JP2008103953A - Surface acoustic wave element chip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make a surface acoustic wave element chip compact while reducing a dip nearby a center frequency. <P>SOLUTION: The surface acoustic wave element chip 52 has two IDTs 54 and 56 disposed in a propagation direction of a surface acoustic wave of a piezoelectric substrate 12. Reflectors 64a and 64b are provided outside the IDTs 54 and 56 across the IDTs 54 and 56. A pair of comb-shaped electrodes 58a and 58b constituting the IDT 54 or 56 have a grating portion 50 (50a and 50b) by a plurality of electrode fingers 20a and 20b forming electrode intersection portions 30 and 32 in a length direction. The grating portion 50 is provided with a wire bonding portion 68 joining a bonding wire 34. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a resonance-type surface acoustic wave element provided with interdigital electrodes and reflectors on a piezoelectric substrate, and more particularly to a surface acoustic wave filter in which interdigital electrodes are formed in two or more directions in the propagation direction of surface acoustic waves. The present invention relates to a surface acoustic wave element piece.

  Surface acoustic wave (SAW) devices such as surface acoustic wave filters are widely used in communication devices such as mobile phones because they are small, have excellent mass productivity, and can be manufactured at low cost. As the surface acoustic wave element pieces constituting the surface acoustic wave filter, a transversal type in which a pair of interdigital electrodes are arranged on the surface of the piezoelectric substrate at an appropriate interval along the propagation direction of the surface acoustic wave is well known. ing. However, the transversal type surface acoustic wave element piece receives the surface acoustic wave that is excited and propagated in one interdigital electrode, and the other interdigital electrode receives the energy of the received surface acoustic wave. small. For this reason, the transversal type surface acoustic wave element piece can form a relatively wide band filter, but has a drawback of increasing insertion loss. Therefore, a resonant surface acoustic wave element piece in which a lattice-like reflector is disposed outside the pair of interdigital electrodes is often used. This resonant surface acoustic wave element piece reflects the surface acoustic wave propagated by the pair of reflectors toward the interdigital electrode, and confines the energy of the surface acoustic wave between the pair of reflectors. For this reason, the resonant surface acoustic wave element piece can reduce the insertion loss.

FIG. 22 is a plan view schematically showing an example of a conventional ordinary resonant surface acoustic wave element piece. In FIG. 22, the surface acoustic wave element piece 10 is provided with a pair of IDTs (Interdigital Transducers) 14 and 16 at the center of the piezoelectric substrate 12. The piezoelectric substrate 12 is made of a piezoelectric material such as quartz, lithium tantalate (LiTaO ₃ ), or lithium niobate (LiNbO ₃ ), and is formed in a rectangular shape in plan view. The pair of IDTs 14 and 16 are disposed along the propagation direction of the surface acoustic wave of the piezoelectric substrate 12. The IDT 14 is composed of a pair of comb-shaped electrodes 18 (18a, 18b), and is disposed so that the electrode fingers 20 (20a, 20b) corresponding to the comb teeth of the comb-shaped electrodes are engaged with each other. And the electrode finger 20a and the electrode finger 20b have one end connected to the corresponding bus bar 24 (24a, 24b). The other IDT 16 is composed of a pair of comb-shaped electrodes 22 (22a, 22b), and is arranged so that the electrode fingers 20 are engaged with each other, like the IDT 14. Similar to the comb-shaped electrode 18, these electrode fingers 20 are connected at one end to the corresponding bus bar 24.

  A pair of reflectors 26 (26a, 26b) are provided outside the IDTs 14, 16 in the propagation direction of the surface acoustic waves with the IDTs 14, 16 in between. Each reflector 26 is formed of a plurality of conductor strips 28 formed in parallel with the electrode fingers 20 and has a lattice shape. The opening width B of the reflector 26 is based on the width W of the electrode intersections 30 and 32 which are overlapping portions in the propagation direction of the surface acoustic waves formed by the electrode fingers 20a and 26b. Wide. The opening width B of the reflector 26 is substantially the same as the width W0 of the waveguides of the IDTs 14 and 16, that is, the width between the bus bars 24a and 24b.

  In such a surface acoustic wave element piece 10, as shown in FIG. 22, the bus bar 24 also serves as a wire bonding portion, and the bonding wire 34 is joined to the bus bar 24. When the bonding wire 34 is not bonded to the bus bar 24, a bonding pad (wire bonding portion) of about 200 μm × 200 μm electrically connected to the bus bar 24 is formed outside the bus bar 24 in the longitudinal direction of the electrode finger 20. . A bonding wire 34 is bonded to the bonding pad. One of the pair of IDTs 14 and 16 (for example, IDT 14) is on the input side, and a signal voltage is applied between the comb-shaped electrodes 18a and 18b via the bonding wires 34, so that the piezoelectric substrate 12 An elastic wave (surface acoustic wave) having a predetermined frequency is excited in the surface layer portion. The other IDT 16 is on the output side and can obtain a voltage proportional to the amplitude of the surface acoustic wave propagating through the piezoelectric substrate 12. The surface acoustic wave element 10 thus configured is used for an RF filter, a duplexer, an IF filter, and the like.

  However, in the surface acoustic wave element piece 10 as described above, when the width W0 of the waveguide formed in the IDTs 14 and 16 is not sufficiently wide (long) with respect to the wavelength λ of the surface acoustic wave excited by the IDT 14, The number of surface acoustic wave guided modes that can propagate through the waveguide is limited. These propagating waveguide modes cause spurious. 23 and 24 show the frequency response characteristics of the surface acoustic wave element piece 10.

  FIG. 23 shows the insertion loss with respect to the frequency of the surface acoustic wave element piece 10. The horizontal axis in FIG. 23 is the frequency, and the deviation from the center frequency F0 is shown in MHz. The vertical axis in FIG. 23 indicates the insertion loss in dB. The center frequency F0 is about 100 MHz. FIG. 24 shows the group delay time response characteristics, where the horizontal axis represents the frequency shown in FIG. 23 and the vertical axis represents the delay time in μsec. In the surface acoustic wave element piece 10 used, the intersection width of the electrode intersections 30 and 32 is 700 μm, and the distance from the electrode intersections 30 and 32 to the bus bar 24 is about 10 μm. 23 and 24 indicate the passband when the surface acoustic wave element piece 10 is used to form a filter.

  As indicated by A in FIG. 23, the surface acoustic wave element piece 10 has a large loss dip in the passband PB and in the vicinity of the center frequency F0. As shown in FIG. 24, at the frequency at which this dip occurs, the transmission time is about 0.4 μsec later than the nearby frequency.

  Therefore, in Patent Documents 1 and 2, a grating region is formed on the outer side in the longitudinal direction of the electrode finger to substantially widen the waveguide, thereby improving spurious (dip). FIG. 25 is a plan view schematically showing such a surface acoustic wave element. In FIG. 25, the surface acoustic wave element piece 40 is provided with two IDTs 42 and 44 along the propagation direction of the surface acoustic wave. Each of these IDTs 42 and 44 includes a pair of comb-shaped electrodes 46 (46a and 46b) and 48 (48a and 48b). The comb electrodes 46 and 48 form electrode intersections 30 and 32 by the electrode fingers 20. Further, the comb-shaped electrodes 46 and 48 have a grating part 50 (50a, 50b) on the side of the electrode finger 20 in the longitudinal direction and a bus bar 24 provided outside the grating part 50. The electrode finger 20, the grating part 50, and the bus bar 24 are integrally formed. Other configurations are substantially the same as those of the surface acoustic wave element piece 10 described above.

  The surface acoustic wave element piece 40 is formed by a region where the waveguides of the IDTs 42 and 44 are provided with the electrode fingers 20 and the grating portion 50. The opening width B of the reflector 24 is larger than the width (intersection width) W of the electrode intersecting portions 30 and 32, and is substantially equal to the waveguide width W0. A bonding wire 34 is bonded to the bus bar 24.

The surface acoustic wave element piece 40 thus formed is formed such that the opening width B of the reflector 24 is substantially equal to the width W0 of the waveguides of the IDTs 42 and 44. For this reason, the pattern of the high-order transverse mode confined in the IDTs 42 and 44 is the same as the pattern of the high-order transverse mode confined in the reflector 24, and spurious based on the high-order transverse mode occurs. Therefore, in Patent Document 3, the aperture width B of the reflector is reduced to 70% or less of the intersecting width W of the electrode intersecting portion so that a part of the higher order transverse mode is not reflected, and the spurious based on the higher order transverse mode is used. Is trying to reduce.
JP-A-10-173467 Japanese Patent Laid-Open No. 11-298286 JP-A-7-86869

  As described in Patent Documents 1 and 2, when the grating portion is formed on the side of the electrode finger in the longitudinal direction, the waveguide can be substantially expanded to suppress the dip near the center frequency. However, when the grating portion is provided, a thick bus bar 24 for joining the bonding wire 34 must be provided outside the grating portion 50 as shown in FIG. The bus bar 24 requires a width (thickness) of about 150 to 200 μm so that the bonding wire 34 can be reliably bonded. For this reason, it is extremely difficult to cope with downsizing that has been strongly demanded in recent years. In addition, when the chip size (the dimension of the piezoelectric substrate 12) is determined according to customer specifications, it is difficult to provide the bus bar 24.

  On the other hand, as described in Patent Document 3, when the opening width B of the reflector 26 is narrower than the intersection width W of the electrode intersections 30 and 32 of the electrode finger 20, spurious due to the higher-order transverse mode can be reduced. However, when the opening width B of the reflector 26 is narrower than the intersection width W of the electrode intersections 30 and 32 of the electrode finger 20, the reflector 26 reflects only a part of the surface acoustic wave excited at the electrode intersection 30. . That is, part of the energy excited at the electrode intersection 30 is lost, the insertion loss is increased, and the crystal impedance is increased.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and aims to reduce the size while reducing the dip in the vicinity of the center frequency.
Another object of the present invention is to reduce the insertion loss.

  In order to achieve the above object, a surface acoustic wave element according to the present invention sandwiches at least two interdigital electrodes formed along a propagation direction of a surface acoustic wave and the two interdigital electrodes in a piezoelectric body. A surface acoustic wave element including a reflector disposed in the above, and a grating portion on a side in a longitudinal direction of a plurality of electrode fingers forming an electrode intersection portion of a pair of comb electrodes constituting the interdigital electrode A wire bonding portion electrically connected to the electrode crossing portion is provided at a position corresponding to the grating portion or the grating portion in the propagation direction of the surface acoustic wave.

  In the present invention as described above, the waveguide can be substantially expanded by forming the grating portion on the side of the electrode finger in the longitudinal direction. Therefore, the dip in the vicinity of the center frequency caused by the narrow width of the waveguide can be reduced. In addition, by providing the wire bonding portion at a position corresponding to a part of the grating portion or the grating portion in the propagation direction of the surface acoustic wave, a wide bus bar for bonding the bonding wires can be omitted. Therefore, the surface acoustic wave element piece can be reduced, and the surface acoustic wave device can be downsized.

  The grating part has a plurality of grids parallel to the electrode fingers. If the grating part is provided with a plurality of grids parallel to the electrode fingers, the grating part can effectively function as a waveguide. The plurality of grids may not correspond to the electrode fingers. The plurality of grids are connected to each other by a short bar. Thereby, ohmic resistance can be made small and insertion loss can be made small.

  The grid part may be formed integrally with the electrode finger, and the wire bonding part may be an end part on the reflector side adjacent to the grating part. When providing a wire bonding part in a grating part, providing in the edge part by the side of the reflector which adjoins a grating part is desirable. Providing a wire bonding part at the center in the longitudinal direction of the grating part is not preferable because the waveguide formed by the grating part is divided by the wire bonding part.

  At least one of the pair of comb electrodes forming the interdigital electrode can be connected to an adjacent reflector, and the wire bonding portion of the comb electrode connected to the reflector can be provided in the reflector. The waveguide formed by the interdigital electrode is not affected by the wire bonding portion. The reflector is divided into two reflecting portions in the longitudinal direction of the electrode fingers forming the comb-shaped electrode, and the pair of comb-shaped electrodes are connected to the corresponding reflecting portions, and the wire bonding portion is It can be provided in the reflection part. As a result, a voltage can be applied between the pair of comb electrodes via the reflector (reflector), or a voltage corresponding to the amplitude of the surface acoustic wave generated between the pair of comb electrodes can be obtained.

  The grating portion may extend to an edge along the grating portion of the piezoelectric substrate. By providing the grating part to the end of the piezoelectric substrate, it is possible to further reduce the size. In this case, when a plurality of short bars connecting the grids to each other are provided in the grating portion, the outermost short bar may be formed inside the edge of the piezoelectric substrate by a predetermined dimension. When a piezoelectric wafer is cut into individual surface acoustic wave element pieces, a diamond blade is generally used, but the cut portion of the wafer may be missing. For this reason, by forming the outermost short bar on the inner side by a predetermined dimension, for example, 10 μm from the end of the piezoelectric substrate forming the surface acoustic wave element piece, it is possible to prevent disconnection of the short bar due to chipping of the piezoelectric substrate, An increase in ohmic resistance can be prevented.

  The opening width of the reflector is preferably equal to or greater than the intersection width of the electrode intersection and smaller than the width between the outer ends of the grating portions formed on both sides of the electrode intersection. By setting the opening width of the reflector to be equal to or greater than the crossing width of the electrode crossing portion, it is possible to reflect all of the surface acoustic wave excited at the electrode crossing portion and to prevent an increase in insertion loss. Moreover, since the opening width of the reflector is narrower than the width between the outer edges of the grating portions formed on both sides of the electrode intersection, the shape of the higher-order transverse mode confined in the interdigital electrode and the height confined in the reflector are high. The shape of the next transverse mode can be greatly different. For this reason, mode conversion occurs between the higher-order transverse mode reflected by the reflector and the higher-order transverse mode confined in the interdigital electrode, and the higher-order mode is greatly suppressed and spurious due to the higher-order transverse mode is reduced. Can do. When the opening width of the reflector is narrower than the width between the outer ends of the grating portions formed on both sides of the electrode crossing portion, the wire bonding portion can be connected to the grating portion provided on the side of the reflector. Thereby, the influence on the substantial waveguide of IDT formed by the interdigital electrode can be eliminated. In addition, since the wire bonding portion is provided on the side of the reflector whose opening width is narrower than the width of the waveguide, the surface acoustic wave element can be downsized.

  A preferred embodiment of a surface acoustic wave element according to the present invention will be described in detail with reference to the accompanying drawings. In addition, about the part corresponding to the part demonstrated in background art, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

FIG. 1 is a plan view of a surface acoustic wave element according to a first embodiment of the present invention. In FIG. 1, the surface acoustic wave element piece 52 includes a pair of IDTs 54 and 56 in the central portion of the piezoelectric substrate 12 along the propagation direction of the surface acoustic wave. In the embodiment, the piezoelectric substrate 12 is made of lithium tantalate (LiTaO ₃ ). Of course, the piezoelectric substrate 12 may be another piezoelectric body such as ST cut quartz crystal or lithium niobate (LiNbO ₃ ).

  Each IDT 54, 56 is composed of a pair of comb-shaped electrodes 58 (58a, 58b) and is formed in a comb shape. That is, the comb-shaped electrode 58 includes a plurality of electrode fingers 20 (20a, 20b) forming the electrode crossing portions 30, 32, and a grating portion 50 (50a, 50b) provided on the side of the electrode fingers 20 in the longitudinal direction. It is made up of. The grating portion 50 is made of the same conductive metal material as the electrode finger 20, for example, aluminum, an aluminum alloy containing aluminum as a main component, and is formed simultaneously with the electrode finger 20 by a photolithography technique or the like.

  In the embodiment, the grating portion 50 has a width (dimension along the longitudinal direction of the electrode finger 20) of 125 μm and includes a plurality of grids 60 and a plurality of short bars 62. The grid 60 is provided corresponding to the electrode finger 20 and is formed in parallel with the electrode finger 20. The short bar 62 is formed orthogonal to the grid 60 and connects the grids 60 to each other so as to reduce the ohmic resistance of the grating portion 50. The short bar 62 is preferably thin. However, the short bars 62 are set to an appropriate thickness and number in consideration of deterioration of the characteristics of the surface acoustic wave device such as an increase in insertion loss due to the ohmic resistance of the grating portion 50. For example, the thickness (width) of the short bar 62 is set to 20 μm or less or the width of the electrode finger 20 or less.

  In the surface acoustic wave element 52, reflectors 64 (64 a and 64 b) are arranged outside the IDTs 54 and 56 with the IDTs 54 and 56 interposed therebetween. The reflector 64 is formed from a plurality of body strips 28 parallel to the electrode fingers 20. In the reflector 64, longitudinal ends of the conductor strips 28 corresponding to the grating portions 50 of the IDTs 54 and 56 are connected to each other by a plurality of short bars 66. Further, in the surface acoustic wave element piece 52, the end portion of the grating portion 50 of each comb-shaped electrode 58 is a wire bonding portion 68 that joins the bonding wire 34. That is, the wire bonding portion 68 is an end portion of each grating 50 on the adjacent reflector 64 side, and the bonding wire 34 is directly bonded to the grid 60 and the short bar 62 of the grating portion 50.

  In the surface acoustic wave element piece 52 according to the first embodiment configured as described above, the grating portions 50 are formed on the sides of the electrode fingers 20 in the longitudinal direction, so that the IDTs 54 and 56 do not have to be formed long. The width of the waveguide can be substantially increased. Therefore, it is possible to reduce (suppress) the dip in the vicinity of the center frequency caused by the narrow width of the waveguide of the IDT. And since the wire bonding part 68 is provided in the grating | lattice-like grating part 50, the position which joins the bonding wire 34 can be easily recognized unlike a bus bar. Therefore, the variation in the bonding position of the bonding wire 34 can be eliminated, and the variation in the characteristics of the surface acoustic wave device due to the variation in the bonding position of the bonding wire 34 can be reduced.

2 and 3 show frequency response characteristics of the surface acoustic wave element piece 52 according to the first embodiment.
FIG. 2 shows the insertion loss with respect to the frequency of the surface acoustic wave element piece 52. The horizontal axis in FIG. 2 indicates the frequency, and the deviation from the center frequency F0 is indicated in MHz. The vertical axis in FIG. 2 indicates the insertion loss in dB. The center frequency F0 is about 100 MHz. FIG. 3 shows the group delay time response characteristics. The horizontal axis represents the frequency as in FIG. 2, and the vertical axis represents the delay time in μsec. In the surface acoustic wave element piece 52 used, the intersection width W of the electrode intersections 30 and 32 is 700 μm, the distance d between the electrode intersections 30 and 32 and the grating part 50 is about 10 μm, and the width W1 of the grating part 50 is 125 μm. Further, the thickness (width) of the short bar 62 is 5 μm, and the number of the short bars 62 is two.

  As shown in FIG. 2, the dip in the vicinity of the center frequency F0 in the passband PB can be greatly improved from about 0.5 dB to about 0.1 dB. Further, as shown in FIG. 3, the group delay time of the frequency where this dip has occurred can be improved to a delay time deviation of about 0.01 μsec as compared with the delay time at the frequency in the vicinity thereof. It was.

  Moreover, the surface acoustic wave element piece 52 of the first embodiment shown in FIG. 1 has a part of the grating part 50 as a wire bonding part 68 and a bonding wire 34 is joined to this part. For this reason, it is not necessary to provide a bus bar having a width capable of wire bonding of about 200 μm or a dedicated bonding pad, and the surface acoustic wave element can be downsized. Further, by providing the wire bonding portion 68 at the end portion on the reflector 64 side adjacent to the grating portion 50, the influence of the wire bonding portion 68 on the waveguide can be reduced. That is, when the wire bonding part 68 is provided from the longitudinal center of the grating part 50 or at the end part on the adjacent grating part side, the waveguide formed by the grating part 50 is divided by the wire bonding part. For this reason, the pair of grating portions does not function as a continuous waveguide, and the ripple generated in the passband cannot be sufficiently improved.

  By the way, the inventor conducted various studies on the influence of the grating portion 50 of the surface acoustic wave element piece 52 on the characteristics of the filter, and found that the short bar 62 has a great influence. 4 and 5 show the relationship between the number of short bars 62 in the surface acoustic wave element piece 52 and frequency response characteristics. FIG. 4 shows the relationship between the number of short bars 62 and the group delay time deviation. The horizontal axis in FIG. 4 represents the number of short bars 62, and the vertical axis represents the deviation of the group delay time within the pass band in units of μsec, that is, the difference between the maximum delay time and the minimum delay time. FIG. 5 shows the relationship between the number of short bars and the maximum insertion loss in the passband. The horizontal axis in FIG. 5 represents the number of short bars 62, and the vertical axis represents the maximum insertion loss in the passband in dB.

  4 and 5, the width W1 of the grating portion 50 is 125 μm, and the width of the short bar 62 is 5 μm. And the arrangement | positioning order of the some short bar 62 in the grating part 50 arrange | positioned so that the grating part 50 might be divided | segmented equally in the width direction. FIG. 6 schematically shows a method for arranging the short bars 62. FIG. 6A shows a case where there is one short bar 62. In this case, the short bar 62 is disposed on the innermost side of the grating portion 50 (from the electrode intersection 30 or from the electrode intersection 32). FIG. 6B shows a case where there are two short bars 62, and the short bars 62 are arranged on the innermost side and the outermost side of the grating portion 50. 6 (3) to (5) show the arrangement state of the short bars 62 when the number of the short bars 62 is increased in this order. The same applies when the number of short bars 62 is six or more.

  As shown in FIG. 4, the deviation of the delay time can be reduced as the number of the short bars 62 decreases. However, if the number of short bars 62 having a thickness of 5 μm is less than 3, the ohmic resistance increases and the maximum insertion loss in the passband increases as shown in FIG. The rightmost data in FIGS. 4 and 5 is data when the entire grating portion 50 is filled with the short bar 62, that is, when the grating portion 50 having a width of 125 μm is replaced with a bus bar having a width of 125 μm.

  7 and 8 are obtained by converting FIGS. 4 and 5 into grating rates. That is, the unevenness ratio in the width direction in the grating portion 50 is shown. The ratio of the recesses in the recesses and projections formed by the short bar 62 and the recesses formed by the surface of the piezoelectric substrate 12 in the grating unit 50 is shown. For example, when the width of the grating part 50 is 125 μm and the width of the short bar 62 is 5 μm, when two short bars 62 are provided in the grating part 50 (125-2 × 5) ÷ 125 = 0.92 It becomes. That is, in this case, the grating rate is 0.92.

  FIG. 7 shows FIG. 4 converted to the above grating rate. FIG. 8 shows FIG. 5 converted into a grating rate. As shown in these figures, it is understood that the grating rate is preferably 0.8 or more and smaller than 0.95. When the grating rate is 1, it means that the short bar 62 is not provided. A grating rate of 0 is when the grating portion 50 is replaced by a bus bar.

  FIG. 9 is a plan view of the surface acoustic wave element according to the second embodiment. In the surface acoustic wave element piece 70 according to this embodiment, a wire bonding portion 72 is provided in the grating portion 50 of each comb-shaped electrode 58. The wire bonding portion 72 is provided at an end portion of each grating portion 50 on the adjacent reflector 64 side. In the wire bonding portion 72, the grid of the grating portion 50 formed by the grid 60 and the short bar 62 is covered with the grid of the grating portion 50 by a metal film forming the grating portion 50, for example, a thin film of aluminum or aluminum alloy. It is. The wire bonding portion 72 configured as described above can bond the bonding wire 34 more firmly, and even when the surface acoustic wave element piece 70 is used under a vibration environment, it can prevent bonding peeling and the like. Can be improved.

  FIG. 10 is a plan view of the surface acoustic wave element according to the third embodiment. In the surface acoustic wave element piece 74 according to the third embodiment, one comb-shaped electrode 58a constituting the IDT 54 is electrically connected to the adjacent reflector 64a. That is, in the comb-shaped electrode 58a, the outer short bar 62 constituting the grating portion 50a is extended to the reflector 64a side and connected to the reflector 64a. And the wire bonding part 72 is formed in the edge part by the side of IDT54 of this reflector 64a, and the position corresponding to the grating part 50a. In the wire bonding portion 72, the mesh formed by the conductor strip 28 and the two short bars 66 is filled with a thin film of the same metal as the metal forming the reflector 64. In the surface acoustic wave element piece 74 formed in this way, the same effect as described above can be obtained. The reflector 64 is made of the same conductive metal film constituting the IDTs 54 and 56, and is formed simultaneously with the IDTs 54 and 56.

  However, since the reflector 64a is electrically connected to the comb-shaped electrode 58a that constitutes the IDT 54, the surface acoustic wave element piece 74 has a stray capacitance (parasitic capacitance) corresponding to the reflector 64a. This stray capacitance may deteriorate the filter characteristics. For this reason, when a surface acoustic wave element piece is formed using a piezoelectric substrate having a high dielectric constant, such as lithium tantalate, the structure in which the IDT is connected to the reflector as shown in FIG. 10 is not preferable.

  In addition, the short bar 62 connected to the reflector 64a may be any of the short bars 62 inside the grating portion 50a or a plurality of the short bars 62. The comb electrode connected to the reflector 64a may be a comb electrode 58b. Further, one of the comb-shaped electrodes 58a and 58b of the IDT 54 is connected to the reflector 64a, and one of the comb-shaped electrodes 58a and 58b of the IDT 56 is connected to the reflector 64b, and the wire bonding portion is connected to the reflector 64b. May be provided.

  FIG. 11 is a plan view of a surface acoustic wave element according to the fourth embodiment. In the surface acoustic wave element piece 76 of this embodiment, one reflector 64a is divided in the longitudinal direction of the electrode fingers 20 of the IDTs 54 and 56, that is, in the longitudinal center of the conductor strip 28, and two reflecting portions 78 (78a and 78b) are divided. ). The gap g between the reflecting portions 78a and 78b is a gap in which the reflecting portion 78a and the reflecting portion 78b are electrically separated and do not affect the reflection of the surface acoustic wave propagating through the piezoelectric substrate 12. It is. The other reflector 64b is integrally formed as in the above embodiment.

  Each of the reflecting portions 78 constituting the reflector 64a is connected to the corresponding grating portion 50 of the comb electrodes 58a and 58b constituting the IDT 54. Further, a wire bonding portion 72 is provided at the end of each reflecting portion 78. The wire bonding portion 72 is provided on the opposite end of the adjacent IDT 54 and at a position corresponding to the grating portion 50 in the propagation direction of the surface acoustic wave. The wire bonding portion 72 for the other IDT 56 is provided at the end of the grating portion 50 adjacent to the reflector 64b, as in the above embodiment.

  Even in this configuration, the same effect as described above can be obtained. Note that the wire bonding part 72 provided in the reflection part 78 may be provided at any position of the reflection part 78 as long as the position corresponds to the grating part 50 in the propagation direction of the surface acoustic wave. Further, the dividing position of the reflector 64 a may not be the central portion in the longitudinal direction of the conductor strip 28. Furthermore, the reflector 64b may be divided into two reflecting portions, and the comb electrodes of the IDT 56 may be connected to each of them.

  FIG. 12 is a plan view of the surface acoustic wave element according to the fifth embodiment. In the surface acoustic wave element piece 80, the grating portions 50 of the IDTs 54 and 56 are constituted by a grid 60 corresponding to the electrode fingers 20 and five short bars 62. In the reflector 64, a portion of the conductor strip 28 corresponding to the grating portion 50 is connected to each other by a short bar 66 corresponding to the short bar 62. Other configurations are the same as those in the above embodiment. Note that the end of the reflector 64 need not be formed in the same manner as the grating unit 50.

  FIG. 13 is a plan view of a surface acoustic wave element according to a sixth embodiment. In the surface acoustic wave element piece 82 according to this embodiment, the grating portions 50 formed on the comb electrodes 58 constituting the IDTs 54 and 56 are formed up to the edge of the piezoelectric substrate 12. That is, the grating part 50a extends to the end edge 84 along the longitudinal direction of the grating part 50a adjacent thereto. Similarly, the grating portion 50b extends adjacent to the grating portion 50b of the piezoelectric substrate 12 to the edge 86 along the grating portion 50b. The outermost short bar 62 forming the grating portion 50 is formed on the inner side by a predetermined distance, for example, 10 μm, from these end edges 84 and 86.

  This is because when the piezoelectric wafer on which the plurality of surface acoustic wave element pieces are formed is divided into individual surface acoustic wave element pieces, the edges 84 and 86 may be chipped. When the outermost short bar 62 is formed at the edge of the piezoelectric substrate 12, if the edges 84, 86 are chipped, a cut portion is generated in the outermost short bar 62 and the ohmic resistance of the grating portion 50 is increased. This may deteriorate the characteristics of the filter. Therefore, the outermost short bar 62 of the grating portion 50 is formed on the inner side by a predetermined distance from the end edges 84 and 86 to prevent disconnection of the short bar 62 and prevent the filter characteristics from deteriorating. Yes. The reflector 64 is also provided to extend to the end edges 84 and 86, and the outermost short bar 66 is also formed inward by a predetermined distance from the end edges 84 and 86, similarly to the grating portion 50. .

  FIG. 14 schematically shows an electrode pattern in which the piezoelectric substrate of the surface acoustic wave element according to the seventh embodiment is omitted. In the surface acoustic wave element piece 90 according to this embodiment, the grating portions 50 of the IDTs 54 and 56 are not electrically connected to the electrode fingers 20 forming the electrode intersection portions 30 and 32. That is, the grating part 50 has a minute gap between the electrode finger 20 and is formed separately from the electrode finger 20.

  The reflectors 64 a and 64 b are divided into two reflecting portions 78 a and 78 b in the longitudinal direction of the conductor strip 28. Comb electrodes 58 constituting IDTs 54 and 56 are electrically connected to these reflecting portions 78. That is, one end of the plurality of electrode fingers 20 constituting the comb-shaped electrode 58 is connected to each other by the connecting bar 92. The connecting bar 92 is formed to have a width that is, for example, two to three times the width of the electrode finger 20, and the tip extends to the adjacent reflecting portion 78 side, and is connected to the short bar 66 of the corresponding reflecting portion 78. It is. Although not shown in the figure, the wire bonding portion is formed at a position corresponding to the grating portion 50 of each reflecting portion 78 as described above. Thereby, size reduction of the surface acoustic wave element piece 90 can be achieved.

  Also in the surface acoustic wave element piece 90 in this embodiment, the grating part 50 functions as a waveguide, and the dip near the center frequency can be reduced. However, the surface acoustic wave element 90 has an ohmic resistance as compared with the case where the electrode finger 20 is electrically connected to the grating portion 50 because the electrode finger 20 is connected to the reflecting portion 78 by the relatively thin connecting bar 92. May increase and insertion loss may increase.

  FIG. 15 shows an electrode pattern of the surface acoustic wave element according to the eighth embodiment. The surface acoustic wave element piece 94 of the eighth embodiment is formed at a position where the grid 60 of the grating portion 50 a does not correspond to the electrode finger 20. That is, the grid 60 of the grating part 50 a is formed in the middle of the position corresponding to the electrode finger 20. However, the number of grids 60 is substantially equal to the number of electrode fingers 20. Also in this embodiment, the dip near the center frequency can be reduced. As shown in the grating portion 50b of FIG. 15, the formation pitch of the grid 60 and the formation pitch of the electrode fingers 20 may be different.

  FIG. 16 shows an electrode pattern of the surface acoustic wave element according to the ninth embodiment. In the surface acoustic wave element piece 96 according to the present embodiment, the number of grids 60 forming the grating portion 50 is smaller than the number of electrode fingers 20 formed. That is, the grid 60 is formed so as to be thinned out with respect to the electrode finger 20. In the surface acoustic wave element piece 96 configured as described above, although the dip suppression effect is reduced as compared with the case where the number of grids 60 formed is the same as the number of electrode fingers 20 formed, the dip is suppressed. Can do.

  FIG. 17 is a plan view of a surface acoustic wave element according to the tenth embodiment. In FIG. 17, the surface acoustic wave element piece 100 includes IDTs 54 and 56 provided along the propagation direction of the surface acoustic wave. Each IDT 54 and 56 has a grating portion 50 on the side of the electrode finger 20 in the longitudinal direction. Each grating portion 50 is provided with a wire bonding portion 72 at an end portion on the adjacent reflector 64 side. As described above, in each of the IDTs 54 and 56, the electrode finger 20 and the grating portion 50 constitute a waveguide. The reflector 64 provided across the IDTs 54 and 56 has an opening width B smaller than the width W0 of the waveguide formed by the IDTs 54 and 56. However, the opening width B of the reflector 64 is wider than the intersection width W of the electrode intersections 30 and 32 formed by the electrode fingers 20.

  In the surface acoustic wave element 100 thus configured, the waveguide width W0 of the IDTs 54 and 56 and the opening width B of the reflector 64 can be greatly different. For this reason, the pattern of the high-order transverse mode confined in the IDTs 54 and 56 and the pattern of the high-order transverse mode confined in the reflector 64 are greatly different, and the spurious based on the high-order transverse mode can be suppressed. Moreover, the opening width B of the reflector 64 is wider than the intersecting width W of the electrode intersecting portions 30 and 32. Therefore, all the surface acoustic waves excited at the electrode intersection 30 can be reflected, and the insertion loss can be reduced. Further, by providing the wire bonding part 72 in the grating part 50, the surface acoustic wave element piece 100 can be reduced in size.

  FIG. 18 shows the relationship between the frequency and insertion loss of the surface acoustic wave element 100 according to the tenth embodiment shown in FIG. The horizontal axis of FIG. 18 is the frequency, and the deviation from the center frequency F0 is shown in MHz. The vertical axis | shaft of FIG. 18 has shown the insertion loss shown by dB. The electrode crossing width W, the waveguide width W0, and the center frequency F0 of the surface acoustic wave 100 are the same as described above. As shown in FIG. 18, it can be seen that the dip near the center frequency F0 is suppressed.

  FIG. 19 is a plan view of a surface acoustic wave element according to an eleventh embodiment. In the surface acoustic wave element piece 102 of this embodiment, the wire bonding portion 68 provided in the grating portion 50 of the IDTs 54 and 56 is not formed of a metal film. That is, the wire bonding part 68 is configured to directly bond the bonding wire 34 to a predetermined position between the grid 60 forming the grating part 50 and the short bar 62. Other configurations are the same as those of the surface acoustic wave element 100 according to the tenth embodiment shown in FIG.

  FIG. 20 is a plan view of a surface acoustic wave element according to a twelfth embodiment. The surface acoustic wave element piece 104 shown in FIG. 20 is formed such that the opening width B of the reflector 64 is substantially equal to the intersection width W of the electrode intersections 30 and 32 of the IDTs 54 and 56. The reflector 64 has a dimension in a direction orthogonal to the propagation direction of the surface acoustic wave substantially equal to the dimension between the grating portions 50a and 50b.

  Each grating portion 50 is provided with a wire bonding portion 106 formed of a conductive metal thin film. These wire bonding portions 106 are narrower than the width dimension W 1 of the grating portion 50. The wire bonding portion 106 is formed so as to protrude toward the reflector 64 adjacent to each grating portion 50 in the propagation direction of the surface acoustic wave. That is, the wire bonding part 106 is provided on the side of the reflector 64 and at a position corresponding to the grating part 50. Other configurations are substantially the same as those of the above embodiment.

  FIG. 21 is a plan view of a surface acoustic wave element according to a thirteenth embodiment. In FIG. 21, the surface acoustic wave element piece 108 has a wire bonding portion 106 connected to each grating portion 50 via a wiring pattern 110. The wire bonding portion 106 is provided on the side of the end portion far from the IDTs 54 and 56 of the reflector 64 and at a position corresponding to the grating portion 50. Other configurations are the same as those of the surface acoustic wave element 104 shown in FIG.

  In addition, each said embodiment is one aspect | mode of this invention, Comprising: It is not limited to these embodiment. For example, in each of the embodiments described above, the case where two IDTs which are interdigital electrodes are provided along the propagation direction of the surface acoustic wave has been described, but three or more IDTs may be provided.

It is a top view of the surface acoustic wave element piece concerning a 1st embodiment of the present invention. It is a figure which shows the relationship between the frequency of the surface acoustic wave element piece and the insertion loss which concern on 1st Embodiment. It is a figure which shows the relationship between the frequency of the surface acoustic wave element piece which concerns on 1st Embodiment, and delay time. It is a figure which shows the relationship between the number of the short bars of the surface acoustic wave element piece which concerns on 1st Embodiment, and the group delay time in a pass band. It is a figure which shows the relationship between the number of the short bars of the surface acoustic wave element piece which concerns on 1st Embodiment, and the maximum insertion loss in a pass band. It is the figure which showed typically embodiment of the method of the order which arrange | positions a short bar. It is a figure which shows the relationship between the grating rate by the short bar of embodiment, and the maximum delay time in a passband. It is a figure which shows the relationship between the grating rate by the short bar of embodiment, and the maximum insertion loss in a passband. It is a top view of the surface acoustic wave element piece concerning a 2nd embodiment. It is a top view of the surface acoustic wave element piece concerning a 3rd embodiment. It is a top view of the surface acoustic wave element piece concerning a 4th embodiment. It is a top view of the surface acoustic wave element piece concerning a 5th embodiment. It is a top view of the surface acoustic wave element piece concerning a 6th embodiment. It is the figure which showed typically the electrode pattern of the surface acoustic wave element piece concerning 7th Embodiment. It is the figure which showed typically the electrode pattern of the surface acoustic wave element piece concerning 8th Embodiment. It is the figure which showed typically the electrode pattern of the surface acoustic wave element piece concerning 9th Embodiment. It is a top view of the surface acoustic wave element piece concerning a 10th embodiment. It is a figure which shows the relationship between the frequency of the surface acoustic wave element piece which concerns on 10th Embodiment, and insertion loss. It is a top view of the surface acoustic wave element piece concerning 11th Embodiment. It is a top view of the surface acoustic wave element piece concerning a 12th embodiment. It is a top view of the surface acoustic wave element piece concerning a 13th embodiment. It is the top view which showed typically an example of the conventional resonance type surface acoustic wave element piece. It is a figure which shows the relationship between the frequency of the conventional surface acoustic wave element piece, and insertion loss. It is a figure which shows the relationship between the frequency and delay time of the conventional surface acoustic wave element piece. It is the top view which showed typically the other conventional resonance type surface acoustic wave element piece.

Explanation of symbols

  12 ......... Piezoelectric substrate, 20a, 20b ......... Electrode fingers, 30, 32 ......... Electrode intersection, 34 ......... Bonding wire, 50a, 50b ......... Grating, 52 ......... Surface acoustic wave element Pieces 54, 56 ... Interdigital electrodes (IDT), 58a, 58b ... Comb electrodes, 60 ... Grid, 62, 66 ... Short bar, 64a, 64b ... Reflector 68 72, 106 ......... Wire bonding part, 70, 74 ......... Surface acoustic wave element pieces, 78a, 78b ......... Reflection part, 80, 82 ......... Surface acoustic wave element pieces, 84, 86 ......... Edges, 90, 94, 96... Surface acoustic wave element pieces, 92... Connecting bars, 102, 104, 108.

Claims (10)

A surface acoustic wave element comprising: a piezoelectric body including at least two interdigital electrodes formed along a propagation direction of the surface acoustic wave; and a reflector disposed between the two interdigital electrodes,
Forming a grating portion on the side in the longitudinal direction of a plurality of electrode fingers forming an electrode intersection of a pair of comb-shaped electrodes constituting the interdigital electrode;
A wire bonding portion electrically connected to the electrode intersection is provided at a position corresponding to the grating portion or the grating portion in the propagation direction of the surface acoustic wave.
A surface acoustic wave element. The surface acoustic wave element piece according to claim 1,
The surface acoustic wave element piece, wherein the grating portion has a plurality of grids parallel to the electrode fingers. The surface acoustic wave element piece according to claim 2, wherein the grating portion includes a short bar that connects the plurality of grids to each other. In the surface acoustic wave element piece according to any one of claims 1 to 3,
The grid portion is formed integrally with the electrode fingers,
The wire bonding part is an end part on the reflector side adjacent to the grating part,
A surface acoustic wave element. In the surface acoustic wave element piece according to any one of claims 1 to 3,
The pair of comb electrodes forming the interdigital electrodes, at least one of which is connected to the adjacent reflector,
The wire bonding portion of the comb electrode connected to the reflector is provided in the reflector.
A surface acoustic wave element. In the surface acoustic wave element piece according to any one of claims 1 to 3,
The reflector is divided into two reflecting portions in the longitudinal direction of the electrode fingers forming the comb electrode,
The pair of comb-shaped electrodes are respectively connected to the corresponding reflective portions, and the wire bonding portions are provided in the reflective portions.
A surface acoustic wave element. In the surface acoustic wave element according to any one of claims 1 to 6,
The surface acoustic wave element piece, wherein the grating portion extends to an edge along the grating portion of the piezoelectric substrate. The surface acoustic wave element piece according to claim 7,
The grating section has a plurality of short bars connecting the plurality of grids to each other,
The outermost short bar is formed inside the edge by a predetermined dimension.
A surface acoustic wave element. In the surface acoustic wave element according to any one of claims 1 to 4,
The surface acoustic wave device, wherein the reflector has an opening width that is equal to or greater than an intersection width of the electrode intersection portion and is narrower than a width between outer ends of the grating portions formed on both sides of the electrode intersection portion. Piece. The surface acoustic wave element piece according to claim 9,
The surface acoustic wave element piece, wherein the wire bonding portion is connected to the grating portion and provided on a side of the reflector.

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