Elastic wave resonator, elastic wave filter, and antenna sharing device using the same

An acoustic wave resonance device includes: piezoelectric substrate (1), first acoustic wave resonator (100) provided on an upper surface of piezoelectric substrate (1) and including first interdigital transducer electrode (110), and second acoustic wave resonator (200) provided on piezoelectric substrate (1) and including second interdigital transducer electrode (210). First acoustic wave resonator (100) and second acoustic wave resonator (200) are connected to each other. An overlap width of a plurality of first comb-shaped electrodes (112) forming first acoustic wave resonator (100) is larger than an overlap width of a plurality of second comb-shaped electrodes (212) forming second acoustic wave resonator (200). With such a configuration, frequencies in which a transverse mode spurious response is generated can be distributed and loss can be reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an acoustic wave filter used in mobile communication equipment and the like.

2. Description of the Related Art

As a conventional acoustic wave filter, as shown inFIG. 19, for example, a configuration in which three acoustic wave resonators D, E, and F are connected in series has been known. With such a configuration, a voltage applied to each pair of comb-shaped electrode fingers is reduced and a mechanical stress intensively applied is distributed so as to improve power durability (see Patent Document 1).

However, such a conventional acoustic wave filter in which a plurality of stages of acoustic wave resonators are connected in series has a problem that loss due to spurious responses is large.

When acoustic wave resonators D, E, and F having an equal overlap width are cascade-connected, if a transverse mode spurious response occurs in acoustic wave resonators D, E, and F, respectively, the spurious responses appear in the same frequency with respect to acoustic wave resonators D, E, and F. Consequently, the transverse mode spurious responses of acoustic wave resonators D, E, and F are strengthened by each other, thus increasing loss in the pass band.

This state is shown inFIGS. 20 and 21.FIG. 20is a graph showing an admittance characteristic of the conventional acoustic wave resonator shown inFIG. 19.FIG. 12is a graph showing a pass characteristic of the acoustic wave resonator. As shown in these graphs, deep transverse mode spurious responses S are largely generated between resonance frequency A and anti-resonant frequency B. As a result, loss in the pass band becomes large in the portions in which transverse mode spurious responses S are generated.

Furthermore, as a conventional acoustic wave filter, as shown inFIG. 22, for example, a configuration in which three acoustic wave resonators G, H, and I are connected in parallel is known. With such a configuration, the bandwidth of the pass band can be widened (see Patent Document 2).

However, such a conventional acoustic wave filter in which a plurality of stages of acoustic wave resonators are connected in parallel also has a problem that loss due to spurious responses is large.

When acoustic wave resonators G, H, and I having an equal overlap width are connected in parallel, if a transverse mode spurious response occurs in acoustic wave resonators G, H, and I, respectively, the spurious responses appear in the same frequency with respect to acoustic wave resonators G, H, and I. Consequently, the transverse mode spurious responses of acoustic wave resonators G, H, and I are strengthened by each other, thus increasing loss in the pass band.

This state is shown inFIGS. 23 and 24.FIG. 23is a graph showing an admittance characteristic of the conventional acoustic wave resonator shown inFIG. 22.FIG. 24is a graph showing a pass characteristic of the acoustic wave resonator. As shown in these graphs, deep transverse mode spurious responses S are largely generated between resonance frequency A and anti-resonant frequency B. As a result, similar to the case of cascade connection, loss in the pass band becomes large in the portions in which transverse mode spurious response S are generated.Patent Document 1: Japanese Patent Unexamined Publication No. H9-205343Patent Document 2: Japanese Patent Unexamined Publication No. 2000-77972

SUMMARY OF THE INVENTION

The present invention relates to an acoustic wave resonance device and an acoustic wave filter in which loss due to spurious responses is suppressed, and an antenna duplexer using the same.

An acoustic wave resonance device of the present invention includes a piezoelectric substrate, a first acoustic wave resonator provided on an upper surface of the piezoelectric substrate and including a first interdigital transducer electrode, and a second acoustic wave resonator having a second provided on the upper surface of the piezoelectric substrate and including a second interdigital transducer electrode. The first acoustic wave resonator and the second acoustic wave resonator are connected to each other. An overlap width of a plurality of first comb-shaped electrodes forming the first acoustic wave resonator is larger than an overlap width of a plurality of second comb-shaped electrodes forming the second acoustic wave resonator.

With such a configuration, it is possible to achieve a low-loss acoustic wave resonance device that is less affected by a transverse mode spurious response.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention are described with reference to drawings. Note here that the present invention is not necessarily limited to these exemplary embodiments.

First Exemplary Embodiment

FIG. 1is a top view showing an acoustic wave resonance device in accordance with a first exemplary embodiment of the present invention. As shown inFIG. 1, the acoustic wave resonance device of this exemplary embodiment includes piezoelectric substrate1made of lithium niobate, and first acoustic wave resonator100and second acoustic wave resonator200provided on an upper surface of piezoelectric substrate1. First acoustic wave resonator100and second acoustic wave resonator200are cascade-connected.

First acoustic wave resonator100includes interdigital transducer electrode110and grating reflectors120and130. Grating reflectors120and130are disposed such that they sandwich interdigital transducer electrode110therebetween on an acoustic wave propagation path.

Interdigital transducer electrode110includes bus bar111and a plurality of comb-shaped electrodes112that have the same length and are electrically connected to each other to bus bar111. Comb-shaped electrodes112are provided on bus bar111at an interval of P1. Furthermore, interdigital transducer electrode110includes a plurality of comb-shaped electrodes113that have the same length and are electrically connected to each other to bus bar114. Comb-shaped electrodes113are provided on bus bar114at an interval of P1. Comb-shaped electrode112and comb-shaped electrode113are disposed alternately and overlapped with an overlap width (a length in which two comb-shaped electrodes are overlapped with each other) of L1. Bus bar111is electrically connected to input terminal2.

Grating reflector120includes a plurality of comb-shaped electrodes122electrically connected to bus bar121. Comb-shaped electrodes122are provided on bus bar121at an interval of P1/2. Grating reflector130includes a plurality of comb-shaped electrodes132electrically connected to bus bar131. Comb-shaped electrodes132are provided on bus bar131at an interval of P1/2.

Similarly, second acoustic wave resonator200includes interdigital transducer electrode210and grating reflectors220and230. Grating reflectors220and230are disposed such that they sandwich interdigital transducer electrode210therebetween on an acoustic wave propagation path.

Interdigital transducer electrode210includes a plurality of comb-shaped electrodes212electrically connected to bus bar211. Comb-shaped electrodes212are provided on bus bar211at an interval of P2. Furthermore, interdigital transducer electrode210includes a plurality of comb-shaped electrodes213electrically connected to bus bar214. Comb-shaped electrodes213are provided on bus bar214at an interval of P2. Comb-shaped electrode212and comb-shaped electrode213are disposed alternately and overlapped with an overlap width of L2. Overlap width L2of comb-shaped electrodes212and213is smaller than overlap width L1of first acoustic wave resonator100. Bus bar214is electrically connected to output terminal4.

Grating reflector220includes a plurality of comb-shaped electrodes222electrically connected to bus bar221. Comb-shaped electrodes222are provided on bus bar221at an interval of P2/2. Grating reflector230includes a plurality of comb-shaped electrodes232electrically connected to bus bar231. Comb-shaped electrodes232are provided on bus bar231at an interval of P2/2.

First acoustic wave resonator100and second acoustic wave resonator200are electrically connected to each other via connection line3so as to form a cascade connection. Note here that connection line3may be omitted, and bus bar114and bus bar211may be directly connected to each other. In this case, since connection line3can be omitted, an acoustic wave resonator can be miniaturized.

Thus, when overlap width L1of comb-shaped electrodes112and113of interdigital transducer electrode110forming first acoustic wave resonator100is allowed to be different from overlap width L2of comb-shaped electrodes212and213of interdigital transducer electrode210forming second acoustic wave resonator200, the below-mentioned effects can be obtained.

When an acoustic wave resonator formed on piezoelectric substrate1made of lithium niobate is used, generation of transverse mode spurious responses is one of the causes deteriorating the resonator performance. The transverse mode spurious response is a spurious response generated in the pass band, which is caused by an occurrence of a standing wave in the direction perpendicular to the acoustic wave propagation direction. Herein, when first acoustic wave resonator100and second acoustic wave resonator200have an equal overlap width as in a conventional example, frequencies in which a transverse mode spurious response is generated coincide with each other as mentioned above. As a result, a deep spurious response is generated in the pass band, thus causing loss.

Furthermore, when first acoustic wave resonator100and second acoustic wave resonator200are not acoustically coupled to each other, frequencies in which the transverse mode spurious response is generated are completely coincide with each other, and therefore, the problem of loss is serious.

However, in this exemplary embodiment, overlap width L1and overlap width L2are allowed to be different from each other. The present applicant has found that by allowing overlap width L1and overlap width L2to be different from each other, generation of transverse mode spurious responses can be distributed in different frequency ranges between first acoustic wave resonator100and second acoustic wave resonator200.

That is to say, frequencies in which a spurious response is generated can be effectively distributed by varying an overlap width for each acoustic wave resonator. As a result, it is possible to achieve a low-loss acoustic wave resonance device that is less affected by transverse mode spurious responses. Furthermore, unlike a configuration by apodization the propagation path of each acoustic wave resonator is not prevented by a dummy electrode, and deterioration of Q value is not caused. Thus, it is possible to obtain an acoustic wave resonance device which has excellent characteristics and in which loss is reduced in the pass band.

This state is described with reference toFIGS. 2 and 3.FIG. 2is a graph showing an admittance characteristic of the acoustic wave resonance device in this exemplary embodiment.FIG. 3is a graph showing a pass characteristic of the acoustic wave resonance device in this exemplary embodiment. The admittance characteristic with respect to frequency in the configuration of this exemplary embodiment shown inFIG. 2is compared with that in a conventional configuration shown inFIG. 20. The comparison result shows that according to this exemplary embodiment, transverse mode spurious responses S observed between resonance frequency A and anti-resonant frequency B are distributed, and an absolute value of admittance Y11per transverse mode spurious response S is reduced. In addition, the pass characteristic in the configuration of this exemplary embodiment shown inFIG. 3is compared with that in a conventional configuration shown inFIG. 21. The comparison result shows that according to this exemplary embodiment, transverse mode spurious responses S are distributed, and an absolute value of insertion loss S21per transverse mode spurious response S is reduced. From the above reasons, according to this exemplary embodiment, loss of the acoustic wave resonance device and the acoustic wave resonance device can be reduced.

Furthermore, it is desirable that number of pairs N1in first acoustic wave resonator100and number of pairs N2in second acoustic wave resonator200shown inFIG. 1satisfy the condition: N1<N2. That is to say, it is preferable that number of pairs N1that is a number of pairs consisting of comb-shaped electrode112and comb-shaped electrode113which form first acoustic wave resonator100is smaller than number of pairs N2that is a number of pairs consisting of comb-shaped electrode212and comb-shaped electrode213which form second acoustic wave resonator200. Capacitance C1of first acoustic wave resonator100is in proportion to the product of number of pairs N1and overlap width L1. Similarly, capacitance C2of second acoustic wave resonator200is in proportion to the product of number of pairs N2and overlap width L2. Therefore, when number of pairs N1in first acoustic wave resonator100is the same as number of pairs N2in second acoustic wave resonator200, the relation: capacitance C1>capacitance C2is satisfied from the relation: overlap width L1>overlap width L2. In general, a voltage applied to second acoustic wave resonator200is in reverse proportion to the capacitance ratio C2/C1of first acoustic wave resonator100to second acoustic wave resonator200. Therefore, when capacitance C1is larger than capacitance C2, a voltage applied to second acoustic wave resonator200is higher than a voltage applied to first acoustic wave resonator100, and thus power durability is deteriorated. Therefore, when the relation: number of pairs N1<number of pairs N2is satisfied, the ratio of capacitance C1to capacitance C2is relaxed and a voltage applied to each comb-shaped electrode213of interdigital transducer electrode210forming second acoustic wave resonator200is reduced. Thus, the power durability can be improved.

Furthermore, it is desirable that the condition: capacitance C1>capacitance C2is satisfied. Even when the acoustic wave resonator has the same capacitance, an acoustic wave resonator having a longer overlap width and a smaller number of pairs is deteriorated in power durability due to heating by resistance loss of the comb-shaped electrodes as compared with an acoustic wave resonator having a shorter overlap width and a larger number of pairs. Therefore, in the condition setting of number of pairs N1and N2, by making capacitance C1be larger than capacitance C2, a voltage applied to each resonance device can be controlled, and thus the power durability can be improved.

By allowing pitch P1of first acoustic wave resonator100and pitch P2of second acoustic wave resonator200to be equal to each other and allowing the resonance frequencies of the acoustic wave resonators to coincide with each other, loss can be minimized. On the contrary, by allowing pitch P1and pitch P2to be different from each other, the bandwidths of the pass band and the attenuation band can be widened. Thus, the degree of freedom in designing can be increased.

This exemplary embodiment describes an acoustic wave resonance device in which first and second acoustic wave resonators100and200are cascade-connected in two stages. However, this exemplary embodiment can be applied to an acoustic wave resonance device in which acoustic wave resonators are cascade-connected in three stages or more.

When an acoustic wave filter is configured by using an acoustic wave resonance device in accordance with this exemplary embodiment, transverse mode spurious responses generated in the pass band can be suppressed effectively, and thus loss can be reduced.

It is desirable that a cut angle of a rotation-Y plate of piezoelectric substrate1shown inFIG. 1is set to about −30° to +30°. When the cut angle is set to an angle in this range, a wide-band acoustic wave resonance device can be achieved.

When at least one of first and second interdigital transducer electrodes110and210is covered with a SiO2thin film (oxide film) having a thickness that is 15% or more of the wavelength of an acoustic wave, loss of the acoustic wave can be reduced, and the temperature property can be also improved. Therefore, it is possible to configure an acoustic wave resonance device which has excellent characteristics and in which loss is reduced in a wide pass band.

FIG. 4is a diagram showing a configuration of an antenna duplexer using an acoustic wave filter including the acoustic resonance device in this exemplary embodiment. InFIG. 4, antenna duplexer10includes transmitting filter11and receiving filter12. At least one of transmitting filter11and receiving filter12is an acoustic wave filter configured by the acoustic wave resonance device of this exemplary embodiment. Transmitting filter11is connected to antenna element14via amplifier13. Receiving filter12is connected to between antenna element14and amplifier15.

Antenna duplexer10transmits a signal in a predetermined bandwidth, which is determined by transmitting filter11among transmitted signals, from antenna element14via amplifier13. Furthermore, antenna duplexer10receives a signal in a predetermined band determined by receiving filter12among the received signals entering into antenna element14and takes it into the inside via amplifier15.

Antenna duplexer10having such a configuration can suppress spurious responses effectively as mentioned above, and therefore loss can be reduced.

The suppression of transverse mode spurious responses by the technique in this exemplary embodiment is particularly effective when piezoelectric substrate1having such a large coupling coefficient that a plurality of transverse mode spurious responses S is generated between resonance frequency A and anti-resonant frequency B. For example, it is particularly effective when piezoelectric substrate1made of lithium niobate-based compounds or potassium niobate-based compounds is used. This is because when frequency interval is narrow such that a single transverse mode spurious response S is generated between resonance frequency A and anti-resonant frequency B, the transverse mode spurious response can be suppressed easily by shifting the transverse mode spurious response to the outside of between the resonance frequency A and anti-resonant frequency B.

Second Exemplary Embodiment

A second exemplary embodiment is different from the first exemplary embodiment in that interdigital transducer electrode110and interdigital transducer electrode210are connected in parallel.

FIG. 5is a top view showing an acoustic wave resonance device in accordance with the second exemplary embodiment of the present invention. The acoustic wave resonance device shown in this exemplary embodiment includes piezoelectric substrate1made of lithium niobate, and first acoustic wave resonator100and second acoustic wave resonator200provided on an upper surface of piezoelectric substrate1as shown inFIG. 5. First acoustic wave resonator100and second acoustic wave resonator200are connected in parallel.

First acoustic wave resonator100includes interdigital transducer electrode110and grating reflectors120and130. Grating reflectors120and130are disposed such that they sandwich interdigital transducer electrode110therebetween on an acoustic wave propagation path.

Interdigital transducer electrode110includes bus bar111and a plurality of comb-shaped electrodes112that have the same length and are electrically connected to each other to bus bar111. The comb-shaped electrodes112are provided on bus bar111at an interval of P1. Furthermore, interdigital transducer electrode110includes bus bar114and a plurality of comb-shaped electrodes113that have the same length and are electrically connected to each other to bus bar114. Comb-shaped electrodes113are provided on bus bar114at an interval of P1.

Comb-shaped electrode112and comb-shaped electrode113are overlapped with an overlap width of L1. Bus bar111is electrically connected to input terminal2. Bus bar114is electrically connected to output terminal4.

Grating reflector120includes a plurality of comb-shaped electrodes122electrically connected to bus bar121. Comb-shaped electrodes122are provided on bus bar121at an interval of P1/2. Grating reflector130includes a plurality of comb-shaped electrodes132electrically connected to bus bar131. Comb-shaped electrodes132are provided on bus bar131at an interval of P1/2.

Similarly, second acoustic wave resonator200includes interdigital transducer electrode210and grating reflectors220and230. Grating reflectors220and230are disposed such that they sandwich interdigital transducer electrode210therebetween on an acoustic wave propagation path.

Interdigital transducer electrode210includes bus bar211and a plurality of comb-shaped electrodes212electrically connected to bus bar211. The comb-shaped electrodes212are provided on bus bar211at an interval of P2. Furthermore, interdigital transducer electrode210includes bus bar214and a plurality of comb-shaped electrodes213that have the same length and are electrically connected to each other to bus bar214. Comb-shaped electrodes213are provided on bus bar214at an interval of P2.

Comb-shaped electrode212and comb-shaped electrode213are overlapped with an overlap width of L2. Overlap width L2of comb-shaped electrodes212and213is smaller than overlap width L1of first acoustic wave resonator100. Bus bar211is electrically connected input terminal2and bus bar214is electrically connected to output terminal4by connection line3, respectively. Thus, first acoustic wave resonator100and second acoustic wave resonator200are connected in parallel.

Grating reflector220includes a plurality of comb-shaped electrodes222electrically connected to bus bar221. Comb-shaped electrodes222are provided on bus bar221at an interval of P2/2. Grating reflector230includes a plurality of comb-shaped electrodes232electrically connected to bus bar231. Comb-shaped electrodes232are provided on bus bar231at an interval of P2/2.

In this way, by allowing overlap width L1of comb-shaped electrodes112and113forming first acoustic wave resonator100to be different from overlap width L2of comb-shaped electrodes212and213forming second acoustic wave resonator200, the below-mentioned effects can be obtained.

In this exemplary embodiment, as in the first exemplary embodiment, overlap width L1is allowed to be different from overlap width L2. Thus, the transverse mode spurious responses can be distributed such that frequencies in which a transverse mode spurious response is generated is allowed to be different frequency bands between first and second acoustic wave resonators100and200. This state is described with reference toFIGS. 6 and 7.FIG. 6is a graph showing an admittance characteristic of the acoustic wave resonance device in accordance with this exemplary embodiment.FIG. 7is a graph showing a pass characteristic of the acoustic wave resonance device in accordance with this exemplary embodiment. The admittance characteristic with respect to frequency in the configuration in this exemplary embodiment shown inFIG. 6is compared with that in a conventional configuration shown inFIG. 23. The comparison result shows that according to this exemplary embodiment, transverse mode spurious responses S observed between resonance frequency A and anti-resonant frequency B are distributed, and an absolute value per transverse mode spurious response S is reduced. In addition, the pass characteristic in this exemplary embodiment shown inFIG. 7is compared with that in a conventional configuration shown inFIG. 24. The comparison result shows that according to this exemplary embodiment, transverse mode spurious responses S are distributed and an absolute value per transverse mode spurious response S is reduced as compared withFIG. 24. From the above reasons, the acoustic wave resonator of this exemplary embodiment can reduce loss.

Herein, when the relation: overlap width L1>overlap width L2is satisfied, capacitance C1and C2of first and second acoustic wave resonators100and200satisfy the relation: capacitance C1>capacitance C2. Then, it is desirable that the ratio of C1and C2is relaxed by allowing the numbers of pairs N1and N2in first and second acoustic wave resonators100and200to satisfy the relation: number of pairs N2>number of pairs N1.

Furthermore, the configuration of this exemplary embodiment is effective in suppressing transverse mode spurious responses S not only in a configuration of an acoustic wave resonator in which one interdigital transducer electrode is sandwiched by two grating reflectors but also in a configuration in which two or more interdigital transducer electrodes are disposed on the propagation path.

By allowing pitch P1of first acoustic wave resonator100and pitch P2of second acoustic wave resonator200to be equal to each other and the resonance frequencies of first and second acoustic wave resonators100and200to coincide with each other, loss can be minimized. On the contrary, by allowing pitch P1and pitch P2to be different from each other, the bandwidths of the pass band and the attenuation band can be widened, and the degree of freedom in designing can be increased.

This exemplary embodiment describes a configuration in which first and second acoustic wave resonators100and200are connected in parallel. However, three or more acoustic wave resonators can be connected in parallel.

When the acoustic wave resonance device is configured by using the acoustic wave resonator of this exemplary embodiment, it is possible to effectively suppress transverse mode spurious responses S generated in the pass band.

It is desirable that a cut angle of a rotation-Y plate of piezoelectric substrate1shown inFIG. 5is set to about −30° to +30°. When the cut angle is set to an angle in this range, a wide-band acoustic wave resonance device can be achieved.

When at least one of first and second interdigital transducer electrodes110and210is covered with a SiO2thin film having a thickness that is 15% or more of the wavelength of the acoustic wave, loss of the acoustic wave can be reduced and the temperature property can be improved. Therefore, it is desirable that an acoustic wave resonance device which has an excellent temperature property and in which loss is reduced in a wide band is configured.

Note here that by configuring a transmitting filter and a receiving filter by using the configuration of this exemplary embodiment, a low-loss acoustic wave antenna duplexer can be configured.

The suppression of transverse mode spurious responses by the technique in this exemplary embodiment is particularly effective when piezoelectric substrate1having such a large coupling coefficient that a plurality of transverse mode spurious responses S is generated between resonance frequency A and anti-resonant frequency B. For example, it is particularly effective when piezoelectric substrate1made of lithium niobate-based compounds or potassium niobate-based compounds is used. This is because when frequency interval is narrow such that a single transverse mode spurious response S is generated between resonance frequency A and anti-resonant frequency B, the transverse mode spurious responses can be suppressed easily by shifting the transverse mode spurious response to the outside of between the resonance frequency A and anti-resonant frequency B.

Third Exemplary Embodiment

An acoustic wave filter in accordance with a third exemplary embodiment of the present invention is described with reference to drawings. In the third exemplary embodiment, a plurality of interdigital transducer electrodes is disposed between two grating reflectors.

FIG. 8is a top view showing an acoustic wave filter in accordance with the third exemplary embodiment of the present invention. InFIG. 8, first acoustic wave resonator300includes interdigital transducer electrodes311,312,313,314, and315having an overlap width of L1and grating reflectors316and317on the upper surface of a piezoelectric substrate. Interdigital transducer electrodes311,312,313,314, and315are disposed on the acoustic wave propagation path with an overlap width of L1(overlap width L1of comb-shaped electrodes of first acoustic wave resonator300). The comb-shaped electrodes of interdigital transducer electrodes311,312,313,314, and315are disposed at pitches of P8, P9, P10, P11, and P12, respectively. Grating reflectors316and317are disposed such that they sandwich interdigital transducer electrodes311,312,313,314, and315therebetween. Interdigital transducer electrodes311,313, and315are electrically connected to each other to input terminal2. Interdigital transducer electrodes312and314are electrically connected to each other to output terminal4.

Second acoustic wave resonator400includes interdigital transducer electrodes411,412,413,414, and415and grating reflectors416and417on the upper surface of the piezoelectric substrate. Interdigital transducer electrodes411,412,413,414, and415are disposed on the acoustic wave propagation path with an overlap width of L2(overlap width L2of the comb-shaped electrodes of second acoustic wave resonator400). The comb-shaped electrodes of interdigital transducer electrodes411,412,413,414, and415are disposed at pitches of P3, P4, P5, P6, and P7, respectively. Grating reflectors416and417are disposed such that they sandwich interdigital transducer electrodes411,412,413,414, and415therebetween. Interdigital transducer electrodes411,413, and415are electrically connected to each other to input terminal2. Interdigital transducer electrodes412and414are electrically connected to each other to output terminal5. Herein, overlap width L2of interdigital transducer electrodes411,412,413,414, and415(second acoustic wave resonator400) is smaller than overlap width L1of interdigital transducer electrodes311,312,313,314, and315(first acoustic wave resonator300).

With such a configuration, as shown inFIG. 9, transverse mode spurious responses S can be distributed and an absolute value per spurious response can be reduced. InFIG. 9, a dotted line shows a conventional admittance characteristic, and a solid line shows an admittance characteristic of this exemplary embodiment. From the comparison between the dotted line and the solid line, transverse mode spurious responses S shown in the solid line are reduced as compared with transverse mode spurious responses S shown in a dotted line.

The third exemplary embodiment describes acoustic wave resonators300and400each having five interdigital transducer electrodes. Even if the number of the interdigital transducer electrodes is not five, the effect of suppressing spurious responses can be also obtained.

Note here that by allowing all of the overlap widths of interdigital transducer electrodes311,312,313,314, and315of first acoustic wave resonator300to be equal to each other, an acoustic wave resonance filter having small loss can be configured. Furthermore, by allowing the pitches of the overlap widths of interdigital transducer electrodes311,312,313,314, and315to be different from each other, the degree of freedom in designing can be increased. The same is true to interdigital transducer electrodes411,412,413,414, and415of second acoustic wave resonator400.

By allowing pitches P8, P9, P10, P11, and P12of first acoustic wave resonator300and pitches P3, P4, P5, P6, and P7of acoustic wave resonator400to be equal to each other (that is, by allowing all the pitches to be equal to each other) and allowing two resonance frequencies of acoustic wave resonators300and400to coincide with each other, loss can be minimized. On the contrary, by allowing at least one pair of pairs of pitches P8and P3, pitches P9and P4, pitches P10and P5, pitches P11and P6, and pitches P12and P7to be different from the other pairs of pitches, the degree of balance between first acoustic wave resonator300and second acoustic wave resonator400can be adjusted.

This exemplary embodiment describes a configuration in which two acoustic wave resonators300and400are connected in parallel. However, three or more acoustic wave resonators can be connected in parallel.

When an acoustic wave filter is configured by using an acoustic wave resonator in accordance with this exemplary embodiment, transverse mode spurious responses generated in the pass band can be suppressed effectively and loss can be reduced.

Note here that it is desirable that a cut angle of a rotation-Y plate of piezoelectric substrate1shown inFIG. 5is set to about −30° to +30°. When the cut angle is set to an angle in this range, a wide-band acoustic wave filter can be achieved.

Note here that when at least one of the first interdigital transducer electrodes (311,312,313,314, and315) and second interdigital transducer electrodes (411,412,413,414, and415) are covered with a SiO2thin film having a thickness that is 15% or more of the wavelength of the acoustic wave, loss of the acoustic wave can be reduced. In addition, the temperature property can be improved. Therefore, it is possible to configure an acoustic wave filter which has an excellent temperature property and in which loss is reduced in a wide band.

Similar to the first and second exemplary embodiments, when a transmitting filter and a receiving filter are configured by using this exemplary embodiment, it is possible to configure a low-loss acoustic wave antenna duplexer with loss reduced.

The above-mentioned exemplary embodiments describe an example in which lithium niobate is used as a piezoelectric material. However, the present invention is not necessarily limited to this material, and a predetermined piezoelectric material such as lithium tantalite can be selected depending upon desired applications and properties of the acoustic wave resonance filter, and the like.

The suppression of transverse mode spurious responses by the technique in this exemplary embodiment is particularly effective when piezoelectric substrate1having such a large coupling coefficient that a plurality of transverse mode spurious responses S is generated between resonance frequency A and anti-resonant frequency B. For example, it is particularly effective when piezoelectric substrate1made of lithium niobate-based compounds or potassium niobate-based compounds is used. This is because when frequency interval is narrow such that a single transverse mode spurious response S is generated between resonance frequency A and anti-resonant frequency B, the transverse mode spurious responses can be suppressed easily by shifting the transverse mode spurious response to the outside of between the resonance frequency A and anti-resonant frequency B.

Fourth Exemplary Embodiment

An acoustic wave resonance device shown in this exemplary embodiment includes piezoelectric substrate1made of lithium niobate, and first and second acoustic wave resonators500and600provided on piezoelectric substrate1as shown inFIG. 10. Acoustic wave resonator500and acoustic wave resonator600are electrically connected to each other in parallel.

First acoustic wave resonator500includes interdigital transducer electrode510and grating reflectors520and530. Grating reflectors520and530are disposed such that they sandwich interdigital transducer electrode510therebetween in the acoustic wave propagation direction.

Interdigital transducer electrode510includes bus bar511, a plurality of comb-shaped electrodes512electrically connected to bus bar511, bus bar514, a plurality of comb-shaped electrodes513electrically connected to bus bar514. Comb-shaped electrode512and comb-shaped electrode513are overlapped with an overlap width of L1. Bus bar511is electrically connected to input terminal2via connection line31, and bus bar514is electrically connected to output terminal4via connection line32.

Grating reflector520includes bus bar521and comb-shaped electrodes522that are provided at an interval of P1/2 and electrically connected to bus bar521. Grating reflector530includes bus bar531and comb-shaped electrodes532that are provided at an interval of P1/2 and electrically connected to bus bar531.

Second acoustic wave resonator600includes interdigital transducer electrode610and grating reflectors620and630. Grating reflectors620and630are disposed such that they sandwich interdigital transducer electrode610therebetween in the acoustic wave propagation direction.

Interdigital transducer electrode610includes bus bar611, a plurality of comb-shaped electrodes612electrically connected to bus bar611, bus bar614, a plurality of comb-shaped electrodes613electrically connected to bus bar614. Comb-shaped electrode612and comb-shaped electrode613are overlapped with an overlap width of L2. Overlap width L2is smaller than overlap width L1of first acoustic wave resonator500. Bus bar611is electrically connected to input terminal2via connection line31, and bus bar614is electrically connected to output terminal4via connection line32.

Grating reflector620includes bus bar621and comb-shaped electrodes622that are provided at an interval of P2/2 and electrically connected to bus bar621. Grating reflector630includes bus bar631and comb-shaped electrodes632that are provided at an interval of P2/2 and electrically connected to bus bar631.

In this way, by allowing overlap width L1of comb-shaped electrodes512and513forming acoustic wave resonator500to be different from overlap width L2of comb-shaped electrodes612and613forming acoustic wave resonator600, it is possible to achieve a low-loss acoustic wave resonance device that is less affected by a transverse mode spurious response. Hereinafter, the relation between the overlap width and the transverse mode spurious response is described.

The transverse mode spurious response is a spurious response generated in the pass band, which is caused by an occurrence of a standing wave in the direction perpendicular to the acoustic wave propagation direction. In particular, when lithium niobate is used for a piezoelectric substrate, the transverse mode spurious responses are generated remarkably, which is one of the causes to deteriorate the resonance performance of an acoustic wave resonator.

Herein, a conventional acoustic wave resonance device in which a plurality of acoustic wave resonators are connected in parallel or series has a problem that a larger spurious response occurs in the pass band as compared with a single acoustic wave resonator. As a result of analysis, it is shown that this problem occurs because the frequencies of the transverse mode spurious responses generated in acoustic wave resonators coincide with each other. That is to say, the transverse mode spurious responses generated in the acoustic wave resonators are strengthened by each other, resulting in generating a deep spurious response in the pass band.

In particular, when pitch P1of acoustic wave resonator500and pitch P2of acoustic wave resonator600are substantially the same as each other, the transverse mode spurious responses generated in acoustic wave resonators500and600are remarkably strengthened by each other. The term “pitch P1of acoustic wave resonator500and pitch P2of acoustic wave resonator600are substantially the same as each other” herein denotes that an absolute value of the difference between pitch P1of acoustic wave resonator500and pitch P2of acoustic wave resonator600is not more than any differences between pitch P1of acoustic wave resonator500and pitches of any resonators other than acoustic wave resonator600in the acoustic wave resonance device.

FIG. 11shows a result of analysis of the relation between the overlap width and the cycle in which a transverse mode spurious response is generated. InFIG. 11, the abscissa shows the overlap width and the ordinate shows the phase velocity (=frequency×pitch of comb-shaped electrodes). For example, when the overlap width is La (=10 W/lambda), a transverse mode spurious response is generated in each of phase velocities PV1to PV6corresponding to each of the points shown by black circles.FIG. 11shows that by adjusting the overlap width, it is possible to adjust the phase velocity at which a transverse mode spurious response is generated. That is to say, by adjusting the overlap width and the pitch of the comb-shaped electrodes, it is possible to adjust the frequency in which a transverse mode spurious response is generated.

In this exemplary embodiment, by using this relation, in acoustic wave resonators500and600having the same pitch, overlap width L1of comb-shaped electrodes512and513forming acoustic wave resonator500is allowed to be different from overlap width L2of comb-shaped electrodes612and613forming second acoustic wave resonator600. With this configuration, frequencies in which a transverse mode spurious response is generated in acoustic wave resonators500and600can be distributed. Consequently, loss of the acoustic wave resonance device can be reduced.

By allowing pitch P1of acoustic wave resonator500and pitch P2of acoustic wave resonator600to be equal to each other and allowing the resonance frequencies of acoustic wave resonators500and600to coincide with each other, loss can be minimized. On the contrary, by allowing pitches P1and P2to be different from each other, the bandwidths of the pass band and the attenuation band can be widened. Thus, the degree of freedom in designing can be increased. In this case, overlap widths L1and L2may be designed by taking pitches P1and P2into account.

Herein, as shown inFIG. 11, even when overlap widths L1and L2are different from each other, transverse mode spurious responses may be generated in the same frequency. For example, when overlap width L1of acoustic wave resonator500is La (10 W/lambda), and overlap width L2of acoustic wave resonator600is Lb (about 13 W/lambda), transverse mode spurious responses are generated in a position corresponding to phase velocity PV3in both acoustic wave resonators500and600. As a result, the transverse mode spurious responses in this position are strengthened by each other, and loss in the pass band of the acoustic wave resonance device may be increased.

Therefore, in order to prevent transverse mode spurious responses generated in acoustic wave resonators500and600from overlapping, overlap widths L1and L2may be designed so as to satisfy the following mathematical formula Math. 1. In the mathematical formula, n represents an integer, and SC represents a cycle in which a transverse mode spurious response is generated in the same frequency with respect to the overlap width in acoustic wave resonator500. That is to say, cycle SC represents an amount of change in which transverse mode spurious response is generated in the same frequency with respect to the overlap width in the first acoustic wave resonator.
L2≠L1+nSC[Math. 1]

Furthermore, by designing overlap widths L1and L2so as to satisfy the following mathematical formula Math. 2, the transverse mode spurious responses can be distributed more effectively.
L2=L1+(n+½)SC[Math. 2]

Note here that in the mathematical formula Math. 1 or 2, overlap width L2may have a range of about 20% with respect to cycle SC. This is because cycle SC has a range of about 20% in the pass band of acoustic wave resonators500and600and therefore an effect of distributing transverse mode spurious responses is obtained in this range.

As mentioned above, when the overlap widths of the acoustic wave resonators provided in the acoustic wave resonance devices are designed so as to satisfy mathematical formula Math. 1 or 2, loss in the pass band in the acoustic wave resonance device can be reduced.

FIGS. 12 and 13show characteristics of the acoustic wave resonance device in this exemplary embodiment. The admittance characteristic with respect to frequency in the configuration of this exemplary embodiment shown inFIG. 12is compared with that in a conventional configuration shown inFIG. 20. The comparison result shows that according to the configuration in this exemplary embodiment, transverse mode spurious responses observed between resonance frequency A and anti-resonant frequency B are distributed, and an absolute value per transverse mode spurious response is reduced. In addition, the characteristic of the insertion loss with respect to the frequency in this exemplary embodiment shown inFIG. 13is compared with that in a conventional configuration shown inFIG. 21. The comparison result shows that according to this exemplary embodiment, transverse mode spurious responses are distributed, and an absolute value per transverse mode spurious response is reduced.

When the relation: overlap width L1<overlap width L2is satisfied, capacitance C1and C2of acoustic wave resonators500and600satisfy the relation: capacitance C1<capacitance C2. Thus, it is desirable that when number of pairs N1and number of pairs N2in acoustic wave resonators500and600satisfy the relation: number of pairs N2<number of pairs N1, the ratio of capacitance C1to capacitance C2is relaxed.

Note here that the present invention is effective in suppressing the transverse mode spurious response not only in acoustic wave resonator500(600) in this exemplary embodiment having a configuration in which one interdigital transducer electrode510(610) is sandwiched by two grating reflectors520and530(620and630) but also in a configuration in which two or more interdigital transducer electrodes are disposed on the propagation path.

This exemplary embodiment describes a configuration in which two acoustic wave resonators500and600are connected in parallel. However, three or more acoustic wave resonators can be connected in parallel.

This exemplary embodiment describes a configuration in which acoustic wave resonators500and600are connected in parallel. However, acoustic wave resonators500and600may be connected in series as shown inFIG. 14. Thus, a voltage applied to one acoustic wave resonator can be reduced, and the withstand voltage property can be improved. At the same time, when the overlap widths have the relation expressed by mathematical formula Math. 1 or 2, transverse mode spurious responses can be suppressed.

When an acoustic wave filter is configured by using the acoustic wave resonance device of the present invention, transverse mode spurious responses generated in the pass band can be effectively suppressed and loss can be reduced.

It is desirable that a cut angle of a rotation-Y plate of piezoelectric substrate1shown inFIG. 10is set to about −30° to +30°. When the cut angle is set to an angle in this range, a wide-band acoustic wave filter can be achieved.

When at least one of first and second interdigital transducer electrodes510and610is covered with a SiO2thin film having a thickness that is 15% or more of the wavelength of the acoustic wave, loss of the acoustic wave can be reduced, and the temperature property can be also improved.

By configuring a transmitting filter and a receiving filter by using the configuration of this exemplary embodiment, a low-loss acoustic wave antenna duplexer can be configured.

Fifth Exemplary Embodiment

Hereinafter, features of a fifth exemplary embodiment are described. As shown inFIG. 15, first acoustic wave filter700is a DMS filter (double-mode SAW filter) including interdigital transducer electrodes711,712,713,714, and715and grating reflectors716and717on piezoelectric substrate1. Furthermore, interdigital transducer electrodes711,712,713,714, and715are disposed on the acoustic wave propagation path. Grating reflectors716and717are disposed such that they sandwich interdigital transducer electrodes711,712,713,714, and715therebetween. An overlap width of interdigital transducer electrodes711,712,713,714, and715is L1. Interdigital transducer electrodes711,713, and715are electrically connected to each other to input terminal2, and interdigital transducer electrodes712and714are electrically connected to each other to output terminal4.

Second acoustic wave filter800is a DMS filter (double-mode SAW filter) including interdigital transducer electrodes811,812,813,814, and815and grating reflectors816and817on piezoelectric substrate1. Furthermore, interdigital transducer electrodes811,812,813,814, and815are disposed on the acoustic wave propagation path. Grating reflectors816and817are disposed such that they sandwich interdigital transducer electrodes811,812,813,814, and815therebetween. An overlap width of interdigital transducer electrodes811,812,813,814, and815is L2. Interdigital transducer electrodes811,813, and815are electrically connected to each other to input terminal2, and interdigital transducer electrodes812and814are electrically connected to each other to output terminal5.

In particular, when pitches P8to P12of acoustic wave filter700and pitches P3to P7of acoustic wave filter800are substantially the same as each other, transverse mode spurious responses generated in the acoustic wave filters are remarkably strengthened by each other. The term “pitches P8to P12of acoustic wave filter700and pitches P3to P7of acoustic wave filter800are substantially the same as each other” herein denotes that an absolute value of the difference between pitches P8to P12of acoustic wave filter700and pitches P3to P7of acoustic wave filter800is not more than any differences between pitches P8to P12of acoustic wave filter700and pitches of any filters other than acoustic wave filter800in the acoustic wave resonance device.

Herein, overlap width L2of second acoustic wave filter800is smaller than overlap width L1of first acoustic wave filter700. When overlap widths L1and L2have the relation expressed by mathematical formula Math. 1, transverse mode spurious responses S can be distributed as shown in a solid line inFIG. 16. Furthermore, when overlap widths L1and L2have the relation expressed by mathematical formula Math. 2, transverse mode spurious responses S can be distributed more effectively. As inFIG. 9, inFIG. 16, a dotted line shows a conventional admittance characteristic, and a solid line shows an admittance characteristic of this exemplary embodiment.

This exemplary embodiment describes acoustic wave filter700(800) having five interdigital transducer electrodes711,712,713,714, and715(811,812,813,814, and815). However, the number of the interdigital transducer electrodes is not necessarily limited to five, and also in such cases, the effect of suppressing spurious responses can be obtained.

Note here that by allowing all of overlap widths L1of interdigital transducer electrodes711,712,713,714, and715of acoustic wave filter700to be equal to each other, a low-loss acoustic wave resonance device can be configured. Furthermore, by allowing the overlap widths L1of interdigital transducer electrodes711,712,713,714, and715to be different from each other, transverse mode spurious responses can be further distributed. The same is true to overlap widths L2of interdigital transducer electrodes811,812,813,814, and815of second acoustic wave filter800.

By allowing pitches P8, P9, P10, P11, and P12of acoustic wave filter700and pitches P3, P4, P5, P6, and P7of acoustic wave filter800to be equal to each other, resonance frequencies of acoustic wave filters700and800can be allowed to coincide with each other. Thus, loss of the acoustic wave filter can be minimized. On the contrary, by allowing at least one pair of pairs of pitches P8and P3, pitches P9and P4, pitches P10and P5, pitches P11and P6, and pitches P12and P7to be different, the degree of balance between acoustic wave filter700and acoustic wave filter800can be adjusted.

This exemplary embodiment describes a configuration in which two acoustic wave filters700and800are connected in parallel. However, three or more acoustic wave filters can be connected in parallel.

When an acoustic wave filter is configured by using an acoustic wave filter of the present invention, transverse mode spurious responses generated in the pass band can be suppressed effectively and loss can be reduced.

Note here that it is desirable that a cut angle of a rotation-Y plate of piezoelectric substrate1shown inFIG. 15is set to about −30° to +30°. When the cut angle is set to an angle in this range, a wide-band acoustic wave filter can be achieved.

Note here that when at least one of interdigital transducer electrodes711,712,713,714, and715of acoustic wave filter700and interdigital transducer electrodes811,812,813,814, and815of acoustic wave filter800are covered with a SiO2 thin film having a thickness that is 15% or more of the wavelength of the acoustic wave, loss of the acoustic wave can be reduced. At the same time, the temperature property can be improved.

By configuring a transmitting filter and a receiving filter by using the configuration of this exemplary embodiment, a low-loss acoustic wave antenna duplexer can be configured.

Sixth Exemplary Embodiment

Hereinafter, features of the sixth exemplary embodiment are described. As shown inFIG. 17, ladder-type filter28includes series-arm acoustic wave resonance devices29and30and parallel-arm acoustic wave resonance devices90,91, and92. Note here thatFIG. 17shows an example of a ladder-type filter. When three or more series-arm acoustic wave resonance devices are disposed and when two or four or more parallel-arm acoustic wave resonance devices are disposed, the effects described below can be obtained.

In ladder-type filter28, by allowing the resonance frequencies of series-arm acoustic wave resonance devices29and30to be substantially equal to the anti-resonant frequencies of parallel-arm acoustic wave resonance devices90,91and92, the band pass characteristic can be obtained.

In acoustic wave resonance device29, acoustic wave resonator291and acoustic wave resonator292are connected in parallel. Herein, overlap width (EL1)29L1of acoustic wave resonator291is smaller than overlap width (EL2)29L2of acoustic wave resonator292. Furthermore, when overlap widths29L1and29L2have the relation expressed by mathematical formula Math. 1 or 2, transverse mode spurious responses can be distributed.

In particular, when acoustic wave resonators291and292are connected to the same series arm, transverse mode spurious responses generated in the acoustic wave resonators are strengthened by each other. The term “connected to the same series arm” herein denotes that acoustic wave resonators are connected to one series arm in series or in parallel like resonators291and292as shown inFIG. 17.

In particular, when pitch29P1of acoustic wave resonator291and pitch29P2of acoustic wave resonator292are substantially the same as each other, transverse mode spurious responses generated in the acoustic wave resonators are remarkably strengthened by each other. The term “pitch29P1of acoustic wave resonator291and pitch29P2of acoustic wave resonator292are substantially the same as each other” herein denotes that an absolute value of the difference between pitch29P1of acoustic wave resonator291and pitch29P2of acoustic wave resonator292is not more than any differences between pitch29P1of acoustic wave resonator291and pitches of any resonators other than acoustic wave resonator292in the acoustic wave resonance device.

In acoustic wave resonance device90, acoustic wave resonator901and acoustic wave resonator902are connected in parallel. Herein, overlap width (GL1)90L1of acoustic wave resonator901is smaller than overlap width (GL2)90L2of acoustic wave resonator902. Furthermore, when overlap widths90L1and90L2have the relation expressed by mathematical formula Math. 1 or 2, transverse mode spurious responses can be distributed.

In particular, when acoustic wave resonators901and902are connected to the same parallel arm, transverse mode spurious responses generated in acoustic wave resonators are strengthened by each other. The term “connected to the same parallel arm” herein denotes that acoustic wave resonators are connected to one parallel arm in series or in parallel as in resonators901and902shown inFIG. 17.

In particular, when pitch90P1of acoustic wave resonator901and pitch90P2of acoustic wave resonator902are substantially the same as each other, transverse mode spurious responses generated in acoustic wave resonators are remarkably strengthened by each other. The term “pitch90P1of acoustic wave resonator901and pitch90P2of acoustic wave resonator902are substantially the same as each other” herein denotes that an absolute value of the difference between pitch90P1of acoustic wave resonator901and pitch90P2of acoustic wave resonator902is not more than any differences between pitch90P1of acoustic wave resonator901and pitches of any resonators other than acoustic wave resonator902in the acoustic wave resonance device.

Furthermore, by allowing all the overlap widths29L1,29L2,90L1, and90L2to be different, frequencies in which a transverse mode spurious response is generated in all the acoustic wave resonators can be distributed. Thus, loss in the pass band can be reduced effectively.

Furthermore, when any combinations of two of overlap widths29L1,29L2,90L1, and90L2are allowed to have the relation expressed by mathematical formula Math. 1 or 2, ladder-type filter28can reliably prevent transverse mode spurious responses generated in the series arm and the parallel arm from overlapping in the same frequency. Thus, loss of the pass band can be reduced effectively.

It is desirable that |29L1−29L2|, which is an absolute value of the difference between overlap width29L1and overlap width29L2, is larger than |90L1−90L2|, which is an absolute value of the difference between overlap width90L1and overlap width90L2.FIG. 2shows that as the phase velocity becomes larger (that is, as the frequency becomes higher), cycle SC in which transverse mode spurious responses are generated becomes smaller. In other words, as the frequency is higher, dependency on the overlap width is larger. Herein, in ladder-type filter28, in order to allow the resonance frequencies of series-arm acoustic wave resonance devices29and30to substantially coincide with the anti-resonant frequencies in parallel-arm acoustic wave resonance devices90,91and92, the resonance frequencies of series-arm acoustic wave resonance devices29and30are set to relatively low, and anti-resonant frequencies of parallel-arm acoustic wave resonance devices90,91and92are set to relatively high. Therefore, in series-arm acoustic wave resonance devices29and30in which the resonance frequency is relatively low, the absolute value |29L1−29L2| that is a difference in overlap widths of the acoustic wave resonator is made to be relatively large, and in parallel-arm acoustic wave resonance devices90,91and92in which the resonance frequency is relatively high, the absolute value |90L1−90L2| that is a difference in overlap widths of the acoustic wave resonator is made to be relatively small. Thus, positions in which a transverse mode spurious response is generated can be distributed easily.

This exemplary embodiment describes a configuration in which two acoustic wave resonators291and292and two acoustic wave resonators901and902are connected in parallel in acoustic wave resonance devices29and90, respectively. However, three or more acoustic wave resonators can be connected in parallel.

This exemplary embodiment describes a configuration in which two acoustic wave resonators291and292and two acoustic wave resonators901and902are connected in parallel in acoustic wave resonance devices29and90, respectively. However, acoustic wave resonators291and292and resonators901and902may be connected in series as shown inFIG. 18. Thus, a voltage applied to one acoustic wave resonator can be reduced, and the withstand voltage property of the acoustic resonance device can be improved. At the same time, when the overlap widths have the relation expressed by mathematical formula Math. 1 or 2, transverse mode spurious responses can be suppressed.

Note here that by allowing pitch29P1of acoustic wave resonator291and pitch29P2of acoustic wave resonator292to be equal to each other, and the resonance frequencies of the acoustic wave resonators to coincide with each other, loss can be minimized. On the contrary, by allowing pitches29P1and29P2to be different from each other, the bandwidths of the pass band and the attenuation band can be widened. Thus, the degree of freedom in designing can be increased. In this case, overlap widths29L1and29L2may be designed by taking pitches29P1and29P2into account. The same is true to pitch90P1of acoustic wave resonator901and pitch90P2of acoustic wave resonator902.

Note here that it is desirable that a cut angle of a rotation-Y plate of the piezoelectric substrate formed in the lower part of these acoustic wave resonators is set to about −30° to +30°. When the cut angle is set to an angle in this range, a wide-band acoustic wave filter can be achieved.

Note here that when at least one of the interdigital transducer electrodes provided in these acoustic wave resonators is covered with a SiO2thin film having a thickness that is 15% or more of the wavelength of the acoustic wave, loss of the acoustic wave can be reduced. At the same time, the temperature property can be improved.

By configuring a transmitting filter and a receiving filter by using the configuration of this exemplary embodiment, a low-loss acoustic wave antenna duplexer can be configured.

An acoustic wave resonance device and an acoustic wave filter in accordance with the present invention can suppress an occurrence of loss due to transverse mode spurious responses, and therefore are useful in a variety of mobile communication equipment such as a portable telephone.