JP2019021997A - Acoustic wave element, splitter, and communication device - Google Patents

Abstract

To provide an acoustic wave element excellent in frequency characteristics.SOLUTION: An acoustic wave element includes a piezoelectric substrate and an IDT electrode positioned on the piezoelectric electrode and including an electrode finger 27 and a dummy electrode finger 29 facing a tip of the electrode finger 27 via a gap Gp. In the IDT electrode, the gap Gp is narrower than an inner part 27y in a width direction at a peripheral part 27x in a width direction of the electrode finger 27.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to an acoustic wave element that is an electronic component using an acoustic wave, a duplexer including the acoustic wave device, and a communication device.

  Conventionally, acoustic wave elements have been widely used for resonators, bandpass filters, and the like. As the acoustic wave element, a surface acoustic wave element using a surface acoustic wave, a boundary acoustic wave element using a boundary acoustic wave, and the like are known.

  In an acoustic wave element such as a boundary acoustic wave element or a surface acoustic wave element, an IDT (interdigital transducer) electrode having a plurality of electrode fingers is used to excite an acoustic wave. Filter characteristics and resonance characteristics are improved by applying cross width weighting to the IDT electrodes. However, even if weighted IDT electrodes are used, it is difficult to obtain sufficient resonance characteristics and filter characteristics.

  Therefore, Patent Document 1 below discloses an acoustic wave element in which the shape of the IDT electrode is improved in order to further improve the resonance characteristics and the filter characteristics.

  Specifically, in Patent Document 1, the shape of an electrode finger constituting an IDT electrode and the shape of a dummy electrode finger positioned so as to be opposed to the tip of the electrode finger via a gap are described in the vicinity of the gap. In at least one of them, a configuration is disclosed in which a protrusion is provided so as to protrude from at least one side edge in the elastic wave propagation direction.

International Publication No. 2008/126614

  It is desired that the shape of the IDT electrode is devised to provide an acoustic wave device, a duplexer, and a communication device that are further excellent in frequency characteristics.

  An acoustic wave device according to an aspect of the present disclosure includes a piezoelectric substrate, an IDT electrode that is located on the piezoelectric substrate, and includes an electrode finger and a dummy electrode finger that faces the tip of the electrode finger via a gap. The tip of the electrode finger is positioned on the dummy electrode finger side compared to the inside on the outside in the width direction, and the tip of the dummy electrode finger is compared to the inside on the outside in the width direction. It is located on the electrode finger side.

  A duplexer according to an aspect of the present disclosure includes an antenna terminal, a transmission filter that filters a signal output to the antenna terminal, and a reception filter that filters a signal input from the antenna terminal. And at least one of the transmission filter and the reception filter includes the elastic wave device.

  A communication apparatus according to an aspect of the present disclosure includes an antenna, the duplexer in which the antenna terminal is connected to the antenna, and the antenna terminal with respect to a signal path with respect to the transmission filter and the reception filter. And an IC connected to the opposite side.

  According to said structure, the elastic wave element excellent in the frequency characteristic, a splitter using the same, and a communication apparatus can be provided.

It is a top view which shows the elastic wave element which concerns on embodiment. It is a principal part expanded sectional view in the II-II line of the elastic wave element of FIG. It is a principal part enlarged plan view of the elastic wave element shown in FIG. FIG. 4 is a cross-sectional view of a main part corresponding to a cross section taken along line IV-IV in FIG. FIG. 5A is a plan view showing a modification of the acoustic wave element shown in FIG. 1, and FIG. 5B is a cross-sectional view of the main part taken along the line V-V in FIG. FIG. 6A to FIG. 6E are top views for each process showing the method of manufacturing the acoustic wave device. It is a circuit diagram which shows typically the structure of the duplexer as an example of utilization of the elastic wave element of FIG. It is a circuit diagram which shows typically the structure of the communication apparatus as an example of utilization of the elastic wave element of FIG. FIG. 4 is a cross-sectional view of a main part corresponding to a cross section taken along line IV-IV in FIG.

  Hereinafter, an embodiment according to the present disclosure will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios and the like on the drawings do not necessarily match the actual ones.

  In the acoustic wave element according to the present disclosure, any direction may be upward or downward. For convenience, an orthogonal coordinate system including a D1 axis, a D2 axis, and a D3 axis is defined below. In some cases, terms such as the upper surface or the lower surface are used with the positive side of the D3 axis as the upper side. Further, in the case of planar view or planar see-through, it means viewing in the D3 axis direction unless otherwise specified. The D1 axis is defined to be parallel to the propagation direction of the elastic wave propagating along the upper surface of the piezoelectric substrate described later, and the D2 axis is defined to be parallel to the upper surface of the piezoelectric substrate and orthogonal to the D1 axis. The D3 axis is defined to be orthogonal to the upper surface of the piezoelectric substrate.

(Whole structure of elastic wave element)
FIG. 1 is a plan view showing a configuration of a main part of the acoustic wave device 1. FIG. 2 is an enlarged cross-sectional view of a main part taken along line II-II in FIG.

  The acoustic wave element 1 includes, for example, a support substrate 12, a piezoelectric substrate 2 bonded to the support substrate 12, and a conductive layer 9 positioned on the upper surface of the piezoelectric substrate 2. The conductive layer 9 constitutes the IDT electrode 3.

  In the acoustic wave element 1, a surface acoustic wave (SAW) propagating through the piezoelectric substrate 2 is excited by applying a voltage to the conductive layer 9. The acoustic wave element 1 constitutes, for example, a resonator and / or a filter that uses this SAW. For example, the support substrate 12 contributes to reinforcing the strength of the piezoelectric substrate 2.

  The material and dimensions of the support substrate 12 may be appropriately set. The material of the support substrate 12 is, for example, an insulating material, and the insulating material is, for example, resin or ceramic. The support substrate 12 may be made of a material having a lower thermal expansion coefficient than that of the piezoelectric substrate 2. In this case, for example, the possibility that the frequency characteristics of the acoustic wave device 1 will change due to temperature changes can be reduced.

  Examples of such a material include a semiconductor such as silicon, a single crystal such as sapphire, and a ceramic such as an aluminum oxide sintered body. The support substrate 12 may be configured by laminating a plurality of layers made of different materials. The support substrate 12 is thicker than the piezoelectric substrate 2, for example.

The piezoelectric substrate 2 is made of a piezoelectric single crystal, and is composed of, for example, a single crystal of lithium tantalate (LiTaO ₃ , LT) or lithium niobate (LiNb ₃ , LN). For example. In the case of using an LT single crystal, the cut angle can be appropriately selected according to the characteristics required by the acoustic wave device 1, but for example, a 40-46 ° rotated Y-cut X propagation substrate may be used. In this case, the X axis of the LT crystal is substantially parallel to the D1 direction. The thickness of the piezoelectric substrate 2 is not particularly limited, but is relatively thin in this example, and is, for example, not less than 0.1λ and not more than 20λ on the basis of λ described later. By setting the thickness of the piezoelectric substrate 2 in this way, the temperature compensation effect by the support substrate 12 can be enhanced, or the influence of bulk waves propagating in the thickness direction of the piezoelectric substrate 2 can be suppressed.

(Schematic configuration of conductive layer)
The conductive layer 9 is made of metal, for example. The metal may be of an appropriate type, for example, aluminum (Al) or an alloy containing Al as a main component (Al alloy). The Al alloy is, for example, an aluminum-copper (Cu) alloy. The conductive layer 9 may be composed of a plurality of metal layers. For example, a relatively thin layer made of titanium (Ti) may be provided between Al or Al alloy and the piezoelectric substrate 2 in order to reinforce these bondability. Moreover, the laminated body which laminated | stacked the some metal layer repeatedly may be sufficient.

  The conductive layer 9 is formed so as to constitute the resonator 15 in the example of FIG. The resonator 15 is configured as a so-called 1-port acoustic wave resonator. When an electric signal having a predetermined frequency is input from one of the terminals 17A and 17B, which is conceptually and schematically illustrated, the resonator 15 resonates. The resulting signal can be output from the other of terminals 17A and 17B.

  The conductive layer 9 (resonator 15) includes, for example, the IDT electrode 3 and a pair of reflectors 21 located on both sides of the IDT electrode 3.

  The IDT electrode 3 includes a pair of comb electrodes 23. In addition, in order to improve visibility, one comb-tooth electrode 23 is hatched. Each comb electrode 23 includes, for example, a bus bar 25, a plurality of electrode fingers 27 extending in parallel from the bus bar 25, and a dummy electrode 29 protruding from the bus bar 25 between the plurality of electrode fingers 27. The pair of comb-tooth electrodes 23 are arranged so that the plurality of electrode fingers 27 mesh with each other (intersect).

  The bus bar 25 is, for example, formed in a long shape having a substantially constant width and extending linearly in the elastic wave propagation direction (D1 axis direction). The pair of bus bars 25 oppose each other in a direction (D2 axis direction) orthogonal to the propagation direction of the elastic wave. Note that the bus bar 25 may change in width or may be inclined with respect to the propagation direction of the elastic wave.

  Each electrode finger 27 is formed in a long shape extending in a straight line in a direction (D2 axis direction) orthogonal to the elastic wave propagation direction with a substantially constant width, for example. In each comb electrode 23, the plurality of electrode fingers 27 are arranged in the propagation direction of the elastic wave. The plurality of electrode fingers 27 of one comb-tooth electrode 23 and the plurality of electrode fingers 27 of the other comb-tooth electrode 23 are basically arranged alternately.

  The pitch p of the plurality of electrode fingers 27 (for example, the distance between the centers of two electrode fingers 27 adjacent to each other) is basically constant in the IDT electrode 3. A part of the IDT electrode 3 may be provided with a narrow pitch part where the pitch p is narrower than the other most part, or a wide pitch part where the pitch p is wider than the other most part.

  In the following description, when the pitch p is referred to, unless otherwise specified, the pitch of a portion (most part of the plurality of electrode fingers 27) excluding a specific portion such as the narrow pitch portion or the wide pitch portion as described above. It shall be said. Further, in the case where the pitch is changed in most of the plurality of electrode fingers 27 excluding the peculiar part, the average value of the pitch of the most plurality of electrode fingers 27 is set as the value of the pitch p. May be used.

  The number of electrode fingers 27 may be appropriately set according to the electrical characteristics required for the resonator 15. Since FIG. 1 is a schematic diagram, the number of electrode fingers 27 is small. Actually, more electrode fingers 27 than shown may be arranged. The same applies to the strip electrode 33 of the reflector 21 described later.

  The lengths of the plurality of electrode fingers 27 are, for example, equal to each other. The IDT electrode 3 may be subjected to so-called apodization in which the lengths of the plurality of electrode fingers 27 (crossing width in another viewpoint) change according to the position in the propagation direction. The length and width of the electrode finger 27 may be appropriately set according to required electrical characteristics and the like.

  For example, the dummy electrode 29 protrudes in a direction orthogonal to the propagation direction of the elastic wave with a substantially constant width. The width is equal to the width of the electrode finger 27, for example. The plurality of dummy electrodes 29 are arranged at the same pitch as the plurality of electrode fingers 27, and the tip of the dummy electrode 29 of one comb-tooth electrode 23 is the tip of the electrode finger 27 of the other comb-tooth electrode 23. And facing through the gap. The IDT electrode 19 may not include the dummy electrode 29.

  The pair of reflectors 21 are located on both sides of the plurality of IDT electrodes 3 in the propagation direction of the elastic wave. Each reflector 21 may be in an electrically floating state, for example, or may be provided with a reference potential. Each reflector 21 is formed in a lattice shape, for example. That is, the reflector 21 includes a pair of bus bars 31 facing each other and a plurality of strip electrodes 33 extending between the pair of bus bars 31. The pitch of the plurality of strip electrodes 33 and the pitch between the electrode fingers 27 and the strip electrodes 33 adjacent to each other are basically the same as the pitch of the plurality of electrode fingers 27.

Although not particularly illustrated, the upper surface of the piezoelectric substrate 2 may be covered with a protective film made of SiO ₂ , Si ₃ N ₄ or the like from above the conductive layer 9. The protective film may be a multi-layered laminate made of these materials. The protective film may be merely for suppressing corrosion of the conductive layer 9 or may contribute to temperature compensation. In the case where a protective film is provided, an additional film made of an insulator or metal may be provided on the upper surface or the lower surface of the IDT electrode 3 and the reflector 21 in order to improve the reflection coefficient of the elastic wave.

  The configurations shown in FIGS. 1 and 2 may be appropriately packaged. For example, the package may be one in which the configuration shown in the figure is mounted on a substrate (not shown) so that the upper surface of the piezoelectric substrate 2 is opposed via a gap, and resin-sealed from above. It may be of a wafer level package type in which a box type cover is provided.

(Operation of the resonator 15)
When a voltage is applied to the pair of comb-tooth electrodes 23, a voltage is applied to the piezoelectric substrate 2 by the plurality of electrode fingers 27, and the piezoelectric substrate 2 that is a piezoelectric body vibrates. Thereby, the elastic wave propagating in the D1 axis direction is excited. The elastic wave is reflected by the plurality of electrode fingers 27. Then, a standing wave is generated in which the pitch p of the plurality of electrode fingers 27 is approximately a half wavelength (λ / 2). An electric signal generated in the piezoelectric substrate 2 by the standing wave is taken out by the plurality of electrode fingers 27. Based on such a principle, the acoustic wave element 1 functions as a resonator having a resonance frequency that is the frequency of an acoustic wave having the pitch p as a half wavelength. Note that λ is usually a symbol indicating the wavelength, and the actual wavelength of the elastic wave may deviate from 2p. However, when the symbol λ is used below, λ must be 2p unless otherwise noted. Shall mean.

(Shape of IDT electrode 3)
The inventor of the present application has found that the frequency characteristics of the resonator 15 can be improved by changing the shape of the IDT electrode 3. Specifically, it is as follows.

  FIG. 3 shows an enlarged plan view of the main part of the region surrounded by the broken line in FIG. As shown in FIG. 3, in the IDT electrode 3, the electrode finger 27 and the dummy electrode finger 29 are opposed to each other via the gap Gp. Here, the tip of the electrode finger 27 is positioned closer to the dummy electrode finger 29 on the outer side in the width direction than on the inner side, and the tip of the dummy electrode finger 29 is on the outer side in the width direction. Located on the side. That is, the tip shapes of the electrode finger 27 and the dummy electrode finger 29 are such that the gap Gp is narrow in the outer peripheral portion 27x located outside the width direction (D1 direction) of the electrode finger 27 and wide in the inner portion 27y located inside. It has changed to become. In other words, at the position of the outer peripheral portion 27x, the distance between the electrode finger 27 and the dummy electrode finger 29 is the shortest.

  In order to satisfy such a relationship, in this example, the tip of the electrode finger 27 forms a recess that opens toward the dummy electrode finger 29, and the tip of the dummy electrode finger 29 opens toward the electrode finger 27. A recess is formed. More specifically, the recesses are formed by making the tips of the electrode fingers 27 and the dummy electrode fingers 29 arcuate.

  When the concave portions face each other, when viewed in the width direction of the electrode finger 27, the gap Gp can be widened from the outer peripheral portion 27x side toward the center of the width.

  Thus, by changing the length of the gap Gp in the width direction of the electrode finger 27, the electrode finger width (w1) can be made constant up to the tip of the electrode finger 27 (Duty can be made constant). ). Therefore, frequency fluctuation is suppressed, resonance characteristics are sharpened, loss can be suppressed, and frequency characteristics of the acoustic wave device 1 can be enhanced.

  In addition, since the distance to the dummy electrode finger 29 can be increased at the center of the width of the electrode finger 27, the occurrence of a spark between the electrode finger 27 and the dummy electrode finger 29 can be suppressed, and the reliability is improved. be able to.

  Further, by changing the length of the gap Gp in the width direction of the electrode finger 27 as described above, the reason will be described later, but the length of the gap Gp is shortened to bring the electrode finger 27 and the dummy electrode finger 29 close to each other. Can be arranged. For this reason, it is possible to provide the acoustic wave element 1 with less loss by suppressing leakage in the lateral direction of the SAW.

  Further, in this example, the concave portions of the electrode finger 27 and the dummy electrode finger 29 are each arcuate and have no corners. For this reason, voltage concentration can be suppressed and the occurrence of sparks can be further suppressed. In addition, the recessed part of the electrode finger 27 and the dummy electrode finger 29 may have a similar shape, and the radii of curvature may be different from each other.

(Modification: Tip shape)
In the above example, the electrode finger 27, the dummy electrode finger 29, and the tip shape are all arcuate recesses, but the present invention is not limited to this example. V shape may be sufficient and the shape dented toward the center of the width | variety in step shape may be sufficient. Furthermore, the shape which comprises the protrusion part which protrudes toward each other only in the outer side of a width | variety, and comprises the flat part in which the width | variety of a gap becomes constant inside a protrusion part may be sufficient. In this case, the proportion of the protruding portion in the width direction may be 10% or less.

(Modification: Underlayer)
In the above example, the planar shape of the underlayer is not particularly specified, but as shown in FIG. 4, the underlayer 7 is formed by extending portions 7 x, exposed from the electrode fingers 27 and the dummy electrode fingers 29 in the gap region. 7y may be provided.

  4 is a cross-sectional view of the main part corresponding to the cross section taken along line Iv-Iv in FIG. As shown in FIG. 4, in the region of the gap Gp, the base layer 7 located below the electrode finger 27 includes a first extending portion 7 x that protrudes toward the dummy electrode finger 29, and the dummy electrode finger The underlayer 7 located below 29 includes a second extending portion 7y protruding toward the electrode finger 27 side. The first extending portion 7x and the second extending portion 7y are opposed to each other with a space therebetween.

  Here, the foundation layer 7 functions as an adhesion layer between the conductive layer 9 and the piezoelectric substrate 2 and is made of, for example, Ti. The thickness is set to 1 to 5% of the thickness of the IDT electrode 3 so that the electrical characteristics of the IDT electrode 3 are not affected. For example, the thickness is about 1 to 9 nm. Since the base layer 7 includes the extension portions 7x and 7y, the tips of the electrode fingers 27 and the dummy electrode fingers 29 can be separated from the outer edges of the extension portions 7x and 7y having strong vibrations. Thereby, the elastic wave element 1 excellent in power durability can be provided.

(Modification: Piezoelectric substrate)
In the above example, the upper surface of the piezoelectric substrate 2 is the same surface. However, as shown in FIG. 5, the portion where the electrode finger 27 and the dummy electrode finger 29 are located and the position where the gap Gp overlaps in plan view. The height of the upper surface may be varied.

  5A is a plan view of a main part corresponding to FIG. 3, and FIG. 5B is a cross-sectional view of the main part taken along the line vv of FIG. 5A.

  Specifically, the concave portion 2x may be provided on the upper surface of the piezoelectric substrate 2 such that the upper surface of the piezoelectric substrate 2 is positioned below the portion where the electrode finger 27 is positioned in the region of the gap Gp. Providing the recess 2x can suppress the occurrence of sparks in the step of patterning the conductive layer 9, and can improve the reliability. Further, when the gap Gp is narrow, since the insulation between the electrode finger 27 and the dummy electrode finger 29 can be ensured by providing the recess 2x, the reliability can be further improved.

  If the depth of the recess 2x as described above is 20% or less of the thickness of the electrode finger 27, the electrical characteristics of the acoustic wave device 1 are not affected. Further, as shown in FIG. 5A, when the recess 2x is provided so as to extend to the area between the plurality of electrode fingers 27, the electrode finger 27 and the dummy electrode finger 29 are closest to each other. Since the upper surface of the piezoelectric substrate 2 is located below the periphery in the portion, an unintended short circuit or spark can be suppressed.

(Modification: Other)
In the above example, the case where the support substrate 12 is located on the lower surface of the piezoelectric substrate 2 has been described, but the support substrate 12 may not be provided. In that case, it is desirable that the piezoelectric substrate 2 has such a thickness that the strength is maintained independently. Specifically, the thickness may be 50 μm or more and 300 μm.

  In the above example, the case where the electrode finger 27 and the dummy electrode finger 29 are composed of one layer has been described, but a laminated structure may be used. FIG. 9 shows a cross-sectional view of the main part when the electrode finger 27 and the dummy electrode finger 29 have a laminated structure of two layers.

  As shown in FIG. 9, the electrode finger 27 includes a first layer 27a and a second layer 27b, and the dummy electrode finger 29 includes a first layer 29a and a second layer 29b. The first layer 27a and the second layer 27b may be made of the same material, or may be a combination of different materials. As an example in the case of using different materials, the first layer 27a close to the piezoelectric substrate 2 is made of a material having a high strength, and the second layer 27b separated from the piezoelectric substrate 2 has a lower strength than the first layer 27a. You may comprise with material with high electrical conductivity. By adopting such a configuration, it is possible to maintain electric characteristics while increasing the power resistance of the electrode fingers 27. In addition, even if it is composed of the same material or different materials, the thickness of each layer can be reduced, so that the disorder of crystals due to the increased thickness is suppressed and each layer is Crystallinity can be increased and power resistance can be increased. The same applies to the dummy electrode fingers 29.

  The underlayer 7 is a first underlayer 7a located between the piezoelectric substrate 2 and the first layers 27a and 29a, and a first underlayer 7 located between the first layers 27a and 29a and the second layers 27b and 29b. 2 base layers 7b. The first underlayer 7a is preferably made of a material that enhances the adhesion between the piezoelectric substrate 2 and the first layers 27a and 29a and helps the crystal growth of the first layers 27a and 29a in a specific orientation. For example, Ti etc. can be illustrated. The second underlayer 7b is preferably made of a material that helps crystal growth in a specific orientation of the second layers 27b and 29b, and Ti can be exemplified.

  Here, both the first base layer 7a and the second base layer 7b are provided with extending portions 7ax, 7bx, 7ay, 7by protruding from the electrode fingers 27, 29. In general, the base layer 7 has lower conductivity than the material constituting the first layers 27a and 29a and the second layers 27b and 29b. The distance between the extending portion 7ax and the extending portion of the underlayer 7 and the distance between the extending portion 7bx and the extending portion 7by are the distance between the first layer 27a and the second layer 29a, and the second layer 27b. And the distance between the electrode fingers 27 and 29 can be suppressed.

(Production method)
The manufacturing method of the above-mentioned elastic wave element 1 is demonstrated based on drawing. The acoustic wave device 1 obtains a desired pattern by bonding a piezoelectric substrate 2 and a support substrate 12, a film forming step of forming a conductor layer 9 on the piezoelectric substrate 2, and patterning the conductor layer 9. And a patterning step.

  In the bonding step, the piezoelectric substrate 2 and the support substrate 2 are bonded via an adhesive layer made of a metal or an inorganic material, or the surfaces of both substrates are activated by irradiation with a FAB gun, an ion gun or the like, and then brought into contact at room temperature. It can be joined directly.

  The film forming process is performed subsequent to the bonding process, and thin film formation such as sputtering, vapor deposition, or CVD (Chemical Vapor Deposition) is performed on the surface of the piezoelectric substrate 2 that is not bonded to the support substrate 12. The conductive layer 9 is formed on one surface by the method.

  In the patterning step, the conductor layer 9 formed on the entire top surface of the piezoelectric substrate 2 is patterned by a film forming step to electrically connect the IDT electrode 3, the reflector 21, the terminals 17, and the like having a desired shape. Get a line. Specifically, a desired shape is obtained by patterning by a photolithography method using a reduction projection exposure machine (stepper) and an RIE (Reactive Ion Etching) apparatus.

  Here, the patterning step will be described in detail. In order to provide the acoustic wave device 1 of the present embodiment, the patterning process is divided into two stages, a first patterning process and a second patterning process. Hereinafter, each step will be described. 6A to 6E are schematic top views showing the patterning process.

(First patterning step: FIGS. 6A to 6B)
First, as shown in FIG. 6A, a joined body of the piezoelectric substrate 2 and the support substrate 7 on which the conductor layer 9 covering the upper surface of the piezoelectric substrate 2 is formed is prepared.

  Next, as shown in FIG. 6B, a resist is formed on the conductor layer 9 and patterned to form two bus bars 25 and an electrode group 20 in which a plurality of strip electrodes 19 are positioned between the two bus bars 25. . The pitch and Duty of the plurality of strip electrodes 19 are the same as those of the electrode fingers 27 of the IDT electrode 3.

(Second patterning step: FIGS. 6C to 6E)
Next, as shown in FIG. 6C, a resist 81 is formed so as to cover the upper surface of the electrode group 20, and an opening 81 x is provided in a portion corresponding to the gap between the electrode finger 27 and the dummy electrode finger 29. In FIG. 6C, the pattern of the electrode group 20 positioned below the resist 81 is indicated by a broken line.

  Next, as shown in FIG. 6D, a part of the electrode group 20 exposed from the opening 81x of the resist 81 is removed by etching. Specifically, a part of the strip electrode 19 can be removed, and the strip electrode 29 can be separated into an electrode finger 27 and a dummy electrode finger 29 as shown in FIG. Here, since the opening 81x of the resist 81 is rectangular and the etching is performed, the etching rate on the side close to the wall of the opening 81x is lower than the etching rate at the center of the opening 81x. The tip shape with the finger 29 can be as shown in FIG.

  As described above, the IDT electrode 3 of this embodiment can be obtained by separating the strip electrode 19 into the electrode finger 27 and the dummy electrode finger 29 through two patterning steps. When the electrode fingers 27 and the dummy electrode fingers 29 are patterned from the conductor layer 9 shown in FIG. 6A by one-step patterning, the tips of the electrode fingers 27 and 29 are gradually tapered. It becomes difficult to make the duty constant over the entire intersection width.

  Further, by separating the electrode finger 27 and the dummy electrode finger 29 after the strip electrode 19 is formed, the gap that is the distance between the electrode fingers 27 and 29 can be reduced in the process. As a result, it is possible to provide the acoustic wave device 1 that suppresses SAW lateral leakage and reduces loss. This is particularly noticeable in a resonator in which the resonance frequency is located in a high frequency band exceeding 2 GHz.

(Application example of elastic wave element: duplexer)
FIG. 7 is a circuit diagram schematically showing the configuration of the duplexer 101 as an example of use of the acoustic wave element 1. As can be understood from the reference numerals shown in the upper left of the figure, in this figure, the comb electrode 23 is schematically shown by a bifurcated fork shape, and the reflector 21 is a single line bent at both ends. It is represented by

  The duplexer 101 filters, for example, the transmission signal from the transmission terminal 105 and outputs it to the antenna terminal 103, and filters the reception signal from the antenna terminal 103 and outputs it to the pair of reception terminals 107. A reception filter 111.

  The transmission filter 109 is constituted by, for example, a ladder type filter configured by connecting a plurality of resonators 15 in a ladder type. That is, the transmission filter 109 connects a plurality (or one) of resonators 15 connected in series between the transmission terminal 105 and the antenna terminal 103, and the series line (series arm) and the reference potential. And a plurality of (or even one) resonators 15 (parallel arms). Note that the plurality of resonators 15 constituting the transmission filter 109 are provided on the same piezoelectric substrate 2, for example.

  The reception filter 111 includes, for example, a resonator 15 and a multimode filter (including a double mode filter) 113. The multimode filter 113 includes a plurality of (three in the illustrated example) IDT electrodes 19 arranged in the propagation direction of the elastic wave, and a pair of reflectors 21 disposed on both sides thereof. Note that the resonator 15 and the multimode filter 113 constituting the reception filter 111 are provided, for example, on the same piezoelectric substrate 2.

  The transmission filter 109 and the reception filter 111 may be provided on the same piezoelectric substrate 2 or may be provided on different piezoelectric substrates 2. FIG. 7 is merely an example of the configuration of the duplexer 101. For example, the reception filter 111 may be configured by a ladder filter in the same manner as the transmission filter 109.

  In addition, although the case where the demultiplexer 101 includes the transmission filter 109 and the reception filter 111 has been described, the present invention is not limited to this. For example, a diplexer or a multiplexer including three or more filters may be used.

(Usage example of elastic wave element: communication device)
FIG. 8 is a block diagram illustrating a main part of the communication device 151 as an example of use of the acoustic wave element 1 (the duplexer 101). The communication device 151 performs wireless communication using radio waves, and includes a duplexer 101.

  In the communication device 151, a transmission information signal TIS including information to be transmitted is modulated and increased in frequency (converted to a high frequency signal of a carrier frequency) by an RF-IC (Radio Frequency Integrated Circuit) 153, and is transmitted to the transmission signal TS. Is done. Unnecessary components other than the transmission passband are removed from the transmission signal TS by the bandpass filter 155, amplified by the amplifier 157, and input to the duplexer 101 (transmission terminal 105). Then, the duplexer 101 (transmission filter 109) removes unnecessary components other than the transmission passband from the input transmission signal TS, and outputs the transmission signal TS after the removal from the antenna terminal 103 to the antenna 159. . The antenna 159 converts the input electric signal (transmission signal TS) into a radio signal (radio wave) and transmits it.

  In the communication device 151, a radio signal (radio wave) received by the antenna 159 is converted into an electric signal (reception signal RS) by the antenna 159 and input to the duplexer 101 (antenna terminal 103). The duplexer 101 (reception filter 111) removes unnecessary components other than the reception passband from the input reception signal RS and outputs the result from the reception terminal 107 to the amplifier 161. The output received signal RS is amplified by the amplifier 161, and unnecessary components other than the reception passband are removed by the band pass filter 163. Then, the reception signal RS is subjected to frequency reduction and demodulation by the RF-IC 153 to be a reception information signal RIS.

  The transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) including appropriate information, for example, analog audio signals or digitized audio signals. The pass band of the radio signal may be set appropriately, and in the present embodiment, a relatively high frequency pass band (for example, 5 GHz or more) is also possible. The modulation method may be any of phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more thereof. As the circuit system, the direct conversion system is illustrated in FIG. 17, but any other appropriate circuit may be used. For example, a double superheterodyne system may be used. FIG. 17 schematically shows only the main part. A low-pass filter, an isolator, or the like may be added at an appropriate position, and the position of an amplifier or the like may be changed.

  1: elastic wave element, 2: piezoelectric substrate, 3: IDT electrode, 27: electrode finger, 27x: outer peripheral part, 27y: central part, dummy electrode finger 29

Claims (6)

A piezoelectric substrate;
An IDT electrode that is located on the piezoelectric substrate and includes an electrode finger and a dummy electrode finger facing the tip of the electrode finger via a gap;
Have
The tip of the electrode finger is located on the side of the dummy electrode finger compared to the inside on the outside in the width direction,
An elastic wave element, wherein the tip end of the dummy electrode finger is positioned closer to the electrode finger than the inner side on the outer side in the width direction. The tip of the electrode finger has a concave shape that opens toward the dummy electrode finger,
The acoustic wave device according to claim 1, wherein a tip end of the dummy electrode finger has a concave shape that opens toward the electrode finger. Comprising an underlayer positioned between the IDT electrode and the piezoelectric substrate;
The underlayer is opposed to the first extension portion extending from the tip end side of the electrode finger toward the dummy electrode finger in the gap in a plan view, with a gap from the first extension portion. The acoustic wave device according to claim 1, further comprising: a second extending portion that extends from the tip of the dummy electrode finger toward the electrode finger.   4. The acoustic wave element according to claim 1, wherein an upper surface of the piezoelectric substrate is positioned on a lower side in a position overlapping with the gap as compared with a position overlapping with the electrode finger. 5. An antenna terminal;
A transmission filter for filtering a signal output to the antenna terminal;
A reception filter for filtering a signal input from the antenna terminal;
Have
A duplexer in which at least one of the transmission filter and the reception filter includes the acoustic wave element according to any one of claims 1 to 4. An antenna,
The duplexer according to claim 5, wherein the antenna terminal is connected to the antenna.
An IC connected to the opposite side of the antenna terminal with respect to the signal path with respect to the transmission filter and the reception filter;
A communication device.