the first dielectric layer 21 can be formed of silicon oxide such as SiO ₂ , and the second dielectric layer 22 can be formed of silicon nitride such as SiN.

In the present embodiment, the IDT electrode 30 and the first and second grating reflectors 33 and 34 have the same film configuration. FIG. 3 shows the film configuration of the IDT electrode 30 as a representative. As shown in FIG. 3, the IDT electrode 30 and the first and second grating reflectors 33 and 34 include first to third main conductive films 30a to 30c. Then, between the first to third main conductive films 30a to 30c, between the first main conductive film 30a and the piezoelectric substrate 20, and between the third main conductive film 30c and the first dielectric layer 21. Adhesive films 30d to 30f or a protective film 30g are provided in each of the gaps.

Specifically, in the present embodiment, a first main conductive film 30a made of Pt is formed on the piezoelectric substrate 20 via an adhesion film 30d made of NiCr. On the first main conductive film 30a, a second main conductive film 30b made of AlCu is formed via an adhesion film 30e made of Ti. A third main conductive film 30c made of Pt is formed on the second main conductive film 30b via an adhesion film 30f made of Ti. A protective film 30g made of Ti is formed between the third main conductive film 30c and the first dielectric layer 21. Note that the main conductive film in the present invention refers to a film containing a relatively high conductive material such as Pt, Al, or Cu, and a relatively thick film.

Next, the planar shapes of the IDT electrode 30 constituting the resonator 29 and the first and second grating reflectors 33 and 34 in the present embodiment will be described with reference to FIG. As shown in FIG. 4, the IDT electrode 30 includes first and second comb electrodes 31 and 32 that are inserted into each other. Each of the first and second comb electrodes 31 and 32 includes bus bars 31a and 32a, electrode fingers 31b and 32b extending from the bus bars 31a and 32a, and dummy electrodes 31c and 32c. The IDT electrode 30 is so-called cross width weighted, and is configured such that the region surrounded by the envelopes l1 and l2 passing through the tips of the electrode fingers 31b and 32b is substantially rhombus. In the present invention, the IDT electrode is not particularly limited, and may be a regular IDT electrode or an IDT electrode to which weighting other than cross width weighting is applied.

The first and second grating reflectors 33 and 34 are disposed on both sides of the IDT electrode 30 in the elastic wave propagation direction.

FIG. 5 is a graph showing the filter characteristics of the boundary acoustic wave filter device according to this embodiment and the impedance characteristics of the parallel arm resonator and the series arm resonator. In FIG. 5, the solid line indicates the filter characteristic of the boundary acoustic wave filter device, the one-dot broken line indicates the impedance characteristic of the series arm resonator, and the two-dot broken line indicates the impedance characteristic of the parallel arm resonator.

As shown in FIG. 5, the resonance point and antiresonance point of the main response Rs1 of the series arm resonator S are higher than the resonance point and antiresonance point of the main response Rp1 of the parallel arm resonator P, respectively. Is located. The resonance frequency of the main response Rs1 of the series arm resonator S and the antiresonance frequency of the main response Rp1 of the parallel arm resonator P are set to be approximately equal. In a frequency band close to the resonance frequency of the main response Rs1 of the series arm resonator S and the antiresonance frequency of the main response Rp1 of the parallel arm resonator P, the impedance value between the input terminal 11 and the output terminal 12 Since the attenuation becomes smaller and the attenuation becomes smaller, a pass band is formed. The boundary acoustic wave filter device 1 of this embodiment is used as a transmission filter.

Attenuation bands are formed on the low band side and high band side of the pass band. Of these attenuation bands, the attenuation band located on the lower side of the pass band is mainly formed by the resonance point of the main response Rp1 of the parallel arm resonator P. On the other hand, the attenuation band located on the high frequency side of the pass band is mainly formed by the antiresonance point of the main response Rs1 of the series arm resonator S. In addition, the impedance value of the parallel arm resonator P in the attenuation band also contributes to the attenuation band located on the high band side of the pass band. The smaller the impedance value of the parallel arm resonator P in the attenuation band, the more in the attenuation band. The amount of attenuation increases.

By the way, when the parallel arm resonator P and the series arm resonator S which are boundary acoustic wave resonators are used, in addition to the main responses Rp1 and Rs1 that contribute to the formation of the passband and the attenuation bands on both sides of the passband. There is a response. Specifically, for example, there are higher-order modes of the main responses Rp1 and Rs1, and responses different in type from the main responses Rp1 and Rs1. For example, when the main responses Rp1 and Rs1 are one of the response by the SH wave and the response by the Stoneley wave, the response by the other boundary acoustic wave exists.

Conventionally, it is considered that when other responses than the main responses Rp1 and Rs1 are located in the vicinity of the main responses Rp1 and Rs1, the filter characteristics are adversely affected. The parallel arm resonator P and the series arm resonator S are designed so that the response is located sufficiently away from the main responses Rp1 and Rs1 so that the filter characteristics are not adversely affected.

As a result of intensive studies on the relationship between the positional relationship between the main responses Rp1 and Rs1 and other responses and the filter characteristics, the inventors have made other responses closer to the main responses Rp1 and Rs1 to some extent. It was found that the attenuation in the attenuation band located on the high frequency side of the pass band can be increased.

Specifically, a value obtained by subtracting the center frequency (f _c = 1747.5 MHz) of the pass band (1710 to 1785 MHz) from the resonance frequency (f _Frh ) of the response Rp2 other than the main response Rp1 of the parallel arm resonator P ( A value _{obtained by normalizing} f _Frh −f _c ) with the center frequency of the passband ((f _Frh −f _c ) / f _c = (f _Frh −1747.5 MHz) /1747.5 MHz) is 0.073 to 0.250. It was found that the attenuation amount in the attenuation band located on the high band side of the pass band can be increased to a sufficient value by setting the value within the range. This will be described in more detail with reference mainly to FIG.

FIG. 6 shows a value (f _c = 1747.5 MHz) obtained by subtracting the center frequency (f _c = 1747.5 MHz) of the pass band (1710 to 1785 MHz) from the resonance frequency (f _Frh ) of the response Rp2 other than the main response Rp1 of the parallel arm resonator P. _Frh −f _c ) normalized by the center frequency of the pass band ((f _Frh −f _c ) / f _c = (f _Frh −1747.5 MHz) /1747.5 MHz) and the pass band (1710 to 1785 MHz) It is a graph showing the relationship with the attenuation amount in 1880 MHz included in the attenuation band located in the high frequency side. From FIG. 6, when the response Rp2 of the parallel arm resonator P approaches the passband in which the main response Rp1 contributes to the formation, the passband is larger than when the response Rp2 is sufficiently far from the passband. It can be seen that the amount of attenuation in the attenuation band located on the high frequency side increases. Then, when the response Rp2 of the parallel arm resonator P further approaches the center frequency of the pass band, conversely, the attenuation amount in the attenuation band located on the high band side of the pass band decreases, and finally the response Rp2 It can be seen that the amount of attenuation is smaller than when the is sufficiently away from the passband. Specifically, from the results shown in FIG. _{6, (f Frh -f c)} / f c is, when in the range of 0.073 to 0.250, the attenuation band which is located on the high frequency side of the pass band It can be seen that the effect of increasing the attenuation at is great. In the present _{embodiment, (f Frh -f c) /} f c is, when in the range of 0.073 ~ 0.250, 39.5dB attenuation in the attenuation band located on the higher frequency side of the pass band This can be done. Moreover, when the film thickness of the electrode which comprises an IDT electrode is too thin, resistance will increase and insertion loss will deteriorate. For this reason, the electrode film thickness needs to be 200 nm or more. At this _{time, (f Frh -f c) /} f c has a value of 0.250 or less. This _also, it is understood that it is preferable to 0.250 for the upper limit of _{(f Frh -f c) / f} c.

Further, from the results shown in FIG. _6, by a (f _Frh -f c) / a _{f c} 0.158 or less, it is possible to further increase the attenuation in the attenuation band located on the higher frequency side of the pass band . _Therefore, it is preferable that _{(f Frh -f c) / f} c is 0.158 or less.

_{Incidentally, (f Frh -f c) /} f c is, when it becomes 0.250 or less, i.e., when the resonance frequency of the response Rp2 approached somewhat above the passband, located at the higher-frequency side of the pass band The reason why the attenuation in the attenuation band increases is not clear, but is considered to be due to the following reason. That is, when the response Rp2 is positioned sufficiently higher than the main response Rp1, the effect of the response Rp2 on the attenuation band on the high frequency side of the pass band formed by the main response Rp1 There is nothing. However, when the resonance frequency of the response Rp2 approaches the attenuation band, the resonance point of the response Rp2 having a small impedance value shifts to the low frequency side and is affected by this, and the high frequency side of the antiresonance point of the main response Rp1 Impedance value at. For this reason, it is considered that the attenuation amount of the attenuation band located on the high frequency side of the pass band becomes large. On the other _{hand, (f Frh -f c) /} f c is, when it becomes 0.073 or less, i.e., the attenuation in the attenuation band of a band higher than the passband when the resonance frequency of the response Rp2 too close to the pass band On the other hand, the resonance point of the response Rp2 having a small impedance value approaches the attenuation band, and the anti-resonance point having a large impedance value also approaches the attenuation band. For this reason, it is considered that the effect of the antiresonance point reducing the attenuation amount of the attenuation band is greater than the effect of the resonance point increasing the attenuation amount of the attenuation band.

If the upper limit of the passband (1785 MHz) is f _h , the range of 0.073 ≦ (f _Frh −f _c ) / f _c ≦ 0.250 is 0.05 ≦ (f _Frh −f _h ) / f It can be converted to _h ≦ 0.212.

As described above, the boundary acoustic wave filter device 1 of the present embodiment is useful for, for example, a duplexer because the amount of attenuation in the attenuation band on the high frequency side of the pass band is large. In particular, for example, it is useful as a transmission filter for a duplexer in which a transmission band (1710 to 1785 MHz) and a reception band (1805 to 1880 MHz) are close to each other.

FIG. 7 is a schematic diagram of a duplexer 3 including the boundary acoustic wave filter device 1 as a transmission filter. As shown in FIG. 7, the duplexer 3 includes the antenna terminal Ant. And transmission side signal terminals Tx and reception side signal terminals Rx1 and Rx2. Only one transmission-side signal terminal Tx is provided, which is an unbalanced signal terminal. On the other hand, two receiving side signal terminals Rx1 and Rx2 are provided, which are balanced signal terminals.

Antenna terminal Ant. The boundary acoustic wave filter device 1 as a transmission filter is connected between the transmission side signal terminal Tx and the transmission side signal terminal Tx. On the other hand, the antenna terminal Ant. And the reception-side signal terminals Rx1 and Rx2, a reception filter 2 is provided. Transmission filter 1 and reception filter 2 and antenna terminal Ant. An inductor L3 is connected between the connection point and the ground potential.

FIG. 8 is a schematic configuration diagram of the reception filter 2. The reception filter 2 shown in FIG. 8 is a longitudinally coupled resonator type acoustic wave filter device. As shown in FIG. 8, an unbalanced signal terminal 41 and a pair of balanced signal terminals 42a and 42b are provided. The unbalanced signal terminal 41 is the antenna terminal plan Ant. It is connected to the. On the other hand, the balanced signal terminals 42a and 42b are connected to the receiving signal terminals Rx1 and Rx2 shown in FIG.

A first boundary acoustic wave filter unit 44a is connected between the unbalanced signal terminal 41 and the first balanced signal terminal 42a. On the other hand, a second boundary acoustic wave filter unit 44b is connected between the unbalanced signal terminal 41 and the second balanced signal terminal 42b. A boundary acoustic wave resonator 43 is connected between the unbalanced signal terminal 41 and the first and second boundary acoustic wave filter units 44a and 44b. The boundary acoustic wave resonators 45a and 45b are connected between the first and second boundary acoustic wave filter units 44a and 44b and the balanced signal terminals 42a and 42b, respectively.

The duplexer 3 is a duplexer in which a transmission band (1710 to 1785 MHz) and a reception band (1805 to 1880 MHz) are close to each other. For this reason, the duplexer 3 is strongly required to have a large amount of attenuation in the high-side attenuation band of the pass band (transmission band) of the boundary acoustic wave filter device 1 constituting the transmission filter. Here, as described above, in the boundary acoustic wave filter device 1 of the present embodiment, the amount of attenuation in the attenuation band on the high frequency side of the pass band is large. Therefore, the duplexer 3 including the boundary acoustic wave filter device 1 of the present embodiment as a transmission filter has a good isolation characteristic between the transmission side signal terminal Tx and the reception side signal terminals Rx1 and Rx2.

Next, a method of controlling the frequency difference between the center frequency of the passband and the resonance frequency of the response Rp2, that is, a method of controlling the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2. Will be described. The method for controlling the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2 is not particularly limited. For example, the film thickness of the main conductive films 30a to 30c constituting the IDT electrode 30 is changed. Can be controlled.

FIG. 9 is a graph showing impedance characteristics of the parallel arm resonator P when the film thickness of the second main conductive film 30b is variously changed in the boundary acoustic wave filter device 1 of the present embodiment having the following design parameters. It is. In FIG. 9, the solid line indicates that the thickness of the second main conductive film 30b made of AlCu is 225 nm (h / λ = 10.6%, where λ is the pitch between the electrode fingers of the parallel arm resonator P. The impedance characteristic when the wavelength is determined. A two-dot broken line indicates impedance characteristics when the film thickness of the second main conductive film 30b made of AlCu is 300 nm (h / λ = 14.1%). The dashed line indicates the impedance characteristic when the film thickness of the second main conductive film 30b made of AlCu is 400 nm (h / λ = 18.8%).

As shown in FIG. 9, when the film thickness of the second main conductive film 30b is changed, the anti-resonance frequency of the main response Rp1 hardly changes, whereas the resonance frequency of the response Rp2 changes greatly. I understand that. From this result, it is understood that the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2 can be controlled by changing the film thickness of at least one of the main conductive films 30a to 30c. Specifically, it can be seen that by increasing the film thickness of the main conductive films 30a to 30c, the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2 can be reduced.

Further, the filter characteristics of the boundary acoustic wave filter device 1 of the present embodiment at various thicknesses of the second main conductive film 30b are shown in FIGS. Further, isolation characteristics between the transmission-side signal terminal Tx and the reception-side signal terminals Rx1 and Rx2 in the duplexer 3 using the boundary acoustic wave filter device 1 of the present embodiment in various thicknesses of the second main conductive film 30b. Is shown in FIG. 10 to 12, the solid line represents data when the film thickness of the second main conductive film 30b made of AlCu is 225 nm (H / λ (S2-1) = 11%). A one-dot broken line is data when the film thickness of the second main conductive film 30b made of AlCu is 450 nm (H / λ (S2-1) = 23%). The two-dot broken line represents data when the film thickness of the second main conductive film 30b made of AlCu is 600 nm (H / λ (S2-1) = 30%).

As shown in FIGS. 10 and 11, as the film thickness of the second main conductive film 30b increases and the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2 decreases, FIG. It can be seen that the amount of attenuation in the circled attenuation band increases.

Similarly, from the result shown in FIG. 12, as the film thickness of the second main conductive film 30b increases and the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2 decreases, the transmission side It can be seen that the isolation characteristics between the signal terminal Tx and the reception-side signal terminals Rx1, Rx2 are improved.

From the results shown in FIGS. 10 to 12, the attenuation amount in the high-side attenuation band of the pass band is increased, and the isolation characteristics between the transmission-side signal terminal Tx and the reception-side signal terminals Rx1 and Rx2 are improved. In order to achieve this, it can be seen that the wavelength normalized film thickness of the main conductive film made of Al or an alloy containing Al as a main component is preferably in the range of 10% to 30%.

(Design parameters)
Series arm resonator S1:
Wavelength (λ): 2013 nm
Cross width: 28.65λ
Logarithm: 118
Duty: 0.5
Parallel arm resonator P1:
Wavelength (λ): 2129 nm
Cross width: 48.90λ
Logarithm: 130
Duty: 0.5
Series arm resonators S21 and S22:
Wavelength (λ): 2022 nm
Cross width: 92.45λ
Logarithm: 121
Duty: 0.5
Series arm resonator S23:
Wavelength (λ): 2008 nm
Cross width: 34.74λ
Logarithm: 81
Duty: 0.5
Parallel arm resonator P2:
Wavelength (λ): 2129 nm
Cross width: 49.03λ
Logarithm: 137
Duty: 0.5
Series arm resonator S3:
Wavelength (λ): 2014 nm
Cross width: 33.22λ
Logarithm: 97
Duty: 0.5
Parallel arm resonator P3:
Wavelength (λ): 2115 nm
Cross width: 34.45λ
Logarithm: 87
Duty: 0.5

Film thickness of each film constituting the IDT electrode:
Adhesion film 30d: 10 nm, first main conductive film 30a: 36 nm, adhesion film 30e: 10 nm, second main conductive film 30b: 225 nm (H / λ (S2-1) = 11%), 300 nm (H / λ (S2-1) = 15%), 400 nm (H / λ (S2-1) = 20%) or 600 nm (H / λ (S2-1) = 30%), adhesion film 30f: 10 nm, third main Conductive film 30c: 22 nm, protective film 30g: 10 nm

First dielectric layer 21: SiO ₂ layer Film thickness of first dielectric layer 21: 1213 nm (H / λ (S2-1) = 60%)
Second dielectric layer 22: SiN layer Film thickness of the second dielectric layer 22: 2200 nm (H / λ (S2-1) = 109%)
Piezoelectric substrate 20: 25 ° YX LiNbO ₃ substrate Thickness of the piezoelectric substrate 20: 500 μm

Also, by changing the thickness of the dielectric layer 21, the frequency difference between the center frequency of the passband and the resonance frequency of the response Rp2, that is, the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2 The frequency difference between and can be controlled.

FIG. 13 is the same as the case where the thickness of the second main conductive film 30b is 225 nm (H / λ (S2-1) = 11%) except for the thickness of the first dielectric layer 21 made of SiO ₂ . 6 is a graph showing impedance characteristics of the parallel arm resonator P when the thickness of the first dielectric layer 21 is variously changed in the boundary acoustic wave filter device 1 having the above design parameters. In FIG. 13, the solid line shows the impedance characteristic when the thickness of the first dielectric layer 21 is 1213 nm (H / λ (S2-1) = 60%). The two-dot broken line indicates the impedance characteristic when the thickness of the first dielectric layer 21 is 1011 nm (H / λ (S2-1) = 50%). The dashed line indicates the impedance characteristic when the thickness of the first dielectric layer 21 is 708 nm (H / λ (S2-1) = 35%).

As shown in FIG. 13, when the thickness of the first dielectric layer 21 is changed, the anti-resonance frequency of the main response Rp1 hardly changes, whereas the resonance frequency of the response Rp2 changes. I understand that. From this result, it is understood that the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2 can be controlled by changing the thickness of the first dielectric layer 21. Specifically, it can be seen that by increasing the thickness of the first dielectric layer 21, the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2 can be reduced.

Further, the filter characteristics of the boundary acoustic wave filter device 1 of the present embodiment at various thicknesses of the first dielectric layer 21 are shown in FIGS. Further, the isolation characteristics between the transmission side signal terminal Tx and the reception side signal terminals Rx1 and Rx2 in the duplexer 3 using the boundary acoustic wave filter device 1 of the present embodiment in various thicknesses of the first dielectric layer 21. Is shown in FIG. The thick solid line is data when the thickness of the first dielectric layer 21 is 1213 nm (H / λ (S2-1) = 60%). A dashed line represents data when the thickness of the first dielectric layer 21 is 1011 nm (H / λ (S2-1) = 50%). The two-dot broken line represents data when the thickness of the first dielectric layer 21 is 809 nm (H / λ (S2-1) = 40%). The thin solid line is data when the thickness of the first dielectric layer 21 is 607 nm (H / λ (S2-1) = 30%). The dotted line represents data when the thickness of the first dielectric layer 21 is 505 nm (H / λ (S2-1) = 25%).

As shown in FIGS. 14 and 15, the thickness of the first dielectric layer 21 increases, and the smaller the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2, the more it is circled. It can be seen that the amount of attenuation in the attenuation band increases. However, when the thickness of the first dielectric layer 21 is less than 809 nm (H / λ (S2-1) = 40%), the attenuation in the attenuation band does not change so much, and the first dielectric layer 21 The attenuation in the attenuation band was greatly improved when the thickness of the film was 809 nm (H / λ (S2-1) = 40%) or more.

Similarly, from the result shown in FIG. 16, as the thickness of the first dielectric layer 21 increases and the frequency difference between the anti-resonance frequency of the main response Rp1 and the resonance frequency of the response Rp2 decreases, the signal on the transmission side It can be seen that the isolation characteristics between the terminal Tx and the reception-side signal terminals Rx1 and Rx2 are good. However, when the thickness of the first dielectric layer 21 is less than 809 nm (H / λ (S2-1) = 40%), the isolation characteristic does not change so much, and the thickness of the first dielectric layer 21 The isolation characteristics were greatly improved when the thickness was 809 nm (H / λ (S2-1) = 40%) or more. From this result, it is understood that the thickness of the first dielectric layer 21 made of SiO ₂ is preferably 809 nm (H / λ (S2-1) = 40%) or more. When the thickness of the first dielectric layer 21 made of SiO ₂ exceeds 70%, the loss is deteriorated. Therefore, the thickness of the first dielectric layer 21 made of SiO ₂ is 70% or less. It is preferable.

Hereinafter, another example of a preferable embodiment in which the present invention is implemented will be described. However, in the following description, members having substantially the same functions as those of the first embodiment are referred to by the same reference numerals, and description thereof is omitted.

(Second Embodiment)
In the first embodiment, the case where the elastic wave filter device is a ladder type filter device has been described. However, the elastic wave filter device of the present invention is not limited to a ladder type filter device. The acoustic wave filter device of the present invention includes a first resonator that contributes to formation of a pass band between an input terminal and an output terminal, and a signal transmission path between the input terminal and the output terminal. As long as it is an elastic wave filter device in which the second resonator is provided between the ground potential and the ground potential, there is no particular limitation. In the acoustic wave filter device in which the second resonator is provided between the signal transmission path between the input terminal and the output terminal and the ground potential, the antiresonance frequency of the second resonator is located in the passband. This is because the amount of attenuation in the attenuation band located on the high frequency side of the pass band depends on the low impedance in the attenuation band of the second resonator. That is, the lower the impedance in the attenuation band of the second resonator, the larger the attenuation in the attenuation band located on the higher side of the pass band, so that the signal transmission path between the input terminal and the output terminal and the ground potential The present invention, which can reduce the impedance in the attenuation band of the second resonator, is suitable for the entire acoustic wave filter device in which the second resonator is provided between them.

For example, the acoustic wave filter device according to the present invention may be a longitudinally coupled resonator type acoustic wave filter having parallel traps as shown in FIG.

As shown in FIG. 17, the boundary acoustic wave filter device 5 of this embodiment includes an input terminal 11 that is an unbalanced signal terminal, and first and second output terminals 12a and 12b that are balanced signal terminals. . Between the input terminal 11 and the first and second output terminals 12a and 12b, longitudinally coupled resonator type acoustic wave filter sections 50a and 50b are connected.

The longitudinally coupled resonator type acoustic wave filter unit 50a is connected between the input terminal 11 and the first output terminal 12a. The longitudinally coupled resonator type acoustic wave filter unit 50a includes first to third IDT electrodes 51a to 53a and first to third IDT electrodes 51a to 53a arranged along the propagation direction of the boundary acoustic wave. The region is provided with first and second grating reflectors 54a and 55a disposed on both sides in the boundary acoustic wave propagation direction. One side of each of the first and third IDT electrodes 51a and 53a is connected to the input terminal 11 via the boundary acoustic wave resonator 56, and the other side is connected to the ground potential. One side of the second IDT electrode 52a is connected to the ground potential, and the other side is connected to the first output terminal 12a.

The longitudinally coupled resonator type acoustic wave filter unit 50b is connected between the input terminal 11 and the second output terminal 12b. The longitudinally coupled resonator type acoustic wave filter unit 50b includes first to third IDT electrodes 51b to 53b and first to third IDT electrodes 51b to 53b arranged along the propagation direction of the boundary acoustic wave. The region is provided with first and second grating reflectors 54b and 55b arranged on both sides in the boundary acoustic wave propagation direction. One side of each of the first and third IDT electrodes 51b and 53b is connected to the input terminal 11 via the boundary acoustic wave resonator 56, and the other side is connected to the ground potential. One side of the second IDT electrode 52b is connected to the ground potential, and the other side is connected to the second output terminal 12b.

A parallel trap 60a as a second resonator is connected between a connection point between the longitudinally coupled resonator type acoustic wave filter unit 50a and the first output terminal 12a and the ground potential. In addition, a parallel trap 60b as a second resonator is connected between the connection point between the longitudinally coupled resonator type acoustic wave filter unit 50b and the second output terminal 12b and the ground potential. Yes.

In the present embodiment, the amount of attenuation in the attenuation band located on the high frequency side of the pass band is increased by the parallel traps 60a and 60b. Specifically, a value (f _Frh −f) obtained by subtracting the center frequency (f _c ) of the pass band from the resonance frequency (f _Frh ) of a response other than the response contributing to the formation of the pass bands of the parallel traps 60 a and 60 b. _c ) is a value ((f _Frh −f _c ) / f _c ) normalized by the center frequency of the pass band is in the range of 0.073 to 0.250. The amount of attenuation in the attenuation band located on the side is increased.

In the first and second embodiments, the boundary acoustic wave filter device using the boundary acoustic wave and the duplexer including the boundary acoustic wave filter device have been described. However, the boundary acoustic wave filter device according to the present invention includes the boundary acoustic wave. It is not limited to what uses. For example, in the present invention, at least one of the first and second resonators may be a surface acoustic wave resonator. That is, the boundary acoustic wave filter device according to the present invention may be a surface acoustic wave filter device.

In the first and second embodiments, a duplexer is used as an example of a duplexer. However, in the present invention, the duplexer may be, for example, a triplexer.

1 ... boundary acoustic wave filter device (transmission filter)
2 ... reception filter 3 ... duplexers L1 to L3 ... inductor S1 ... first series arm resonator P1 ... first parallel arm resonator S2 ... second series arm resonator P2 ... second parallel arm resonator S3 ... 3rd series arm resonator P3 ... 3rd parallel arm resonator 5 ... boundary acoustic wave filter device 11 ... input terminal 12 ... output terminal 12a ... 1st output terminal 12b ... 2nd output terminal 13 ... series arm 13a 13c ... Connection point 14a ... first parallel arm 14b ... second parallel arm 14c ... third parallel arm 15a, 15b ... ground electrode 20 ... piezoelectric substrate 21 ... first dielectric layer 22 ... second dielectric Body layer 29 ... resonator 30 ... IDT electrode 30a ... first main conductive film 30b ... second main conductive film 30c ... third main conductive films 30d to 30f ... adhesion film 30g ... protective films 31, 32 ... comb teeth Electrode 31a, 32a ... bus bar 31 32b ... electrode fingers 31c, 32c ... dummy electrodes 33, 34 ... second grating reflector 41 ... unbalanced signal terminal 42a ... first balanced signal terminal 42b ... second balanced signal terminal 43 ... boundary acoustic wave resonator 44a ... first boundary acoustic wave filter unit 44b ... second boundary acoustic wave filter units 45a, 45b ... boundary acoustic wave resonator 50a ... longitudinally coupled resonator type acoustic wave filter unit 50b ... longitudinally coupled resonator type acoustic wave filter Part 51a, 51b ... 1st IDT electrode 52a, 52b ... 2nd IDT electrode 53a, 53b ... 3rd IDT electrode 54a, 54b ... 1st grating reflector 55a, 55b ... 2nd grating reflector 56 ... Boundary wave resonators 60a, 60b ... parallel traps

Claims (10)

An input terminal;
An output terminal;
A first resonator provided between the input terminal and the output terminal;
A connection point between the input terminal or the output terminal and the first resonator, and a second resonator connected between a ground potential,
An elastic wave filter device in which a pass band and an attenuation band are formed on a high frequency side of the pass band by the first and second resonators,
The second resonator has a response other than the response contributing to the formation of the passband;
A value (f _Frh −f _c ) _obtained by subtracting the center frequency (f _c ) of the pass band from the resonance frequency (f _Frh ) of a response other than the response contributing to the formation of the pass band of the second resonator. The acoustic wave filter device has a value ((f _Frh −f _c ) / f _c ) normalized by the center frequency of the passband within a range of 0.073 to 0.250. In the series arm connecting the input terminal and the output terminal, the first resonator is provided so as to constitute a series arm resonator,
2. The elastic device according to claim 1, wherein the second resonator is provided so as to constitute a parallel arm resonator disposed on a parallel arm connected between the series arm and a ground potential. Wave filter device. The first resonator constitutes a longitudinally coupled resonator type acoustic wave filter unit connected between the input terminal and the output terminal,
The second resonator is connected between a connection point between the input terminal or the output terminal and the longitudinally coupled resonator type acoustic wave filter unit, and a ground potential. Elastic wave filter device. Each of the first and second resonators includes a piezoelectric substrate, a first dielectric layer formed on the piezoelectric substrate, and between the piezoelectric substrate and the first dielectric layer. The elastic wave filter device according to any one of claims 1 to 3, which is a boundary acoustic wave resonator having an IDT electrode formed at a boundary. Each of the first and second resonators further includes a second dielectric layer that is formed on the first dielectric layer and has a higher sound velocity than the first dielectric layer. The acoustic wave filter device according to claim 4, wherein the acoustic wave filter device is a three-medium type boundary acoustic wave resonator. In the series arm connecting the input terminal and the output terminal, the first resonator is provided so as to constitute a series arm resonator connected in series with each other,
The second resonator is provided so as to constitute a parallel arm resonator disposed in a parallel arm connected between the series arm and a ground potential,
The IDT electrode has a conductive film made of Al or an alloy containing Al as a main component as a main conductive film, and is standardized at a wavelength determined by an electrode finger pitch of the IDT electrode of the first resonator. 6. The acoustic wave filter device according to claim 4, wherein the film thickness of the main conductive film is in the range of 10% to 30%. In the series arm connecting the input terminal and the output terminal, the first resonator is provided so as to constitute a series arm resonator connected in series with each other,
The second resonator is provided so as to constitute a parallel arm resonator disposed in a parallel arm connected between the series arm and a ground potential,
The first dielectric layer is made of silicon oxide, and the thickness of the first dielectric layer normalized by the wavelength determined by the electrode finger pitch of the IDT electrode of the first resonator is 40% to 70%. The elastic wave filter device according to any one of claims 4 to 6, which is in the range of. The response other than the response contributing to the formation of the passband of the second resonator is a higher-order mode response of the response contributing to the formation of the passband. An elastic wave filter device according to claim 1. The response other than the response contributing to the formation of the passband of the second resonator is a response different in type from the response contributing to the formation of the passband. An elastic wave filter device according to claim 1. A duplexer comprising the elastic wave filter device according to any one of claims 1 to 9.

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