JP2008054163A - Lamb-wave type high-frequency resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Lamb-wave type high-frequency resonator that has a high Q value, high phase velocity and superior frequency temperature characteristics. <P>SOLUTION: The Lamb-wave type high-frequency resonator 10 has a liquid crystal substrate 20, an IDT electrode 30 constituted by interposing a first cross finger electrode 31 and a second cross finger electrode 32 into the main surface of the liquid crystal substrate 20 and reflectors 40, 50 arranged on both sides of the traveling direction of the Lamb wave of the IDT electrode 30. If the crossing width between the first cross finger electrode 31 and the second cross finger electrode 32 is W and the wavelength of the Lamb wave is λ, the crossing width W is set within a range, expressed by 21λ≤W≤54λ. In addition, the IDT electrode 30 is formed so that the segmentation angle of the liquid crystal substrate 20 and the propagating direction of the Lamb wave become (0, θ, 0) by Euler angle representation and within a range, in which the angle θ is expressed as being 35 degrees ≤θ≤47.2 degrees, normalized substrate thickness t/λ, expressed by a relation between the thickness t of the liquid crystal substrate 20 and the wavelength λ of the Lamb wave, set to be within a range of 0.176≤t/λ≤1.925. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a Lamb wave type high frequency resonator. Specifically, the present invention relates to a configuration of a piezoelectric substrate and an IDT electrode in a Lamb wave type high frequency resonator.

  Conventionally, as a high-frequency resonator, a Rayleigh wave type surface acoustic wave resonator in which an IDT electrode is formed in the X-axis direction on which a surface acoustic wave propagates on the surface of a quartz substrate called an ST cut crystal, an ST cut Representative examples include SH wave surface acoustic wave elements using STW cut quartz crystal that propagates transverse waves whose propagation direction of surface acoustic wave is shifted by 90 degrees with respect to quartz, and Lamb wave type resonators using AT cut quartz. The

  In particular, Lamb wave type resonators have a much faster phase velocity than the above-described resonators using surface acoustic waves, have a large electromechanical coupling coefficient, have good excitation efficiency, and reflect on reflectors on Lamb wave propagation paths. Therefore, it is considered as a high-frequency element.

  For example, in a Lamb wave resonator in which an IDT electrode is formed on the surface of an AT-cut quartz substrate, a Lamb wave in which the thickness H of the quartz substrate and the wavelength λ of the Lamb wave are expressed by 0 <2H / λ ≦ 10 A type high-frequency resonator is known (for example, see Patent Document 1).

  In addition, the theoretical analysis of the frequency temperature characteristics of a Lamb wave resonator in which an IDT electrode is formed on an AT-cut quartz substrate and the experimental results thereof have been published (for example, see Non-Patent Document 1).

JP 2003-258596 A The Institute of Electronics, Information and Communication Engineers, C Vol. J89-C No. 1, pages 34-39, “Temperature characteristics of Lamb wave type elastic wave device substrate”, Akihiko Nakagawa

  Although the Rayleigh wave type surface acoustic wave resonator using the ST-cut quartz described above exhibits excellent frequency-temperature characteristics as a surface acoustic wave device, it cannot be said to be sufficient as a resonator that requires high accuracy. Further, the theoretical value of the phase velocity is as slow as about 3100 m / s, and it is difficult to cope with the high frequency band.

  Further, it is known that an SH wave type surface acoustic wave device using an STW cut crystal has a frequency temperature characteristic worse than that of the above-mentioned ST cut crystal. In addition, since tantalum or tungsten having a density higher than that of aluminum is used as the electrode material, the electrical resistance loss increases, the Q value decreases, and the excitation efficiency decreases. Furthermore, it is known that there is a problem that the phase velocity is lowered.

  In addition, the Lamb wave type high frequency resonator according to Patent Document 1 described above has an excellent frequency temperature characteristic by using an AT cut quartz substrate having a quartz substrate thickness of 5 wavelengths or less with respect to the wavelength of the elastic wave. Although it is said to be suitable, it is not necessarily better than ST cut quartz and is still not satisfactory.

  Further, in Non-Patent Document 1 described above, the theoretical value and the experimental value when the IDT electrode is composed of a double-type cross finger electrode and the cross width of the cross finger electrode is set to 50λ with respect to the wavelength λ of the Lamb wave. Thus, it is proposed that the frequency temperature characteristic is improved. However, when a double-type cross finger electrode is used, the crossing occurs because two electrode fingers of the second cross finger electrode are inserted in the inter-electrode pitch (corresponding to the wavelength λ) of the first cross finger electrode. The width of the finger electrode is (1/8) λ, and in the high frequency band, the width of the crossed finger electrode is ½ that of a single type in which one electrode finger is inserted. It has a problem of becoming.

  An object of the present invention is to provide a Lamb wave type high frequency resonator having a high Q value, a high phase velocity, and excellent frequency temperature characteristics.

A Lamb wave type high frequency resonator according to the present invention includes a piezoelectric substrate, an IDT electrode configured by interposing a first cross finger electrode and a second cross finger electrode on a main surface of the piezoelectric substrate, and the IDT electrode Reflectors disposed on both sides of the traveling direction of the Lamb wave, and when the cross width of the first cross finger electrode and the second cross finger electrode is W and the wavelength of the Lamb wave is λ, the cross width W is set in a range represented by 21λ ≦ W ≦ 54λ.
Here, the intersection width means a range in which the first intersection finger electrode and the second intersection finger electrode intersect in the direction perpendicular to the traveling direction of the Lamb wave.

  Although details will be described in an embodiment to be described later, according to the present invention, by designing the intersection width W of the first cross finger electrode and the second cross finger electrode in a range of 21λ ≦ W ≦ 54λ. A Lamb wave type that has a frequency temperature characteristic superior to that of the Rayleigh wave type surface acoustic wave resonator using the above-described ST cut crystal and has a high Q value, so that it can cope with a high frequency band (a region where the phase velocity is high). A high frequency resonator can be realized.

Further, it is preferable that the first cross finger electrode and the second cross finger electrode are configured such that one electrode finger is alternately inserted.
The IDT electrode configured in this way is called a single-type electrode.

  Accordingly, one electrode finger of each of the second cross finger electrodes (or the first cross finger electrodes) is interposed between the pitches of the first cross finger electrodes (or the second cross finger electrodes) (corresponding to the wavelength λ). By adopting the insertion structure, the width of the electrode finger can be doubled compared to the double electrode as in Non-Patent Document 1 described above, so a wide electrode finger can be used at the same frequency. There is an effect that it is much easier to manufacture.

The piezoelectric substrate is preferably a quartz substrate.
By using a quartz substrate as the piezoelectric substrate and using the Lamb wave as a vibration mode, the resonator has excellent compatibility with the high frequency band compared to the ST cut quartz described above, and has excellent frequency temperature characteristics compared to the STW cut quartz. Can be realized.

  Further, the crystal substrate and the IDT electrode are formed such that the cut-out angle of the crystal substrate and the propagation direction of the Lamb wave are (0, θ, 0) in Euler angle display, and the angle θ is 35 In the range represented by degrees ≦ θ ≦ 47.2 degrees, the relationship between the thickness t of the quartz substrate and the wavelength λ of the Lamb wave is represented by 0.176 ≦ t / λ ≦ 1.925 It is desirable to be set to.

Although details will be described in an embodiment described later, the frequency temperature characteristics, frequency band, and excitation stability of the Lamb wave type high frequency resonator are determined by the cut-out angle of the quartz substrate and the propagation direction of the elastic wave, that is, the Euler angles (0, The angle θ in θ, 0) and the normalized substrate thickness t / λ expressed by the relationship between the substrate thickness t and the wavelength λ. By making each of the relational expressions as described above, it becomes possible to cope with the frequency temperature characteristics and the high frequency band which are superior to those of the above-described prior art STW cut crystal and ST cut crystal, and also the excitation of the quartz substrate. Since the electromechanical coupling coefficient (K ² ) representing the efficiency can be increased, it is possible to provide a Lamb wave type high frequency resonator that is easily excited and has a stable frequency characteristic.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 12 show the structure and characteristics of the Lamb wave type high frequency resonator of this embodiment. In addition, the figure showing the structure of the Lamb wave type | mold high frequency resonator referred in the following description is a schematic diagram from which the vertical and horizontal scale of a member thru | or a part differs from an actual thing for convenience of illustration.

  FIG. 1 shows a cutting direction of a crystal substrate 20 according to an embodiment of the present invention. The quartz substrate 20 is a thin plate composed of the X-axis called the electrical axis, the Y-axis called the mechanical axis, and the Z-axis called the optical axis, but the cut-out orientation of the quartz substrate 20 in this embodiment is the thickness direction This is a rotated Y-cut quartz crystal in which the Z-axis is rotated by an angle θ to Z ′, and is cut out so that the longitudinal direction is the X-axis, the width direction is Y ′, and the thickness direction is Z ′ (FIG. 2). An IDT electrode (Interdigital Transducer) 30 is formed in the X-axis direction. Therefore, the traveling direction of the Lamb wave is the X axis direction.

Next, the structure of the Lamb wave type high frequency resonator 10 according to the present embodiment will be described.
FIG. 2 is a perspective view showing a Lamb wave type high frequency resonator according to the present embodiment, and FIG. 3 is a cross-sectional view showing the AA cut plane of FIG. 2 and 3, a Lamb wave type high frequency resonator 10 includes an IDT electrode 30 composed of a pair of crossed finger electrodes 31 and 32 on the main surface of a quartz substrate 20 as a piezoelectric substrate, and the IDT electrode. The reflector 50 is disposed on both sides of the traveling direction of the 30 Lamb waves and includes the grid-like electrode fingers 50a and 50b, and the reflector 40 having a similar electrode finger configuration. Hereinafter, the cross finger electrode 31 is represented as a first cross finger electrode 31 and the cross finger electrode 32 is represented as a second cross finger electrode 32.

  2 and 3, the number of electrode fingers of each of the IDT electrode 30 and the reflectors 40 and 50 is one example, and is not limited to the number shown.

  The first cross finger electrode 31 and the second cross finger electrode 32 of the IDT electrode 30 are configured to be inserted in parallel with each other in the X-axis direction. That is, as shown in FIG. 2, the electrode finger 32 a of the second cross finger electrode 32 is inserted between the electrode finger 31 a and the electrode finger 31 b of the first cross finger electrode 31, and the electrode of the second cross finger electrode 32. The electrode finger 31b of the first cross finger electrode 31 is interposed between the finger 32a and the electrode finger 32b. Thus, the IDT electrode 30 in which each electrode finger is inserted is called a single-type electrode.

  In FIG. 3, the distance from the end of the comb-shaped electrode finger 31a constituting the first intersecting finger electrode 31 to the electrode finger 31b is the wavelength λ of the Lamb wave, and the width of each of the electrode fingers 31a and 31b is Li.

  The distance between the end of the electrode finger 31a and the electrode finger 32a of the second intersecting finger electrode 32 inserted between the electrode fingers 31a and 31b (sometimes referred to as an interelectrode pitch) is expressed as Pi. The width of the electrode finger 32a is also Li. Therefore, the wavelength λ of the Lamb wave is twice the interelectrode pitch Pi of the IDT electrode 30.

  Further, the distance from the end of the electrode finger 50a of the reflector 50 to the electrode finger 50b is Pr (sometimes referred to as an inter-electrode pitch), and the width of each of the electrode fingers 50a and 50b is Lr.

  Further, the width of crossing in the range where the first cross finger electrode 31 and the second cross finger electrode 32 cross in the direction perpendicular to the traveling direction of the Lamb wave, that is, in the Y ′ direction is represented as W. (See FIG. 2). The Q value of the Lamb wave type high frequency resonator 10 varies depending on the size of the intersection width W.

  FIG. 4 is a graph showing experimental values regarding the relationship between the crossing width W and the Q value of the Lamb wave type high frequency resonator 10 (hereinafter sometimes simply referred to as a Lamb wave), and Rayleigh using an ST cut crystal. A comparison with a wave-type surface acoustic wave resonator (hereinafter, sometimes simply referred to as a Rayleigh wave) is shown. The intersection width W is represented by a multiple of the Lamb wave wavelength λ.

  In FIG. 4, the Lamb wave type high frequency resonator 10 of the present embodiment is represented by a quadratic curve having an extreme value in the vicinity of the intersection width W of 38λ. In the Rayleigh wave, the Q value increases up to around 20λ as in the case of the Lamb wave. Here, in the range where the intersection width is 21λ ≦ W ≦ 54λ, the Q value of the Lamb wave is a region higher than that of the Rayleigh wave. That is, by increasing the Q value, it is easier to excite than the Rayleigh wave, a stable resonance frequency can be obtained, and high frequency can be achieved.

Subsequently, the phase temperature in the Lamb wave type high frequency resonator 10 (see FIGS. 2 and 3), the frequency temperature deviation with respect to each of the normalized substrate thickness t / λ and the angle θ in the Euler angles (0, θ, 0) ( The results calculated by simulation for the relationship between the frequency temperature fluctuation amount), the phase velocity, and the electromechanical coupling coefficient K ² will be described with reference to the drawings.

5 and 6 show the relationship between the frequency temperature variation and the angle θ in the Euler angles (0, θ, 0), and the relationship between the frequency temperature variation, the thickness t of the quartz substrate 20 and the wavelength λ of the Lamb wave (standardization). It is a graph which shows board | substrate thickness t / (lambda). 5 and 6, the range of the angle θ that has better frequency temperature characteristics than STW cut quartz is 35 degrees ≦ θ ≦ 47.2 degrees, and the range of the normalized substrate thickness t / λ is 0.176 ≦ t / λ. ≦ 1.925.
Further, the relationship among the angle θ, the normalized substrate thickness t / λ, the phase velocity, the frequency temperature fluctuation amount, and the electromechanical coupling coefficient K ² will be described in detail.

  FIG. 7 shows the relationship between the angle θ at the Euler angles (0, θ, 0) and the phase velocity. Here, the normalized substrate thickness t / λ is set in six stages from 0.2 to 2.0, and the phase velocity at each t / λ is shown by a graph. From FIG. 7, in all cases except the case where the normalized substrate thickness t / λ = 2.0, a phase velocity of 5000 m / s or more can be obtained when the angle θ is in the range of 30 degrees to 50 degrees. Show.

  FIG. 8 shows the relationship between the normalized substrate thickness t / λ and the phase velocity. The angle θ at the Euler angles (0, θ, 0) is set in five stages from 30 degrees to 50 degrees, and the phase velocity at each angle θ is shown by a graph. FIG. 8 shows that the variation in the phase velocity is small at each angle θ, and that a phase velocity of 5000 m / s or more can be obtained in the most range where t / λ is 0.2-2.

Next, the relationship between the Euler angle (0, θ, 0) angle θ, the normalized substrate thickness t / λ, the phase velocity, the frequency temperature fluctuation amount, and the electromechanical coupling coefficient K ² will be described.
FIG. 9 shows the relationship between the angle θ at the Euler angles (0, θ, 0), the phase velocity, and the amount of frequency temperature fluctuation. Here, the normalized substrate thickness t / λ is 1.7. From FIG. 9, the range of θ in which the frequency temperature fluctuation amount is smaller than that of the STW cut crystal is 35 degrees ≦ θ ≦ 47.2 degrees (see also FIG. 6), and a phase velocity of 5000 m / s or more is obtained in this range. It is shown that.

FIG. 10 shows the relationship between the angle θ at the Euler angles (0, θ, 0), the electromechanical coupling coefficient K ^2, and the frequency temperature fluctuation amount. From FIG. 10, the range of the angle θ at the Euler angles (0, θ, 0) in which the frequency temperature fluctuation amount is smaller than that of the STW cut quartz is 35 degrees ≦ θ ≦ 47.2 degrees (see also FIG. 5). In this range, the electromechanical coupling coefficient K ² greatly exceeds the standard value 0.02. When the range of the angle θ is 32.5 degrees ≦ θ ≦ 47.2 degrees, the electromechanical coupling coefficient K ² is 0.03 or more, and the range of the angle θ is 34.2 degrees ≦ θ ≦ 47.2 degrees. In this case, the electromechanical coupling coefficient K ² is 0.04 or more, and when the range of the angle θ is 36 degrees ≦ θ ≦ 47.2 degrees, the electromechanical coupling coefficient K ² is 0.05 or more. .

FIG. 11 shows the relationship among the normalized substrate thickness t / λ, the phase velocity, and the frequency temperature fluctuation amount. From FIG. 11, the range of t / λ in which the frequency temperature fluctuation amount is smaller than that of the STW cut quartz is 0.176 ≦ t / λ ≦ 1.925 (see also FIG. 6), and the phase velocity is large in this range. 5000 m / s or more is obtained in the range of the part. In the range of the normalized substrate thickness t / λ, the smaller the normalized substrate thickness t / λ, the faster the phase velocity and the higher frequency band can be obtained. That is, the phase velocity can be adjusted by adjusting the normalized substrate thickness t / λ.
Next, the relationship between t / λ, the electromechanical coupling coefficient K ^2, and the frequency temperature fluctuation amount will be described.

FIG. 12 shows the relationship among the normalized substrate thickness t / λ, the electromechanical coupling coefficient K ^2, and the frequency temperature fluctuation amount. From FIG. 12, the range of the normalized substrate thickness t / λ in which the frequency temperature fluctuation amount is smaller than that of the STW cut quartz is 0.176 ≦ t / λ ≦ 1.925 (see also FIGS. 6 and 11). In the range, the electromechanical coupling coefficient K ² is 0.02 or more in the most range. In the range where the normalized substrate thickness t / λ is close to 1, a high region where the electromechanical coupling coefficient K ² is 0.05 or more is obtained.

From the results described above, the angle θ at the Euler angles (0, θ, 0) is in a range expressed by 35 degrees ≦ θ ≦ 47.2 degrees, and the normalized substrate thickness t / λ is 0.176 ≦ t / λ ≦ 1.925. By designing in the range represented by, the frequency temperature characteristics are superior to STW cut quartz, and a high phase velocity of 5000 m / s or higher can be obtained. Further, it is shown that the electromechanical coupling coefficient K ² can be secured to 0.02 or more which is preferable for practical use.

  Therefore, according to the above-described embodiment, by designing the cross width W of the first cross finger electrode 31 and the second cross finger electrode 32 in the range of 21λ ≦ W ≦ 54λ, the Rayleigh using the ST cut crystal described above. A Lamb wave type high frequency resonator having a frequency temperature characteristic superior to that of a wave type surface acoustic wave resonator is realized. Further, since it has a high Q value, it is possible to realize a Lamb wave type high frequency resonator that can easily cope with a high frequency band (high phase velocity) and has stable resonance characteristics.

  In addition, each electrode finger of the second cross finger electrode 32 (or the first cross finger electrode 31) during the inter-electrode pitch (corresponding to the wavelength λ) of the first cross finger electrode 31 (or the second cross finger electrode 32). By adopting a single-type electrode structure in which each electrode is inserted one by one, the width of the electrode finger can be doubled compared to the double-type electrode as described in Non-Patent Document 1 described above. Therefore, if the frequency is the same, a wide electrode finger may be used, so that there is an effect that it is much easier to manufacture.

Further, in this embodiment, the quartz substrate 20 is used as the piezoelectric substrate, and the angle θ at the cut-off angle of the quartz substrate 20 and the propagation direction of the Lamb wave in the Euler angle display (0, θ, 0) is 35 degrees ≦ θ The normalized substrate thickness t / λ is set to a range represented by 0.176 ≦ t / λ ≦ 1.925. By doing so, it becomes possible to cope with the frequency temperature characteristics and the high frequency band which are superior to those of the above-described prior art STW cut crystal and ST cut crystal, and the electromechanical coupling representing the excitation efficiency of the crystal substrate 20 Since the coefficient (K ² ) can be increased, it is possible to provide the Lamb wave type high frequency resonator 10 that is easily excited and has a stable frequency characteristic.

  It should be noted that the present invention is not limited to the above-described embodiment, but includes modifications and improvements as long as the object of the present invention can be achieved.

  For example, in the embodiment described above, a quartz substrate is used as the piezoelectric substrate, but in addition to the quartz substrate, lithium tantalate, lithium niobate, lithium tetraborate, langasite, and potassium niobate can be employed. Further, it can be applied to piezoelectric thin films such as zinc oxide, aluminum nitride, and tantalum pentoxide, and piezoelectric semiconductors such as cadmium sulfide, zinc sulfide, gallium arsenide, and indium antimony.

  In the above-described embodiment, the 1-port resonator is exemplified as the Lamb wave type high-frequency resonator. However, for example, a 2-port resonator or a filter including an IDT electrode and a reflector may be used. .

  In the above-described embodiment, the reflectors 40 and 50 are provided. However, an end face reflection type configuration without these reflectors may be employed.

  Therefore, according to the present embodiment, a quartz substrate in which the normalized substrate thickness t / λ and the angle θ at (0, θ, 0) in the Euler angle display are set in the above-described range is adopted, and the IDT electrode intersection width W Is set to an appropriate range, it is possible to provide a Lamb wave type high frequency resonator having a high Q value, a high phase velocity, and excellent frequency temperature characteristics.

Explanatory drawing which shows the cutting-out direction of the crystal substrate which concerns on embodiment of this invention. The perspective view which shows the Lamb wave type | mold high frequency resonator which concerns on embodiment of this invention. Sectional drawing showing the AA cut surface of FIG. The graph showing about the relationship between the crossing width W of the Lamb wave type | mold high frequency resonator which concerns on embodiment of this invention, and Q value. The graph which shows the relationship between the frequency temperature variation | change_quantity of the Lamb wave type | mold high frequency resonator which concerns on embodiment of this invention, and angle (theta) in Euler angles (0, (theta), 0). The graph which shows the relationship between the amount of frequency temperature fluctuations of the Lamb wave type high frequency resonator concerning the embodiment of the present invention, and standardized substrate thickness t / λ. The graph which shows the relationship between the angle (theta) in Euler angles (0, (theta), 0), and normalized substrate thickness t / (lambda) of the Lamb wave type | mold high frequency resonator which concerns on embodiment of this invention. The graph which shows the relationship between the angle (theta) in Euler angles (0, (theta), 0), and normalized substrate thickness t / (lambda) of the Lamb wave type | mold high frequency resonator which concerns on embodiment of this invention. The graph which shows the angle (theta) in Euler angles (0, (theta), 0) of the Lamb wave type | mold high frequency resonator which concerns on embodiment of this invention, frequency temperature fluctuation amount, and the relationship of a phase velocity. Euler angles of the lamb wave type high frequency resonator according to an embodiment of the present invention (0, θ, 0) graph showing the relationship between the angle theta and the frequency variation with temperature and the electromechanical coupling coefficient K ² in. The graph which shows the relationship between the normalized board | substrate thickness t / (lambda) of the Lamb wave type | mold high frequency resonator which concerns on embodiment of this invention, frequency temperature fluctuation amount, and phase velocity. Graph showing the relationship between the normalized substrate thickness t / lambda and the frequency variation with temperature and the electromechanical coupling coefficient K ² of the lamb wave type high frequency resonator according to an embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Lamb wave type | mold high frequency resonator, 20 ... Quartz substrate as a piezoelectric substrate, 30 ... IDT electrode, 31 ... 1st cross finger electrode, 32 ... 2nd cross finger electrode, 40, 50 ... Reflector.

Claims (4)

A piezoelectric substrate, an IDT electrode configured by interposing a first cross finger electrode and a second cross finger electrode on the main surface of the piezoelectric substrate, and a lamb wave traveling direction on both sides of the IDT electrode are disposed. A reflector, and
When the cross width of the first cross finger electrode and the second cross finger electrode is W and the wavelength of the Lamb wave is λ, the cross width W is set in a range represented by 21λ ≦ W ≦ 54λ. Lamb wave type high frequency resonator. In the lamb wave type high frequency resonator according to claim 1,
A lamb wave type high frequency resonator, wherein the first cross finger electrode and the second cross finger electrode are configured such that each electrode finger is alternately inserted one by one. In the Lamb wave type high frequency resonator according to claim 1 or 2,
A Lamb wave type high frequency resonator, wherein the piezoelectric substrate is a quartz substrate. In the Lamb wave type high frequency resonator according to claim 3,
The crystal substrate and the IDT electrode are formed so that the cut-out angle of the crystal substrate and the propagation direction of the Lamb wave are (0, θ, 0) in Euler angle display,
In the range where the angle θ is expressed by 35 degrees ≦ θ ≦ 47.2 degrees, the relationship between the thickness t of the quartz substrate and the wavelength λ of the Lamb wave is 0.176 ≦ t / λ ≦ 1. A Lamb wave type high frequency resonator characterized by being set in a range represented by 925.

Images