JP2015073308A - Elastic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an elastic wave device capable of keeping a sufficient bandwidth as a filter and stabilizing frequency characteristics for temperature.SOLUTION: In the elastic wave device comprising a piezoelectric substrate, an IDT electrode formed on the piezoelectric substrate and exciting Rayleigh wave having a predetermined wavelength λ as main elastic wave, and a dielectric film covering the piezoelectric substrate and the IDT electrode, the dielectric film has salients provided vertically above at least a part of electrode fingers of the IDT electrode, and a cross area for each salient, where an area of a region having the salient provided at a position upper than a horizontal line passing through the lowest part of an upper end edge of the dielectric film in its cross section in an extension direction of the electrode fingers of the IDT electrode, is equal to or less than 0.0125λ.

Description

  The present invention relates to an acoustic wave device used for a band filter or the like.

In recent years, acoustic wave devices in which comb-shaped IDT electrodes are formed on the surface of a piezoelectric substrate are used as circuit elements such as resonators and filters in the field of information communication equipment such as cellular phones. Since the frequency characteristic of the piezoelectric substrate varies with temperature, the frequency characteristic of the acoustic wave device using the piezoelectric substrate also varies with temperature. FIG. 16 shows how the frequency characteristics of the acoustic wave device vary with temperature. FIG. 16 is a graph showing an example of resonance characteristics (relationship between frequency and admittance) of an acoustic wave device at 25 ° C. and 85 ° C. It can be seen that the resonance frequency and the anti-resonance frequency vary with temperature. Conventionally, in an acoustic wave device, the piezoelectric substrate and the IDT electrode are covered with a dielectric film having a temperature-dependent characteristic smaller than that of the piezoelectric substrate or having an opposite sign, thereby reducing the variation in frequency characteristics due to temperature, that is, TCF ( The absolute value of the (frequency temperature coefficient) value is reduced. For example, Patent Document 1 discloses an acoustic wave device 1000 shown in FIG. FIG. 17 is a cross-sectional view of the acoustic wave device 1000 by a plane perpendicular to the extending direction of the electrode fingers of the IDT electrode. In the acoustic wave device 1000, an IDT electrode 1002 made of aluminum or the like is disposed on a piezoelectric substrate 1001 made of lithium niobate (LiNbO ₃ ), and a dielectric film 1003 made of silicon dioxide (SiO ₂ ) is coated so as to have a flat surface. Is formed.

JP 2005-509259 A

In such an elastic wave device, if the thickness of the dielectric film is kept flat while keeping the surface of the dielectric film flat, the absolute value of the TCF value can be reduced, but the loss of the excited surface acoustic wave is reduced. As the value increases, the K ² (electromechanical coupling coefficient) value decreases, and it becomes difficult to secure a bandwidth when applied to a filter or the like. That is, in the conventional acoustic wave device, it has been difficult to achieve both stabilization of frequency characteristics with respect to temperature and securing of a sufficient band as a filter.

  Therefore, an object of the present invention is to stabilize frequency characteristics with respect to temperature while maintaining a sufficient band as a filter in an acoustic wave device.

  A first aspect of the present invention is formed to cover a piezoelectric substrate, an IDT electrode formed on the piezoelectric substrate and exciting a Rayleigh wave having a predetermined wavelength λ as a main elastic wave, and the piezoelectric substrate and the IDT electrode. The dielectric film has a convex portion vertically above at least a part of the electrode fingers of the IDT electrode, and the extending direction of the electrode fingers of the IDT electrode In the cross section perpendicular to the horizontal axis, the area of the region including the convex portion above the horizontal line passing through the lowest portion of the upper edge of the dielectric film, the cross sectional area per one convex portion is 0.0125λ2 or less It is an elastic wave device.

  In the above-mentioned cross section, the height of the convex portion from the horizontal line is preferably 0.04λ or more.

  The piezoelectric substrate is preferably lithium niobate with θ = 35 ° or more and 40 ° or less when the cut angle and propagation angle are represented by Euler angles (φ, θ, ψ) in right-handed orthogonal coordinates.

  The coating thickness of the dielectric film on the piezoelectric substrate is preferably 0.12λ or more and 0.72λ or less.

  Such an acoustic wave device preferably further includes a protective film coated on the surface of the dielectric film.

  According to a second aspect of the present invention, there is provided a duplexer including a first filter, a second filter having a pass band on a higher frequency side than a pass band of the first filter, and a matching circuit. The filter is a ladder filter using the above-described acoustic wave device as a series resonator and a parallel resonator, and has a cross-sectional area per one protrusion of the first filter formed in at least one series resonator. Is a standardized cross-sectional area obtained by normalizing the cross-sectional area per one convex portion formed in at least one parallel resonator with the excitation wavelength of the parallel resonator. It is a duplexer that is larger than the chemical cross section.

  The first filter further includes a double-coupled mode filter using the above-described elastic wave device, and the cross-sectional area per one convex portion formed in the double-coupled mode filter is determined as the coupled double-mode filter. The standardized cross-sectional area normalized by the excitation wavelength of the parallel resonator is larger than the standardized cross-sectional area obtained by normalizing the cross-sectional area per one convex portion formed in at least one parallel resonator at the excitation wavelength of the parallel resonator. It is preferable.

  A third aspect of the present invention is a duplexer including a first filter, a second filter having a pass band on a higher frequency side than the pass band of the first filter, and a matching circuit. The filter is a ladder filter using the above-mentioned acoustic wave device as a series resonator and a parallel resonator, and a cross-sectional area per one convex portion of the second filter formed in at least one parallel resonator. Is a standardized cross-sectional area obtained by normalizing the cross-sectional area per one convex portion formed in at least one series resonator with the excitation wavelength of the series resonator. It is a duplexer that is larger than the chemical cross section.

  The second filter further includes a coupled double mode filter using the above-described acoustic wave device, and the cross sectional area per one convex portion formed in the coupled double mode filter is determined as the coupled double mode filter. The standardized cross-sectional area normalized by the excitation wavelength of is larger than the standardized cross-sectional area obtained by normalizing the cross-sectional area per protrusion formed in at least one series resonator at the excitation wavelength of the series resonator. It is preferable.

  According to a fourth aspect of the present invention, a piezoelectric substrate, at least one IDT electrode formed on the piezoelectric substrate and using a Rayleigh wave having a predetermined wavelength λ as a main elastic wave, and the piezoelectric substrate and the IDT electrode are covered. Each of the IDT electrodes includes a bus bar and a plurality of electrode fingers and dummy electrode fingers extending alternately from the bus bar, and each of the electrode fingers of the IDT electrode includes: Alternatingly arranged with the electrode fingers of the other IDT electrode, and arranged to face the dummy electrode of the other IDT electrode, the tip of each electrode finger of the IDT electrode and the other IDT electrode dummy facing the electrode finger The distance d from the tip of the electrode is an acoustic wave device that is 1λ or more and 3λ or less.

  According to a fifth aspect of the present invention, a piezoelectric substrate, at least one IDT electrode formed on the piezoelectric substrate and using a Rayleigh wave having a predetermined wavelength λ as a main elastic wave, and the piezoelectric substrate and the IDT electrode are covered. The IDT electrode includes a bus bar and a plurality of electrode fingers alternately extending from the bus bar, and each electrode finger of the IDT electrode is the other IDT electrode. In this elastic wave device, the distance d between the tip of each electrode finger of the IDT electrode and the edge of the other IDT electrode is 1λ or more and 3λ or less.

  According to the present invention, in an acoustic wave device, it is possible to stabilize frequency characteristics with respect to temperature while maintaining a sufficient band as a filter.

The figure which shows the cross section of the elastic wave device which concerns on the 1st and 2nd embodiment of this invention Diagram showing the characteristics of a conventional acoustic wave device The figure which shows the cross section of the examination example of the elastic wave device which concerns on the 1st and 2nd embodiment of this invention The figure which shows the characteristic of the examination example of the elastic wave device which concerns on the 1st and 2nd embodiment of this invention The figure which shows the characteristic of the examination example of the elastic wave device which concerns on the 1st and 2nd embodiment of this invention The figure which shows the characteristic of the examination example of the elastic wave device which concerns on the 1st and 2nd embodiment of this invention The figure which shows the characteristic of the examination example of the elastic wave device which concerns on the 1st and 2nd embodiment of this invention The figure which shows the characteristic of the examination example of the elastic wave device which concerns on the 1st and 2nd embodiment of this invention The figure which shows the characteristic of the examination example of the elastic wave device which concerns on the 2nd Embodiment of this invention. The figure which shows the characteristic of the examination example of the elastic wave device which concerns on the 2nd Embodiment of this invention. The figure which shows the cross section of the elastic wave device which concerns on the 3rd Embodiment of this invention. The figure which shows the cross section and characteristic of the duplexer which concerns on the 4th Embodiment of this invention. The figure which shows the structure of the ladder filter which concerns on the 4th Embodiment of this invention. The figure which shows the structure of the elastic wave device which concerns on the 5th Embodiment of this invention. The figure which shows the characteristic of the elastic wave device which concerns on the 5th Embodiment of this invention Diagram showing the characteristics of a conventional acoustic wave device Diagram showing a cross section of a conventional acoustic wave device

(First embodiment)
A first embodiment of the present invention will be described below. FIG. 1 is a cross-sectional view showing the structure of an acoustic wave device 100 according to this embodiment. The acoustic wave device 100 is configured by forming an IDT electrode 102 on a piezoelectric substrate 101 and further covering a dielectric film 103. The dielectric film 103 is formed so as to have a convex portion 104 above the IDT electrode 102 (a portion covering the IDT electrode 102). The convex portion 104 can be formed by controlling the bias applied to the piezoelectric substrate 101 when the dielectric film 103 is formed by bias sputtering.

The piezoelectric substrate 101 uses a rotating Y-cut lithium niobate substrate, and uses Rayleigh waves as main surface acoustic waves. When the cut angle and propagation angle of the piezoelectric substrate 101 are expressed as Euler angles (φ, θ, ψ) in right-handed orthogonal coordinates, it is preferably lithium niobate having θ = 35 ° or more and 40 ° or less. Note that φ and ψ are arbitrary values of −20 ° to 20 °, respectively. In this embodiment, the piezoelectric substrate 101 is a rotated Y-cut lithium niobate (cut angle 129 °) substrate, that is, a substrate with Euler angles (φ, θ, ψ) = (0 °, 39 °, 0 °). Further, as the IDT electrode 102, a laminated electrode of molybdenum and aluminum each having a thickness of 0.04λ is used. Here, λ is the wavelength of the surface acoustic wave to be excited, and is defined as twice the pitch of the IDT electrode 102. Further, silicon dioxide (SiO ₂ ) is used as the dielectric film.

The inventor believes that by forming the convex portion 104 in an appropriate shape, the frequency characteristics with respect to temperature can be stabilized while maintaining a sufficient band as a filter, and the K ² value for the Rayleigh wave is considered. The following conditions were examined for suitable conditions for the shape of the convex portion 104 to improve the TCF value for the Rayleigh wave without deteriorating.

First, in the acoustic wave device 100, the relationship between the thickness of the dielectric film 103, the K ² (electromechanical coupling coefficient) value, and the TCF value in the case where the convex portion 104 is not provided as in the conventional case is shown in FIG. The results shown are obtained. FIG. 2 is a graph showing the relationship between the thickness of the dielectric film and the K ² value for the Rayleigh wave and the TCF value (TCF_fa value) at the anti-resonance frequency of the Rayleigh wave. Without the protrusion 104 provided on the surface of the dielectric film, while the flat and uniformly increasing the thickness, as shown in FIG. 2, may be the absolute value of TCF_fa value improves decreases, K ² The value of (electromechanical coupling coefficient) is greatly reduced and deteriorated.

Next, the case where the coating thickness of the dielectric film 103 on the piezoelectric substrate 101 was set to 0.25λ and the convex portion 104 was provided was examined as follows. In FIG. 3, the example of the shape of the convex part 104 which concerns on examination is shown typically. 3A and 3B are cross-sectional views of the acoustic wave device 100 taken along a plane perpendicular to the extending direction of the electrode fingers of the IDT electrode 102. FIG. FIG. 3A shows a cross section of the convex portion 104 made triangular, and FIG. 3B shows a rectangular shape. The convex part 104 is formed in the upper part of each IDT electrode 102, and the symmetry axis of the electrode finger of the convex part 104 and the IDT electrode 102 corresponds in sectional drawing. In each shape of FIGS. 3A and 3B, the height of the convex portion 104 from the horizontal line including the lowest portion of the upper end edge of the dielectric film 103 in this cross section (projection amount) and along the horizontal line The relationship between the cross-sectional area determined by the width, the TCF value (TCF_fa value) at the anti-resonance frequency of the Rayleigh wave, and the K ² value for the Rayleigh wave was examined, and the results shown in FIGS. 4 to 7 were obtained.

FIG. 4 is a graph showing the relationship between the cross-sectional area per protrusion 104 and the K ² value for Rayleigh waves when the cross section of the protrusion 104 is a triangle of each height. FIG. 5 is a graph showing the relationship between the cross-sectional area per protrusion 104 and the K ² value for the Rayleigh wave when the cross section of the protrusion 104 is a rectangle of each height. FIGS. 4 and 5 also show, as a comparative value, the K ² value for the Rayleigh wave when the thickness of the dielectric film 103 is 0.25λ when the six convex portions 104 shown in FIG. 2 are not provided. It is. As shown in FIG. 4, when the cross-sectional shape of the convex portion 104 is a triangle, even if the convex portion 104 is provided, the K ² value for the Rayleigh wave does not decrease more than the comparison value, and no deterioration occurs. It was confirmed. In particular, when the height of the convex portion 104 is 0.04λ or more, the K ² value is increased, or the decrease width is suppressed, which is preferable. In addition, as shown in FIG. 5, when the shape of the cross section of the convex portion 104 is a rectangle, by providing the convex portion 104, the K ² value for the Rayleigh wave becomes substantially larger than the comparison value, which is improved. confirmed.

  FIG. 6 is a graph showing the relationship between the cross-sectional area per protrusion 104 and the TCF_fa value for Rayleigh waves when the cross section of the protrusion 104 is a triangle of each height. FIG. 7 is a graph showing the relationship between the cross-sectional area per protrusion 104 and the TCF_fa value for the Rayleigh wave when the protrusion 104 has a rectangular cross section. 6 and 7 also show a TCF_fa value as a comparative value when the thickness of the dielectric film 103 is 0.25λ when the protrusion 104 shown in FIG. 2 is not provided. As shown in FIGS. 6 and 7, it was confirmed that the TCF_fa value was improved by providing the convex portion 104 regardless of whether the cross-sectional shape of the convex portion 104 is a triangle or a rectangle.

To summarize the above results, the convex portion 104 of the elastic wave device 100 improves the TCF_fa value while suppressing the deterioration of the K ² value of the Rayleigh wave, which is the main wave, by setting the height to 0.04λ or more. can do. Moreover, this condition is applicable not only when the cross-sectional shape of the convex part 104 is a triangle or a rectangle, but also when it is a trapezoid that is an intermediate shape between a triangle and a rectangle as shown in FIG. In addition, the shape of the convex portion 104 formed by the bias sputtering method can be approximated to any of a triangle, a rectangle, and a trapezoid even when the contour of the cross-sectional shape includes a curve, and this condition is applied. it can.

When the cross-sectional shape of the convex portion 104 of the acoustic wave device 100 is a trapezoidal shape having an upper base of 0.04λ, a lower base of 0.09λ, and a height of 0.08λ, the thickness of the dielectric film 103 and the Rayleigh wave K ² values and examined the relationship between the TCF_fa values. The result is shown in FIG. In the conventional acoustic wave device using lithium tantalate (LiTaO ₃ ) as a piezoelectric substrate, the TCF_fa value is about −50 ppm / K. According to FIG. If the thickness is 0.12λ or more and 0.72λ or less, the absolute value of the TCF_fa value of the acoustic wave device 100 is smaller than 50 ppm / K, and the TCF_fa value can be improved as compared with the conventional case.

(Second Embodiment)
A second embodiment of the present invention will be described below. The elastic wave device according to the present embodiment is such that the K ² value for an SH wave that is an unnecessary spurious is set to a predetermined value or less in the elastic wave device 100 according to the first embodiment.

Inventors, the acoustic wave device 100 according to the first embodiment, and less than a predetermined value K ² value for SH waves were examined as follows for the preferred conditions of the shape of the convex portion 104.

FIG. 9 is a graph showing the relationship between the cross-sectional area per protrusion 104 and the K ² value for the SH wave that becomes an unnecessary wave when the cross section of the protrusion 104 is a triangle of each height. is there. FIG. 10 shows the relationship between the cross-sectional area per protrusion 104 and the K ² value for the SH wave that becomes an unnecessary wave when the cross section of the protrusion 104 is a rectangle of each height. It is a graph. As shown in FIG. 9 and FIG. 10, if the cross-sectional area of each convex portion 104 is 0.0125λ ² or less regardless of whether the cross-sectional shape of the convex portion 104 is a triangle or a rectangle, ^{The binary} value was approximately 0.005% or less, and it was confirmed that the K ² value of the unnecessary wave can be reduced to a practically sufficient level.

When the above results and the results in the first embodiment are arranged, the height of the convex portion 104 of the acoustic wave device is set to 0.04λ or more, and the sectional area per one is set to 0.0125λ ² or less. Further, it is possible to improve the TCF_fa value while suppressing deterioration of the K ² value of the Rayleigh wave that is the main wave, and to sufficiently reduce the K ² value for the SH wave that is an unnecessary wave. In addition, this condition can be applied to the general shape of the convex portion 104 that can be approximated to any one of a triangle, a rectangle, and a trapezoid, as in the condition in the first embodiment.

In the first and second embodiments, a rotating Y-cut lithium niobate (cut angle: 129 °) substrate is used as the piezoelectric substrate 101, and silicon dioxide (SiO ₂ ) is used as the dielectric film. The present invention can also be applied to piezoelectric substrates having different materials and cut angles, and dielectric films of different materials, and preferable conditions for the shape of the convex portion 104 can be obtained according to the characteristics of each material.

(Third embodiment)
A third embodiment of the present invention will be described below. The acoustic wave device 300 according to the present embodiment is the acoustic wave device according to the first or second embodiment, in which a protective film 305 is further provided on the surface of the dielectric film 103. FIG. 11 shows a cross-sectional view of the acoustic wave device 300. The protective film 305 protects the dielectric film 103 including the convex portion 104 and also functions as a frequency adjustment film. Examples of the material of the protective film 305 include silicon nitride (SiN) and silicon oxynitride (SiON). In addition, the thickness of the protective film 305 is preferably about 5 nm to 20 nm.

(Fourth embodiment)
A fourth embodiment of the present invention will be described below. In this embodiment, the elastic wave device according to the first to third embodiments is applied to a duplexer. FIG. 12A shows the configuration of the duplexer 400 according to the present embodiment. The duplexer 400 includes a first ladder filter 401 connected to the first terminal 404, a second ladder filter 402 connected to the second terminal 405, and a matching circuit 403 connected to the third terminal 406. It consists of. Further, the first ladder filter 401 and the second ladder filter 402 are each connected to a matching circuit 403. The first ladder filter 401 and the second ladder filter are configured using the acoustic wave devices according to the first to third embodiments.

  FIG. 12B schematically shows the pass characteristics (admittance) between the terminals of the duplexer 400. As shown in FIG. 12B, the pass band between the third terminal 406 indicating the pass band of the first ladder filter 401 and the first terminal 404 is the pass band of the second ladder filter 402. It is on the lower frequency side than the pass band between the second terminal 405 and the third terminal 406 shown.

  An example of the configuration of the first ladder filter 401 is shown in FIG. As shown in FIG. 13A, the first ladder filter 401 includes an input terminal 411 and an output terminal 412, a series resonator 413 connected in series therebetween, and one end of the series resonator 413. And a parallel resonator 414 that is connected and grounded at the other end.

In a portion constituting the series resonator 413 of the first ladder filter 401, a normalized cross-sectional area (cross-sectional area / λ1 ^{2) obtained} by normalizing the cross-sectional area per one convex portion 104 with the excitation wavelength λ1 of the series resonator 413. ) Is larger than the normalized cross-sectional area (cross-sectional area / λ2 ² ) obtained by normalizing the cross-sectional area of each convex portion 104 with the excitation wavelength λ2 of the parallel resonator 414 in the portion constituting the parallel resonator 414. Thereby, in the first ladder filter 401, the TCF value of the series resonator 413 is improved more than the TCF value of the parallel resonator 414. In general, since the slope characteristic on the high frequency side of the passband of the ladder filter depends on the slope characteristic on the high frequency side of the resonance frequency of the series resonator, the first ladder filter 401 has a slope on the high frequency side of the passband. The TCF value of the part will be further improved.

  Similarly to the first ladder filter 401, the second ladder filter 402 has an input terminal and an output terminal, a series resonator connected in series between them, and one end connected to the series resonator. And a parallel resonator whose end is grounded.

However, in the second ladder filter 402, in a portion constituting the parallel resonator, a normalized cross-sectional area (cross-sectional area / cross-sectional area / section) obtained by normalizing the cross-sectional area per protrusion 104 with the excitation wavelength λ3 of the parallel resonator. λ3 ² ) is larger than the normalized cross-sectional area (cross-sectional area / λ4 ² ) obtained by normalizing the cross-sectional area of each convex portion 104 with the excitation wavelength λ4 of the series resonator in the portion constituting the series resonator. . Thereby, in the second ladder filter 402, the TCF value of the parallel resonator is improved over the TCF value of the series resonator. In general, since the slope characteristic on the low frequency side of the passband of the ladder filter depends on the slope characteristic on the low frequency side of the resonance frequency of the parallel resonator, the second ladder filter 402 has a slope on the low frequency side of the passband. The TCF value of the part will be further improved.

  As described above, the TCF value can be improved in the frequency band between the passbands of the first ladder filter 401 and the second ladder filter 402, which is important for demultiplexing performance when viewed as the entire duplexer 400. it can.

The first ladder filter 401 may have a configuration shown in FIG. In this configuration example, a DMS filter (coupled double mode filter) 451 is connected to the series resonator 413 in the configuration example shown in FIG. In this case, in a portion constituting the DMS filter 451 of the first ladder filter 401, a normalized cross-sectional area (cross-sectional area / λ5) obtained by normalizing the cross-sectional area of each convex portion 104 with the excitation wavelength λ5 of the DMS filter 421. ² ) is larger than the normalized cross-sectional area (cross-sectional area / λ6 ² ) obtained by normalizing the cross-sectional area of each convex portion 104 with the excitation wavelength λ6 of the parallel resonator 414 in the portion constituting the parallel resonator 414. It should be.

Similarly to the first ladder filter 401, the second ladder filter 402 may be connected to the DMS filter 461. In this case, in the portion constituting the DMS filter 461 of the second ladder filter 402, the normalized cross-sectional area (cross-sectional area / λ7) in which the cross-sectional area per protrusion 104 is normalized by the excitation wavelength λ7 of the DMS filter 461. ² ) is larger than the normalized cross-sectional area (cross-sectional area / λ8 ² ) obtained by normalizing the cross-sectional area of each convex portion 104 with the excitation wavelength λ8 of the series resonator 423 in the portion constituting the parallel resonator 414. It should be.

  Further, the duplexer 400 may use one of the first ladder filter 401 and the second ladder filter 402 as described above as one of the two filters, and may use another filter as the other filter.

(Fifth embodiment)
A fifth embodiment of the present invention will be described below. FIG. 14A is a top view transparently showing the acoustic wave device 500 according to the present embodiment. The acoustic wave device 500 is configured by forming two IDT electrodes 502 and a reflector 504 on a piezoelectric substrate 501, and further covering a dielectric film 503 (not shown).

  The IDT electrode 502 includes a bus bar 511, electrode fingers 512 and dummy electrode fingers 513 that alternately extend from the bus bar 511. The electrode fingers 512 of the two IDT electrodes 502 are alternately arranged with the other electrode finger 512 and arranged to face the other dummy electrode finger 513. The tip of the electrode finger 512 and the tip of the opposing dummy electrode finger 513 are separated by a distance d.

  FIG. 15 is a graph showing the relationship between the distance d in the acoustic wave device 500 and the Qp value that is the Q value at the antiresonance point. According to FIG. 15, it can be seen that as the distance d increases, the elastic wave confinement effect improves and the Qp value tends to increase. In particular, when the distance is larger than the excitation wavelength λ, the Qp value exceeds 1500, and it can be seen that a filter with sufficiently reduced loss can be configured. However, when the distance d exceeds 3λ, the propagation loss of elastic waves tends to increase. Therefore, the acoustic wave device 500 having suitable attenuation characteristics can be configured by setting the distance d in the range of λ to 3 inclusive.

  In the acoustic wave device 500, as shown in FIG. 14B, the IDT electrode 502 does not include the dummy electrode finger 513, and the tip of each electrode finger 512 of the two IDT electrodes 502 and the other IDT electrode Even if the distance from the edge of the bus bar 511 of 502 is the distance d, the acoustic wave device 500 having suitable damping characteristics can be configured by setting the distance d in the range of λ to 3λ.

  The present embodiment can be applied to the first to third acoustic wave devices, and can also be applied to other acoustic wave devices.

  The present invention is useful in a surface acoustic wave device used for information communication equipment and the like.

100, 200, 300, 500, 1000 Elastic wave device 101, 1001 Piezoelectric substrate 102, 502, 1002 IDT electrodes 103, 503, 1003 Dielectric film 104 Convex part 305 Protective film 400 Duplexer 401, 402 Ladder filter 403 Matching circuit 404, 405, 406, 411, 412, 421, 422 Terminals 413, 423 Series resonators 414, 424 Parallel resonators 451, 461 Coupled dual mode filter 504 Reflector 511 Bus bar 512 Electrode finger 513 Dummy electrode finger

Claims (11)

A piezoelectric substrate;
An IDT electrode formed on the piezoelectric substrate and exciting a Rayleigh wave having a predetermined wavelength λ as a main elastic wave;
An acoustic wave device comprising a dielectric film formed so as to cover the piezoelectric substrate and the IDT electrode,
The dielectric film has a convex portion vertically above at least some of the electrode fingers of the IDT electrode,
Per area of the area including the convex part above the horizontal line passing through the lowest part of the upper edge of the dielectric film in a cross section perpendicular to the extending direction of the electrode fingers of the IDT electrode. An elastic wave device having a cross-sectional area of 0.0125λ ² or less.   2. The acoustic wave device according to claim 1, wherein in the cross section, a height of the convex portion from the horizontal line is 0.04λ or more.   The piezoelectric substrate is lithium niobate having θ = 35 ° or more and 40 ° or less when a cut angle and a propagation angle are expressed by Euler angles (φ, θ, ψ) in right-handed orthogonal coordinates. The elastic wave device according to any one of the above.   4. The acoustic wave device according to claim 1, wherein a coating thickness of the dielectric film on the piezoelectric substrate is 0.12λ or more and 0.72λ or less.   The elastic wave device according to claim 1, further comprising a protective film coated on a surface of the dielectric film. A first filter;
A second filter having a pass band on a higher frequency side than the pass band of the first filter;
A duplexer comprising a matching circuit,
The first filter is a ladder filter using the acoustic wave device according to any one of claims 1 to 6 as a series resonator and a parallel resonator,
The normalized cross-sectional area obtained by normalizing the cross-sectional area per one of the convex portions formed in the at least one series resonator of the first filter by the excitation wavelength of the series resonator is at least one of the A duplexer, wherein a cross-sectional area per one of the convex portions formed in the parallel resonator is larger than a normalized cross-sectional area normalized by the excitation wavelength of the parallel resonator. The first filter further includes a double coupled mode filter using the acoustic wave device according to any one of claims 1 to 6,
A normalized cross-sectional area obtained by normalizing a cross-sectional area per one of the convex portions formed in the double coupled mode filter with an excitation wavelength of the coupled double mode filter is formed in at least one of the parallel resonators. The duplexer according to claim 6, wherein a cross-sectional area per one of the convex portions is larger than a normalized cross-sectional area normalized by the excitation wavelength of the parallel resonator. A first filter;
A second filter having a pass band on a higher frequency side than the pass band of the first filter;
A duplexer comprising a matching circuit,
The second filter is a ladder filter using the acoustic wave device according to any one of claims 1 to 6 as a series resonator and a parallel resonator,
The normalized cross-sectional area obtained by normalizing the cross-sectional area per one of the convex portions formed in the at least one parallel resonator of the second filter with the excitation wavelength of the parallel resonator is at least one of the above-mentioned A duplexer, wherein a cross-sectional area per one of the convex portions formed in the series resonator is larger than a normalized cross-sectional area normalized by the excitation wavelength of the series resonator. The second filter further includes a coupled double mode filter using the acoustic wave device according to any one of claims 1 to 6,
A normalized cross-sectional area obtained by normalizing the cross-sectional area per one of the convex portions formed in the coupled double mode filter with the excitation wavelength of the coupled double mode filter is formed in at least one of the series resonators. The duplexer according to claim 8, wherein a cross-sectional area per one of the convex portions is larger than a normalized cross-sectional area normalized by the excitation wavelength of the series resonator. A piezoelectric substrate;
At least one set of IDT electrodes formed on the piezoelectric substrate and using a Rayleigh wave having a predetermined wavelength λ as a main elastic wave;
An acoustic wave device comprising a dielectric film formed so as to cover the piezoelectric substrate and the IDT electrode,
Each of the IDT electrodes has a bus bar and a plurality of electrode fingers and dummy electrode fingers alternately extending from the bus bar,
Each electrode finger of the IDT electrode is arranged alternately with the electrode finger of the other IDT electrode, and is arranged to face the dummy electrode of the other IDT electrode,
The elastic wave device, wherein a distance d between the tip of each electrode finger of the IDT electrode and the tip of the other IDT electrode dummy electrode facing the electrode finger is 1λ or more and 3λ or less. A piezoelectric substrate;
At least one set of IDT electrodes formed on the piezoelectric substrate and using a Rayleigh wave having a predetermined wavelength λ as a main elastic wave;
An acoustic wave device comprising a dielectric film formed so as to cover the piezoelectric substrate and the IDT electrode,
Each of the IDT electrodes has a bus bar and a plurality of electrode fingers extending alternately from the bus bar,
The electrode fingers of the IDT electrode are arranged alternately with the electrode fingers of the other IDT electrode,
A distance d between the tip of each electrode finger of the IDT electrode and the edge of the other IDT electrode is 1λ or more and 3λ or less.

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