JP2009212580A - Surface acoustic wave device and surface acoustic wave filter device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a surface acoustic wave device capable of improving a confinement effect of a surface wave without causing an increase in electric resistance, thereby reducing a loss. <P>SOLUTION: The surface acoustic wave device has a structure in which an IDT electrode 3 is formed on a piezoelectric substrate 2, first and second bus bars 6 and 7 of the IDT electrode 3 each have a first layer 12 and a second layer 13 formed on the first layer 12, the second layer is made of a metal film, a plurality of metal strips 14 and a plurality of metal strips 15 are alternately disposed on the first layer 12, and an insulation film 16 is formed between the plurality of metal strips 14 and 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave device such as a resonator and a bandpass filter using surface acoustic waves, and more particularly to a surface acoustic wave device and a surface acoustic wave filter device having an improved IDT electrode bus bar structure.

  Surface acoustic wave resonators and surface acoustic wave filter devices are widely used for resonators or bandpass filters. In the surface acoustic wave device, at least one IDT electrode is formed on a piezoelectric substrate. The IDT electrode includes first and second bus bars, a plurality of first electrode fingers extending from the first bus bar toward the second bus bar, and the first bus bar from the second bus bar. And a plurality of second electrode fingers extending toward. The first and second electrode fingers are interleaved with each other.

  The following Patent Document 1 discloses a surface acoustic wave device 501 shown in FIG. 17 as an example of such a surface acoustic wave device. In the surface acoustic wave device 501, the electrode structure shown in the schematic plan view of FIG. 17 is formed on a piezoelectric substrate. This electrode structure includes an IDT electrode 502 and reflectors 503 and 504 disposed on both sides of the IDT electrode 502 in the surface wave propagation direction. The IDT electrode 502 includes first and second bus bars 505 and 506. A plurality of first electrode fingers 507 having one end connected to the first bus bar 505 and a plurality of second electrode fingers 508 electrically connected to the second bus bar 506 are interleaved with each other. Yes.

  Here, the first and second bus bars 505 and 506 include metal films 505a and 506a and metal films 505b and 506b stacked so as to cover a part of the metal films 505a and 506a. By forming the first and second bus bars 505 and 506 from the laminated metal film, the thickness of the bus bars 505 and 506 is made thicker than the thickness of the electrode fingers 507 and 508. Thereby, the energy of the surface wave can be effectively confined and the resistance can be lowered, so that the loss can be reduced.

On the other hand, the following Non-Patent Document 1 describes that an electric field accompanying the propagation of SAW induces a charge in the metal strip grating, and this charge re-excites the SAW, thereby effectively reflecting. Yes.
JP2002-1000095 “Introduction to surface acoustic wave (SAW) device simulation technology” (Kenya Hashimoto, Realize, PAGE 46, 3.4.1)

  In the surface acoustic wave device described in Patent Document 1, since the first and second bus bars 505 and 506 are made of laminated metal films, the loss can be reduced, but the first contribution to confinement of surface waves is as follows. However, the effect of confining surface waves was still insufficient.

  Further, when the metal strip grating described in Non-Patent Document 1 is applied to the bus bar, the surface wave propagated from the electrode finger portion of the IDT electrode to the bus bar is reflected by the metal strip grating of the bus bar, and the surface wave It is thought that the confinement effect can be improved. However, in a bus bar using such a metal strip grating, the electrical resistance is higher than that of a bus bar made of a normal metal film, and the resistance loss may increase.

  The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to effectively confine the surface wave without causing much increase in electrical resistance, thereby further reducing the loss. An object of the present invention is to provide a surface acoustic wave device and a surface acoustic wave filter device.

  A surface acoustic wave device according to the present invention includes a piezoelectric substrate and an IDT electrode formed on the piezoelectric substrate, wherein the IDT electrode includes first and second bus bars, A plurality of first electrode fingers extending from one bus bar toward the second bus bar; a plurality of first electrode fingers extending from the second bus bar toward the first bus bar; A plurality of second electrode fingers arranged so as to be interleaved with the electrode fingers, and the first and second bus bars are formed on the first layer and the first layer. A first layer of the first bus bar, and a plurality of first metal strips respectively connected to the plurality of first electrode fingers, and a first layer in the surface wave propagation direction. A plurality of metal strips alternately arranged with one metal strip and extended in the direction in which the electrode fingers extend A second metal strip; and a first insulating film provided so as to fill a space between the first and second strips, wherein the first layer of the second bus bar includes a plurality of Third metal strips respectively connected to the second electrode fingers and a plurality of third metal strips alternately arranged in the surface wave propagation direction and extending in the direction in which the electrode fingers extend A fourth metal strip and a second insulating film provided between the adjacent third and fourth strips, and each second layer of the first and second bus bars is made of a metal film. It is characterized by that.

  In a specific aspect of the surface acoustic wave device according to the present invention, the IDT electrode is opposed to a tip of the first electrode finger via a gap and is connected to the second bus bar. The first dummy electrode is opposed to the tip of the second electrode finger via a gap, extends in the direction in which the electrode finger extends, and is connected to the first bus bar. In the IDT electrode, the IDT electrode is subjected to cross width weighting so that the cross width decreases from the portion where the electrode finger cross width is maximum to both sides in the surface acoustic wave propagation direction. The side of the first bus bar to which the first electrode finger and the second dummy electrode are connected is arranged with a certain distance from the cross-weighted envelope. Surface acoustic wave propagation The side of the second bus bar connected to the second electrode finger and the first dummy electrode is connected to the cross-weighted envelope. The second dummy electrode is connected to the second strip, and has an inclined portion inclined with respect to the surface acoustic wave propagation direction so as to be arranged at a certain distance. A dummy electrode is connected to the fourth strip. In this case, since the first and second dummy electrodes are not so long, resistance loss due to the dummy electrodes can be reduced. Further, the surface acoustic wave device can be miniaturized.

  Further, in still another specific aspect of the surface acoustic wave device according to the present invention, all the first and second dummy electrodes are connected to the fourth strip and the second strip, respectively. The second and first dummy electrodes are arranged so as to be opposed to the respective tips of all the first and second electrode fingers, whereby each second of the first and second bus bars. A structure in which the second strip and the second dummy electrode are connected from the edge on the second and first bus bar side of the layer, and a structure in which the fourth strip and the first dummy electrode are connected. It protrudes toward the second bus bar or the first bus bar. In this case, it is desired that the second layer of the first and second bus bars and the second and first electrode fingers be displaced due to misalignment when the second layers are formed in the first and second bus bars. Can prevent short circuit.

In the surface acoustic wave device according to the present invention, preferably, each of the second layers of the first to fourth strips and the first and second bus bars is made of Au, Ag, Cu, Al, Fe, Ni, It is made of at least one metal material selected from W, Ta, Pt, Ma, Cr, Ti and an alloy mainly composed of at least one of these metals, and the insulating film is made of SiO ₂ . In this case, the loss can be reduced by using a lower resistance material.

  The surface acoustic wave device according to the present invention can be applied to various surface acoustic wave resonators and surface acoustic wave filter devices, and the electrode structure is not particularly limited, but according to another specific aspect of the present invention. A ladder-type surface acoustic wave filter device having at least one series arm resonator and a parallel arm resonator, wherein the at least one series arm resonator is a surface acoustic wave device configured according to the present invention. A surface acoustic wave filter device is provided. In this surface acoustic wave filter device, since at least one series arm resonator is configured according to the present invention, it is possible to achieve a low loss, and in particular, the steepness of the filter characteristics on the high pass band side. Can be increased.

  According to the surface acoustic wave device of the present invention, the first bus bar has a structure in which a first layer composed of a plurality of first and second metal strips and a second layer composed of a metal film are stacked. And the second bus bar similarly has the third and fourth metal strips and the second layer made of the metal film, so that the confinement efficiency of the surface wave can be increased without increasing the electrical resistance. Can be increased. Therefore, according to the present invention, it is possible to provide a surface acoustic wave device having a much lower loss than that of a conventional surface acoustic wave device.

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

(First embodiment)
FIG. 1 is a schematic plan view showing a surface acoustic wave device according to a first embodiment of the present invention, and FIG. 3 is a partially cutaway cross-sectional view showing a portion taken along line III-III in FIG. .

The surface acoustic wave device 1 of the present embodiment is a surface acoustic wave resonator. The surface acoustic wave device 1 includes an IDT electrode 3 and reflectors 4 and 5 disposed on both sides of the IDT electrode 3 in the surface wave propagation direction on a piezoelectric substrate 2. In the present embodiment, the piezoelectric substrate 2 is a 126 ° Y-cut X-propagation LiNbO ₃ substrate. However, the material constituting the piezoelectric substrate 2 is not particularly limited, may be a LiNbO ₃ of other crystal orientations may be another piezoelectric single crystal such as LiTaO _3, and using the piezoelectric ceramic It may be formed. Preferably, LiNbO ₃ is preferably used because the present structure can optimize the relationship between the sound speed of the IDT and the busbar, and can confine the surface wave energy more efficiently.

  The IDT electrode 3 has first and second bus bars 6 and 7. In this embodiment, the first bus bar 6 and the second bus bar 7 are extended in the surface wave propagation direction. The first and second bus bars 6 and 7 are arranged in parallel at a predetermined distance in a direction orthogonal to the surface wave propagation direction.

  A plurality of first electrode fingers 8 are formed so as to extend from the inner edge 6 a of the first bus bar 6, that is, from the edge 6 a on the second bus bar 7 side toward the second bus bar 7. .

  On the other hand, a plurality of second electrode fingers 9 extend from the inner edge 7 a of the second bus bar 7, that is, from the edge 7 a on the first bus bar 6 side, so as to extend toward the first bus bar 6 side. Is formed. The plurality of first electrode fingers 8 and the plurality of second electrode fingers 9 are interleaved with each other. Adjacent first electrode fingers 8 and second electrode fingers 9 have adjacent portions, that is, intersecting regions when viewed in the surface wave propagation direction.

  In the present embodiment, the crossing width where the plurality of first and second electrode fingers 8 and 9 cross each other changes in the surface wave direction. That is, as shown by envelopes A and B in FIG. 1, the IDT electrode 3 has the largest cross width in the center of the surface wave propagation direction, and the cross width decreases toward the end in the surface wave propagation direction. Thus, cross width weighting is applied to the IDT electrode 3.

  The envelope is an imaginary line connecting the tips of the first and second electrode fingers 8 and 9, and is a line defined to indicate the cross width region. A space between the envelope A and the envelope B corresponds to a cross width region, that is, a region to which a voltage for exciting a surface wave is applied.

  In this embodiment, the IDT electrode 3 is subjected to the above-mentioned cross width weighting. However, in the present invention, the IDT electrode does not necessarily need to be weighted.

  In the present embodiment, a plurality of first dummy electrodes 10 and a plurality of second dummy electrodes 11 are arranged in a region between the first and second bus bars 6 and 7.

  The first dummy electrode 10 extends from the edge 7 a of the second bus bar 7 to the first bus bar 6 side. The tip of the first dummy electrode 10 is opposed to the first electrode finger 8 with a gap therebetween. In other words, the first dummy electrode 10 is located in the extending direction of the first electrode finger 8.

  On the other hand, the second dummy electrode 11 extends from the inner edge 6a of the first bus bar 6 to the second bus bar 7 side, and the tip of the second dummy electrode 11 is separated from the second electrode finger 9 by a gap. It is opposed to. In other words, the second dummy electrode 11 is disposed on the extended line in the extending direction of the second electrode finger 9 with a gap from the tip of the second electrode finger 9.

  The surface acoustic wave device 1 according to this embodiment is characterized by the first and second bus bars 6 and 7. FIGS. 2 and 3 are a partially cutaway plan view and a partially cutaway front sectional view schematically showing the main part of the second bus bar 7. As shown in FIG. 3, a second bus bar 7 is formed on the piezoelectric substrate 2. The second bus bar 7 has a first layer 12 and a second layer 13. The first layer 12 has a structure in which a plurality of third metal strips 14 and a plurality of fourth metal strips 15 are alternately arranged in the surface wave propagation direction. The third and fourth metal strips 14 and 15 extend in a direction parallel to the direction in which the first and second electrode fingers 8 and 9 extend, that is, in a direction orthogonal to the surface acoustic wave propagation direction. In the present embodiment, the first and second electrode fingers 8 and 9 and the optional first and second dummy electrodes 10 and 11 described above all have the same width direction dimension. The third and fourth metal strips 14 and 15 have the same width direction dimension. Here, the width of the electrode finger and the dummy electrode and the width of the metal strip are dimensions along the surface wave propagation direction.

  The third metal strip 14 is electrically connected to the second electrode finger 9. In the present embodiment, the third metal strip 14 is provided by extending the second electrode finger 9 to the region where the bus bar 7 is provided. However, as long as the third metal strip 14 is electrically connected to the second electrode finger 9, the formation position may be shifted from the second electrode finger 9 in the surface wave propagation direction.

  The fourth metal strip 15 is connected to the first dummy electrode 10 described above. However, in the present invention, the fourth metal strip 15 may not be connected to the first dummy electrode 10.

A second insulating film 16 is formed between the third and fourth metal strips 14 and 15. In the present embodiment, the insulating film 16 is made of SiO ₂ and has the same thickness as the third and fourth metal strips 14 and 15. Therefore, the upper surfaces of the third and fourth metal strips 14 and 15 and the upper surface of the insulating film 16 provided so as to fill the gap between the third and fourth metal strips 14 and 15 are flush with each other.

  A second layer 13 is formed so as to cover the upper surfaces of the third and fourth metal strips 14 and 15 and the insulating film 16. The second layer 13 is made of a metal film.

  Accordingly, the bus bar 7 is formed of a laminated film in which the first layer 12 and the second layer 13 are laminated.

  Note that the first bus bar 6 is configured in the same manner as the second bus bar 7. That is, the first bus bar 6 is formed from the first metal strip 17 connected to the first electrode finger 8, the second metal strip 18 connected to the second dummy electrode 11, and the first insulating film 19. And a second layer 20 stacked on the first layer.

  In the present embodiment, since the second bus bar 7 side is a bus bar connected to the ground potential, the second bus bar 7 is formed so as to be electrically connected to the reflectors 4 and 5.

  The reflectors 4 and 5 are well-known grating type reflectors, and both ends of a plurality of electrode fingers are short-circuited.

  In the present embodiment, the bus bars 4a, 4b, 5a, and 5b in which both ends of the plurality of electrode fingers of the reflectors 4 and 5 are short-circuited also use the same laminated structure as the first and second bus bars 6 and 7. It has been. In the reflectors 4 and 5, the bus bars 4a, 4b, 5a, and 5b do not necessarily have a structure in which the first and second layers are laminated.

  As the metal material constituting the first and second electrode fingers 8 and 9, the first and second dummy electrodes 10 and 11, the metal strips 14, 15, 17, and 18 and the reflectors 4 and 5, Metal can be used. As such a metal, Au, Ag, Cu, Al, Fe, Ni, W, Ta, Pt, Mo, Cr, Ti and at least one of these metal materials can be used. Note that the metal material can be preferably used as the metal material constituting the second layer 13. By using these metal materials, the loss can be reduced by using a material having a lower resistance.

  Note that the metal material constituting the second layer 13 may be different from the metal material constituting the first and second electrode fingers 8 and 9 and the metal strips 14, 15, 17 and 18.

  Further, the first and second electrode fingers 8 and 9 may be formed of a metal material different from that of the metal strips 14, 15, 17 and 18.

  The surface acoustic wave device 1 according to the present embodiment is characterized in that the bus bars 6 and 7 have the laminated structure, thereby increasing the confinement efficiency of the surface waves without increasing the electrical resistance. Therefore, the loss can be reduced.

  As described above, since the bus bars 6 and 7 have the first and second layers, the reason why the loss can be reduced is considered as follows. That is, in Non-Patent Document 1 described above, in the metal grating, it is described that an electric field accompanying the propagation of the surface wave induces a charge in the metal strip, and this charge re-excites the SAW, thereby effectively reflecting. Has been. In the present invention, in the first layer of the bus bars 6 and 7, the first and second metal strips 17 and 18 or the third and fourth metal strips 14 and 15 are provided, that is, the metal grating structure is provided. It has been. Therefore, electric charges are induced in the first and second metal strips 17 and 18 or the third and fourth metal strips 14 and 15 by an electric field generated along with the propagation of the surface wave. Therefore, the surface wave is re-excited by the induced electric charge, whereby effective reflection occurs, the surface wave leaking to the bus bars 6 and 7 is reflected, and the confinement efficiency of the surface wave is effectively enhanced. it is conceivable that.

  Next, the effect of this embodiment will be described based on a more specific experimental example.

  In the present experimental example, the first and second electrode fingers 8 and 9 have a thickness of 90 nm / 10 nm / 70 nm / 10 nm in order of four layers of AlCu / Ti / Pt / NiCr in order from the top. Formed. The first and second dummy electrodes 10 and 11 were formed in the same manner. Similarly, the metal strips 14, 15, 17 and 18 were formed simultaneously with the first and second electrode fingers 8 and 9 and the first and second dummy electrodes 10 and 11.

Next, an SiO ₂ film was formed on the piezoelectric substrate 2 and patterned by photolithography to form insulating films 16 and 19. Note that either the formation of the insulating films 16 and 19 or the formation of the metal strips 14, 15, 17, and 18 may be performed first.

  Next, as the second layers 13 and 20, stacked metal films made of Al / Ti / AlCu / Ti were formed in order from the top so that the thicknesses were 1140 nm / 100 nm / 500 nm / 100 nm, respectively.

In the present experimental example, in the region sandwiched between the bus bars 6 and 7, the SiN film / SiO ₂ is formed as a protective film in order from the top so as to cover the first and second electrode fingers 8 and 9 of the IDT electrode. A film was formed to a thickness of 30 nm / 1000 nm. In FIG. 1, this protective film is not shown. This is to clearly show the shape and weighting of the electrode fingers 8 and 9. Moreover, this protective film is not necessarily essential.

  Further, the maximum crossing width of the IDT electrode 3 is 90 μm, the number of electrode fingers is 100 pairs, the electrode finger pitch is 1.966 μm, the dimension in the extending direction of the electrode fingers 8 and 9 of the bus bars 6 and 7, that is, the width dimension is 20 μm. .

  The impedance Z and return loss of the surface acoustic wave device 1 obtained as described above were measured.

  For comparison, a surface acoustic wave device 601 of a comparative example shown in FIGS. 4 to 6 was prepared. In the surface acoustic wave device 601, the first and second bus bars in the IDT electrode do not have the metal grating composed of the first and second metal strips 17 and 18 or the third and fourth metal strips 14 and 15 described above. Except for this, the configuration is the same as the surface acoustic wave device 1 of the first embodiment. More specifically, as shown in FIG. 4, the IDT electrode 3 has first and second bus bars 606 and 607. 5 and 6, the second bus bar 607 includes a first layer 612 formed on the piezoelectric substrate 2, a second bus bar 607, and a second bus bar 607. Layer 13. Here, the first layer 612 does not have a grating structure and is formed of a metal film. This metal film is formed of a laminated metal film similar to the metal strips 17 and 18 of the above embodiment.

  The return loss frequency characteristics and impedance frequency characteristics of the surface acoustic wave devices 1 and 601 of the first embodiment and the comparative example were measured. The results are shown in FIG. In FIG. 12, the solid line shows the result of the first embodiment, and the alternate long and short dash line shows the result of the comparative example.

  It can be said that the surface acoustic wave resonator exhibits good characteristics when the resonance frequency is in the vicinity of 900 MHz and the anti-resonance frequency is in the vicinity of 930 MHz and the return loss is small in the vicinity of these frequencies.

  As can be seen from FIG. 12, according to the present embodiment, the return loss near 900 MHz, which is the resonance frequency, is smaller than that of the comparative example. That is, it can be seen that the loss is reduced.

  On the other hand, the return loss in the vicinity of 930 MHz, which is the antiresonance frequency, is about the same.

(Second Embodiment)
7 and 8 are a schematic plan view showing a surface acoustic wave device according to a second embodiment of the present invention and a partially cutaway plan view showing an enlarged main part thereof.

  The surface acoustic wave device 101 of the second embodiment is the same as that of the first embodiment except that the planar shapes of the first and second bus bars 106 and 107 are different from the planar shape of the reflector bus bar. It is almost the same as the wave device 1. Therefore, about the same part, the same reference number is attached | subjected and it abbreviate | omits by using description of 1st Embodiment.

  In the surface acoustic wave device 101 of the second embodiment, the inner edges 106a and 107a of the first and second bus bars 106 and 107 of the IDT electrode 3 are separated from the envelope A and the envelope B by a certain distance. It has the inclined part 106b, 106c, 107b, 107c extended. That is, the end edges 106a and 107a of the bus bars 106 and 107 are brought closer to the cross width region.

  The cross section taken along the line III-III in FIG. 8 is the same as FIG. 3 showing the surface acoustic wave device 1 of the first embodiment. Therefore, the content and description of FIG. 3 are used. That is, also in this embodiment, the second bus bar 107 is laminated on the first layer including the first and second metal strips 14 and 15 and the second insulating film 16. And a second layer 13.

  Similarly, the first bus bar 106 also includes first and second metal strips 17 and 18, a first insulating film 19, and a second layer 13.

  Therefore, in the present embodiment, it is considered that the return loss can be improved and the loss can be reduced as in the first embodiment.

  The distance between the inclined portions 106b and 106c and the envelope A and the distance between the inclined portions 107b and 107c and the envelope B are set to 10 μm, and the other points are the surface acoustic waves of the first embodiment. The surface acoustic wave device 101 of the second embodiment was produced in the same manner as the device 1. The return loss-frequency characteristics of the surface acoustic wave device 101 according to the second embodiment are shown by broken lines in FIG. As can be seen from FIG. 12, according to the second embodiment, the return loss in the vicinity of the resonance frequency of 900 MHz can be reduced not only in the comparative example but also in the first embodiment. That is, in the second embodiment, the inner edges 106a and 107a of the first and second bus bars 106 and 107 are brought close to the cross width region, so that the first and second electrode fingers 8 and 9 and the second It is considered that the electrical resistance loss generated in the first and second dummy electrodes 10 and 11 can be reduced, and the return loss is further improved thereby.

(Third embodiment)
FIG. 9 is a plan view of a surface acoustic wave device 201 according to the third embodiment of the present invention, and FIG. 10 is a schematic plan view showing the main part thereof. The surface acoustic wave device 201 of the third embodiment is the same as that of the first embodiment except that the width of the bus bars 206 and 207 is smaller than that of the surface acoustic wave device 1 of the first embodiment. This is the same as the surface acoustic wave device 1. Here, the width of the first and second bus bars 206 and 207 is set to 20 μm to 10 μm in the first embodiment. In FIG. 9, the widths of the first and second bus bars 206 and 207 are shown smaller than the actual ratio for easy comparison.

  The return loss frequency characteristic of the surface acoustic wave device of the third embodiment obtained as described above is shown by a two-dot chain line in FIG. In FIG. 13, the return loss characteristic of the second embodiment is also shown.

  As is clear from FIG. 13, the surface acoustic wave device 201 of the third embodiment also has a return loss of about 0.61 dB in the vicinity of 900 MHz, which is worse than that of the second embodiment, but is shown in FIG. It can be seen that the return loss can be reduced as compared with the comparative example.

  However, in the third embodiment, the return loss improvement effect in the vicinity of the resonance frequency is substantially smaller than in the first and second embodiments described above. This is presumably because the effect of reducing electrical resistance is reduced due to the small size of the bus bar in the width direction.

  In the first and second bus bars 206 and 207, the width direction dimension of the second layers 213 and 220 is as small as 10 μm. Here, the width of the bus bar and the width of the second layer refer to dimensions along the direction in which the electrode fingers extend.

  As representative of the second bus bar 207, the second bus bar 207 includes a first layer composed of third and fourth metal strips 214 and 215 and a second insulating film 216, and a first layer. And a second layer 213 formed on the other layer. Here, the width of the second layer 213 is narrower than the width of the bus bar 207. The inner edge 207 a of the bus bar 207 is a portion along the connection wiring 221. Here, the plurality of metal strips 214 and 215 on the second bus bar 207 side are short-circuited by the connection wiring 221, and the outer portion from the connection wiring 221 is the second bus bar 207. The second layer 213 is formed in a narrower region in the width direction than the first layer.

  As is clear from the fact that the connection wiring 221 constitutes the inner edge of the second bus bar 207, in the present invention, the bus bar means that the electrode fingers connected to the same potential adjacent to each other are electrically connected. In the third embodiment, the connection wiring 221 also constitutes a part of the bus bar.

  As in the third embodiment, in the first and second bus bars, the second layer is not necessarily formed on the entire upper surface of the first layer. However, as in the first and second embodiments, it is preferable that the second layer is formed over the entire upper surface of the first layer, that is, over the entire width direction of the bus bar. Thereby, the electrical resistance can be further reduced.

(Modification)
FIG. 11 is a schematic partially cutaway plan view for explaining a preferred modification of the surface acoustic wave device 1 according to the first embodiment. In the surface acoustic wave device 301 of this modification, an offset electrode 302 that does not exist in the surface acoustic wave device 1 is provided on the second bus bar 7 side. That is, as indicated by an arrow C in FIG. 1, the first dummy electrode 10 did not exist on the distal end side of the first electrode finger 8 in the maximum crossing width portion. Similarly, the second dummy electrode 11 is not opposed to the tip end side of the second electrode finger 9 in the maximum crossing width portion.

  On the other hand, as shown in FIG. 11, in the maximum crossing width portion, in the present modification, a dummy electrode 302 is formed at the tip of the first electrode finger 8 via a gap. The dummy electrode 302 is one of the first dummy electrodes, but is an electrode that did not exist in the first embodiment.

  The dummy electrode 302 protrudes from the edge 7a of the second bus bar 7 toward the first bus bar 6 side. That is, in the present modification, the first dummy electrode 302 is formed at the tip of the first electrode finger through the gap even at the maximum crossing width portion, and similarly, the tip of the second electrode finger is also formed. The second dummy electrode is formed in the maximum crossing width portion. Thus, if a dummy electrode is provided on the tip side of all the electrode fingers 8, 9, positioning when forming the second layer of the bus bars 6, 7 can be facilitated. That is, in the first embodiment, the gap between the electrode finger tips and the bus bars 6 and 7 are close to each other in the vicinity of the maximum crossing width of the IDT electrode 3. Therefore, when the formation positions of the second layers 13 and 20 of the bus bars 6 and 7 are shifted in the extending direction of the electrode fingers due to manufacturing variations, the bus bars and the counterpart electrode fingers may come into contact with each other and short-circuit. . On the other hand, if the electrode structure is formed so that the dummy electrode 302 exists, even if the formation position of the second layer 13 is slightly shifted in the extending direction of the electrode finger, the short circuit is surely prevented. can do. That is, the tolerance of the formation position in the extending direction of the electrode finger of the second layer 13 can be increased only by the length portion of the offset electrode 302.

  The longer the length of the first dummy electrode 302 having the shortest length, the higher the tolerance, which is preferable. However, if the length of the dummy electrode 302 becomes too long, the resistance loss increases. Therefore, it is desirable that the length of the first and second dummy electrodes with the shortest length be about 1 μm.

  The elastic surface of the present modification, which is configured in the same manner as in the first embodiment except that the first and second dummy electrodes are provided on the tip side of all the first and second electrode fingers. The return loss-frequency characteristic of the wave device 301 is shown by a solid line in FIG. For comparison, in FIG. 14, the return loss frequency characteristics of the first embodiment are also shown by broken lines. As can be seen from FIG. 14, even when the offset electrode 302 is provided, the return loss can be 0.6 dB or less near the resonance frequency near 900 MHz.

(Other structural examples)
As is clear from the first to third embodiments described above, the surface acoustic wave device of the present invention is preferably applied to a surface acoustic wave resonator having one IDT electrode. The present invention can also be applied to a surface acoustic wave resonator or a surface acoustic wave filter having a structure.

  Preferably, the surface acoustic wave device of the present invention can be suitably used as the series arm resonator or the parallel arm resonator of the ladder filter shown in FIG.

  A ladder filter 401 shown in FIG. 15 includes a plurality of series arm resonators S1 to S7 inserted in a series arm connecting an input end and an output end, and a parallel arm resonance connected between the series arm and a ground potential. It has children P1 to P3. The ends on the ground potential side of the parallel arm resonators P1 and P2 are connected in common and connected to the ground potential via an inductance L1. An inductance L2 is also connected between the parallel arm resonator P3 and the ground potential.

  In the ladder type filter 401, the surface acoustic wave device 101 of the second embodiment is used as the series arm resonators S1 to S7, and a transmission side band filter of an EGSM type mobile phone is formed. In this case, the pass band is 880 to 915 MHz. For comparison, a ladder-type filter was prepared in the same manner except that the series arm resonators S1 to S7 were configured using the surface acoustic wave resonators of the comparative example, and the attenuation frequency characteristics were measured. did. FIG. 16 is a diagram showing attenuation frequency characteristics of the ladder type filter and a ladder type filter prepared for comparison. A broken line shows the result of the above embodiment, and a one-dot chain line shows the result of the comparative example. As can be seen from FIG. 16, the ladder type filter configured using the surface acoustic wave device 101 of the above embodiment reduces the insertion loss in the passband as compared with the ladder type filter prepared for comparison. It can be seen that it is possible to reduce the insertion loss especially on the high side of the passband. This is because the series arm resonators S1 to S7 are configured by using the surface acoustic wave device 1 of the second embodiment.

  The present invention is not limited to the bandpass filter of the mobile phone described above, and can be generally used for a surface acoustic wave device constituting various filter circuits.

1 is a schematic plan view of a surface acoustic wave device according to a first embodiment of the present invention. It is a partial notch top view which shows the principal part of the surface acoustic wave apparatus of 1st Embodiment. It is sectional drawing which follows the III-III line of FIG. It is a schematic plan view of a surface acoustic wave device prepared for comparison. FIG. 5 is a partially cutaway plan view showing a main part of the surface acoustic wave device of the comparative example shown in FIG. It is sectional drawing which shows the part which follows the VI-VI line of FIG. It is a schematic plan view of a surface acoustic wave device according to a second embodiment of the present invention. It is a partial notch top view which shows the principal part of the surface acoustic wave apparatus of 2nd Embodiment. It is a schematic plan view of a surface acoustic wave device according to a third embodiment of the present invention. It is a typical partial notch top view which shows the principal part of the surface acoustic wave apparatus of 3rd Embodiment. It is a partial notch top view for demonstrating the modification of the surface acoustic wave apparatus of 1st Embodiment. It is a figure which shows the return loss-frequency characteristic of the surface acoustic wave apparatus of 1st, 2nd embodiment and a comparative example. It is a figure which shows the return loss-frequency characteristic of the surface acoustic wave apparatus of 2nd Embodiment and 3rd Embodiment. It is a figure which shows the return loss-frequency characteristic of the surface acoustic wave apparatus of 2nd Embodiment and a comparative example. It is a figure which shows the circuit structure of the ladder type filter which used the surface acoustic wave apparatus of this invention as a series arm resonator. It is a figure which shows the attenuation amount frequency characteristic of the ladder type filter which used the surface acoustic wave apparatus of this invention as a series arm resonator, and the ladder type filter prepared for the comparison. It is a top view for demonstrating an example of the conventional surface acoustic wave apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave apparatus 2 ... Piezoelectric substrate 3 ... IDT electrode 4, 5 ... Reflector 4a, 4b, 5a, 5b ... Bus bar 6 ... 1st bus bar 6a ... End edge 7 ... 2nd bus bar 7a ... End edge 8 ... 1st electrode finger 9 ... 2nd electrode finger 10 ... 1st dummy electrode 11 ... 2nd dummy electrode 12 ... 1st layer 13 ... 2nd layer 14 ... 3rd metal strip 15 ... 4th Metal strip 16 ... Second insulating film 17 ... First metal strip 18 ... Second metal strip 19 ... First insulating film 20 ... Second layer 101 ... Surface acoustic wave device 106 ... First bus bar 106a ... End edge 106b, 106c, 106d, 106e ... Inclined portion 107 ... Second bus bar 107a ... End edge 107b, 107c ... Inclined portion 201 ... Surface acoustic wave device 206 ... First bus bar 207 ... Second bus bar 20 a ... edge 213 ... second layer 214,215 ... metal strip 214a ... edge 216 ... connection wiring 217 ... bus bar 220 ... second layer 221 ... connection wiring 301 ... surface acoustic wave device 302 ... dummy electrode 401 ... ladder Type filter 601 ... Surface acoustic wave device 606 ... First bus bar 607 ... Second bus bar 612 ... First layer L1 ... Inductance L2 ... Inductance P1 to P3 ... Parallel arm resonator S1 to S7 ... Series arm resonator

Claims (5)

A piezoelectric substrate;
A surface acoustic wave device comprising an IDT electrode formed on the piezoelectric substrate,
The IDT electrode includes first and second bus bars, a plurality of first electrode fingers extending from the first bus bar toward the second bus bar, and the first bus bar from the first bus bar. A plurality of second electrode fingers extending toward the bus bar and disposed so as to interpose with the plurality of first electrode fingers, wherein the first and second bus bars are first And a second layer formed on the first layer,
The first layers of the first bus bars are alternately arranged with a plurality of first metal strips respectively connected to the plurality of first electrode fingers and with the first metal strips in the surface wave propagation direction. And a plurality of second metal strips extending in the direction in which the electrode fingers extend, and a first insulating film provided so as to fill between the first and second strips,
The first layer of the second bus bar is alternately arranged with third metal strips respectively connected to a plurality of second electrode fingers and a plurality of third metal strips in the surface wave propagation direction. A plurality of fourth metal strips extending in the direction in which the electrode fingers extend, and a second insulating film provided between the adjacent third and fourth strips,
A surface acoustic wave device in which each second layer of the first and second bus bars is made of a metal film. A first dummy electrode which is opposed to the tip of the first electrode finger via a gap and connected to the second bus bar;
A second dummy electrode facing the tip of the second electrode finger via a gap, extending in the direction in which the electrode finger extends, and connected to the first bus bar; Prepared,
In the IDT electrode, the IDT electrode is subjected to cross width weighting so that the cross width decreases from the portion where the electrode finger cross width is maximum to both sides of the surface acoustic wave propagation direction.
An elastic surface such that a side of the first bus bar to which the first electrode finger and the second dummy electrode are connected is arranged at a certain distance from the cross-weighted envelope. Having an inclined portion inclined with respect to the wave propagation direction;
An elastic surface such that a side of the second bus bar to which the second electrode finger and the first dummy electrode are connected is arranged at a certain distance from the cross-weighted envelope. Having an inclined portion inclined with respect to the wave propagation direction;
2. The surface acoustic wave device according to claim 1, wherein the second dummy electrode is connected to the second strip, and the first dummy electrode is connected to the fourth strip.   All the first and second dummy electrodes are connected to the fourth strip and the second strip, respectively, and are opposed to the tips of all the first and second electrode fingers. The second and first dummy electrodes are arranged on the second strip, whereby a second strip is formed from the second and first bus bar side edges of the second layers of the first and second bus bars. And a structure in which the second dummy electrode is connected, and a structure in which the fourth strip and the first dummy electrode are connected protrude toward the second bus bar or the first bus bar. Item 3. The surface acoustic wave device according to Item 2. The first to fourth strips and the second layers of the first and second bus bars are Au, Ag, Cu, Al, Fe, Ni, W, Ta, Pt, Mo, Cr, Ti, and this. is the result of at least one metal material selected from an alloy mainly containing at least one metal, the insulating film is made of SiO _2, the surface acoustic wave according to any one of claims 1 to 3 apparatus.   5. A ladder-type surface acoustic wave filter device having at least one series arm resonator and a parallel arm resonator, wherein the at least one series arm resonator is according to claim 1. A surface acoustic wave filter device comprising a surface acoustic wave device.

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