JP5760321B2 - Elastic wave filter - Google Patents

Description

  The present invention relates to an acoustic wave filter, for example, a (SAW: Surface Acoustic Wave) filter.

  The SAW device uses surface acoustic waves, and an electrode called IDT (interdigital transducer) is disposed on a piezoelectric substrate as an input side electrode and an output side electrode along the propagation direction of the elastic wave. An electrical-mechanical mutual conversion between an electric signal and an elastic wave is performed between two electrodes to give a frequency selection (band filter) characteristic. A SAW filter, which is one of SAW devices, is used as a panda-pass filter for various communication devices such as mobile phones that have been improved in function and size. Accordingly, it is required that the insertion loss is small, the frequency selectivity is excellent (has a steep attenuation characteristic), the pass frequency band is wide, and the flatness of the attenuation characteristic is high in the pass frequency band.

  As a technique for widening the pass frequency band as described above, for example, a method using the following filter is known. As shown in FIG. 9, this filter has a taper arranged so that the width dimension and the distance dimension of the electrode fingers 102 are widened from the bus bar 101 on one side (front side) toward the bus bar 101 on the other side (back side). The type IDT electrode 103 is arranged as the input side IDT electrode 104 and the output side IDT electrode 105 along the propagation direction of the elastic wave, and a square metal film (shield electrode 106) is arranged between the electrodes 104 and 105. It has a configuration. In order to reduce insertion loss, that is, to configure the IDT electrodes 104 and 105 as unidirectional electrodes (SPUD: Single Phase Unidirectional Transducer), for example, DART (Distributed Acoustic Reflection Transducer) along the electrode finger 102. Reflective electrodes 107 are provided at a plurality of locations.

  In FIG. 9, λ is a period unit (wavelength) that is repeated at a predetermined interval depending on the width dimension and interval dimension of the electrode finger 102 and the reflective electrode 107 so as to correspond to the wavelength of the propagating elastic wave, and the propagation direction of the elastic wave So as to propagate from an elastic wave of a short wavelength track (propagation path) to an elastic wave of a long wavelength track from the bus bar 101 on one side to the bus bar 101 on the other side. In other words, the pass frequency band is widened. In this example, the width dimension of the electrode finger 102, the separation dimension between the electrode fingers 102 and 102, and the separation dimension between the electrode finger 102 and the reflection electrode 107 are each set to λ / 8, and the width dimension of the reflection electrode 107 is 3λ. / 8 is set. Therefore, in the input-side IDT electrode 104, the direction from the input-side IDT electrode 104 to the output-side IDT electrode 105 is the forward direction, and the direction from the output-side IDT electrode 105 to the input-side IDT electrode 104 is the reverse direction. In the electrode 105, if the direction from the output IDT electrode 105 toward the input IDT electrode 104 is the forward direction, and the direction from the input IDT electrode 104 toward the output IDT electrode 105 is the reverse direction, the elastic wave propagating in the forward direction. For example, the elastic wave propagating in the opposite direction becomes the same phase at the center position of each reflective electrode 107, and the elastic wave propagating in the reverse direction has an opposite phase to the elastic wave propagating in the forward direction at the central position of the reflective electrode 107, for example. Will be offset. Therefore, this filter is configured so that an elastic wave apparently propagates in the forward direction. In FIG. 9, reference numeral 108 denotes a piezoelectric substrate such as quartz, and 109 denotes a sound absorbing material for absorbing unnecessary elastic waves that pass through the IDT electrodes 104 and 105 and propagate to the end region of the piezoelectric substrate 108. is there.

In this filter, in order to increase the selectivity as described above, for example, a method of increasing the number of pairs (number) of the electrode fingers 102 is employed.
In order to improve the flatness of the attenuation characteristic in the pass frequency band, for example, a method of thinning the weight of the reflective electrode 107 is known in order to adjust the energy of the elastic wave reflected by each of the reflective electrodes 107. ing. Specifically, in the reflective electrode 107 arranged as shown in FIG. 10A, as shown in FIG. 10B, the gap region 110 having a width dimension of λ / 8 is reflected along the length direction. The weight of the reflective electrode 107 is thinned out so as to be formed at the center of the electrode 107. Then, as shown in FIG. 11, by arranging the reflection electrode 107 thinned out (the elastic wave is not reflected in the forward direction) at a predetermined position and suppressing reflection of the elastic wave at the reflection electrode 107, The flatness of the attenuation characteristic is obtained. In FIG. 10, the electrode finger 102 and the reflective electrode 107 are schematically drawn.

By the way, in the above filter, since the electrode finger 102 is formed in a taper shape, as shown in FIGS. 9 and 11, for example, diffraction occurs when an elastic wave is emitted from the input-side IDT electrode 104. As will be described later with reference to FIG. 5 as a conventional example, the amount of attenuation on the low-frequency side and high-frequency side in the pass frequency band is particularly large, and so-called shoulder sag occurs. Further, as described above, when the logarithm of the electrode finger 102 is increased in order to improve the selectivity of the filter, the deterioration of the passband due to the diffraction is further increased. Therefore, in order to improve the flatness of the attenuation characteristic in this filter, for example, it is necessary to reduce only the attenuation amount on the low frequency side and the high frequency side without changing the attenuation characteristic on the center side of the pass frequency band. Furthermore, for example, in the pass frequency band, the attenuation amount may increase at a predetermined frequency in addition to the low frequency side and the high frequency side. In this case, without changing the attenuation characteristics of other frequencies in the same manner, It is necessary to adjust only the frequency at which the attenuation characteristic deteriorates. However, in the above thinning-out method, it is difficult to independently adjust the attenuation amount at an arbitrary frequency from the low frequency side to the high frequency side of the pass frequency band, and thus good flatness cannot be obtained.
Patent Document 1 describes a tapered electrode, but does not suggest any of the above problems.

JP-A-63-35005

  The present invention has been made in view of such circumstances, and an object of the present invention is to obtain an attenuation characteristic having high flatness in a pass frequency band in an elastic wave filter in which an input-side IDT electrode and an output-side IDT electrode are tapered. It is an object of the present invention to provide an elastic wave filter that can be used.

The elastic wave filter of the present invention is
An input-side IDT electrode and an output-side IDT electrode that are spaced apart from each other in the propagation direction of the elastic wave;
The input-side IDT electrode and the output-side IDT electrode have a pair of bus bars formed so as to be parallel to each other, and extend from each of the bus bars alternately in a comb-tooth shape, and have a width dimension and a separation dimension that are the same as those described above. In an elastic wave filter comprising a tapered IDT electrode provided with a plurality of electrode fingers formed so as to spread from one side of the bus bar to the other side,
At least one of the input side IDT electrode and the output side IDT electrode includes one or more reflective electrodes arranged to extend along the length direction of the electrode fingers,
In the input-side IDT electrode, a direction from the input-side IDT electrode toward the output-side IDT electrode is a forward direction, a direction from the output-side IDT electrode to the input-side IDT electrode is a reverse direction, and the output-side IDT electrode In this case, the direction from the output IDT electrode to the input IDT electrode is the forward direction, and the direction from the input IDT electrode to the output IDT electrode is the reverse direction.
At least one of the reflective electrodes is formed from one end to the other end side in the length direction of the reflective electrode, and one first region weighted so that an elastic wave is reflected in the forward direction. The other first region formed from the other end to the one end side in the length direction of the reflective electrode and weighted so as to reflect the elastic wave in the forward direction, and the one first region And a second region formed in a region sandwiched between the first region and the other first region and weighted so as not to reflect an elastic wave in the forward direction .
When the period unit of the dimension in the propagation direction of the elastic wave of the set consisting of the reflective electrode and a pair of electrode fingers adjacent to the reflective electrode and alternately extending from each of the pair of bus bars is λ,
The reflective electrode has a width dimension of 3λ / 8 in the propagation direction of the elastic wave,
The first region is composed of a metal film having a width dimension of 3λ / 8 in the propagation direction of the elastic wave ,
The second region is a metal film having a width dimension of λ / 8 by forming a slit extending from the one first region to the other first region at the center in the width direction of the reflective electrode. two areas formed of, characterized in that it is constituted are respectively arranged in the propagation direction of the acoustic wave width dimension through the gap region of the lambda / 8.
The elastic wave filter of another invention is
An input-side IDT electrode and an output-side IDT electrode that are spaced apart from each other in the propagation direction of the elastic wave;
The input-side IDT electrode and the output-side IDT electrode have a pair of bus bars formed so as to be parallel to each other, and extend from each of the bus bars alternately in a comb-tooth shape, and have a width dimension and a separation dimension that are the same as those described above. In an elastic wave filter comprising a tapered IDT electrode provided with a plurality of electrode fingers formed so as to spread from one side of the bus bar to the other side,
At least one of the input side IDT electrode and the output side IDT electrode includes one or more reflective electrodes arranged to extend along the length direction of the electrode fingers,
In the input-side IDT electrode, a direction from the input-side IDT electrode toward the output-side IDT electrode is a forward direction, a direction from the output-side IDT electrode to the input-side IDT electrode is a reverse direction, and the output-side IDT electrode In this case, the direction from the output IDT electrode to the input IDT electrode is the forward direction, and the direction from the input IDT electrode to the output IDT electrode is the reverse direction.
At least one of the reflective electrodes has an energy of an elastic wave propagating in the forward direction on each of the low-frequency side and the high-frequency side of the passing region, and an energy of an elastic wave propagating in the forward direction in a band between them. In order to increase the size, one first region and the other first region are weighted so that elastic waves are reflected in the forward direction at one end and the other end in the length direction of the reflective electrode, respectively. , Provided in a region sandwiched between the one first region and the other first region from one first region to the other first region, and does not reflect elastic waves in the forward direction and a second region weighted decimated as,
When the period unit of the dimension in the propagation direction of the elastic wave of the set consisting of the reflective electrode and a pair of electrode fingers adjacent to the reflective electrode and alternately extending from each of the pair of bus bars is λ,
The reflective electrode has a width dimension of 3λ / 8 in the propagation direction of the elastic wave,
The first region is composed of a metal film having a width dimension of 3λ / 8 in the propagation direction of the elastic wave ,
The second region is formed with a metal film having a width dimension of λ / 8 by forming a slit extending from one end portion of the reflective electrode to the other end portion at a central portion in the width direction of the reflective electrode . two regions, characterized in that it is constituted are respectively arranged in the propagation direction of the acoustic wave width dimension through the gap region of the lambda / 8.

The elastic wave filter of the present invention includes an input-side IDT electrode and an output-side IDT electrode that are spaced apart from each other in the propagation direction of the elastic wave,
The input-side IDT electrode and the output-side IDT electrode have a pair of bus bars formed so as to be parallel to each other, and extend in a comb shape from each of the bus bars toward the opposite bus bar, and the width dimension thereof. And an elastic wave filter comprising a taper type IDT electrode provided with a plurality of electrode fingers formed so that a spacing dimension increases from one side of the bus bar to the other side,
At least one of the input-side IDT electrode and the output-side IDT electrode is configured to be a periodic unit corresponding to the wavelength of the propagating elastic wave according to the width dimension of the four electrode fingers and the separation dimension between the electrode fingers. ,
In the input-side IDT electrode, a direction from the input-side IDT electrode toward the output-side IDT electrode is a forward direction, a direction from the output-side IDT electrode to the input-side IDT electrode is a reverse direction, and the output-side IDT electrode In this case, the direction from the output IDT electrode to the input IDT electrode is the forward direction, and the direction from the input IDT electrode to the output IDT electrode is the reverse direction.
At least one of the sets of four electrode fingers constituting the periodic unit has a main electrode finger and an auxiliary electrode finger having a width larger than that of the main electrode finger alternately adjacent to each other from each of the pair of bus bars. Are connected to the first region where the elastic wave is reflected in the forward direction, and to each of the main electrode finger and the auxiliary electrode finger in the first region, respectively. Electrode fingers formed so as to have the same width dimension are arranged, and the second region configured so as not to reflect elastic waves in the forward direction is arranged in the length direction thereof ,
Each of the input-side IDT electrode and the output-side IDT electrode is configured so that elastic waves having different period units are propagated between the pair of bus bars .
It is preferable that the main electrode fingers and the auxiliary electrode fingers are configured such that their width dimensions become equal from the first region toward the second region.

  The present invention relates to an input-side IDT electrode and an output-side IDT electrode that are formed so that the width dimension and interval dimension of a plurality of electrode fingers and one or more reflective electrodes increase from one side of the bus bar to the other side. The input side IDT electrode is used as either or both of the side IDT electrodes, and in the input side IDT electrode, the direction from the input side IDT electrode to the output side IDT electrode is the forward direction, and the input side is input from the output side IDT electrode. The direction toward the side IDT electrode is the reverse direction. In the output side IDT electrode, the direction from the output side IDT electrode to the input side IDT electrode is the forward direction, and the direction from the input side IDT electrode to the output side IDT electrode is the reverse direction. Then, the first region weighted so that the elastic wave is reflected in the forward direction is overlapped with the elastic wave so that the elastic wave is not reflected in the forward direction. A second region with the decimated, the are arranged in the length direction of the reflective electrode. Alternatively, when the elastic wave period unit is constituted by a set of four electrode fingers, a pair of a main electrode finger and an auxiliary electrode finger having a larger width than the main electrode finger is paired with respect to at least one of the set. A first region provided at least one so as to alternately extend adjacent to each other from each of the bus bars, and connected to each of the main electrode finger and the auxiliary electrode finger in the first region A second region in which electrode fingers formed so as to have the same width dimension are arranged in the length direction. Therefore, the distribution of the energy of the elastic wave propagating in the forward direction from the low wavelength side to the high wavelength side of the elastic wave propagating through the tapered IDT electrode can be adjusted. High attenuation characteristics can be obtained. Therefore, for example, when the first regions are arranged at both ends of the reflective electrode, even in the case of a tapered IDT electrode, attenuation of attenuation characteristics due to diffraction is suppressed and attenuation with high flatness in the pass frequency band is achieved. Characteristics can be obtained.

It is a top view which shows an example of the elastic wave filter which concerns on embodiment of this invention. It is the top view which expanded a part of above-mentioned elastic wave filter. It is a schematic diagram which shows a mode that an elastic wave propagates in the above-mentioned elastic wave filter. It is a schematic diagram which shows a mode that an elastic wave propagates in the above-mentioned elastic wave filter. It is a characteristic view which shows the characteristic acquired about the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the conventional elastic wave filter. It is a top view which shows the conventional elastic wave filter. It is a top view which shows the conventional elastic wave filter. It is a schematic diagram for demonstrating the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter. It is a top view which shows the other example of the above-mentioned elastic wave filter.

  An elastic wave filter according to an embodiment of the present invention will be described with reference to FIGS. The acoustic wave filter of the present invention includes an input-side IDT electrode 12 and an output-side IDT electrode 13 that have substantially the same configurations as the input-side IDT electrode 104 and the output-side IDT electrode 105 described above. It is formed on the substrate 11. These IDT electrodes 12 and 13 are provided at intervals along the elastic wave propagation direction, and a square shield electrode 16 is disposed between the IDT electrodes 12 and 13. In this filter, for example, a metal film such as aluminum is formed on the entire surface of the piezoelectric substrate 11, and then a region other than the electrodes 12, 13, and 16 is etched through a mask layer laminated on the metal film. It is formed by photolithography. In FIG. 1, reference numerals 25 and 25 denote sound absorbing materials (dampers) for absorbing unnecessary elastic waves propagating to the end region of the piezoelectric substrate 11 through the IDT electrodes 12 and 13.

  In the input-side IDT electrode 12, reference numerals 14a and 14b denote a bus bar on one side and a bus bar on the other side, respectively, so that they are parallel to each other along the propagation direction of the elastic wave. Is formed. The bus bar 14 a on one side is grounded, and the bus bar 14 b on the other side is connected to the input port 21. Reference numeral 15 in FIG. 1 denotes electrode fingers extending from each of the bus bars 14a and 14b of the input side IDT electrode 12 so as to be alternately comb-shaped. Here, in the input-side IDT electrode 12, the direction from the input-side IDT electrode 12 to the output-side IDT electrode 13 is the forward direction, the direction from the output-side IDT electrode 13 to the input-side IDT electrode 12 is the reverse direction, and In the output-side IDT electrode 13, the direction from the output-side IDT electrode 13 to the input-side IDT electrode 12 is the forward direction, and the direction from the input-side IDT electrode 12 to the output-side IDT electrode 13 is the reverse direction.

  The input-side IDT electrode 12 has a length direction of the electrode finger 15 in order to reflect an elastic wave to be propagated in the opposite direction of the input-side IDT electrode 12 toward the output-side IDT electrode 13 (forward direction). , Reflective electrodes 26 extending from one bus bar 14a toward the other bus bar 14b are provided at a plurality of locations. Therefore, the IDT electrode 12 is configured as a unidirectional electrode (SPUD: Single Phase Uni-Transducer Transducer), for example, a DART (Distributed Acoustic Reflector Transducer).

As shown in FIG. 2, the electrode fingers 15 and the reflective electrodes 26 include a pair of electrode fingers 15, 15 formed adjacent to each other from the bus bars 14 a, 14 b, and these electrode fingers 15, 15. A pair of reflective electrodes 26 extending from the bus bar 14a so as to be adjacent to each other are arranged in a set so as to be repeated periodically along the propagation direction of the elastic wave in a predetermined cycle unit λ. In this filter, an elastic wave having the same length as the period unit λ propagates.
The arrangement pattern of the electrode fingers 15 and the reflective electrodes 26 is such that the distance between the electrode fingers 15 and 15 and the distance between the electrode fingers 15 and the reflective electrodes 26 from the one bus bar 14a on the near side to the other bus bar 14b on the far side. The distance between the electrodes is gradually increased, and the width of each electrode finger 15 and the reflection electrode 26 is also gradually increased. Accordingly, when the track that is the propagation path of the elastic wave is Tr, in a direction orthogonal to the propagation direction of the elastic wave, the cycle unit λ is narrow from Tr1 to wide Tr2 from the front bus bar 14a to the back bus bar 14b. Will be formed. In FIG. 1, the width dimensions of the electrode fingers 15 and the reflective electrodes 26 are drawn as being constant for simplification of illustration.

  In this example, the width dimension of the reflective electrode 26 and the dimension between the straight lines passing through the centers of the electrode fingers 15 in the adjacent electrode fingers 15 and 15 are 3λ / 8 and λ / 4, respectively. The propagating elastic waves are in phase with each other at, for example, the center position of each reflective electrode 26, and the elastic waves propagating in the opposite direction are, for example, in phase opposite to the elastic wave propagating in the forward direction at the central position of the reflecting electrode 26 It is configured. Moreover, the width dimension of the electrode finger 15 and the separation distance between the electrode fingers 15 and 15 are each λ / 8.

  Next, the reflective electrode 26 will be described in detail with reference to FIG. As shown in the left side of FIG. 2, the reflective electrode 26 has a metal film on the entire surface so that elastic waves are reflected toward the output-side IDT electrode 13 (forward direction) from Tr1 to Tr2. In order to adjust the reflection of the elastic wave in the forward direction from Tr1 to Tr2, as shown on the right side of the figure, and the main reflective electrode 27 that is uniformly weighted in the length direction by forming Auxiliary reflective electrodes 30 having weights adjusted in the length direction are arranged. As with the main reflective electrode 27, the auxiliary reflective electrode 30 includes a first region 28 weighted so that the elastic wave is reflected in the forward direction, and a first region 28 weighted so that the elastic wave is not reflected in the forward direction. Two regions 29 are arranged in the length direction as follows.

  The auxiliary reflective electrode 30 is formed with a metal film on the entire surface in the width direction in each region adjacent to the bus bars 14a, 14b on both sides, that is, at both ends of the auxiliary reflective electrode 30, and the first regions 28, 28 described above. In addition, a region sandwiched between the first regions 28 and 28 in the length direction of the auxiliary reflective electrode 30 forms a second region 29. The second region 29 is a strip 31 made of two bar-shaped metal films that extend in parallel along the length direction of the auxiliary reflective electrode 30 so as to be connected to each of the first regions 28, 28. , 31. The strips 31 are formed so that the width dimension is λ / 8 and the separation dimension is λ / 8. That is, in the second region 29, the weight is thinned by thinning (not forming) the metal film on the center side along the propagation direction of the elastic wave. A region between the strips 31, 31 forms a gap region 32.

  Therefore, as shown in FIG. 3, the auxiliary reflection electrode 30 apparently has elastic waves that are directed in opposite directions at both ends (first region 28) of the auxiliary reflection electrode 30 adjacent to the bus bars 14a and 14b. Reflected in the forward direction, elastic waves are not reflected in the forward direction in the second region 29 on the center side. The length of each of the first region 28 and the second region 29 in the length direction of the auxiliary electrode 30 is such that the attenuation amount in the pass frequency band of the electrical signal output from the output port 22 is substantially constant. That is, it is set so as to obtain good flatness. In the input-side IDT electrode 12, as shown in FIG. 1 described above, the main reflection electrode 27 and the auxiliary reflection electrode 30 are arranged in a predetermined arrangement order along the propagation direction of the elastic wave. In this example, the auxiliary reflective electrode 30 is arranged so that the first region 28 and the second region 29 have the same arrangement pattern in the length direction.

  As shown in FIG. 1 described above, the output-side IDT electrode 13 includes a bus bar 14c on one side and a bus bar 14d on the other side. The bus bar 14c on one side is disposed on the front side in FIG. 1 and connected to the output port 22, and the bus bar 14d on the other side is disposed on the back side and grounded. Similarly to the input-side IDT electrode 12, the output-side IDT electrode 13 has a constant cycle unit λ along the elastic wave propagation direction, and the cycle unit from the one side bus bar 14c toward the other side bus bar 14d. The electrode fingers 15 and the reflective electrodes 26 are arranged so that λ becomes an array pattern extending from Tr1 to Tr2. In the output-side IDT electrode 13, the reflective electrode 26 is connected to the other bus bar 14d.

  Further, the width dimension and interval dimension of the electrode finger 15 and the reflective electrode 26 of the output side IDT electrode 13 are formed in the same manner as the dimensions of the electrode finger 15 and the reflective electrode 26 of the input side IDT electrode 12 described above. The main reflection electrode 27 and the auxiliary reflection electrode 30 are arranged in a predetermined arrangement order, and the first region 28 and the second region 29 in the auxiliary reflection electrode 30 are in the input side IDT electrode 12 in the length direction. The first region 28 and the second region 29 are arranged so as to have the same arrangement pattern. Therefore, in the auxiliary reflecting electrode 30 of the output side IDT electrode 13, the elastic wave is reflected in the forward direction (direction toward the input side IDT electrode 12) in the first regions 28 and 28 adjacent to the pair of bus bars 14c and 14d. However, in the second region 29 which is a region between the first regions 28 and 28, the light propagates toward the damper 25 on the right side of the output-side IDT electrode 13 without being reflected in the forward direction. 1 and 2, the electrodes 12, 13, and 16 are hatched so as to be easily distinguished from the region of the piezoelectric substrate 11. The same applies to the following figures.

  In such an acoustic wave filter, when a frequency signal is input to the input-side IDT electrode 12 via the input port 21, a surface acoustic wave (SAW) is generated. This elastic wave propagates in the forward and reverse directions on the track Tr in which the periodic unit λ corresponding to the wavelength length (λ) is formed in the input-side IDT electrode 12. The elastic waves traveling in the forward direction have the same phase at each of the reflection electrodes 26 and propagate toward the output-side IDT electrode 13 while increasing the amplitude. On the other hand, the elastic wave propagating in the reverse direction is reflected in the forward direction by the reflective electrode 26 as described above, but as shown in FIG. 4, the main reflective electrode 27 is uniform from Tr1 to Tr2. On the other hand, the auxiliary reflection electrode 30 reflects in the forward direction in the first region 28 adjacent to the bus bars 14a and 14b, and propagates in the reverse direction as it is in the second region 29 on the center side.

  Thus, in the input-side IDT electrode 12, the energy of the elastic wave that propagates in the forward direction from the center side toward the output-side IDT electrode 13 on the low-wavelength side and the high-wavelength side that propagate in the regions close to the bus bars 14 a and 14 b. Is getting bigger. When elastic waves are emitted from the input-side IDT electrode 12 toward the output-side IDT electrode 13 (shield electrode 16), the electrode fingers 15 are formed in a tapered shape as described above. As shown in the figure, in the region close to the bus bars 14a and 14b, it is partially propagated toward the outer region outside the region between the bus bars 14a and 14b due to diffraction. However, as described above, the first regions 28, 28 are provided in the regions close to the bus bars 14a, 14b, and the energy of the elastic wave propagating through the regions 28, 28 is increased, so that the input side IDT electrode The elastic wave propagating from 12 to the output-side IDT electrode 13 has a substantially uniform energy distribution from Tr1 to Tr2, or in the region close to Tr1 and Tr2, the energy is slightly smaller than the center side. It will propagate in the forward direction in the state.

  When this elastic wave reaches the output-side IDT electrode 13, the elastic wave propagates from the left side (shield electrode 16 side) to the right side between the electrode fingers 15 and 15 in which the period unit λ corresponding to the wavelength of the elastic wave is formed. As a result, it is gradually converted into an electrical signal and output to the output port 22. At this time, since the auxiliary reflective electrode 30 of the output side IDT electrode 13 is provided with the first areas 28 and 28 in the area close to the bus bars 14c and 14d as in the case of the input side IDT electrode 12, the bus bar 14c Therefore, the elastic wave in the vicinity of 14d is intensified, so that the electrical signal output from the output port 22 has a substantially constant attenuation amount from the low frequency side to the high frequency side, and has excellent flatness. It becomes a state. FIG. 5 shows the characteristics obtained by simulation in this filter. In the present invention, the attenuation characteristics on the low frequency side and the high frequency side are improved compared to the conventional filter shown in FIG. It can be seen that sex is obtained. Note that the characteristics of the filter of the present invention shown in FIG. 9 are actually obtained by adjusting the lengths of the regions 28 and 29 in each auxiliary reflective electrode 30.

According to the above-described embodiment, the input-side IDT electrode 12 and the output side formed so that the width dimension and the interval dimension of the plurality of electrode fingers 15 and the reflection electrode 26 increase from one side to the other side of the bus bar 14. In the elastic wave filter provided with the IDT electrode 13, as at least one of the reflection electrodes 26, the first region 28 weighted so as to reflect the elastic wave in the forward direction and the elastic wave not to be reflected in the forward direction. The auxiliary reflective electrode 30 is disposed in which the second region 29 with thinned weights is disposed in the length direction thereof. Therefore, the energy distribution of the elastic wave propagating in the forward direction from the low wavelength side to the high wavelength side of the elastic wave can be adjusted, so that the attenuation characteristic is adjusted more finely than the filter of FIG. Therefore, it is possible to obtain attenuation characteristics with high flatness in the pass frequency band. Furthermore, in the above example, since the first region 28 is disposed in each region adjacent to the pair of bus bars 14a and 14b, the IDT electrodes 12 and 13 in which the electrode fingers 15 are disposed in a tapered shape are used. However, the deterioration of attenuation characteristics due to diffraction can be suppressed, and in particular, the influence of diffraction on the low frequency side and high frequency side close to the bus bars 14a and 14b can be suppressed. (Small), an attenuation characteristic with high flatness can be obtained.
Further, when providing the first region 28 and the second region 29 with thinned weights in one reflective electrode 26 as described above, the IDT electrode 12 having a structure in which the width dimension of the reflective electrode 26 is 3λ / 8, 13 is used, the regions 28 and 29 can be easily formed simply by forming the gap region 32 in the central portion along the length direction of the reflective electrode 26.
Furthermore, since the influence of diffraction can be suppressed by providing the auxiliary reflecting electrode 30, the number of pairs of the electrode fingers 15 can be increased and the selectivity of the filter can be increased.

  In the above example, the regions 28 and 29 in each auxiliary reflective electrode 30 are uniformly arranged. However, as shown in FIG. 6, each auxiliary reflective electrode 30 is provided so as to obtain good flatness. You may arrange independently. In FIG. 6, with respect to the input side IDT electrode 12, a narrow (short) auxiliary reflection electrode 30 of the first region 28 is arranged on both sides, and the auxiliary reflection electrode gradually becomes wider (long) of the first region 28 from the left side. 30 is arranged. As for the output side IDT electrode 13, the auxiliary reflection electrode 30 having a wider first region 28 than the auxiliary reflection electrode 30 of FIG. 1 is arranged on the input side IDT electrode 12 side, and the first ID is more than that of the auxiliary reflection electrode 30. The auxiliary reflection electrodes 30 having a wide area 28 are arranged in the propagation direction of the elastic wave.

Further, one or more auxiliary reflection electrodes 30 may be provided on the IDT electrode 12 (13). For the reflection electrodes 26 other than the auxiliary reflection electrode 30, the main reflection electrode 27 or the already described FIG. As shown in FIG. 4, a reflective electrode 26 with thinning weights may be provided so that elastic waves are not reflected from Tr1 to Tr2 over the length direction. Further, the auxiliary reflective electrode 30 may be disposed only on one of the IDT electrodes 12 and 13. In the IDT electrode 12 (13) not provided with the auxiliary reflective electrode 30, instead of the auxiliary reflective electrode 30, the main reflective electrode 27 or the reflective electrode 26 thinned out as described above may be provided. Alternatively, without providing the reflective electrode 26, a pair of electrode fingers 15 and 15 extending alternately from each of the bus bars 14a (14c) and 14b (14d) may be disposed to form a bidirectional electrode.
Also in these cases, similarly to the above example, the energy distribution of the elastic wave is adjusted from Tr1 to Tr2, and an attenuation characteristic with excellent flatness can be obtained.

  In the above example, the first region 28 is disposed in the region adjacent to the bus bars 14a and 14b. However, the present invention is not limited to such an example, and a flat attenuation characteristic can be obtained in the pass frequency band. The respective regions 28 and 29 may be disposed. For example, the first region 28 may be disposed on the track corresponding to the frequency at which the attenuation amount increases, and the second region 29 may be disposed on the other tracks. This example will be described with a specific example. For example, as shown in FIG. 7, the second region 29 may be arranged only in a region close to one bus bar 14, or as shown in FIG. As described above, the second region 29 may be disposed in a region close to both the bus bars 14 and 14, and the first region 28 may be provided on the center side. That is, in the present invention, in order to obtain an attenuation characteristic with excellent flatness, in the length direction (direction substantially orthogonal to the propagation direction of the elastic wave), the first region 28 where the reflection of the elastic wave occurs in the forward direction; What is necessary is just to arrange | position with the 2nd area | region 29 where reflection of an elastic wave does not occur in a forward direction with a predetermined layout. Further, although the shield electrode 16 is disposed between the IDT electrodes 12 and 13, the shield electrode 16 may not be provided.

  In each of the above-described examples, the IDT electrodes 12 and 13 which are the unidirectional electrodes including the reflective electrode 26, for example, the DART electrodes are described. However, the four electrode fingers 15 and the distance between these electrode fingers 15 are different. The present invention may be applied to a unidirectional electrode in which one periodic unit λ is configured. Specifically, as shown schematically in FIG. 12 (a), two of these four electrode fingers 15 have a width dimension smaller than λ / 8, and the remaining one-way electrode has a remaining width. Two of them are configured to have a width dimension larger than λ / 8, and are described in, for example, Patent Documents (Japanese Unexamined Patent Publication Nos. 2000-91869 and 2001-251158). This unidirectional electrode is called, for example, a DWSF (Differential-Width Split-Finger) electrode. In FIG. 12, in order to simplify the configuration of the DWSF electrode, the width dimension of the electrode finger 15 between the bus bars 14a and 14b and the separation dimension between the electrode fingers 15 and 15 are drawn constant.

  Of these electrode fingers 15, the electrode finger 15 having a narrow width dimension is referred to as “main electrode finger 15 a”, and the electrode finger 15 having a large width dimension is referred to as “auxiliary electrode finger 15 b”. The set of the main electrode finger 15a and the auxiliary electrode finger 15b is elastic wave so that the auxiliary electrode finger 15b adjacent to the main electrode finger 15a extends alternately from the bus bar 14a (14b) and the bus bar 14b (14a). A plurality of unidirectional electrodes are arranged along the propagation direction. That is, the set of main electrode fingers 15a and auxiliary electrode fingers 15b are weighted so that the elastic wave is reflected in the forward direction as described above by setting the respective width dimensions as described above. It can be said. Therefore, as shown in FIG. 12 (b), by forming the main electrode fingers 15a and the auxiliary electrode fingers 15b to have the same width, the weighting is thinned out so that the elastic waves are not reflected in the forward direction. It is burned.

  In forming each of the first region 28 in which elastic waves are reflected in the forward direction and the second region 29 in which elastic waves are not reflected in the forward direction in the DWSF electrode, FIGS. 12 (a) and 12 (b). The main electrode finger 15a and the auxiliary electrode finger 15b having the structure are formed between the bus bars 14a and 14b. Specifically, as shown in FIG. 13, for example, in the input-side IDT electrode 12, first regions 28, 28 are formed in regions close to the bus bars 14 a, 14 b, respectively, and the first regions 28, 28 are formed. A second region 29 is arranged between them, and these regions 28, 29, 28 are connected at the boundary L in the length direction of the main electrode finger 15 a and the auxiliary electrode finger 15 b. Accordingly, in the region (first region 28) adjacent to the bus bars 14a and 14b, the electrode fingers 15a and 15b having different width dimensions are alternately arranged, and the second region 29 between the first regions 28 and 28 is disposed. Then, electrode fingers 15a and 15b having the same width dimension are arranged. In this example, the width dimensions of the main electrode finger 15a and the auxiliary electrode finger 15b in the first region 28 are 0.0833λ and 0.1667λ, respectively (the ratio of the width dimensions of the electrode fingers 15a and 15b is 1: 2). The distance between the main electrode finger 15a and the auxiliary electrode finger 15b is 0.125λ.

  In this DWSF electrode, the same effect as that of the DART electrode described above can be obtained. Also in this example, the regions 28 and 29 may be arranged in an arbitrary layout along the length direction of the electrode fingers 15 (15a and 15b) as shown in FIGS. In addition to the electrode fingers 15 in which the regions 28 and 29 are disposed along the electrode fingers 15, the electrode fingers 15 in which only one of the regions 28 and 29 is formed in the length direction may be provided. In the center of FIG. 13, two main electrode fingers 15a and two auxiliary electrode fingers 15b each having a first region 28 formed in the length direction are shown. That is, two electrode fingers 15a and 15b having different width dimensions are arranged in the length direction.

  Further, each of the regions 28 and 29 is formed for all of the four electrode fingers 15a and 15b constituting one cycle unit λ, and a pair of electrodes adjacent to each other among these four electrode fingers 15a and 15b. The regions 28 and 29 may be arranged for the fingers 15a and 15b, and only one of the regions 28 and 29 may be arranged for the remaining set of electrode fingers 15a and 15b. Furthermore, among the four electrode fingers 15 constituting one cycle unit λ, for example, three are arranged so as to extend from the common bus bar 14a (14b), and the remaining one is from the bus bar 14b (14a). The regions 28 and 29 may be formed by electrode fingers 15a and 15b adjacent to each other so as to extend. Similarly, the output side IDT electrode 13 together with the input side IDT electrode 12 may be configured as a DWSF electrode in which the regions 28 and 29 are arranged. 29 and the other IDT electrodes 12 and 13 may be provided with the first region 28 or the second region 29. Further, the width dimension of each electrode finger 15a, 15b may be formed so that the width dimension of the main electrode finger 15a is smaller than the width dimension of the auxiliary electrode finger 15b, in addition to the example described above.

Further, as shown in FIG. 14, for example, in the first region 28, the width dimension of each electrode finger 15a (15b) is formed so as to gradually become thicker (thinner) toward the second region 29, The electrode fingers 15a and 15b may be arranged so that the width dimensions of the regions 28 and 29 are equal at the boundary L. That is, from the bus bar 14 side along the length direction of the electrode finger 15 between the first region 28 where the elastic wave is reflected in the forward direction and the second region 29 where the elastic wave is not reflected in the forward direction. You may arrange | position the 3rd area | region 100 where the reflection amount of an elastic wave becomes small gradually toward the center part side. In this case, in the first region 28 (third region 100), the degree to which the elastic wave is reflected in the forward direction can be continuously adjusted along the length direction of the electrode fingers 15a and 15b.
When the electrode finger 15a (15b) is formed so that the width dimension of the electrode finger 15a (15b) gradually becomes thicker (thinner) toward the second region 29 as described above, the length of the electrode finger 15a (15b) as shown in FIG. The width dimension may be changed linearly along the direction, or may be formed in a curved shape. Also in this case, the regions 28 (100) and 29 may be arranged in an arbitrary layout along the length direction of the electrode fingers 15 and the propagation direction of the elastic wave. Furthermore, the electrode fingers 15a and 15b shown in FIG. 14 may be arranged together with the electrode fingers 15a and 15b having the configuration shown in FIG.

DESCRIPTION OF SYMBOLS 11 Piezoelectric substrate 12 Input side taper type IDT electrode 13 Output side taper type IDT electrode 14 Bus bar 15 Electrode finger 26 Reflective electrode 27 Main reflective electrode 28 First region 29 Second region 30 Auxiliary reflective electrode

Claims (5)

An input-side IDT electrode and an output-side IDT electrode that are spaced apart from each other in the propagation direction of the elastic wave;
The input-side IDT electrode and the output-side IDT electrode have a pair of bus bars formed so as to be parallel to each other, and extend from each of the bus bars alternately in a comb-tooth shape, and have a width dimension and a separation dimension that are the same as those described above. In an elastic wave filter comprising a tapered IDT electrode provided with a plurality of electrode fingers formed so as to spread from one side of the bus bar to the other side,
At least one of the input side IDT electrode and the output side IDT electrode includes one or more reflective electrodes arranged to extend along the length direction of the electrode fingers,
In the input-side IDT electrode, a direction from the input-side IDT electrode toward the output-side IDT electrode is a forward direction, a direction from the output-side IDT electrode to the input-side IDT electrode is a reverse direction, and the output-side IDT electrode In this case, the direction from the output IDT electrode to the input IDT electrode is the forward direction, and the direction from the input IDT electrode to the output IDT electrode is the reverse direction.
At least one of the reflective electrodes is formed from one end to the other end side in the length direction of the reflective electrode, and one first region weighted so that an elastic wave is reflected in the forward direction. The other first region formed from the other end to the one end side in the length direction of the reflective electrode and weighted so as to reflect the elastic wave in the forward direction, and the one first region And a second region formed in a region sandwiched between the first region and the other first region and weighted so as not to reflect an elastic wave in the forward direction.
When the period unit of the dimension in the propagation direction of the elastic wave of the set consisting of the reflective electrode and a pair of electrode fingers adjacent to the reflective electrode and alternately extending from each of the pair of bus bars is λ,
The reflective electrode has a width dimension of 3λ / 8 in the propagation direction of the elastic wave,
The first region is composed of a metal film having a width dimension of 3λ / 8 in the propagation direction of the elastic wave,
The second region is a metal film having a width dimension of λ / 8 by forming a slit extending from the one first region to the other first region at the center in the width direction of the reflective electrode. An elastic wave filter characterized in that the two regions formed are respectively arranged in the propagation direction of the elastic wave through a gap region having a width dimension of λ / 8. A plurality of the reflective electrodes are provided along the propagation direction of the elastic wave,
The length dimension of the slit in the first reflection electrode included in the plurality of reflection electrodes and the length dimension of the slit in the second reflection electrode different from the first reflection electrode included in the plurality of reflection electrodes. the elastic wave filter according to claim 1, wherein the mutually different. An input-side IDT electrode and an output-side IDT electrode that are spaced apart from each other in the propagation direction of the elastic wave;
The input-side IDT electrode and the output-side IDT electrode have a pair of bus bars formed so as to be parallel to each other, and extend from each of the bus bars alternately in a comb-tooth shape, and have a width dimension and a separation dimension that are the same as those described above. In an elastic wave filter comprising a tapered IDT electrode provided with a plurality of electrode fingers formed so as to spread from one side of the bus bar to the other side,
At least one of the input side IDT electrode and the output side IDT electrode includes one or more reflective electrodes arranged to extend along the length direction of the electrode fingers,
In the input-side IDT electrode, a direction from the input-side IDT electrode toward the output-side IDT electrode is a forward direction, a direction from the output-side IDT electrode to the input-side IDT electrode is a reverse direction, and the output-side IDT electrode In this case, the direction from the output IDT electrode to the input IDT electrode is the forward direction, and the direction from the input IDT electrode to the output IDT electrode is the reverse direction.
At least one of the reflective electrodes has an energy of an elastic wave propagating in the forward direction on each of the low-frequency side and the high-frequency side of the passing region, and an energy of an elastic wave propagating in the forward direction in a band between them. In order to increase the size, one first region and the other first region are weighted so that elastic waves are reflected in the forward direction at one end and the other end in the length direction of the reflective electrode, respectively. , Provided in a region sandwiched between the one first region and the other first region from one first region to the other first region, and does not reflect elastic waves in the forward direction A second region where the weighting is thinned out as follows:
When the period unit of the dimension in the propagation direction of the elastic wave of the set consisting of the reflective electrode and a pair of electrode fingers adjacent to the reflective electrode and alternately extending from each of the pair of bus bars is λ,
The reflective electrode has a width dimension of 3λ / 8 in the propagation direction of the elastic wave,
The first region is composed of a metal film having a width dimension of 3λ / 8 in the propagation direction of the elastic wave,
The second region is formed with a metal film having a width dimension of λ / 8 by forming a slit extending from one end portion of the reflective electrode to the other end portion at a central portion in the width direction of the reflective electrode. An elastic wave filter, wherein two regions are arranged in the propagation direction of the elastic wave through a gap region having a width dimension of λ / 8. An input-side IDT electrode and an output-side IDT electrode that are spaced apart from each other in the propagation direction of the elastic wave;
The input-side IDT electrode and the output-side IDT electrode have a pair of bus bars formed so as to be parallel to each other, and extend in a comb shape from each of the bus bars toward the opposite bus bar, and the width dimension thereof. And an elastic wave filter comprising a taper type IDT electrode provided with a plurality of electrode fingers formed so that a spacing dimension increases from one side of the bus bar to the other side,
At least one of the input-side IDT electrode and the output-side IDT electrode is configured to be a periodic unit corresponding to the wavelength of the propagating elastic wave according to the width dimension of the four electrode fingers and the separation dimension between the electrode fingers. ,
In the input-side IDT electrode, a direction from the input-side IDT electrode toward the output-side IDT electrode is a forward direction, a direction from the output-side IDT electrode to the input-side IDT electrode is a reverse direction, and the output-side IDT electrode In this case, the direction from the output IDT electrode to the input IDT electrode is the forward direction, and the direction from the input IDT electrode to the output IDT electrode is the reverse direction.
At least one of the sets of four electrode fingers constituting the periodic unit has a main electrode finger and an auxiliary electrode finger having a width larger than that of the main electrode finger alternately adjacent to each other from each of the pair of bus bars. Are connected to the first region where the elastic wave is reflected in the forward direction, and to each of the main electrode finger and the auxiliary electrode finger in the first region, respectively. Electrode fingers formed so as to have the same width dimension are arranged, and the second region configured so as not to reflect elastic waves in the forward direction is arranged in the length direction thereof,
Each of the input-side IDT electrode and the output-side IDT electrode is configured so that elastic waves having different period units are propagated between the pair of bus bars. 5. The elasticity according to claim 4 , wherein the main electrode finger and the auxiliary electrode finger are configured such that each width dimension becomes equal from the first region toward the second region. Wave filter.

Images