JP2011041082A - One-port type elastic wave resonator and elastic wave filter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a one-port type elastic wave resonator capable of making the ripples on a frequency side which is a lower frequency side than the resonance frequency small. <P>SOLUTION: In the one-port type elastic wave resonator 1, an IDT electrode 3 and intersection width weighting is performed on the IDT electrode 3 on a piezoelectric substrate 1; an area which is one on the side of a first end 3a, which is one end in the elastic wave propagation direction of the IDT electrode from the center O of the IDT electrode 3 and surrounded by an envelope to be specified by the intersection width weighting; and an area on the side of a second end 3b which is the other end in the elastic wave propagation direction of the IDT electrode from the center O and surrounded by the envelope to be specified by the intersection width weighting are set asymmetrical. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a one-port elastic wave resonator and an elastic wave filter device using the elastic wave resonator, and more specifically, a one-port elastic wave resonator in which cross width weighting is applied to an IDT electrode, and The present invention relates to an elastic wave filter device using the elastic wave resonator.

Conventionally, in various acoustic wave filter devices, in order to form a series trap or a parallel trap, a one-port type acoustic wave resonator is connected in series or in parallel to an acoustic wave filter unit. As an example of the acoustic wave resonator used for such applications, the following Patent Document 1 discloses a one-port surface acoustic wave resonator 1001 shown in FIG. A one-port surface acoustic wave resonator 1001 includes a LiTaO ₃ substrate 1002, an IDT electrode 1003 provided on the LiTaO ₃ substrate 1002, and reflectors 1004 and 1005.

  Here, the metallization ratio in the IDT electrode 1003 is in the range of 0.55 to 0.85, and the IDT electrode 1003 is weighted in the cross width. Thereby, it is said that frequency variation can be reduced and the Q value at the anti-resonance frequency can be improved.

International Publication No. 2005/011117 Pamphlet

  Although the one-port surface acoustic wave resonator 1001 can reduce frequency variation, it has been found that a large ripple appears in a frequency region on the lower frequency side than the resonance frequency in terms of resonance characteristics.

  For this reason, when such a one-port surface acoustic wave resonator 1001 is connected in series to a bandpass filter and used as a series trap, there is a problem that the insertion loss in the passband of the filter deteriorates.

  An object of the present invention is to improve the above-mentioned drawbacks of the prior art, a one-port elastic resonator having good resonance characteristics with a small ripple in a region lower than the resonance frequency, and the one-port elastic resonance An object of the present invention is to provide an elastic wave filter device having a child as a series trap.

  According to the present invention, there is provided a one-port type acoustic wave resonator in which a piezoelectric substrate, an IDT electrode provided on the piezoelectric substrate, and the IDT electrode are cross-weighted, and from the center of the IDT electrode. Also, the region on the first end side that is one end of the IDT electrode in the elastic wave propagation direction and the region surrounded by the envelope defined by the cross width weighting is closer to the IDT electrode than the center of the IDT electrode. Provided is a one-port type acoustic wave resonator that is asymmetrical with a region on the second end side that is the other end in the elastic wave propagation direction and surrounded by an envelope defined by cross width weighting Is done.

  In a specific aspect of the one-port acoustic wave resonator according to the present invention, the shape of the region surrounded by the envelope of the IDT electrode is a first corner portion at the first end portion of the IDT electrode. And has a second corner at the second end.

  According to another specific aspect of the one-port elastic wave resonator of the present invention, the position along the direction orthogonal to the elastic wave propagation direction of the first corner and the elasticity of the second corner The position along the direction orthogonal to the wave propagation direction is asymmetric with respect to the center of the IDT electrode.

  In another specific aspect of the one-port elastic wave resonator according to the present invention, an inner angle of the first corner is different from an inner angle of the second corner.

  In the one-port elastic wave resonator according to the present invention, a plurality of at least one of the first and second corners may be provided.

  In still another specific aspect of the one-port acoustic wave resonator according to the present invention, the first reflector disposed on the outer side in the acoustic wave propagation direction of the first end, and the second end And a second reflector provided outside the elastic wave propagation direction. Thus, in the present invention, the first and second reflectors may be provided.

  An acoustic wave filter device according to the present invention includes a longitudinally coupled resonator type acoustic wave filter unit and a one-port connected in series to the longitudinally coupled resonator type acoustic wave filter unit and configured according to the present invention. A type elastic wave resonator.

  In the one-port acoustic wave resonator according to the present invention, in the IDT electrode cross width weighting, it is a region on the first end side which is one end in the elastic wave propagation direction of the IDT electrode with respect to the center of the IDT electrode and the crossover. A region surrounded by an envelope defined by width weighting and a region on the second end side which is the other end of the IDT electrode in the elastic wave propagation direction from the center of the IDT electrode and is defined by cross width weighting Since the region surrounded by the envelope is asymmetric, the ripple in the frequency region on the lower frequency side than the resonance frequency on the resonance characteristics can be made extremely small.

  In the acoustic wave filter device according to the present invention, since the one-port acoustic wave resonator of the present invention is connected in series to the longitudinally coupled resonator acoustic wave filter unit, the insertion loss in the passband can be reduced. it can.

(A) is a top view of the 1 port type | mold elastic wave resonator which concerns on the 1st Embodiment of this invention, (b) is a schematic plan view which shows the shape of a crossing area | region, (c) is 2 It is a circuit diagram which shows the structure by which the one-port type | mold elastic wave resonator of 1st Embodiment is connected in series. 1 shows an acoustic wave filter device as a second embodiment of the present invention, in which a one-port acoustic wave resonator according to a first embodiment of the present invention is connected in series to a longitudinally coupled resonator acoustic wave filter unit. It is a typical circuit diagram. It is the typical top view which shows the IDT electrode with which the conventional cross width weighting was prepared for the comparison. FIG. 9 is a schematic plan view showing an IDT electrode of a one-port elastic wave resonator according to a modification of the present invention. It is a figure which shows the return loss characteristic of the 1st Embodiment of this invention and the conventional 1 port type | mold elastic wave resonator prepared for the comparison. It is a figure which shows the return loss characteristic of the 1 port type | mold elastic wave resonator which concerns on the modification of this invention, and the conventional elastic wave resonator prepared for the comparison. It is a top view which shows the IDT electrode for demonstrating the further another modification of the 1 port type | mold elastic wave resonator of 1st Embodiment. It is a top view which shows another modification of the 1 port type | mold elastic wave resonator of 1st Embodiment. It is a typical front view for demonstrating a boundary acoustic wave resonator. It is a top view which shows the conventional 1 port type | mold surface acoustic wave resonator.

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

  FIG. 1A is a plan view of a one-port acoustic wave resonator according to the first embodiment of the present invention. The one-port surface acoustic wave resonator according to this embodiment is a one-port surface acoustic wave resonator using a surface acoustic wave.

The one-port elastic wave resonator 1 has a piezoelectric substrate 2. In this embodiment, the piezoelectric substrate 2 is made of 42 ° Y-cut LiTaO ₃ . The piezoelectric material constituting the piezoelectric substrate 2 is not limited to 42 ° Y-cut LiTaO ₃ , and an appropriate piezoelectric material such as a piezoelectric single crystal such as LiTaO ₃ , LiNbO ₃ or quartz, or a piezoelectric ceramic such as PZT can be used. .

  An IDT electrode 3 is formed on the piezoelectric substrate 2. In the present embodiment, the IDT electrode 3 has a laminated structure of AlCu (Al main component) and Ti. One end of the IDT electrode 3 in the elastic wave propagation direction is a first end 3a, and the other end is a second end 3b.

  The metal constituting the IDT electrode 3 is not limited to a laminated structure of AlCu (Al main component) and Ti, and an appropriate metal or alloy such as Au, Pt, Cu, W, Ta, and Al can be used. Moreover, these electrodes may be formed of a laminated metal film formed by laminating a plurality of metal films.

  The characteristic of the one-port elastic wave resonator 1 is the weighting of the IDT electrode 3. This will be described in more detail.

  The IDT electrode 3 includes a first bus bar 3c and a second bus bar 3d arranged so as to face the first bus bar 3c. One end of a plurality of first electrode fingers 3e is connected to the first bus bar 3c. The other ends of the plurality of first electrode fingers 3e are located on the second bus bar 3d side. Similarly, one end of a plurality of second electrode fingers 3f is connected to the second bus bar 3d. The other ends of the plurality of second electrode fingers 3f are located on the first bus bar 3c side.

  The plurality of first and second electrode fingers 3e and 3f extend in a direction orthogonal to the elastic wave propagation direction. A plurality of first dummy electrode fingers 3g are formed with a gap from the tips of the plurality of first electrode fingers 3e. The plurality of first dummy electrode fingers 3g are connected to the second bus bar 3d. Similarly, a plurality of second dummy electrode fingers 3h are formed with gaps from the tips of the plurality of second electrode fingers 3f. The plurality of second dummy electrode fingers 3h are connected to the first bus bar 3c. The first and second dummy electrode fingers 3g and 3h may not be provided. However, by providing a plurality of first and second dummy electrode fingers 3g and 3h, excitation in the transverse mode can be suppressed.

  In the IDT electrode 3, as shown in FIG. 1A, the length of a portion where a plurality of first electrode fingers 3 e and a plurality of second electrode fingers 3 f intersect in the elastic wave propagation direction. That is, the crossing width, which is the length of the overlapping portion, changes in the elastic wave propagation direction. In this way, the cross width is weighted. The crossing region where the first and second electrode fingers 3e and 3f cross is surrounded by first and second envelopes A and B indicated by broken lines in the drawing. Here, the first envelope A is a virtual line that connects the tips of the plurality of second electrode fingers 3f, and the second envelope B connects the tips of the plurality of first electrode fingers 3e. It is a virtual line.

  Accordingly, the planar shape of the crossing region is expressed as shown in FIG. In the present embodiment, the first and second envelopes A and B are united at the first end 3a, and the first and second envelopes A are moved away from the first end 3a. , B are continuously increased, and in the central portion of the IDT electrode 3, the first and second envelopes A, B are substantially parallel to the bus bars 3c, 3d. In addition, the first and second envelopes A and B are united also on the second end 3b side, and the first and second envelopes are moved inward from the second end 3b. The distance between A and B is sequentially increased.

  Accordingly, as shown in FIG. 1B, the planar shape surrounding the crossing region where the first and second electrode fingers 3e and 3f cross is surrounded by the first and second envelopes A and B. And has a corner X on the first end 3a side and a corner Y on the second end 3b side.

  In the present embodiment, the corner portion X is located at the center of the direction connecting the first and second bus bars 3c, 3d, and the corner portion Y is also centered in the direction connecting the first and second bus bars 3c, 3d. Is located. That is, the corner portion X and the corner portion Y are in the same position in the direction orthogonal to the elastic wave propagation direction.

This embodiment is characterized, in the crossover region, the internal angle theta _X of the first corner X, lies in that the internal angle theta _Y corners Y are different, whereby the center O of the IDT electrode 3 The crossing region on the first end 3a side and the crossing region on the second end 3b side from the center O are asymmetric. As a result, as shown in an experimental example to be described later, it is possible to reduce a ripple appearing in a frequency region lower than the resonance frequency.

  Two one-port acoustic wave resonators 1 of the first embodiment were prepared and connected in series as shown in FIG. The return loss characteristic of the structure in which the two one-port elastic wave resonators 1 are connected in series is shown by a solid line in FIG.

  For comparison, an acoustic wave resonator device in which two one-port acoustic wave resonators configured in the same manner as described above are connected in series except that the IDT electrode 1101 shown in FIG. 3 is provided is prepared. did. The return loss characteristics of this acoustic wave resonator device are shown by broken lines in FIG.

  The design parameters of the prepared acoustic wave resonator are as follows.

Piezoelectric substrate 2: 42 ° cut LiTaO ₃
IDT electrode 3: The material is a laminated structure of AlCu (Al main component) and Ti. Thickness is AlCu = 218 nm, Ti = 10 nm. Number of electrode finger pairs = 75 pairs. Inner angle θ _X = 72 ° of corner X, inner angle θ _Y = 53 ° of corner _Y , electrode finger pitch = 1.0427 μm. Distance between first and second end portions 3a and 3b = 155.8037 μm.

  As can be seen from FIG. 5, when the one-port acoustic wave resonator of this embodiment is used, the ripple in the frequency region indicated by the arrow C is smaller than that of the acoustic wave resonator prepared for comparison. You can see that In other words, it is possible to reduce the ripple in the frequency range lower than the resonance frequency of 1835 MHz. This is because the crossing area on the first end 3a side from the center O and the crossing area on the second end 3b side of the center O are asymmetric in the cross width weighting in the IDT electrode 3. Generally, in a reflector using a grating structure, periodicity appears in the reflection characteristics outside the stop band, and ripples are generated. When weighting is performed, since the dummy electrode also operates as a reflector, similarly, a ripple due to the dummy electrode is generated outside the stop band. By making the weighting asymmetrical, it is considered that the frequency characteristics of reflection from the left and right are shifted, so that the ripple can be dispersed.

  Therefore, for example, in the elastic wave filter device 11 of the embodiment shown in FIG. 2, a series trap is configured by connecting the one-port elastic wave resonator 1 in series to the longitudinally coupled resonator type elastic wave filter unit 12. The loss in the pass band of the acoustic wave filter device 11 can be effectively reduced.

  In the present embodiment, the crossing region on the first end 3a side from the center O and the crossing region on the second end 3b side are asymmetrical, so that the resonance frequency is lower than the resonance frequency as described above. It is characterized in that the ripple in can be reduced. Therefore, the weighted asymmetric structure is not limited to the shape shown in FIGS.

  FIG. 4 is a plan view of an IDT electrode according to a modification of the first embodiment of the present invention. The elastic wave resonator according to this modification is the same as the one-port elastic wave resonator 1 of the first embodiment except that the weighting of the IDT electrode 13 is different. As shown in FIG. 4, in this modification, in the planar shape of the crossing region surrounded by the envelopes A and B of the IDT electrode 13, on the first end portion 13a side, as in the case of the first embodiment. Corners X are formed. On the other hand, on the second end portion 13b side, the second envelope B reaches the first bus bar 3c side, and the corner portion Y is positioned in the vicinity of the inner side of the first bus bar 3c.

Therefore, the corners X and Y not only have different internal angles θ _X and θ _Y, but also the position in the direction orthogonal to the elastic wave propagation direction of the corner X and the direction orthogonal to the elastic wave propagation direction of the corner Y. Also, the crossing region on the first end portion 13a side and the crossing region on the second end portion 13b side are asymmetrical because the position along the center O is asymmetric with respect to the center O.

  In FIG. 6, the return loss characteristic of the elastic wave resonator having a structure in which two elastic wave resonators of the above modification are connected in series is shown by a solid line. For comparison, a return loss characteristic of a structure in which two acoustic wave resonators having the electrode structure shown in FIG. 2 are connected in series is shown by a broken line in FIG.

In the IDT electrode 13, the inner angle θ _X of the corner portion X was 72 °, and the inner angle θY of the corner portion Y was 45 °.

  The parameters of the IDT electrode 13 are as follows.

    Number of electrode fingers = 78 pairs. Electrode finger pitch = 1.0427 μm. Distance between first and second end portions 3a, 3b = 161.0172 μm.

  As is apparent from FIG. 6, even when the one-port type acoustic wave resonator of this modification is used, the frequency indicated by C is higher than when the conventional acoustic wave resonator prepared for comparison is used. In the region, that is, in the frequency region lower than the resonance frequency, the ripple can be reduced.

  Further, as apparent from a comparison between FIG. 5 and FIG. 6, according to the modification, the ripple on the lower frequency side than the resonance frequency can be further reduced as compared with the first embodiment. This is considered to be due to the fact that the asymmetry is enhanced by not only the differences in the internal angles of the corner X and the corner Y but also the positions of the corner X and the corner Y.

  In the acoustic wave resonator prepared for comparison, the internal angle θ of the corner is set to θ = 70 ° in both the first end portion and the second end portion.

  The parameters of the IDT electrode 13 are as follows.

    Number of electrode fingers = 78 pairs. Electrode finger pitch = 1.0427 μm. Distance between first and second end portions 3a and 3b = 162.0599 μm.

  FIG. 7 is a plan view showing still another modification of the IDT electrode of the acoustic wave resonator according to the present invention. In this modification, in the IDT electrode 23, the first and second envelopes A and B are not united at the first end portion and the second end portions 23a and 23b. Therefore, the outer shape of the crossing region is formed by the first and second envelopes A and B and the broken lines D and E shown in FIG.

  The portions indicated by broken lines D and E are virtual lines that connect the separated first and second envelopes A and B in the direction orthogonal to the elastic wave propagation direction at the first and second ends 23a and 23b, respectively. It is a line part. Since the first and second envelopes A and B are separated by the first and second end portions 23a and 23b, the outer shape of the crossing region is the first end portion 23a and the second end portion 23b. Are defined by the broken lines D and E, respectively.

  Therefore, in the part where the broken line D and the first envelope A are united, one first corner X1 is formed, and in the part where the second envelope B and the broken line D are united Another one of the first corners X2 is formed. In other words, a plurality of first corner portions X1 and X2 are formed on the first end portion 23a side. Similarly, a plurality of second corners Y1, Y2 are formed on both sides of the broken line E on the second end 23b side.

Also in this modified example, the inner angles θ _X1 and θ _{X2 of} the first corner portions X1 and X2 and the inner angles θ _Y1 and θ _{Y2 of} the second corner portions Y1 and Y2 are different from each other. The shape of the crossing region on the first end 23a side and the shape of the crossing region on the second end 23b side are asymmetric. Therefore, as in the first embodiment, the ripple on the lower frequency side than the resonance frequency can be effectively reduced.

  As is apparent from FIG. 7, in the present invention, the number of corners is not limited to one in the first end and the second end, and may be plural. That is, a plurality of corners may be formed in at least one of the first and second ends of the IDT electrode.

  In the above embodiment, no reflector is provided, but reflectors 4 and 5 may be provided on both sides of the IDT electrode 3 as in the modification shown in FIG. Specifically, the 1st reflector 4 is formed in the elastic wave propagation direction outer side of the 1st edge part 3a. A second reflector 5 is formed outside the second end portion 3b in the elastic wave propagation direction.

  The first and second reflectors 4 and 5 are grating reflectors formed by short-circuiting a plurality of electrode fingers at both ends. The first and second reflectors 4 and 5 have a laminated structure of AlCu (Al main component) and Ti.

  The metal constituting the reflectors 4 and 5 is not limited to the laminated structure of AlCu (Al main component) and Ti, and an appropriate metal or alloy such as Au, Pt, Cu, W, Ta, and Al can be used. Moreover, these electrodes may be formed of a laminated metal film formed by laminating a plurality of metal films.

  The one-port type acoustic wave resonator 1 according to the embodiment and the modification is a surface acoustic wave resonator using a surface acoustic wave. However, the present invention is not limited to a one-port type elastic boundary using a boundary acoustic wave. It may be a wave resonator. FIG. 9 is a schematic front sectional view showing a one-port boundary acoustic wave resonator. Here, the one-port boundary acoustic wave resonator 31 includes a piezoelectric substrate 32 and a dielectric layer 33 laminated on the piezoelectric substrate 32, and an IDT electrode is provided at the interface between the piezoelectric substrate 32 and the dielectric layer 33. 34 and reflectors 35 and 36 are formed. The reflectors 35 and 36 may be omitted. Since the present invention is characterized by the weighting of the IDT electrode, even in such a one-port boundary acoustic wave resonator 31, the weighting of the IDT electrode 34 is formed according to the present invention, so that Similarly, the ripple on the lower frequency side than the resonance frequency can be effectively reduced.

DESCRIPTION OF SYMBOLS 1 ... 1 port type | mold elastic wave resonator 2 ... Piezoelectric substrate 3 ... IDT electrode 3a ... 1st edge part 3b ... 2nd edge part 3c ... 1st bus bar 3d ... 2nd bus bar 3e ... 1st electrode finger 3f ... 2nd electrode finger 3g ... 1st dummy electrode finger 3h ... 2nd dummy electrode finger 4 ... 1st reflector 5 ... 2nd reflector 11 ... Elastic wave filter apparatus 12 ... Longitudinal coupled resonator type Elastic wave filter part 13 ... IDT electrode 13a ... 1st edge part 13b ... 2nd edge part 23 ... IDT electrode 23a ... 1st edge part 23b ... 2nd edge part 31 ... 1 port type boundary acoustic wave resonator 32 ... Piezoelectric substrate 33 ... Dielectric layer 34 ... IDT electrode 35 ... Reflector 36 ... Reflector 1001 ... One-port surface acoustic wave resonator 1002 ... Substrate 1003 ... IDT electrode 1004 ... Reflector 1005 ... Reflector 1101 ... IDT electrode

Claims (7)

A piezoelectric substrate;
An IDT electrode provided on the piezoelectric substrate;
A one-port acoustic wave resonator in which the IDT electrode is cross-weighted,
A region on the first end side which is one end of the IDT electrode in the elastic wave propagation direction from the center of the IDT electrode and surrounded by an envelope defined by cross width weighting is a center of the IDT electrode. A one-port type that is asymmetrical with the region surrounded by the envelope defined by the cross-weight weighting, and the region on the second end side, which is the other end of the IDT electrode in the elastic wave propagation direction, Elastic wave resonator.   The shape of the region surrounded by the envelope of the IDT electrode has a first corner at the first end of the IDT electrode, and a second corner at the second end. The one-port elastic wave resonator according to claim 1, wherein   The position along the direction orthogonal to the elastic wave propagation direction of the first corner and the position along the direction orthogonal to the elastic wave propagation direction of the second corner are asymmetric with respect to the center of the IDT electrode. The one-port acoustic wave resonator according to claim 2.   4. The one-port acoustic wave resonator according to claim 2, wherein an inner angle of the first corner is different from an inner angle of the second corner. 5.   5. The one-port acoustic wave resonator according to claim 2, wherein a plurality of at least one of the first and second corners is provided. A first reflector disposed on the outer side in the elastic wave propagation direction of the first end;
6. The one-port acoustic wave resonator according to claim 1, further comprising a second reflector provided outside the second end portion in the acoustic wave propagation direction.   A one-port type acoustic wave resonator according to any one of claims 1 to 6, which is connected in series with a longitudinally coupled resonator type acoustic wave filter unit and the longitudinally coupled resonator type acoustic wave filter unit. An elastic wave filter device.

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