JPWO2018079574A1 - Elastic wave element - Google Patents

Abstract

In the IDT electrode 3 including the first electrode finger 32a and the second electrode finger 32b that are connected to different potentials and are spaced apart from each other, the tip part 34 of the electrode finger 32 is not included, and the first electrode finger 32 is Assuming the central region Ac including the intersecting portion, the first electrode finger 32a, the second electrode finger 32b, and the second dummy electrode 33b are closer to the second bus bar 31b than the central region Ac. The acoustic wave element 1 is thicker and thinner than the electrode finger 32.

Description

  The present invention relates to an acoustic wave device using a surface acoustic wave (SAW).

  An acoustic wave element having an IDT (InterDigital Transducer) electrode provided on the main surface of a piezoelectric substrate is known (for example, Patent Document 1). Such an acoustic wave element is used for, for example, a transmission filter and a reception filter of a duplexer.

  The IDT electrode includes, for example, a pair of opposing bus bars, a plurality of electrode fingers alternately extending from each bus bar to the other bus bar, and a dummy electrode extending from the other bus bar in the extending direction of the electrode fingers. And.

  According to International Publication No. 2006/1099591, an example in which resonance characteristics are improved by widening the electrode finger width in the vicinity of the gap between the tip of the electrode finger and the dummy electrode is disclosed.

  In such an acoustic wave device using an IDT electrode, further improvement in resonance characteristics is required. Specifically, it is desired to provide an acoustic wave element with less loss among resonance characteristics.

  The present disclosure has been devised in view of such circumstances, and an object of the present disclosure is to provide an acoustic wave device with little loss.

  An acoustic wave device as one aspect of the present disclosure includes a piezoelectric substrate and an IDT electrode disposed on an upper surface of the piezoelectric substrate. The IDT electrode includes a first bus bar and a second bus bar, a first electrode finger and a second electrode finger, a first dummy electrode, and a second dummy electrode. The first bus bar and the second bus bar are connected to different potentials and are spaced from each other. The first electrode finger is connected to the first bus bar and extends toward the second bus bar. The second electrode finger is connected to the second bus bar and extends toward the first bus bar. The first electrode fingers and the second electrode fingers are alternately arranged so as to be adjacent along the elastic wave propagation direction. The first dummy electrode is connected to the first bus bar and faces the second electrode finger via a second gap. The second dummy electrode is connected to the second bus bar and faces the first electrode finger via a first gap. Here, a central region extending along the elastic wave propagation direction is assumed. The central region does not include the tip portion of the first electrode finger and the second electrode finger, but includes a portion where the first electrode finger and the second electrode finger intersect. The first electrode finger, the second electrode finger, and the second dummy electrode are thicker and narrower on the second bus bar side than the central region, compared to the first electrode finger and the second electrode finger in the central region. It has become.

  The acoustic wave device having the above configuration and the acoustic wave device using the same reduce the bulk wave leaking from between the tip of the electrode finger and the dummy electrode by making the vibration distribution in the vicinity of the tip of the electrode finger different. As a result, the loss is reduced.

It is a top view of an elastic wave device concerning an embodiment of this indication. It is sectional drawing in the II-II line of FIG. It is a principal part enlarged view of an IDT electrode. It is a diagram which shows the frequency characteristic of an Example and a comparative example. It is a principal part enlarged view of a comparative example. FIG. 6A, FIG. 6B, and FIG. 6C are diagrams showing the frequency characteristics of the example and the comparative example. It is a principal part expanded sectional view of the elastic wave element of a modification.

  Hereinafter, an acoustic wave device (hereinafter referred to as a SAW device) according to an embodiment of 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.

  Moreover, in a modification etc., about the structure which is common or similar to already demonstrated embodiment, the code | symbol common to already described embodiment may be used, and illustration and description may be abbreviate | omitted.

<Embodiment>
(Configuration of SAW element)
(Basic configuration)
FIG. 1 is a plan view showing a basic configuration of a SAW element 1 according to an embodiment of the present disclosure. FIG. 2 is a cross-sectional view of an essential part taken along line II-II in FIG. The SAW element 1 uses SAW as an elastic wave and has a piezoelectric substrate 2 and an excitation electrode 3 (hereinafter referred to as an IDT electrode 3) provided on the upper surface 2A of the piezoelectric substrate 2 as shown in FIG. ing. The IDT electrode 3 has two bus bars 31 facing each other, a plurality of electrode fingers 32 extending from each bus bar 31 toward the other bus bar 31, and a dummy electrode 33 facing each electrode finger 32. A portion of each electrode finger 32 that faces the dummy electrode 33 is a tip portion 34.

  Here, in the present embodiment, the end region A1 between the tip portion 34 of one electrode finger 32 and the other bus bar 31 and between the tip portion 34 of the other electrode finger 32 and one bus bar 31. , A2 (see FIG. 3 to be described later), the SAW element 1 with less loss can be provided by adopting the shapes of the electrode fingers 32 and the dummy electrodes 33 to be described later. Hereinafter, each configuration will be described in detail.

The piezoelectric substrate 2 is composed of a single crystal substrate having piezoelectricity made of lithium niobate (LiNbO ₃ ) crystal, lithium tantalate (LT: LiTaO ₃ ) crystal, or crystal (SiO ₂ ). The cut angle may be appropriate. For example, for LT, 42 ° ± 10 ° Y-X cut, 0 ° ± 10 ° Y-X cut, and the like. In the case of lithium niobate, it is 128 ° ± 10 ° YX cut or 64 ° ± 10 ° YX cut.

  In the following description, an example in which the piezoelectric substrate 2 is YX cut of 38 ° to 48 ° mainly made of LT will be described. Unless otherwise noted, the simulation results and the like described later are those of YX cut of 38 ° to 48 ° made of LT.

  The planar shape and various dimensions of the piezoelectric substrate 2 may be set as appropriate. As an example, the thickness (z direction) of the piezoelectric substrate 2 is constant over the entire plane direction, and can be exemplified by 0.2 mm or more and 0.5 mm or less.

  An IDT electrode 3 is disposed on the upper surface 2 </ b> A of the piezoelectric substrate 2. As shown in FIG. 1, the IDT electrode 3 includes a first comb electrode 30a and a second comb electrode 30b. In the following description, the first comb-teeth electrode 30a and the second comb-teeth electrode 30b are simply referred to as the comb-teeth electrode 30 and may not be distinguished from each other.

  As shown in FIG. 1, the comb electrode 30 includes two bus bars 31 (first bus bar 31a and second bus bar 31b) facing each other, and a plurality of electrode fingers 32 extending from each bus bar 31 to the other bus bar 31 side. And have. The pair of comb-shaped electrodes 30 are arranged so that the first electrode fingers 32a and the second electrode fingers 32b mesh with each other in the elastic wave propagation direction. The first electrode finger 32a is electrically connected to the first bus bar 31a, and the second electrode finger 32b is electrically connected to the second bus bar 31b.

  Here, the first bus bar 31a and the second bus bar 31b are connected to different potentials.

  In addition, the comb electrode 30 has a dummy electrode 33 facing each electrode finger 32. The first dummy electrode 33a extends from the first bus bar 31a toward the second electrode finger 32b. The second dummy electrode 33b extends from the second bus bar 31b toward the first electrode finger 32a. Here, a gap between the second dummy electrode 33b and the first electrode finger 32a is defined as a first gap Gp1. Similarly, a gap between the first dummy electrode 33a and the second electrode finger 32b is defined as a second gap Gp2.

  The bus bar 31 is formed in a long shape extending linearly with a substantially constant width, for example. Accordingly, the edges of the bus bars 31 facing each other are linear. For example, the plurality of electrode fingers 32 are formed in an elongated shape extending in a straight line with a substantially constant width, and are arranged at substantially constant intervals in the propagation direction of the elastic wave.

  The width of the bus bar 31 may not be constant. The edges on the opposite sides (inner side) of the bus bar 31 need only be linear, and for example, the inner edge may have a trapezoidal base.

  Hereinafter, the first bus bar 31a and the second bus bar 31b are simply referred to as the bus bar 31, and the first and second may not be distinguished. Similarly, the first electrode finger 32a and the second electrode finger 32b are simply referred to as the electrode finger 32, the first dummy electrode 33a and the second dummy electrode 33b are simply referred to as the dummy electrode 33, and the first gap Gp1 and the second gap Gp2 Is simply referred to as a gap Gp, and the first and second may not be distinguished.

  The plurality of electrode fingers 32 of the pair of comb electrodes 30 constituting the IDT electrode 3 are arranged so as to be repeatedly arranged in the x direction of the drawing. More specifically, as shown in FIG. 2, the first electrode fingers 32a and the second electrode fingers 32b are alternately and repeatedly arranged on the upper surface 2A of the piezoelectric substrate 2 with an interval.

  In this way, the plurality of electrode fingers 32 of the pair of comb electrodes 30 constituting the IDT electrode 3 are set to have a pitch Pt1. The pitch Pt1 is an interval (repetition interval) between the centers of the plurality of electrode fingers 32, and is provided, for example, to be equal to a half wavelength of the wavelength λ of the elastic wave at a frequency to be resonated. The wavelength λ (2 × Pt1) is, for example, not less than 1.5 μm and not more than 6 μm. The IDT electrode 3 can generate elastic waves efficiently because most of the plurality of electrode fingers 32 are arranged at a pitch Pt1 so that the plurality of electrode fingers 32 are arranged at a constant repetition interval. .

  Here, as shown in FIG. 2, the pitch Pt1 indicates a distance from the center of the first electrode finger 32a to the center of the second electrode finger 32b adjacent to the first electrode finger 32a in the propagation direction of the elastic wave. It is. In each electrode finger 32, the width w1 in the propagation direction of the elastic wave is appropriately set according to the electrical characteristics required for the SAW element 1. The width w1 of the electrode finger 32 is, for example, not less than 0.3 times and not more than 0.7 times the pitch Pt1.

  FIG. 2 is a cross-sectional view in the central region Ac (described later) of the intersecting region of the electrode fingers 32. The central region Ac refers to a region where the electrode fingers 32 intersect with each other except for the tip portion 34 of the electrode finger 32, and occupies most of the intersecting portion. In other words, the central region Ac is a region extending along the repeated arrangement direction of the electrode fingers 32 (elastic wave propagation direction) with a width that occupies most of the intersecting portion. In other words, the central area Ac is an area obtained by excluding the area overlapping the tip portion 34 of the electrode finger 32 from the intersecting area of the electrode fingers.

  For example, the center region Ac may have a width of 85% or more of the crossing width in a direction orthogonal to the elastic wave propagation direction. Here, the electrode thickness in the central region Ac of each electrode finger 32 is referred to as s, and the portion of each electrode finger 32 located in the central region Ac is referred to as the central portion 35.

  Elastic waves that propagate in a direction orthogonal to the plurality of electrode fingers 32 are generated. Accordingly, in consideration of the crystal orientation of the piezoelectric substrate 2, the two bus bars 31 are arranged so as to face each other with a gap in the direction intersecting the direction in which the elastic wave is desired to propagate. The plurality of electrode fingers 32 are formed to extend in a direction orthogonal to the direction in which the elastic wave is desired to propagate. In addition, although the propagation direction of an elastic wave is specified by the direction of the several electrode finger 32, etc., in this embodiment, the direction of the several electrode finger 32 is demonstrated on the basis of the propagation direction of an elastic wave for convenience. Sometimes.

  The lengths of the plurality of electrode fingers 32 (the length from the bus bar 31 to the tip of the electrode finger 32) are set to be approximately the same, for example. In addition, the length of each electrode finger 32 may be changed, for example, it may be lengthened or shortened as it proceeds in the propagation direction. Specifically, the apodized IDT electrode 3 may be configured by changing the length of each electrode finger 32 with respect to the propagation direction. In this case, it is possible to reduce the spurious in the transverse mode and improve the power durability.

  As shown in FIG. 2, the IDT electrode 3 is composed of a conductive layer 15 made of metal, for example. Examples of the metal include Al or an alloy containing Al as a main component (Al alloy). The Al alloy is, for example, an Al—Cu alloy. The IDT electrode 3 may have a plurality of metal layers laminated. Various dimensions of the IDT electrode 3 are appropriately set according to electrical characteristics required for the SAW element 1. The thickness s (z direction) is, for example, not less than 50 nm and not more than 600 nm.

  The IDT electrode 3 may be directly disposed on the upper surface 2A of the piezoelectric substrate 2 or may be disposed on the upper surface 2A of the piezoelectric substrate 2 via another member. Another member is made of, for example, Ti, Cr, or an alloy thereof. When the IDT electrode 3 is disposed on the upper surface 2A of the piezoelectric substrate 2 via another member, the thickness of the other member has a thickness that hardly affects the electrical characteristics of the IDT electrode 3 (for example, in the case of Ti) The thickness is set to about 5% of the thickness of the IDT electrode 3).

  When a voltage is applied, the IDT electrode 3 excites an elastic wave propagating in the x direction in the vicinity of the upper surface 2A of the piezoelectric substrate 2. The excited elastic wave is reflected at the boundary with the non-arranged region of the electrode fingers 32 (the long region between the adjacent electrode fingers 32). And the standing wave which makes the pitch Pt1 of the electrode finger 32 a half wavelength is formed. The standing wave is converted into an electric signal having the same frequency as that of the standing wave, and is taken out by the electrode finger 32. In this way, the SAW element 1 functions as a 1-port resonator.

  The reflector 4 is disposed so as to sandwich the IDT electrode 3 in the propagation direction of the elastic wave. The reflector 4 is generally formed in a lattice shape. That is, the reflector 4 includes reflector bus bars 41 facing each other in a direction intersecting the propagation direction of the elastic wave, and a plurality of reflective electrode fingers 42 extending between the bus bars 41 in a direction orthogonal to the propagation direction of the elastic wave. Have. The reflector bus bar 41 is formed, for example, in an elongated shape extending in a straight line with a substantially constant width, and is disposed in parallel with the propagation direction of the elastic wave.

  The plurality of reflective electrode fingers 42 are basically arranged at a pitch that reflects the elastic wave excited by the IDT electrode 3. The pitch of the reflective electrode fingers 42 is the interval (repetitive interval) between the centers of the plurality of reflective electrode fingers 42. When the pitch Pt1 of the IDT electrodes 3 is set to a half wavelength of the wavelength λ of the elastic wave, the pitch Pt1 Should be set to the same level as.

  The plurality of reflective electrode fingers 42 are formed in a long shape extending in a straight line with a substantially constant width. The width of the reflective electrode finger 42 can be set substantially equal to the width w1 of the electrode finger 32, for example. For example, the reflector 4 is made of the same material as the IDT electrode 3 and has a thickness equivalent to that of the IDT electrode 3.

  As shown in FIG. 2, the protective layer 5 is provided on the piezoelectric substrate 2 so as to cover the IDT electrode 3 and the reflector 4. Specifically, the protective layer 5 covers the surfaces of the IDT electrode 3 and the reflector 4, and covers the portion of the upper surface 2 </ b> A of the piezoelectric substrate 2 that is exposed from the IDT electrode 3 and the reflector 4. The thickness of the protective layer 5 is 1 nm or more and 50 nm or less, for example. As such a protective layer 5, a SiOx film or a SiNx film can be used.

(Configuration of end regions A1 and A2)
Here, the shape of the electrode finger 32 and the dummy electrode 33 of the IDT electrode 3 in the end regions A1 and A2 will be described in detail. Here, the end region A1 refers to the region closer to the first bus bar 31a than the central region Ac, and the end region A2 refers to the region closer to the second bus bar 31b than the central region Ac.

  FIG. 3 shows an enlarged plan view of a main part of the IDT electrode 3. The IDT electrode 3 is thicker and thinner in the end regions A1 and A2 than in the central region Ac. Specifically, in the end region A1, the first electrode finger 32a, the first dummy electrode 33a, and the second electrode finger 32b are thicker and narrower than the electrode finger 32 in the central region Ac. . Similarly, in the end region A2, the first electrode finger 32a, the second electrode finger 32b, and the second dummy electrode 33b are thicker and narrower than the electrode finger 32 in the central region Ac. Furthermore, in this example, the thickness of the bus bar 31 is also thicker than the thickness of the electrode finger 32 in the central region Ac. In FIG. 3, the thickened portion is hatched.

  With such a configuration, the SAW element 1 can reduce the occurrence of loss.

  Next, the effect of this configuration will be verified. In FIG. 4, the result of having simulated the frequency characteristic of Example 1 and Comparative Examples 1 and 2 by FEM method (finite element method) is shown. Example 1 models the SAW element 1 including the IDT electrode 3 shown in FIG. In Comparative Example 1, a SAW element including an IDT electrode having a uniform film thickness and electrode width in the end regions A1 and A2 and the central region Ac was modeled. In Comparative Example 2, a SAW element including an IDT electrode in which all of the electrode fingers 32 and the dummy electrodes 33 located at the end regions A1 and A2 are thickened is modeled. That is, Comparative Example 2 differs from Example 1 in that the electrode widths of the end regions A1 and A2 are not changed.

  The basic configuration of the SAW element of Comparative Example (reference model) 1 is as follows.

<Basic configuration>
Piezoelectric substrate material: 42 ° Y-cut X-propagation LiTaO ₃
Piezoelectric substrate thickness: ∞ (usually assuming LT substrate)
Electrode finger material: Al
Electrode finger thickness: 121 nm
Number of electrode fingers: Infinite number (periodic boundary condition)
Electrode finger pitch: 0.77 μm
Electrode finger width: 0.385 μm (Duty 0.5)
Crossing width: 30.8μm
Gap length: 0.3 μm
Dummy electrode length: 3.08 μm

  In the basic configuration described above, the gap length (the length of Gp in the y direction, that is, the distance between the tip of the electrode finger and the tip of the dummy electrode) is slightly longer than that of a general SAW element.

  On the other hand, in the first embodiment, in the end regions A1 and A2, the electrode film thickness is increased by 15% with respect to the thickness of the central region Ac (139 nm thickness) and the electrode width is set to 0.308 μm (Duty 0.4). ), The simulation was performed with the length occupied by the tip 34 of the electrode finger 32 being 3.25% (1 μm). The electrode thickness in end region A1, A2 of the comparative example 2 was also 139 nm. The result of the simulation performed on such a model is shown in FIG.

  In FIG. 4, the horizontal axis represents the normalized frequency (dimensionless amount), the vertical axis represents the real part of impedance (unit: Ohm), and the right axis represents the impedance phase (deg). The larger the real part of the impedance, the greater the loss, and the greater the phase of the impedance is from + 90 ° and −90 °, the greater the loss. In the figure, the solid line represents the impedance characteristic, and the broken line represents the phase characteristic. Here, the normalized frequency is obtained by multiplying the frequency by the pitch of the electrode finger and dividing the frequency by an appropriate speed (SSBW: Sound Speed of Surface Skiing Bulk Wave).

  In the model of Comparative Example 1, it was confirmed that a loss occurred on the high frequency side of the resonance frequency. This is particularly noticeable when the gap length cannot be made sufficiently narrow when the applied frequency is a high frequency such as 2.3 GHz. However, since the tendency has been confirmed even at the normalized frequency, It is presumed that this phenomenon can occur without being limited to the belt.

  In the model of Comparative Example 2, it can be confirmed that the loss is relatively reduced on the high frequency side of the resonance frequency, but it can be confirmed that the loss is increased on the low frequency side of the resonance frequency.

  On the other hand, in the case of the SAW element 1 of Example 1, it was confirmed that the occurrence of loss on the high frequency side of the resonance frequency confirmed in Comparative Example 1 can be reduced. Furthermore, it was confirmed that the SAW element 1 of Example 1 reduces the occurrence of loss on the lower frequency side than the resonance frequency.

  That is, it was confirmed that the SAW element 1 of Example 1 can reduce the loss near the resonance frequency.

  This mechanism will be considered based on a simulation result of a bulk wave leakage distribution (vibration distribution) in the thickness direction of the piezoelectric substrate 2.

  As a result of simulating the vibration distribution directly under the IDT electrode, in the frequency band higher than the resonance frequency, it is possible to reduce the leakage of bulk waves by increasing the electrode thickness in the region overlapping the tip 34 as viewed from the SAW propagation direction. confirmed.

  On the other hand, even in the same configuration, in the frequency band lower than the resonance frequency, the electrode is thick, so that the tip portion 34 is inclined downward toward the lower surface 2B side of the piezoelectric substrate 2. It was found that leaking bulk waves increased. In other words, in the frequency band lower than the resonance frequency, it was found that increasing the thickness of the electrode increases the bulk wave leaking from the tip 34 toward the dummy electrode 33 side beyond the gap Gp. . Therefore, when viewed along the SAW propagation direction, in the region overlapping the tip 34 that is the starting point of leakage, the leakage of bulk waves on the frequency side lower than the resonance frequency is reduced by narrowing the electrode width. I confirmed that I can do it. That is, it was confirmed that the loss can be reduced on both the high frequency side and the low frequency side of the resonance frequency by adopting the configuration of Example 1.

  Note that, due to the mechanism described above, the leakage of bulk waves in the gap Gp and its vicinity causes the loss. For example, when the gap length is approximately 0.2 times the electrode finger pitch, the leakage of bulk waves from the tip 34 in the substrate thickness direction cannot be ignored, and the loss on the high frequency side of the resonance frequency becomes significant. For this reason, the IDT electrode 3 of the present disclosure is preferably configured when the gap length is 0.2 times or more the electrode finger pitch.

  Here, the central portion 35 of the electrode finger 32 is a portion that determines the characteristics of the SAW to be excited, and occupies most of the electrode finger 32. For this reason, the length extending in the y direction with respect to the distal end portion 34 of the electrode finger 32 is shorter than that of the central portion 35, for example, 5% or less of the length of the electrode finger 32. Further, the thickness of the portion where the electrode thickness is increased may be thicker than the normal thickness, but specifically, it may be set in the range of 1.05 to 1.5 times the normal thickness. If the thickness is smaller than 1.05 times, the loss increases on the high frequency side of the resonance frequency. On the other hand, if the thickness exceeds 1.6 times, the loss tends to increase on the lower frequency side than the resonance frequency. As described above, the electrode thickness in the end regions A1 and A2 may be 1.05 to 1.5 times the thickness s of the electrode finger 32 in the central region Ac. Furthermore, the width of the portion for reducing the electrode width may be narrower than the width of the central portion 35, but may be 0.6 to 0.95 times the width of the central portion, for example. By setting it to 0.6 times or more, occurrence of disconnection or the like can be reduced. By setting it to 0.95 times or less, the effect of reducing bulk wave leakage on the lower frequency side than the resonance frequency can be enhanced. More specifically, it may be about 0.8 times the width of the central portion.

  With such a configuration, the sectional area of the electrodes (electrode finger 32 and dummy electrode 33) in the end regions A1 and A2 along the elastic wave propagation direction is equal to or smaller than the sectional area of the electrode finger 32 in the central region Ac. It becomes the area.

<Effect verification by changing the electrode width>
Next, in order to reduce the loss on the low frequency side of the resonance frequency described above, it is verified which part the electrode width needs to be narrowed. First, in addition to Comparative Example 2 in which only the thickness was increased and the electrode width was not changed, simulations were performed on models of Comparative Examples 3 to 5. FIG. 5 shows models of these comparative examples 2 to 5. In Comparative Example 3, the electrode width is reduced only for the dummy electrode 33. In Comparative Example 4, in addition to the dummy electrode 33, the electrode width of the electrode finger 32 located in the region overlapping with the dummy electrode 33 is also narrowed. In Comparative Example 5, in addition to the dummy electrode 33, the electrode width on the base side (side connected to the bus bar 31) of the electrode finger 32 located in the end regions A1 and A2 is narrowed. In other words, the line width of the portion excluding the tip end portion 34 of the electrode fingers 32 located in the end region A1, A2 is narrowed. In FIG. 5, as in FIG. 3, the thick portion is hatched.

  The result is shown in FIG. In FIG. 6A, the horizontal axis represents the normalized frequency, and the vertical axis represents the real part of the impedance. In FIG. 6B, the horizontal axis represents the normalized frequency, and the horizontal axis represents the phase. FIG. 6C is an enlarged view of the main part of FIG. As is clear from FIG. 6, it can be confirmed that the electrode widths of all the electrode fingers 32 located in the end regions A1 and A2 and the dummy electrode 33 need to be narrowed.

<Other variations>
In the above-described example, the case where the electrode thickness is increased and the electrode width is reduced in both the end regions A1 and A2 has been described, but only one of the regions may be provided.

  In the above example, the case where the piezoelectric substrate is sufficiently thick has been described. However, a support substrate may be bonded to the lower surface of the piezoelectric substrate.

  FIG. 7 shows a cross-sectional view of a modified example of the SAW element 1. In FIG. 7, the support substrate 7 is bonded to the lower surface 2 </ b> B of the piezoelectric substrate 2. That is, in this example, the element substrate is constituted by a bonded substrate of the piezoelectric substrate 2 and the support substrate 7.

  In such a case, the thickness of the piezoelectric substrate 2 may be set to 0.5 μm to 30 μm, for example.

  The support substrate 7 is formed of, for example, a material having a smaller thermal expansion coefficient than the material of the piezoelectric substrate 2. Thereby, the temperature change of the electrical characteristics of the SAW element 1 can be compensated. 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 7 may be configured by laminating a plurality of layers made of different materials.

  For example, the thickness of the support substrate 7 is constant over the entire planar direction of the support substrate 7, and the size thereof may be appropriately set according to the specifications required for the SAW element 1. However, the thickness of the support substrate 7 is made larger than the thickness of the piezoelectric substrate 2 so that temperature compensation can be suitably performed and the strength of the piezoelectric substrate 2 can be reinforced. As an example, the thickness of the support substrate 7 is 100 μm or more and 300 μm or less. For example, the planar shape and various dimensions of the support substrate 7 are the same as those of the piezoelectric substrate 2.

The piezoelectric substrate 2 and the support substrate 7 are bonded to each other through an adhesive layer (not shown), for example. The material of the adhesive layer may be an organic material or an inorganic material. Examples of the organic material include a resin such as a thermosetting resin. Examples of the inorganic material include SiO ₂ . In addition, the piezoelectric substrate 2 and the support substrate 7 may be bonded together by so-called direct bonding, in which the bonding surface is bonded without a bonding layer after being activated by plasma or the like.

  In such a SAW element using an element substrate, the electrode structure shown in FIG. 3 can reduce spurious in the vicinity of the resonance frequency in addition to the loss.

  In the above example, the simulation was performed when the gap length was 0.2 times the electrode finger pitch. This is because when the gap length is approximately 0.2 times the electrode finger pitch, bulk wave leakage from the tip 34 in the substrate thickness direction cannot be ignored, and loss on the high frequency side of the resonance frequency becomes significant. Because. For this reason, when the gap length is 0.2 times or more of the electrode finger pitch, it is particularly preferable to provide the above-described electrode configuration.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects, and the above-described embodiments may be combined as appropriate.

DESCRIPTION OF SYMBOLS 1 ... Elastic wave apparatus 2 ... Piezoelectric substrate 3 ... IDT electrode 30 ... Comb electrode 31 ... Bus bar 32 ... Electrode finger 33 ... Dummy electrode 34 ... Tip part 7 ... Supporting substrate A1 ··· First end region A2 ··· Second end region Ac ··· Central region

Claims (5)

A piezoelectric substrate, and an IDT electrode disposed on the upper surface of the piezoelectric substrate,
The IDT electrode is
A first bus bar and a second bus bar connected to different potentials and spaced apart from each other;
A first electrode finger connected to the first bus bar and extending toward the second bus bar, and a second electrode connected to the second bus bar and extending toward the first bus bar, disposed adjacent to each other along the elastic wave propagation direction. Electrode fingers,
A second dummy electrode connected to the second bus bar and facing the first electrode finger via a first gap;
A first dummy electrode connected to the first bus bar and facing the second electrode finger via a second gap;
Assuming a central region that extends along the elastic wave propagation direction and does not include the tip portions of the first electrode finger and the second electrode finger and includes a portion where the first electrode finger and the second electrode finger intersect each other When
The first electrode finger, the second electrode finger, and the second dummy electrode have a thickness that is closer to the second bus bar than the center region compared to the first electrode finger and the second electrode finger in the center region. Is an elastic wave element that is thick and thin.   The first electrode finger, the second electrode finger, and the second dummy electrode are thicker on the first bus bar side than the central region, compared to the first electrode finger and the second electrode finger in the central region. The elastic wave device according to claim 1, wherein the thickness is thin and the thickness is thin.   3. The acoustic wave device according to claim 1, wherein the first gap is 0.2 times or more a center distance of a width between the first electrode finger and the second electrode finger.   The acoustic wave device according to claim 1, wherein a support substrate made of a material having a smaller linear expansion coefficient than the piezoelectric substrate is disposed on a lower surface of the piezoelectric substrate.   5. The acoustic wave device according to claim 1, wherein the second bus bar is thicker than the first electrode finger in the central region.