JP2009267904A - Elastic wave element and resonator using the same, filter, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress loss due to bulk radiation when an elastic wave element is a boundary wave element. <P>SOLUTION: The elastic wave element 6 comprises a piezoelectric substrate 7, an interdigital electrode 8 provided on the piezoelectric substrate 7, a first dielectric layer 9 provided on the piezoelectric substrate 7 to cover the interdigital electrode 8, and a second dielectric layer 10 provided on the first dielectric layer 9. The speed Vs of a lateral wave of a bulk wave propagated in the second dielectric layer 10 is faster the speed V of an elastic wave excited by the interdigital electrode 8, the speed V of the elastic wave excited by the interdigital electrode 8 is slower than the speed Vb of the slowest lateral wave of a bulk wave propagated in the piezoelectric substrate 7, and the cut angle of a rotary Y plate of the piezoelectric substrate 7 is not less than 15° and not larger than 25°. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an acoustic wave element and a resonator, filter, and electronic device using the same.

  A conventional acoustic wave device will be described with reference to FIG. FIG. 13 is a schematic cross-sectional view of a conventional acoustic wave device.

  In FIG. 13, the conventional acoustic wave element 1 is provided so as to cover the comb-tooth electrode 3 on the piezoelectric substrate 2, the comb-tooth electrode 3 provided on the piezoelectric substrate 2, and the piezoelectric substrate 2. A first dielectric layer 4 and a second dielectric layer 5 provided on the first dielectric layer 4 are provided. The material of the second dielectric layer 5 is determined so that the velocity Vs of the transverse wave among the bulk waves propagating through the second dielectric layer 5 is faster than the velocity V of the elastic wave excited in the comb electrode 3. It was.

  Thereby, the elastic wave excited near the comb electrode 3 can be confined, and as a result, the elastic wave element 1 as a boundary wave element has been realized.

As prior art document information relating to this application, for example, Patent Document 1 is known.
JP 2007-267366 A

  In such a conventional acoustic wave device 1, the velocity Vs of the transverse wave among the bulk waves propagating through the second dielectric layer 5 is made faster than the velocity V of the elastic wave mainly composed of the transverse wave excited in the comb electrode 3. Since the material of the second dielectric layer 5 has been determined, the velocity V of the elastic wave mainly composed of the transverse wave excited by the comb-tooth electrode 3 is increased under the influence of the second dielectric layer 5. . As a result, the velocity V of the elastic wave mainly composed of the transverse wave excited at the comb-tooth electrode 3 becomes faster than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate 2 and is excited at the comb-tooth electrode 3. The acoustic wave leaks into the piezoelectric substrate 2 as a bulk wave, which causes deterioration of insertion loss when the acoustic wave element 1 is used as a resonator. That is, when the acoustic wave element 1 is a boundary wave element having the second dielectric layer 2, the loss due to the bulk radiation has been a serious problem.

  Therefore, an object of the present invention is to suppress loss due to bulk radiation when the acoustic wave element is a boundary wave element.

  In order to achieve this object, an acoustic wave device according to the present invention is provided so as to cover a piezoelectric substrate, a comb electrode provided on the piezoelectric substrate, and the comb electrode on the piezoelectric substrate. The first dielectric layer and the second dielectric layer provided on the first dielectric layer, and the velocity Vs of the transverse wave among the bulk waves propagating through the second dielectric layer is The velocity V of the elastic wave mainly of the transverse wave excited is higher than the velocity V of the elastic wave mainly of the transverse wave excited by the comb electrode, and is slower than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate. The cut angle of the rotating Y plate in the piezoelectric substrate is 15 degrees or more and 25 degrees or less.

  With this configuration, the velocity V of the elastic wave mainly composed of the transverse wave excited in the comb-tooth electrode becomes slower than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate, and the elastic wave excited in the comb-tooth electrode. Can be prevented from leaking into the piezoelectric substrate as a bulk wave. As a result, it is possible to prevent deterioration of insertion loss when the acoustic wave element is used as a resonator.

  Further, by setting the cut angle of the rotating Y plate in the piezoelectric substrate to 25 degrees or less, the coupling coefficient of the elastic wave mainly composed of the transverse wave excited in the comb electrode can be increased.

  Furthermore, by setting the cut angle of the rotating Y plate in the piezoelectric substrate to 15 degrees or more, SV (shear vertical) that appears mainly as a component of displacement in the propagation direction excited in the comb electrode and the thickness direction of the piezoelectric substrate and appears as an unnecessary wave. ) The wave coupling coefficient can be reduced, and an acoustic wave device with less spurious response can be realized.

  That is, in the above configuration, by setting the cut angle of the rotating Y plate in the piezoelectric substrate to 15 degrees or more and 25 degrees or less, it is possible to secure the coupling coefficient of the elastic wave mainly composed of the transverse wave excited in the comb-tooth electrode and to suppress the spurious response. It is possible to achieve both.

(Embodiment 1)
Hereinafter, the acoustic wave device according to the first embodiment of the present invention will be described with reference to the drawings. 1 is a schematic cross-sectional view of an acoustic wave device according to Embodiment 1. FIG.

  In FIG. 1, an acoustic wave element 6 includes a piezoelectric substrate 7, a comb electrode 8 provided on the piezoelectric substrate 7, and a first electrode provided on the piezoelectric substrate 7 so as to cover the comb electrode 8. A first dielectric layer 9 and a second dielectric layer 10 provided on the first dielectric layer 9 are provided. The elastic wave element 6 includes a bulk wave propagating through the second dielectric layer 10, and the transverse wave velocity Vs is higher than the transverse wave-based elastic wave velocity V excited in the comb-tooth electrode 8. The velocity V of the elastic wave mainly composed of the transverse wave excited in the tooth electrode 8 is slower than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate 7, and the cut angle of the rotating Y plate in the piezoelectric substrate 7 is 15 degrees or more. It is characterized by being 25 degrees or less.

  The piezoelectric substrate 7 is made of, for example, lithium niobate, lithium tantalate, or potassium niobate. For example, when the piezoelectric substrate 7 is lithium niobate, the slowest velocity Vb of the bulk wave propagating through the piezoelectric substrate 7 is 4024 m / sec.

  The comb-teeth electrode 8 is, for example, a single metal made of aluminum, copper, silver, or gold, or an alloy containing these.

  The first dielectric layer 9 is, for example, silicon oxide, tantalum pentoxide, or tellurium dioxide. Here, it is desirable to use silicon oxide as the first dielectric layer 9. This is because the temperature characteristic coefficient of silicon oxide has a sign opposite to the temperature characteristic coefficient of the piezoelectric substrate 7, and thus a temperature characteristic compensation effect can be obtained. Further, since the velocity of the transverse wave propagating through the silicon oxide is slower than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate 7, the velocity of the elastic wave mainly composed of the transverse wave excited in the vicinity of the comb electrode 8 is set. The effect of suppressing bulk radiation into the piezoelectric substrate 7 can be expected by lowering effectively.

  The second dielectric layer 10 is, for example, silicon nitride or aluminum nitride. For example, when the second dielectric layer 10 is silicon nitride, the velocity Vs of the transverse wave among the bulk waves propagating through the second dielectric layer 10 is approximately 6100 m / second. This is sufficiently faster than the velocity V of the elastic wave mainly composed of the transverse wave excited by the comb-teeth electrode 8, and if the wavelength of the elastic wave mainly composed of the transverse wave excited by the comb-teeth electrode 8 is λ, the second dielectric layer The boundary wave element having no displacement on the upper surface of the second dielectric layer 10 is realized by sufficiently increasing the thickness of 10 to 1λ or more.

  In such an acoustic wave device 6, the velocity Vs of the transverse wave among the bulk waves propagating through the second dielectric layer 10 is sufficiently higher than the velocity V of the elastic wave mainly composed of the transverse wave excited by the comb electrode 8. Since the material of the second dielectric layer 10 has been determined, the velocity V of the elastic wave mainly composed of the transverse wave excited by the comb-tooth electrode 8 is increased under the influence of the second dielectric layer 10. Therefore, in order to suppress the deterioration of the insertion loss as in the conventional elastic wave element 1, the elastic wave element 6 according to the first embodiment has a velocity V of the elastic wave mainly composed of the transverse wave excited by the comb-tooth electrode 8 as a piezoelectric element. The bulk wave propagating through the substrate 7 is characterized by being slower than the slowest transverse wave velocity Vb.

  Thereby, the velocity V of the elastic wave mainly composed of the transverse wave excited at the comb-tooth electrode 8 becomes slower than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate 7 and is excited at the comb-tooth electrode 8. It is possible to suppress leakage of elastic waves mainly composed of transverse waves into the piezoelectric substrate 7 as bulk waves. As a result, it is possible to prevent deterioration of insertion loss when the acoustic wave element 6 is used as a resonator.

  A condition in which the velocity V of the elastic wave mainly excited by the comb-teeth electrode 8 is slower than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate 7 will be described with reference to FIG. Here, the piezoelectric substrate 7 is lithium niobate, the first dielectric 9 is silicon oxide, and the second dielectric 10 is silicon nitride. Further, the cut angle of the rotating Y plate of the piezoelectric substrate 7 is θ, the ratio of the density of the comb electrode 8 to the copper density is a, the wavelength of the elastic wave mainly composed of the transverse wave excited in the comb electrode 8 is λ, and the comb electrode The film thickness of 8 is h, and the film thickness of the first dielectric layer 9 is H. The vertical axis in FIG. 2 represents the normalized film thickness H / λ of the first dielectric layer 9 normalized by the wavelength λ of the transverse wave-dominated elastic wave excited in the comb electrode 8. Also, the horizontal axis of FIG. 2 is the cut angle θ of the rotating Y plate of the piezoelectric substrate 7.

  The standard of the first dielectric layer 9 in which the velocity V of the elastic wave mainly composed of the transverse wave excited by the comb-teeth electrode 8 by simulation and the velocity Vb of the slowest transverse wave among the bulk waves propagating in the piezoelectric substrate 7 are the same. The relationship between the formed film thickness H / λ and the cut angle θ of the rotating Y plate in the piezoelectric substrate 7 was determined. For example, the five straight lines shown in FIG. 2 indicate the first dielectric when the electrode film thickness h is 0.09λ / a, 0.10λ / a, 0.11λ / a, 0.12λ / a, and 0.13λ / a, respectively. The relationship between the normalized film thickness H / λ of the layer 9 and the cut angle θ of the rotating Y plate in the piezoelectric substrate 7 is linearly approximated by a linear equation. That is, the region satisfying the above condition is a region above each straight line shown in FIG.

As shown in the five examples of FIG. 2, the condition that the velocity V of the elastic wave mainly composed of the transverse wave excited in the comb electrode 8 is slower than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate 7 is as follows.
When 0.085λ / a <h <0.095λ / a, H / λ> -0.0018θ + 0.1909
When 0.095λ / a <h <0.105λ / a, H / λ> -0.0014θ + 0.1376
When 0.0105λ / a <h <0.115λ / a, H / λ> -0.0013θ + 0.1017
When 0.115λ / a <h <0.125λ / a, H / λ> -0.0011θ + 0.0754
When 0.125λ / a <h <0.135λ / a, H / λ> -0.0009θ + 0.0536
It is.

  By adopting the cut angle θ of the rotating Y plate of the piezoelectric substrate 7 satisfying these conditions, the film thickness h of the comb electrode 8, and the film thickness H of the first dielectric layer 9, the comb electrode 8 is excited. The velocity V of the elastic wave mainly composed of the transverse wave becomes slower than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate 7, and the elastic wave mainly composed of the transverse wave excited by the comb-teeth electrode 8 becomes the bulk wave. 7 can be prevented from leaking.

  Further, in FIGS. 3, 4, 5, 6, and 7, the electrode film thicknesses h are 0.09λ / a, 0.10λ / a, 0.11λ / a, 0.12λ / a, and 0.13λ / a, respectively. The dependence of the coupling coefficient of the elastic wave mainly composed of transverse waves excited on the comb-tooth electrode 8 on the normalized film thickness H / λ of the first dielectric layer 9 and the cut angle θ of the rotating Y plate is shown. From this, it can be seen that the coupling coefficient becomes approximately 15% or more by setting the cut angle of the rotating Y plate to 25 degrees or less. As described above, by setting the cut angle of the rotating Y plate in the piezoelectric substrate 7 to 25 degrees or less, the coupling coefficient of the elastic wave mainly composed of the transverse wave excited in the comb electrode 8 can be increased. For example, when the elastic wave element 6 is applied to a system having a wide band such as W-CDMA, the coupling coefficient of the elastic wave mainly composed of the transverse wave excited in the comb electrode 8 is desirably about 15% or more. Therefore, for example, when the piezoelectric substrate 7 is lithium niobate, the first dielectric 9 is silicon oxide, and the normalized film thickness of the first dielectric 9 is 0.09λ to 0.11 / a, the rotation is performed. By setting the cut angle of the Y plate to 25 degrees or less, the coupling coefficient of the elastic wave mainly composed of the transverse wave excited in the comb electrode 8 can be made approximately 15% or more.

  8, 9, 10, 11, and 12, the electrode thicknesses h are 0.09λ / a, 0.10λ / a, 0.11λ / a, 0.12λ / a, and 0.13λ / a, respectively. The normalized film thickness H / λ of the first dielectric layer 9 of the coupling coefficient of the SV wave, which appears mainly as a component of displacement in the propagation direction excited in the comb electrode 8 and the thickness direction of the piezoelectric substrate 7, is rotated. The dependence on the cut angle θ of the Y plate is shown. As can be seen from the graph, the SV wave coupling coefficient decreases as the cut angle of the rotating Y plate increases, and spurious can be suppressed. In this way, by setting the cut angle of the rotating Y plate in the piezoelectric substrate 7 to 15 degrees or more, the propagation component excited in the comb electrode 8 and the displacement component in the thickness direction of the piezoelectric substrate 7 are mainly used as unnecessary waves. The coupling coefficient of the appearing SV wave can be reduced, and an elastic wave device with less spurious response can be realized.

  That is, in the above configuration, by setting the cut angle of the rotating Y plate in the piezoelectric substrate 7 to 15 degrees or more and 25 degrees or less, it is possible to ensure the coupling coefficient of the elastic wave mainly composed of the transverse wave excited in the comb electrode 8 and to reduce the spurious response. It is possible to achieve both suppression.

  The elastic wave element 6 that suppresses the loss due to the bulk radiation may be applied to a resonator (not shown) or may be applied to a filter (not shown) such as a ladder type filter or a DMS filter. Absent. Further, the acoustic wave element 6 is applied to an electronic apparatus including the filter, a semiconductor integrated circuit element (not shown) connected to the filter, and a reproducing device connected to the semiconductor integrated circuit element (not shown). It may be applied. Thereby, the signal loss in a resonator, a filter, and an electronic device can be suppressed.

  The elastic wave device according to the present invention has an effect of suppressing loss due to bulk radiation when the elastic wave device is a boundary wave device, and is useful in electronic devices such as mobile phones.

Sectional schematic diagram showing an acoustic wave device according to Embodiment 1 of the present invention. Diagram showing the characteristics of the acoustic wave device Diagram showing the relationship between the normalized film thickness and the cut angle Diagram showing the relationship between the normalized film thickness and the cut angle Diagram showing the relationship between the normalized film thickness and the cut angle Diagram showing the relationship between the normalized film thickness and the cut angle Diagram showing the relationship between the normalized film thickness and the cut angle Diagram showing the relationship between the normalized film thickness and the cut angle Diagram showing the relationship between the normalized film thickness and the cut angle Diagram showing the relationship between the normalized film thickness and the cut angle Diagram showing the relationship between the normalized film thickness and the cut angle Diagram showing the relationship between the normalized film thickness and the cut angle Cross-sectional schematic diagram showing a conventional acoustic wave device

Explanation of symbols

6 acoustic wave element 7 piezoelectric substrate 8 comb-tooth electrode 9 first dielectric layer 10 second dielectric layer

Claims (5)

A piezoelectric substrate;
A comb electrode provided on the piezoelectric substrate;
A first dielectric layer provided on the piezoelectric substrate so as to cover the comb electrodes;
A second dielectric layer provided on the first dielectric layer;
The velocity Vs of the transverse wave among the bulk waves propagating through the second dielectric layer is faster than the velocity V of the elastic wave mainly composed of the transverse wave excited by the comb electrode, and
The velocity V of the elastic wave excited in the comb electrode is slower than the velocity Vb of the slowest transverse wave among the bulk waves propagating through the piezoelectric substrate, and the cut angle of the rotating Y plate in the piezoelectric substrate is 15 degrees or more and 25. An elastic wave device that is less than or equal to degrees When the piezoelectric substrate is lithium niobate and the first dielectric is silicon oxide,
The cut angle of the rotating Y plate of the piezoelectric substrate is θ, the ratio of the density of the comb electrode to the copper density is a, the wavelength of the elastic wave mainly composed of the transverse wave excited in the comb electrode, λ, When the film thickness is h and the film thickness of the first dielectric layer is H,
When 0.085λ / a <h <0.095λ / a, H / λ> -0.0018θ + 0.1909
When 0.095λ / a <h <0.105λ / a, H / λ> -0.0014θ + 0.1376
When 0.0105λ / a <h <0.115λ / a, H / λ> -0.0013θ + 0.1017
When 0.115λ / a <h <0.125λ / a, H / λ> -0.0011θ + 0.0754
When 0.125λ / a <h <0.135λ / a, H / λ> -0.0009θ + 0.0536
The acoustic wave device according to claim 1, wherein: A resonator using the acoustic wave device according to claim 1. A filter using the acoustic wave device according to claim 1. A filter according to claim 4;
A semiconductor integrated circuit element connected to the filter;
An electronic apparatus comprising: a reproduction device connected to the semiconductor integrated circuit element.

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