JPWO2010137648A1 - Ladder type filter and elastic wave resonator - Google Patents

Abstract

Provided is a ladder type filter that can be miniaturized and that can reduce the insertion loss in the passband and can improve the filter characteristics. The series arm resonators S1 to S9 are arranged on the series arm connecting the input terminal 2 and the output terminal 3, and the parallel arm resonators P1 to P3 are arranged on the parallel arm arranged to connect the series arm and the ground potential. Are arranged, the series arm resonators S1 to S9 and the parallel arm resonators P1 to P3 are made of elastic wave resonators having IDT electrodes, and the IDT electrodes 4 of the series arm resonators S1 to S9 are connected to the elastic wave propagation direction. Is weighted so that two maximum values of the crossing width appear, and the IDT electrodes 10 of the parallel arm resonators P1 to P3 are weighted so that one maximum value of the crossing width appears in the elastic wave propagation direction. A ladder type filter 1.

Description

  The present invention relates to a ladder-type filter and an acoustic wave resonator using boundary acoustic waves and surface acoustic waves, and more particularly to a ladder-type filter and an acoustic wave resonator having IDT electrodes subjected to cross width weighting.

  2. Description of the Related Art Conventionally, a surface acoustic wave filter device having a ladder-type circuit configuration has been used for, for example, a band filter of an RF stage of a mobile phone. Patent Document 1 below discloses an example of a surface acoustic wave filter device having this type of ladder circuit configuration. As shown in FIG. 13, the surface acoustic wave filter device 1001 described in Patent Document 1 has a series arm that connects an input terminal 1002 and an output terminal 1003. A plurality of series arm resonators 1004 are arranged on this series arm. A plurality of parallel arms are formed so as to connect the series arm and the ground potential. A parallel arm resonator 1005 is disposed on each parallel arm. Here, in the parallel arm resonator 1005, cross width weighting is applied to the IDT electrode. More specifically, the cross width is maximum at the center of the IDT electrode in the surface acoustic wave propagation direction, and the rhombus is formed so that the cross width gradually decreases from the portion where the cross width is maximum toward both sides of the IDT electrode. Weighting is applied. It is said that the ripple on the low frequency side of the pass band can be suppressed by this weighting.

JP-A-9-246911

  Also in the surface acoustic wave filter device and the acoustic wave resonator, downsizing is strongly demanded as in other electronic components. In this case, if the aspect ratio of the IDT electrode is decreased, the acoustic wave resonator and the ladder filter using the elastic wave resonator can be reduced in size.

  However, in the surface acoustic wave filter device described in Patent Document 1, it has been found that when the aspect ratio is reduced, the resistance value at the antiresonance frequency is lowered, and the frequency characteristics near the antiresonance frequency are deteriorated. For this reason, it has been found that when the surface acoustic wave filter device 1001 having a ladder circuit configuration is further downsized, the insertion loss in the passband is deteriorated.

  The object of the present invention is to reduce the size in view of the above-described state of the prior art, and to prevent the deterioration of characteristics in the vicinity of the anti-resonance frequency of the used acoustic wave resonator. It is an object of the present invention to provide a ladder filter capable of improving characteristics and an elastic wave resonator in which characteristics are hardly deteriorated in the vicinity of an antiresonance frequency even when downsizing is advanced.

  According to the present invention, the series arm resonator disposed in the series arm connecting the input end and the output end, and the parallel arm resonator disposed in the parallel arm disposed so as to connect the series arm and the ground potential, The series arm resonator and the parallel arm resonator are each formed of an elastic wave resonator having an IDT electrode, and at least one IDT electrode of the series arm resonator has a maximum value of the crossing width in the elastic wave propagation direction. A ladder-type filter that is weighted so that two appear and the IDT electrodes of at least one of the parallel arm resonators are weighted so that one maximum value of the crossing width appears in the elastic wave propagation direction Is provided.

  In a specific aspect of the ladder filter according to the present invention, a plurality of the series arm resonators and parallel arm resonators are provided, and when the wavelength of the elastic wave excited with the IDT electrode is λ, When the maximum crossing width of the IDT electrode is Sλ and the number of electrode fingers is P, the aspect ratio defined by S / P = R is 0.20 or more and 0.30 or less in at least one series arm resonator. In at least one parallel arm resonator, the aspect ratio is 0.30 or more. In this case, downsizing of the series arm resonator can be promoted, and deterioration of insertion loss on the high band side in the passband can be more effectively suppressed.

  More preferably, the aspect ratio of all series arm resonators is 0.20 or more and 0.30 or less, and the aspect ratio of all parallel arm resonators is 0.30 or more. In this case, even when downsizing is further advanced, the insertion loss in the high frequency region within the passband can be further reduced.

  According to another wide aspect of the ladder-type filter according to the present invention, the serial arm resonator disposed in the series arm connecting the input end and the output end, and the parallel disposed so as to connect the series arm and the ground potential. A parallel arm resonator disposed on an arm, wherein the series arm resonator and the parallel arm resonator include an elastic wave resonator having an IDT electrode, and at least one IDT electrode of the series arm resonator is elastic. The cross widths are weighted so that three maximum values of the cross width appear in the wave propagation direction, and at least one IDT electrode of the parallel arm resonator shows one maximum value of the cross width in the elastic wave propagation direction. A ladder filter is provided that is cross-weighted.

  In still another specific aspect of the ladder filter according to the present invention, in the at least one series arm resonator in which three maximum values appear, the aspect ratio is 0.10 or more and 0.20 or less. In at least one parallel arm resonator, the aspect ratio is 0.30 or more. In this case, it is possible to further reduce the size of the series arm resonator and to more effectively suppress the deterioration of the insertion loss on the high passband side. In this case, preferably, the aspect ratio of all series arm resonators is 0.10 or more and 0.20 or less, and the aspect ratio of all parallel arm resonators is 0.30 or more. Thereby, the insertion loss in the high frequency region in the pass band can be further reduced.

  In another specific aspect of the ladder filter according to the present invention, the elastic wave resonator is a boundary acoustic wave resonator. In this case, since a package having a cavity is not required, the size can be further reduced.

  An elastic wave resonator according to the present invention includes a piezoelectric substrate and an IDT electrode formed on the piezoelectric substrate, and the IDT electrode has n (n is a natural number) cross width maximum values in the elastic wave propagation direction. The cross ratio is weighted such that the aspect ratio is 0.30 or more when n = 1, the aspect ratio is 0.20 or more and 0.30 or less when n = 2, and n = In the case of 3, the aspect ratio is 0.10 or more and 0.20 or less.

  In a specific aspect of the elastic wave resonator according to the present invention, a boundary acoustic wave is used as the elastic wave, thereby forming the boundary acoustic wave resonator. In this case, since a package having a cavity is not required, it is possible to further downsize the acoustic wave resonator and further downsize the electronic component on which the acoustic wave resonator is mounted.

  In the ladder type filter according to the present invention, the series arm resonator has an IDT electrode having two cross width maximum values in the elastic wave propagation direction, and the parallel arm resonator has one aspect ratio cross width maximum value. Since the IDT electrode is provided, it is difficult for the characteristics of the series arm resonator and the parallel arm resonator to deteriorate in the vicinity of the antiresonance frequency. Accordingly, not only can the aspect ratio be reduced to reduce the size, but also the insertion loss in the high frequency region within the passband of the ladder filter can be reduced, and good filter characteristics can be obtained.

  In the acoustic wave resonator according to the present invention, the aspect ratio is in the specific range according to the number of poles having the maximum cross width in the acoustic wave propagation direction, so that the resistance value at the anti-resonance frequency can be increased. And deterioration of characteristics at the anti-resonance frequency can be suppressed. Therefore, it is possible to provide an elastic wave resonator that is small in size and has excellent characteristics near the antiresonance frequency.

FIG. 1 is a schematic plan view for explaining an electrode structure of a ladder filter according to an embodiment of the present invention. FIG. 2 is a diagram showing attenuation frequency characteristics of a ladder filter according to an embodiment of the present invention and a ladder filter of a comparative example prepared for comparison. 3A and 3B are a schematic plan view showing an electrode structure of an acoustic wave resonator used as a parallel arm resonator in the ladder filter according to the embodiment of the present invention, and the acoustic wave resonator. It is typical front sectional drawing of. FIG. 4 is a schematic plan view for explaining the aspect ratio of the IDT electrode of the acoustic wave resonator according to the present invention. FIG. 5 is a diagram showing the relationship between the resonance resistance and the aspect ratio = cross width / logarithm in an elastic wave resonator weighted so that one maximum value of the cross width appears. FIG. 6 is a diagram showing the relationship between the aspect ratio = cross width / logarithm and anti-resonance resistance in an elastic wave resonator weighted so that one maximum value of the cross width appears. FIG. 7 is a diagram showing the relationship between the aspect ratio = crossover width / logarithm and impedance ratio in an elastic wave resonator weighted so that one maximum value of the crossover width appears. FIG. 8 is a schematic plan view showing an electrode structure of an acoustic wave resonator used as a series arm resonator in one embodiment of the present invention. FIG. 9 is a diagram showing the relationship between the resonance resistance and the aspect ratio = crossing width / logarithm in an elastic wave resonator weighted so that two maximum values of the crossing width appear. FIG. 10 is a diagram illustrating the relationship between the aspect ratio = cross width / logarithm and anti-resonance resistance in an acoustic wave resonator weighted so that two maximum values of the cross width appear. FIG. 11 is a diagram showing a relationship between an aspect ratio = crossover width / logarithm and an impedance ratio in an acoustic wave resonator weighted so that two maximum values of the crossover width appear. 12 (a)-(c) show the maximum cross width / logarithm of an IDT electrode with one diamond weighted portion, an IDT electrode with two diamond weighted portions and an IDT electrode with three diamond weighted portions. It is each typical top view for demonstrating the relationship between a magnitude | size and antiresonance resistance. FIG. 13 is a schematic circuit diagram illustrating a circuit configuration of a ladder filter described in the related art.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIG. 1 is a schematic plan view showing an electrode structure of a ladder filter according to an embodiment of the present invention.

  The ladder filter 1 has an input terminal 2 and an output terminal 3. A plurality of series arm resonators S <b> 1 to S <b> 9 are arranged on the series arm connecting the input terminal 2 and the output terminal 3. The series arm resonators S1 to S9 are connected to each other in series.

  Each of the series arm resonators S1 to S9 is a boundary acoustic wave resonator having the illustrated electrode structure. The series arm resonator S1 will be described as a representative. The series arm resonator S1 includes an IDT electrode 4 and reflectors 5 and 6 disposed on both sides of the IDT electrode 4 in the elastic wave propagation direction. The other series arm resonators S2 to S9 also have the same electrode structure.

  The IDT electrode 4 and the reflectors 5 and 6 are formed on a piezoelectric substrate (not shown). A dielectric layer made of silicon oxide is formed so as to cover the piezoelectric substrate. In the present embodiment, the electrode structure is formed at the interface between the piezoelectric substrate and the dielectric layer, thereby forming a boundary acoustic wave resonator.

  The specific structure of the boundary acoustic wave resonator will be described in more detail when describing the parallel arm resonator.

  On the other hand, the parallel arm resonator P1 is disposed on the parallel arm extending between the connection point 7 between the series arm resonator S3 and the series arm resonator S4 and the ground potential. Similarly, the parallel arm resonator P2 is disposed on the parallel arm extending between the connection point 8 between the series arm resonator S5 and the series arm resonator S6 and the ground potential.

  A parallel arm resonator P3 is connected between the connection point 9 between the series arm resonator S9 and the output terminal 3 and the ground potential, that is, to the output terminal 3.

  The parallel arm resonator P1 will be described as a representative. The parallel arm resonator P1 includes a 1-port elastic wave having an IDT electrode 10 and reflectors 11 and 12 arranged on both sides of the IDT electrode 10 in the elastic wave propagation direction. It is a resonator.

  With reference to FIGS. 3A and 3B, the parallel arm resonator P1 will be described in more detail. An IDT electrode 10 and reflectors 11 and 12 are formed on the piezoelectric substrate 13. A dielectric layer 14 is formed so as to cover the IDT electrode 10 and the reflectors 11 and 12.

In the present embodiment, the piezoelectric substrate 13 is made of a piezoelectric single crystal such as LiTaO ₃ or LiNbO ₃ . The piezoelectric substrate 13 may be formed of piezoelectric ceramics such as PZT.

  The IDT electrode 10 and the reflectors 11 and 12 are made of a metal such as Al, Ag, Cu, W, Ta, Au, Pt, or an alloy mainly composed of these metals. The IDT electrode 10 and the reflectors 11 and 12 may be formed of a laminated metal film formed by laminating a plurality of metal films.

  The dielectric layer 14 is formed of silicon oxide in this embodiment, but may be formed of other dielectric materials such as silicon nitride, silicon oxynitride, aluminum oxide, zirconium oxide, diamond-like carbon (DLC). Good.

  The material and thickness of the dielectric layer 14 and the material constituting the piezoelectric substrate 13 are such that boundary acoustic waves are excited when the IDT electrode 10 is excited at the interface between the piezoelectric substrate 13 and the dielectric layer 14. Is selected. That is, the parallel arm resonator P1 is a boundary acoustic wave resonator having the above structure.

  The parallel arm resonators P2 and P3 are configured similarly to the parallel arm resonator P1.

  As described above, the series arm resonator S1 similarly has a structure in which the IDT electrode 4 and the reflectors 5 and 6 are arranged at the interface between the piezoelectric substrate and the dielectric layer. Therefore, the description with reference to FIG. 3B is used for the description of the structure of the series arm resonator S1, and the detailed description of the series arm resonator S1 is omitted.

  Therefore, the ladder filter 1 includes series arm resonators S1 to S9 made of 1-port boundary acoustic wave resonators and parallel arm resonators P1 to P3 made of 1-port boundary acoustic wave resonators.

  In this embodiment, a plurality of series arm resonators S1 to S9 and a plurality of parallel arm resonators P1 to P3 are provided, but only one series arm resonator and one parallel arm resonator are used. May be.

  The ladder filter 1 is characterized in that, in the series arm resonators S1 to S9, the IDT electrode 4 is weighted so that two maximum values of the cross width appear in the elastic wave propagation direction, and the parallel arm resonator. The IDT electrodes 10 of P1 to P3 are subjected to cross width weighting so that one maximum value of the cross width appears in the elastic wave propagation direction. As a result, it is possible to reduce the size and to reduce the loss in the high frequency region within the passband. This will be described with reference to FIG.

  FIG. 2 is a diagram showing the attenuation frequency characteristics of the ladder filter 1 of the present embodiment and the attenuation frequency characteristics of a ladder filter prepared for comparison. A solid line shows the result of the embodiment, and a broken line shows the result of the comparative example.

  This frequency characteristic is a characteristic when the piezoelectric substrate 13, the dielectric layer 14, the IDT electrode 4, the reflectors 5 and 6, the IDT electrode 10 and the reflectors 11 and 12 are formed with the following specifications.

[Specifications of series arm resonators S1 to S9]
The wavelength λ determined by the pitch of the IDT electrodes 4 was 1.9 μm. Piezoelectric substrate material: LiNbO ₃ , dielectric layer 14: silicon oxide film, thickness = 0.63λ.

  IDT electrode 10: The electrode material is Pt. The thickness is 0.025λ. Number of pairs of electrode fingers = 117, maximum cross width = 33.0λ, aspect ratio = maximum cross width / number of pairs of electrode fingers = 0.282.

  Reflector: The electrode material is the same as the IDT electrode 4. Number of electrode fingers of reflector = 21, electrode finger pitch = λ.

[Specifications of parallel arm resonators P1 to P3]
Piezoelectric substrate 13: made of LiNbO ₃ .

Dielectric layer 14: silicon oxide film, thickness 0.60λ
IDT electrode 10: electrode material = Pt, thickness = 0.024λ. Wavelength λ determined by the pitch of electrode fingers = 2.0 μm. The number of pairs of electrode fingers = 82, the maximum crossing width = 28.9λ. Aspect ratio = maximum crossover width / logarithm = 0.352.

  Reflectors 11 and 12: The electrode material is the same as that of the IDT electrode 10. Electrode finger pitch = λ, number of electrode fingers = 21.

  In the ladder type filter of the comparative example, each of the series arm resonators S1 to S9 is a so-called one rhombus having only one maximum cross width in the elastic wave propagation direction, like the parallel arm resonator P1. Except for the use of weighted IDT electrodes, this was the same as in the above embodiment. The specification of the IDT electrode of this series arm resonator was as follows.

  Specification of IDT electrode of series arm resonator of comparative example: The number of electrode materials and electrode fingers is the same as that of the series arm resonator S1 of the embodiment. Maximum crossover width = 33.0λ. Aspect ratio = maximum crossover width / number of electrode fingers = 0.282.

  In the present invention, the aspect ratio refers to the ratio of the “maximum cross width” to the “log number of electrode fingers” in the IDT electrode to which so-called rhombus weighting is applied as described above. As shown in FIG. 4, taking the parallel arm resonator P1 as an example, in the parallel arm resonator P1, the IDT electrode 10 has a maximum crossover value in the elastic wave propagation direction so that one maximum appears. Weighting is performed so that the crossing width gradually decreases from the width portion toward one end side and the other end side of the IDT electrode 10. Therefore, the shape indicated by the envelopes A and B is a substantially rhombus shape. Such weighting is referred to as rhombus weighting in this specification.

  Here, the maximum crossing width portion is located at the center of the IDT electrode. That is, the one side and the other side are symmetrical with respect to the maximum crossing width portion.

  The envelope is a virtual line that connects the tips of a plurality of electrode fingers connected to the same potential of the IDT electrode 10. A region surrounded by the envelope A and the envelope B is a crossing region, and a region where elastic waves are actively excited.

  As is apparent from FIG. 2, according to the embodiment, it is possible to reduce the insertion loss in the high frequency region in the pass band, more specifically, in the vicinity of about 1875 to 1920 MHz, as compared with the comparative example. It turns out that it is said. That is, it can be seen that, according to the embodiment, better filter characteristics can be obtained as compared with the comparative example.

  Moreover, in the series arm resonators S1 to S9, two maximum values of the crossing width appear in the elastic wave propagation direction as described above. In other words, the diamonds are weighted so that two diamonds are continuous in the elastic wave propagation direction. For this reason, it is possible to reduce the size and the resistance as compared with the case where the IDT electrodes of the serial arm resonator of the comparative example having the same number of electrode fingers are used. The reason for this will be described more specifically with reference to FIGS.

  5 to 7 show the aspect ratios of an elastic wave resonator to which one rhombus is weighted, for example, an elastic wave resonator such as the parallel arm resonator P1 shown in FIGS. 3 (a) and 3 (b). It is a figure which shows the relationship between a certain crossing width / logarithm, resonance resistance, antiresonance resistance, and impedance ratio, respectively. 5 to 7 show results when the weighting ratio is 10% and when the weighting ratio is 30%. Here, the weighting ratio is a value defined by the minimum crossing width value / maximum crossing width value.

  As is apparent from FIG. 5, it can be seen that the resonance resistance increases linearly as the aspect ratio = (crossover width / logarithm) increases regardless of whether the weighting ratio is 10% or 30%.

  On the other hand, as is clear from FIG. 6, the anti-resonance resistance is significantly smaller when the (crossover width / logarithm), that is, the aspect ratio is less than 0.30, compared with the case of 0.30 or more. I understand. More specifically, in both cases where the weighting ratio is 30% and 10%, when the aspect ratio is less than 0.30, the anti-resonance resistance is 59 dB or less, and as the aspect ratio becomes smaller, the anti-resonance resistance Can be seen to be significantly smaller. On the other hand, when the aspect ratio is 0.30 or more, that is, the cross width / logarithm is 0.30 or more, the anti-resonance resistance is as high as 63 dB or more even if the cross width / logarithm is increased. Moreover, it can be seen that the anti-resonance resistance does not change greatly depending on the value of the cross width / logarithm.

  Further, as shown in FIG. 7, the impedance ratio is less than 0.30 when the crossing width / logarithm of the IDT electrode is less than 0.30, particularly compared with the case of 0.30 to 0.60. You can see that it ’s small.

  Accordingly, as clearly shown in FIGS. 5 to 7, particularly as clearly shown in FIG. 6, the anti-resonance resistance can be sufficiently increased by setting the cross width / logarithm to 0.30 or more. It can be seen that the characteristics near the antiresonance frequency can be improved.

  Further, if the cross width / logarithm is too large, the electrode resistance increases and cannot be ignored.

  The elastic wave resonator to which the weight of one rhombus is applied is used as the parallel arm resonators P1 to P3 described above. Therefore, when the antiresonance frequency is sufficiently high, the insertion loss near the center of the passband can be sufficiently reduced.

  On the other hand, FIG. 8 is a schematic plan view showing an enlarged electrode structure of the series arm resonator S1. Here, as shown in the envelopes C and D, the rhombus is weighted so that the IDT electrodes 4 are cross-width-weighted so that the two rhombuses are continuous along the elastic wave propagation direction. Therefore, in the elastic wave propagation direction, there are first and second portions X and Y in which the crossing width has a maximum value.

  The weighted portion X of the first rhombus is located on the reflector 5 side, and the weighted portion Y of the second rhombus is located on the reflector 6 side.

  In the center of the IDT electrode 4 in the elastic wave propagation direction, the first rhombic weighted portion and the second rhombic weighted portion are continuous. In the weighted portions of the first and second rhombuses, in each of the weighted portions X and Y, the portion where the cross width is the maximum value is located at the center. In the weighting portion of the first rhombus, the crossing width gradually decreases from the maximum portion toward the reflector 5 and toward the weighting portion of the second rhombus. In the rhombus shape, the cross width regions on both sides are formed symmetrically via the cross width maximum portion. The second rhombic weighted portion Y is similarly configured.

  9 to 11 show the aspect ratio of the acoustic wave resonator having the first and second rhombic weighted portions X and Y shown in FIG. 8, that is, (cross width / logarithm), resonance resistance, anti-resonance resistance, and It is a figure which shows the relationship with an impedance ratio, respectively. Again, the results are shown for a weighting ratio of 10% and a weighting ratio of 30%.

  As is apparent from FIG. 9, it can be seen that also in the elastic wave resonator shown in FIG. 8, the resonance resistance is linearly increased as the crossing width / logarithm increases.

  On the other hand, as is clear from FIG. 10, the anti-resonance resistance is as low as 60 dB or less when the cross width / logarithm is less than 0.20, and the antiresonance resistance is significantly lower as the cross width / logarithm becomes smaller. You can see that It can also be seen that the anti-resonance resistance is higher than 60 dB when the crossing width / logarithm is 0.20 or more, and is particularly high as 62 dB or more when the crossing width / logarithm is 0.20 or more and 0.47 or less.

  On the other hand, as is clear from FIG. 11, the impedance ratio is as high as 57.7 dB or more when the crossing width / logarithm is 0.20 or more and 0.30 or less.

  The acoustic wave resonator is used as the series arm resonators S <b> 1 to S <b> 9 in the ladder filter 1. Therefore, the resonance frequency is located in the pass band, and the anti-resonance frequency forms an attenuation pole on the high side of the pass band. Therefore, the higher the anti-resonance resistance is, the more preferable, and the higher the impedance ratio is desirable. Therefore, it is understood that the cross width / logarithm, that is, the aspect ratio is preferably 0.20 or more and 0.30 or less in order to obtain good filter characteristics.

  In the ladder type filter 1 of the present embodiment, the reason why the insertion loss is reduced in the high frequency side frequency region in the pass band is that the parallel arm resonators P1 to P3 are weighted with one rhombus as described above. The serial arm resonators S1 to S9 have IDT electrodes 4 having first and second rhombic weighted portions, and the aspect ratio is 0. 52. The aspect ratio is 0.352. This is because the value is 282. As a result, as described with reference to FIGS. 5 to 11, the characteristics of the parallel arm resonators P1 to P3 and the series arm resonators S1 to S9 in the vicinity of the antiresonance frequency are improved. In particular, it is possible to sufficiently reduce the insertion loss in the frequency region on the high frequency side in the passband.

  As described above, in a surface acoustic wave filter having a ladder circuit configuration using a single-diamond weighted elastic wave resonator described in Patent Document 1, insertion in the passband is performed when downsizing is advanced. It is known that the loss will deteriorate. On the other hand, in this embodiment, it turns out that the insertion loss in a passband can be improved as mentioned above.

  In order to reduce the size of the ladder filter 1, the aspect ratio of the IDT electrode 4 or the IDT electrode 10 may be reduced. That is, since the aspect ratio = maximum cross width / logarithm, the maximum cross width can be relatively reduced by reducing the aspect ratio. In particular, the series arm resonators S <b> 1 to S <b> 9 are connected in series with each other at the series arm connecting the input terminal 2 and the output terminal 3. Therefore, in the series arm resonators S1 to S9, it is possible to further reduce the size by reducing the maximum crossing width, in other words, by reducing the aspect ratio.

  In the present embodiment, the aspect ratio of the series arm resonators S1 to S9 is as small as 0.282, and thus the size reduction can be promoted. Moreover, as described above, it is possible to improve the insertion loss in the passband.

  As described above, in this embodiment, in the serial arm resonators S1 to S9, the aspect ratio of the IDT electrode 4 is 0.282, and in the parallel arm resonators P1 to P3, the aspect ratio of the IDT electrode 10 is 0.352. However, as apparent from the results of FIGS. 5 to 11 described above, the aspect ratio of the series arm resonators S1 to S9 is in the range of 0.20 or more and 0.30 or less, and the parallel arm resonators P1 to P3 are If the value is 0.30 or more, it is possible to improve the filter characteristics while simultaneously reducing the size.

  In the above embodiment, the aspect ratio of all the series arm resonators S1 to S9 is 0.282. However, in at least one series arm resonator, the aspect ratio is 0.20 or more,. 30 or less, even in the parallel arm resonators P1 to P3, if at least one parallel arm resonator has an aspect ratio of 0.30 or more, it is inferior to the above embodiment, but the filter is similarly reduced in size while being advanced. The characteristics can be improved. According to the experiment of the present inventor, except that the aspect ratio of one series arm resonator among the plurality of series arm resonators S1 to S9 is changed from 0.40 to 0.28 from the configuration of the above embodiment. Then, when a ladder type filter was created in the same manner as the series arm resonator of the above embodiment, the insertion loss was reduced to 0.02 dB at 1847 MHz, which is a high frequency side frequency band in the pass band, as compared with the comparative example described above. It has been confirmed that it can be improved. Moreover, when it is the same as that of the said embodiment except having changed only the aspect ratio of one parallel arm resonator P1 with respect to the said embodiment from 0.25 to 0.352, compared with the comparative example mentioned above. It has been confirmed that the insertion loss at 1847 MHz can be reduced by 0.04 dB.

  However, as in the above-described embodiment, the aspect ratio is 0.20 or more and 0.30 or less in all the series arm resonators S1 to S9, and the aspect ratio is 0.30 or more in all the parallel arm resonators P1 to P3. Most preferably.

  In the present invention, even if the aspect ratio is not in the specific range, the parallel arm resonators P1 to P3 have IDT electrodes that are weighted so as to have the one diamond-shaped weighted portion, and the series arm resonance. As long as the IDT electrode is weighted so as to have a child or two diamond-shaped weighted portions, miniaturization can be promoted as in the above embodiment. That is, as described above, since the downsizing of the series arm resonator greatly contributes to the downsizing of the ladder filter, the series arm resonator has the first and second rhombic weighted portions, regardless of the aspect ratio. When formed using an IDT electrode, even if the aspect ratio is reduced, the anti-resonance characteristics are unlikely to deteriorate. Therefore, it is possible to reduce the insertion loss in the passband by reducing the size.

  In the present invention, in addition to the ladder type filter, the acoustic wave resonator itself used as the above-described parallel arm resonator and series arm resonator can be downsized and the anti-resonance characteristics can be improved.

  That is, as shown in FIGS. 5 to 7, in the acoustic wave resonator having the IDT electrode 10 having one rhombic weighting portion shown in FIG. Resonance characteristics can be improved.

  In the acoustic wave resonator shown in FIG. 8 having the first and second rhombic weighted portions, as shown in FIGS. 9 to 11, if the aspect ratio is 0.20 or more and 0.30 or less, The characteristics near the antiresonance frequency can be improved. In addition, in the present invention, the number of the diamond-shaped weighted portions in the IDT electrode may be three. In this case, the aspect ratio needs to be 0.10 or more and 0.20 or less. This will be described with reference to FIGS.

  FIG. 12A shows an electrode structure of an acoustic wave resonator having the IDT electrode 101 provided with the one diamond-shaped weighted portion, and FIG. 12B shows the first and second diamond-shaped weighted portions. It is a schematic diagram which shows the electrode structure of the elastic wave resonator which has the IDT electrode 102 provided. In FIG. 12B, the IDT electrode 102 is schematically shown by being divided into two IDT electrode portions 102a and 102b in the elastic wave propagation direction.

  On the other hand, FIG. 12C schematically shows an electrode structure of an acoustic wave resonator having the IDT electrode 103 in which three maximum values of the crossing width exist in the acoustic wave propagation direction. Also here, the structure of the IDT electrode 103 is schematically shown by being divided into three IDT electrode portions 103a to 103c each having one diamond-shaped weighted portion.

  In the structure of FIG. 12A, as described above, the anti-resonance resistance can be sufficiently increased if the aspect ratio is greater than 0.3.

  On the other hand, the structure of FIG. 12B corresponds to a structure in which the structure of FIG. Therefore, based on the aspect ratio = S / P ≧ 0.3, it is considered that the anti-resonance resistance can be sufficiently increased if S / 2P ≧ 0.15. Note that S / 2P ≧ 0.2 is based on the results of FIGS. 9 to 11 as described above. Considering similarly, the structure of FIG. 12C corresponds to a structure in which three IDT electrodes of FIG. 12A are connected in parallel. Therefore, if S / 3P ≧ 0.10, the anti-resonance resistance is increased. I think it can be done. Therefore, when the number of local maximum values is n (n is a natural number), if S / (n × P) ≧ 0.3 / n, the anti-resonance resistance can be sufficiently increased, and the characteristics near the anti-resonance frequency are obtained. Can be improved. Therefore, when the number of maximum values of the crossing width is n, when n is 3, it can be seen that the aspect ratio should be 0.10 or more. When n is 3 or more, the aspect ratio determined by S / (n × P) ≧ 0.3 / n may be set.

  Therefore, when n = 3 in at least one series arm resonator, the aspect ratio is set to 0.10 or more and 0.20 or less, and in at least one parallel arm resonator, the aspect ratio is set to 0.30 or more. Thus, in the ladder type filter, the insertion loss in the high frequency region in the pass band can be further reduced, as in the above-described embodiment. More preferably, in a plurality of series arm resonators with n = 3 or n = 3, the aspect ratio of all series arm resonators is set to 0.10 or more and 0.20 or less, and the aspect ratio of all parallel arm resonators is set. By setting the value to 0.30 or more, the insertion loss on the high frequency side in the pass band can be further reduced.

  In the above-described embodiment, the structure using the boundary acoustic wave resonator has been described. However, the present invention may be a surface acoustic wave resonator instead of the boundary acoustic wave resonator. That is, in the present invention, the elastic wave is not limited to the boundary acoustic wave, and a surface acoustic wave may be used. In the case of a surface acoustic wave resonator, an IDT electrode may be formed on a piezoelectric substrate, and a dielectric layer is not necessarily required. Of course, a dielectric layer may be provided. In this case, the thickness and material of the dielectric layer are selected, and the surface acoustic wave is efficiently excited, so that the surface acoustic wave resonator can be provided. The invention can be applied.

  Therefore, also in the ladder type filter of the present invention, the surface acoustic wave resonator may be a surface acoustic wave resonator. In the ladder filter of the present invention, both the boundary acoustic wave resonator and the surface acoustic wave resonator may be used as the acoustic wave resonator.

  The ladder filter of the present invention may be used as a single filter, or may be used on the DPX transmission side or reception side.

DESCRIPTION OF SYMBOLS 1 ... Ladder type filter 2 ... Input terminal 3 ... Output terminal 4 ... IDT electrode 5, 6 ... Reflector 7-9 ... Connection point 10 ... IDT electrode 11, 12 ... Reflector 13 ... Piezoelectric substrate 14 ... Dielectric layer 101- 103 ... IDT electrodes 102a, 102b ... IDT electrode parts 103a to 103c ... IDT electrode parts

Claims (9)

A series arm resonator disposed on a series arm connecting the input end and the output end, and a parallel arm resonator disposed on a parallel arm disposed so as to connect the series arm and the ground potential,
The series arm resonator and the parallel arm resonator are elastic wave resonators having IDT electrodes,
The IDT electrode of at least one of the series arm resonators is cross-weighted so that two maximum cross-width values appear in the elastic wave propagation direction,
A ladder filter in which at least one IDT electrode of the parallel arm resonator is weighted so that one maximum value of the crossing width appears in the elastic wave propagation direction. A plurality of series arm resonators and parallel arm resonators are provided,
When the wavelength of the elastic wave excited with the IDT electrode is λ, the maximum cross width of the IDT electrode is Sλ, and the logarithm of the electrode finger is P, the aspect ratio defined by S / P = R is In at least one series arm resonator, it is 0.20 or more and 0.30 or less,
The ladder filter according to claim 1, wherein an aspect ratio of at least one parallel arm resonator is 0.30 or more.   The ladder filter according to claim 2, wherein the aspect ratio of all series arm resonators is 0.20 or more and 0.30 or less, and the aspect ratio of all parallel arm resonators is 0.30 or more. . A series arm resonator disposed on a series arm connecting the input end and the output end, and a parallel arm resonator disposed on a parallel arm disposed so as to connect the series arm and the ground potential,
The series arm resonator and the parallel arm resonator are elastic wave resonators having IDT electrodes,
The IDT electrodes of at least one of the series arm resonators are cross-weighted so that three maximum values of the cross-width appear in the elastic wave propagation direction,
A ladder filter in which at least one IDT electrode of the parallel arm resonator is weighted so that one maximum value of the crossing width appears in the elastic wave propagation direction.   In at least one of the series arm resonators in which three maximum values appear, the aspect ratio is set to 0.10 or more and 0.20 or less, and in at least one parallel arm resonator, the aspect ratio is 0. The ladder filter according to claim 4, wherein the ladder type filter is 30 or more.   The ladder filter according to claim 5, wherein the aspect ratio of all series arm resonators is 0.10 or more and 0.20 or less, and the aspect ratio of all parallel arm resonators is 0.30 or more. .   The ladder filter according to any one of claims 1 to 6, wherein the elastic wave resonator is a boundary acoustic wave resonator. A piezoelectric substrate;
An IDT electrode formed on the piezoelectric substrate;
The IDT electrodes are weighted so that n (n is a natural number) cross width maximum values appear in the elastic wave propagation direction. When n = 1, the aspect ratio is 0.30 or more, and n An elastic wave resonator having an aspect ratio of 0.20 or more and 0.30 or less when = 2 and an aspect ratio of 0.10 or more and 0.20 or less when n = 3.   The elastic wave resonator according to claim 8, wherein the elastic wave is a boundary acoustic wave, thereby forming a boundary acoustic wave resonator.

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