JP2006238290A - Resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resonator which is available, even in a high-temperature environment and uses bulk waves and whose temperature characteristics of the resonance frequency is influenced only slightly by a cut-surface working errors. <P>SOLUTION: The resonator comprises a piezoelectric body 2 consisting of a langasite single crystal and a pair of electrodes 3 and 4. A cut angle of the piezoelectric body is in the area surrounded with (11.7°, 39.9°), (11.7°, 66.5°), (51.2°, 66.5°) and (51.2°, 39.9°), the region surrounded with (68.8°, 39.9°), (68.8°, 66.5°), (108.3°, 66.5°) and (108.3°, 39.9°), the region surrounded with (8.8°, 113.5°), (8.8°, 140.1°), (48.3°, 140.1°), and (48.3°, 113.5°), the region surrounded with (71.7°, 113.5°), (71.7°, 140.1°), (111.2°, 140. 1°) and (111.2°, 113.5°), or the region equivalent to these regions due to symmetry. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a resonator used in, for example, a piezoelectric oscillator and a bandpass filter.

As a resonator using a piezoelectric body, a resonator using a bulk wave propagating inside the piezoelectric body (hereinafter referred to as a bulk resonator), and a resonator using a surface acoustic wave (hereinafter referred to as a surface acoustic wave resonator) Called).
Here, as a wireless non-powered sensor system using a bulk resonator, an air pressure sensor system that detects the air pressure inside the tire has been proposed (see, for example, Patent Document 1). This air pressure sensor system uses a bulk resonator made of crystal and is configured to detect by oscillating a resonance frequency corresponding to air pressure.

On the other hand, as a surface acoustic wave resonator, the melting point is higher than that of quartz and there is no phase transition point from room temperature to the melting point, so that it is possible to use it in a higher temperature environment (La ₃ Ga _5.5). ta _0.5 O ₁₄₎ that using the single crystal has been proposed (e.g., see Patent documents 2 and 3). This langagate single crystal is obtained by replacing the constituent element Si of the langasite single crystal with the element Ta, that is, a type of substitutional single crystal of the langasite single crystal series, and has a crystal structure similar to that of langasite. . Therefore, since the langasite single crystal has a stable characteristic with respect to temperature, the langate single crystal also has a stable temperature characteristic. Langatate has a high melting point of about 1500 ° C. and has no phase transition between room temperature and the melting point, so that it can be used at a higher temperature.
Japanese Patent No. 3494440 JP 2000-138557 A JP 2004-282515 A

However, although it has been proposed to use a quartz crystal for the resonator using the conventional bulk wave, the crystal does not exhibit piezoelectricity due to a phase transition at 573 ° C. Even at 573 ° C. or lower, the piezoelectricity may deteriorate with time due to high temperature, and thus there is a restriction on temperature when processing the resonator. As described above, it has been proposed to use a langate single crystal that can be used in a higher temperature environment in a resonator using surface acoustic waves, but it has been proposed to be applied to a bulk resonator. There wasn't.
Furthermore, an AT cut is used in a bulk resonator using quartz. This cut surface is a good cut surface having a frequency fluctuation of about ± 30 ppm in the range of −30 ° C. to 120 ° C. However, the dependence of the resonance frequency on the temperature characteristic is highly dependent on the cut angle, and in order to maintain a stable temperature characteristic, high-accuracy cut surface processing is required, and a reduction in the resonator yield has been a problem.

  The present invention has been made in view of the above-described problems, and provides a resonator using a bulk wave that can be used even in a high-temperature environment and is less affected by temperature characteristics of the resonance frequency due to errors in cut surface processing. For the purpose.

  The present invention employs the following configuration in order to solve the above problems. That is, a flat piezoelectric body and a pair of electrodes respectively disposed on two opposing planes of the piezoelectric body are provided, and the piezoelectric body is formed of a langate crystal.

  According to the present invention, by using a langate having a high melting point of about 1500 ° C. and no phase transition between room temperature and the melting point, deterioration with time does not occur even at a high temperature. Therefore, for example, it can be applied as a bulk resonator used for a temperature sensor in a high temperature environment.

Further, in the resonator of the present invention, the cut angle of the piezoelectric body is represented by Euler angles (φ, θ), point a1 (11.7 °, 39.9 °), point a2 (11.7 °, 66). .5 °), a point A3 (51.2 °, 66.5 °) and a point a4 (51.2 °, 39.9 °) and a point b1 (68.8 °, 39.9). °), point b2 (68.8 °, 66.5 °), point b3 (108.3 °, 66.5 °) and region B4 surrounded by point b4 (108.3 °, 39.9 °) , Point c1 (8.8 °, 113.5 °), point c2 (8.8 °, 140.1 °), point c3 (48.3 °, 140.1 °) and point c4 (48.3 °) , 113.5 °), point d1 (71.7 °, 113.5 °), point d2 (71.7 °, 140.1 °), point d3 (111.2 °, 140) .1 °) and point d4 It is preferable to be in any one of the region D surrounded by (111.2 °, 113.5 °) and the region A to D equivalent to the symmetry of the Langate crystal.
According to the present invention, the cut surface of the rangate is in any one of the regions A to D and the regions equivalent to the regions A to D, so that the temperature of the resonance frequency in the range of −40 ° C. to 140 ° C. Dependency is reduced. In addition, since the influence on the temperature dependency of the resonance frequency due to the processing deviation of the cut surface processing is small, the yield is good, and a resonator using bulk waves can be manufactured stably.

According to the resonator of the present invention, a bulk resonator having stable resonance characteristics can be obtained without causing deterioration with time or phase transition even under a high temperature environment.
In addition, the temperature dependency of the resonance frequency is small, and the influence on the temperature dependency of the resonance frequency due to the machining deviation of the cut surface processing is small.

Hereinafter, an embodiment of a resonator according to the present invention will be described with reference to the drawings.
The resonator 1 according to the present embodiment is a resonator used in, for example, a temperature sensor, and is formed of a single crystal of langate (La ₃ Ga _5.5 Ta _0.5 O ₁₄ ) as shown in FIG. And the pair of electrodes 3 and 4 provided on the upper and lower surfaces of the piezoelectric body 2.

The piezoelectric body 2 has a Euler angle display (φ, θ) on its cut surface.
Point a1 (11.7 °, 39.9 °), Point a2 (11.7 °, 66.5 °), Point a3 (51.2 °, 66.5 °) and Point a4 (51.2 °, Area A surrounded by 39.9 °),
Point b1 (68.8 °, 39.9 °), point b2 (68.8 °, 66.5 °), point b3 (108.3 °, 66.5 °) and point b4 (108.3 °, Region B surrounded by 39.9 °),
Point c1 (8.8 °, 113.5 °), Point c2 (8.8 °, 140.1 °), Point c3 (48.3 °, 140.1 °) and Point c4 (48.3 °, Region C surrounded by 113.5 °),
Point d1 (71.7 °, 113.5 °), point d2 (71.7 °, 140.1 °), point d3 (111.2 °, 140.1 °) and point d4 (111.2 °, Region D surrounded by 113.5 °),
It is formed so as to be in any one of these regions A to D.
The piezoelectric body 2 generates a thickness shear vibration by applying a voltage between the electrodes 3 and 4 provided on two parallel planes facing each other. This thickness shear vibration has three vibration modes of a slow transverse wave and a fast transverse wave and a longitudinal wave depending on the resonance frequency.

  Therefore, the temperature dependence of the resonance frequency at each cut angle of the langate single crystal was calculated by applying the tangate physical constant to the Christoffel equation. 2 and 3 show the resonance frequency change rates with respect to temperature changes in the slow and fast transverse waves, respectively. In addition, the resonant frequency change rate in FIG.2 and FIG.3 is using the value which divided the difference of the maximum value of the resonant frequency in the range of -40 degreeC-140 degreeC with the minimum value by the resonant frequency in 20 degreeC, The smaller the absolute value, the smaller the temperature dependency. Tables 1 to 3 show the resonance frequency change rate in a slow transverse wave in the range of 0 ° to 90 ° in the φ direction and 0 ° to 60 ° in the θ direction, and Tables 4 to 6 show a fast transverse wave in the same range. The resonant frequency change rate in is shown.

In the slow transverse wave shown in FIG. 2, which is a cut surface having a small temperature dependency of the resonance frequency, −40 ° C. to 140 ° C. of the cut surface of (φ, θ) = (18.8 °, 130.1 °) in Euler angle display. FIG. 4 shows the resonance frequency change rate in the range of ° C. Further, in the fast transverse wave shown in FIG. 3, which is a cut surface having a small temperature dependency of the resonance frequency, −40 ° C. of the cut surface of (φ, θ) = (21.7 °, 56.5 °) in Euler angle display. The resonance frequency change rate in the range of ˜140 ° C. is shown in FIG.
In addition, the langate single crystal was actually cut with cut surfaces of Euler angle display (φ, θ) = (18.8 °, 130.1 °), (21.7 °, 56.5 °), and −40 The resonance frequency change rate in the range from ℃ to 140 ℃ was measured. The results are shown in FIG. 4 and FIG.
4 and 5, the calculated resonance frequency change rate and the actual measurement show slightly different profiles, but the temperature stability of the resonance frequency is almost the same.

  Next, the influence on the temperature dependence due to the change of the cut angle was calculated. First, in a slow transverse wave, when the cut angle is shifted by ± 0.1 ° in the θ and φ directions on the cut surface of (φ, θ) = (18.8 °, 130.1 °) in the Euler angle display, respectively. The resonance frequency change rate in the range of −40 ° C. to 140 ° C. is shown in FIGS. 6 and 7, respectively. Further, in the case of a fast transverse wave, the cut angles of (φ, θ) = (21.7 °, 56.5 °) in the Euler angle display are the same as described above, and the cut angles are ± 0.1 in the θ and φ directions, respectively. Resonant frequency change rates in the range of −40 ° C. to 140 ° C. when shifted by degrees are shown in FIGS. 8 and 9, respectively. Furthermore, in the AT cut surface of quartz, the resonance frequency change rate in the range of −40 ° C. to 140 ° C. when the cut angles are shifted by ± 0.1 ° in the θ and φ directions, respectively, is shown in FIGS. .

From FIG. 6 to FIG. 11, the quartz crystal varies about 60 ppm at 120 ° C. when the resonance frequency at 20 ° C. is used as a reference. The Langate single crystal has a fluctuation of about 20 ppm at 120 ° C. with reference to the resonance frequency at 20 ° C., which is about 1/3 of that of quartz.
Generally, it is desired that the variation in the temperature characteristic of the resonance frequency between the resonators is about ± several ppm in the range of −40 ° C. to 140 ° C. Therefore, the crystal needs to have a cut angle of about 40 seconds. On the other hand, in the rangate single crystal, even if the accuracy of the cut angle is about 1 to 2 minutes, the above condition is satisfied, so that the control of the cut angle is easy.

  Note that, on the other cut surface of the crystal, the resonance frequency change rate in the range of −40 ° C. to 140 ° C. is about −60 ppm to about 60 ppm with respect to the deviation of ± 0.1 ° in the θ direction, and ±± in the φ direction. About −40 ppm to about 40 ppm for a deviation of 0.1 °. Further, on the other cut surface of the langate single crystal, the resonance frequency change rate in the range of −40 ° C. to 140 ° C. is about −25 ppm to about 25 ppm with respect to the deviation of ± 0.1 ° in the θ direction in the slow transverse wave. , About −32 ppm to about 32 ppm for a deviation of ± 0.1 ° in the φ direction. Further, in the case of a fast transverse wave, about −20 ppm to about 20 ppm for a deviation of ± 0.1 ° in the θ direction, and about −25 ppm to about 25 ppm for a deviation of ± 0.1 ° in the φ direction. In this way, at any cut angle, Langate has less dependency on the cut angle of the resonance frequency change rate than quartz.

Since the langate single crystal belongs to the point group 32 as in the case of quartz, there is an orientation in which the temperature dependence of the resonance frequency is the same from the symmetry of the crystal structure, that is, an equivalent orientation. That is, in the range of 0 ° ≦ φ ≦ 120 ° and 0 ° ≦ φ ≦ 180 °, if 0 ° ≦ φ ≦ 60 ° and 0 ° ≦ θ ≦ 90 °,
In the region of 60 ° ≦ φ ′ ≦ 120 ° and 0 ° ≦ θ ′ ≦ 90 °, (φ ′, θ ′) and (120 ° −φ, θ) are equivalent,
In the regions of 0 ° ≦ φ ′ ≦ 60 ° and 90 ° ≦ θ ′ ≦ 180 °, (φ ′, θ ′) and (60 ° −φ, 180 ° −θ) are equivalent,
In the region of 60 ° ≦ φ ′ ≦ 120 ° and 90 ° ≦ θ ′ ≦ 180 °, (φ ′, θ ′) and (60 ° + φ, 180 ° −θ) are equivalent.
Furthermore, 0 ° ≦ φ ≦ 120 ° is equivalent to 120 ° ≦ φ ≦ 240 ° and 240 ° ≦ φ ≦ 360 °, and 0 ° ≦ φ ≦ 180 ° and 180 ≦ φ ≦ 360 ° are equivalent. .
Therefore, the azimuth range of the piezoelectric body 2 used in the resonator of the present invention includes such an equivalent azimuth.

From the above, the region A and the equivalent region are expressed by Euler angle (φ, θ), (11.7 ° + 120 ° × m, 39.9 ° + 180 ° × n), (11.7 ° + 120 °). × m, 66.5 ° + 180 ° × n), (51.2 ° + 120 ° × m, 66.5 ° + 180 ° × n) and (51.2 ° + 120 ° × m, 39.9 ° + 180 ° × n).
Similarly, the region B and the equivalent region are (68.8 ° + 120 ° × m, 39.9 ° + 180 ° × n), (68.8 ° + 120 ° × m, 66.5 ° + 180 ° × n), (108.3 ° + 120 ° × m, 66.5 ° + 180 ° × n) and (108.3 ° + 120 ° × m, 39.9 ° + 180 ° × n).
The region C and the equivalent region are (8.8 ° + 120 ° × m, 113.5 ° + 180 ° × n), (8.8 ° + 120 ° × m, 140.1 ° + 180 ° × n). ), (48.3 ° + 120 ° × m, 140.1 ° + 180 ° × n) and (48.3 ° + 120 ° × m, 113.5 ° + 180 ° × n).
The region D and the equivalent region are (71.7 ° + 120 ° × m, 113.5 ° + 180 ° × n), (71.7 ° + 120 ° × m, 140.1 ° + 180 ° × n). ), (111.2 ° + 120 ° × m, 140.1 ° + 180 ° × n) and (111.2 ° + 120 ° × m, 113.5 ° + 180 ° × n). Note that n and m described above are m = 0, 1, and 2, and n = 0 and 1.

  As described above, according to the resonator 1 of the present embodiment, it can be used in a high temperature environment as compared with the crystal. Further, the influence on the temperature dependency due to the processing deviation of the cut surface processing is small, and a resonator can be provided with a high yield.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
For example, in the above-described embodiment, a piezoelectric body is formed using a langate single crystal, but a langate single crystal added with an additive or a material obtained by substituting a part of constituent elements may be used.
Further, the thickness of the piezoelectric body may be appropriately changed according to the resonance frequency to be used.

It is a perspective view which shows the resonator in one Embodiment of this invention. It is a figure which shows the change rate of the resonant frequency of each cut surface in a slow transverse wave in the temperature range of -40 degreeC-140 degreeC of a langate single crystal. It is a figure which shows the change rate of the resonant frequency of each cut surface in a fast transverse wave in the temperature range of -40 degreeC-140 degreeC of a langate single crystal. It is a figure which shows the change rate of the resonant frequency in the slow transverse wave of the cut surface of ((phi), (theta)) = (18.8 degrees, 130.1 degrees). It is a figure which shows the change rate of the resonant frequency in the fast transverse wave of the cut surface of ((phi), (theta)) = (21.7 degrees, 56.5 degrees). It is a figure which shows the change rate of the resonant frequency in a slow transverse wave when a cut angle is shifted in the (theta) direction in the cut surface (18.8 degrees, 130.1 degrees) of a langate single crystal. It is a figure which shows the change rate of the resonant frequency in a slow transverse wave when a cut angle is shifted in a (phi) direction by the cut surface (18.8 degrees, 130.1 degrees) of a langate single crystal. It is a figure which shows the change rate of the resonant frequency in a quick transverse wave when a cut angle is shifted in the (theta) direction in the cut surface of a Langatate single crystal (21.7 degrees, 56.5 degrees). It is a figure which shows the change rate of the resonant frequency in a quick transverse wave when a cut angle is shifted in the (phi) direction by the cut surface (21.7 degrees, 56.5 degrees) of a langate single crystal. It is a figure which shows the change rate of the resonant frequency when the cut angle is shifted in the θ direction on the AT cut surface of quartz. It is a figure which shows the change rate of the resonant frequency when the cut angle is shifted in the φ direction on the AT cut surface of quartz.

Explanation of symbols

1 Resonator 2 Piezoelectric 3, 4 Electrode

Claims (2)

A plate-like piezoelectric body, and a pair of electrodes disposed on two opposing planes of the piezoelectric body,
A resonator in which the piezoelectric body is made of a langate crystal. The cut angle of the piezoelectric body is Euler angle display (φ, θ),
Point a1 (11.7 °, 39.9 °), Point a2 (11.7 °, 66.5 °), Point a3 (51.2 °, 66.5 °) and Point a4 (51.2 °, A region A surrounded by 39.9 °),
Point b1 (68.8 °, 39.9 °), point b2 (68.8 °, 66.5 °), point b3 (108.3 °, 66.5 °) and point b4 (108.3 °, A region B surrounded by 39.9 °),
Point c1 (8.8 °, 113.5 °), Point c2 (8.8 °, 140.1 °), Point c3 (48.3 °, 140.1 °) and Point c4 (48.3 °, Region C surrounded by 113.5 °),
Point d1 (71.7 °, 113.5 °), point d2 (71.7 °, 140.1 °), point d3 (111.2 °, 140.1 °) and point d4 (111.2 °, Region D surrounded by 113.5 °),
2. The resonator according to claim 1, wherein the resonator is in any one of the regions A to D due to symmetry of the Langate crystal. 3.

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