JP2001230655A - Piezoelectric vibrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for suppressing a thickness-bend vibration mode which is coupled with thickness-shear vibrations in a strip-like vibrator. SOLUTION: The piezoelectric vibrator is constituted, by providing an electrode on the trapezoidal projecting parts of elevation angles θ1 deg. and θ2 deg., which are formed on the center of a strip-like AT cut crystal substrate with the lengthwise direction as X-axis, breadthwise direction as Z'-axis and thickness direction as Y'-axis and the other electrode confronting the former on the rear side of the substrate facing these projecting parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric vibrator,
In particular, the present invention relates to a piezoelectric vibrator in which a thickness bending vibration mode coupled to a thickness shear vibration is suppressed.

[0002]

2. Description of the Related Art Piezoelectric vibrators, for example, AT-cut quartz vibrators, are widely used from communication devices to electronic devices because they are small in size and can easily obtain high-accuracy and high-stable frequencies. FIG. 4 is a perspective view showing the configuration of a conventional surface-mount type crystal unit (SMD crystal unit), in which electrodes 12a opposed to both main surfaces of an AT-cut crystal substrate 11 cut out from a crystal in a strip shape. , 12b and the electrode 1
The lead electrodes 13a and 13b extend from 2a and 12b toward the ends of the substrate 11, respectively, to form the crystal resonator element S. Next, the crystal vibrating element S is housed in a ceramic package (not shown) and its lead electrodes 13a, 13
b is conductively fixed to a terminal electrode provided at a step portion inside the package using a conductive adhesive or the like. Further, the quartz oscillator is placed in a vacuum device, finely adjusted to a desired frequency by means such as vapor deposition, and then a metal cover is resistance-welded to form a quartz oscillator.

As shown in FIG. 4, a rectangular quartz resonator generally has a longitudinal direction set to the X axis, a width direction set to the Z 'axis, and a thickness direction set to the Y' axis. As is well known, if the dimensions of each part of the piezoelectric substrate are not appropriate, the bending vibration generated on the XY ′ plane will be combined with the thickness-shear vibration, causing fluctuations in the frequency and crystal impedance (CI) of the vibration. Become. In recent years, a strip-shaped substrate having a smaller side ratio (ratio of a contour dimension to a thickness) has been adopted in order to further reduce the size of a crystal resonator. For this reason, there is a problem that the coupling between the thickness vibration, which is the main vibration, and the contour vibration, such as the surface slip vibration and the bending vibration, is caused even by a slight processing error.

For example, as a means for avoiding coupling with contour vibrations, a quartz crystal resonator in which the main surface of a piezoelectric substrate is processed has been devised as shown in the sectional views of FIGS. 5 (a), 5 (b) and 5 (c). ,
Have been used. That is, FIG. 5A has a shape in which the end of the main surface is cut off obliquely, and is generally called a chamfered vibrator (beveling vibrator). FIG. 5B is a so-called convex oscillator (plano-convex oscillator) in which the main surface is processed into a lens shape, and FIG. 5C is a vibrator in which a part of the main surface is processed into a convex shape (mesa shape). Vibrator). In each case, the vibration energy of the thickness-shear vibration is concentrated on the central portion of the substrate, and also acts to weaken the coupling with the contour vibration.

[0005] A flat strip-shaped vibrator shown in FIG.
FIG. 6C shows the difference between the vibration displacement distribution and the mesa vibrator shown in FIG. 6B obtained by simulation using the finite element method. That is, the dimension X _{0 in} the longitudinal direction of the substrate.
4800 μm, width dimension Z ₀ is 780 μm, thickness Y ₀ is 128 μm
The dimension of the gold electrode D is 3600 μm, and the vibration energy distribution P of the crystal unit having a thickness of 0.9 μm is shown.
In addition, the amount corresponding to the frequency reduction caused by the electrode D is converted into the thickness of the mesa structure, and the vibration energy distribution of the crystal resonator in which the thickness t of the convex portion is 12.98 μm is indicated by T. At this time,
A thin electrode film (electrode film having conductivity but having no mass load effect) was attached to the convex portion and the back surface of the substrate facing the convex portion. The vertical axis represents the square of the vibration displacement, that is, the vibration energy is normalized by the value at the center of the substrate, and the horizontal axis represents the distance from the center of the substrate. As is clear from FIG. 6C, in each case, displacement due to higher-order thickness bending vibration occurs at the end of the substrate, but the mesa-shaped vibrator (T) has a flat plate vibrator (P It can be seen that the vibration displacement is smaller than in ().

[0006]

However, although a quartz crystal resonator having a mesa structure can suppress thickness bending vibration to some extent compared to a conventional flat plate-shaped crystal resonator, it may not be able to sufficiently suppress it. There is a problem in that the frequency-temperature characteristic of the vibration is shifted from a smooth cubic curve, or the CI-temperature characteristic is varied (CI dip), in combination with the thickness-shear vibration. The present invention has been made to solve the above problem, and has as its object to provide a crystal resonator in which thickness bending vibration is suppressed.

[0007]

According to a first aspect of the present invention, there is provided a piezoelectric vibrator according to the present invention, wherein a longitudinal direction is an X axis, a width direction is a Z 'axis, and a thickness direction is a Y direction. A convex portion having a trapezoidal XY cross section is formed integrally with the quartz substrate on a strip-shaped AT-cut quartz substrate on the axis, and a counter electrode is provided on the upper surface of the convex portion and on the back surface of the substrate facing the quartz substrate. A piezoelectric vibrator characterized in that: The invention according to claim 2 is
When the elevation angles between the inclined surface of the projection and the substrate surface are θ1 and θ2, each of the elevation angles θ1 and θ2 is smaller than 90 °. The invention according to claim 3 is the piezoelectric vibrator, wherein the elevation angles θ1 and θ2 are set to approximately 35 ° and 63 °, respectively.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. FIG. 1A is a perspective view showing a configuration of a piezoelectric vibrator according to the present invention, in which a longitudinal direction of a length L is an X axis, a width direction of a length W is a Z ′ axis, and a thickness direction of a thickness H is a thickness direction. , The length of the top side in the X-axis direction is L2, the elevation angles at which the top side L2 is desired are θ ₁ and θ ₂ , respectively, and the length of the top side in the Z′-axis direction is the Y ′ axis. The XY ′ cross section, where W is the thickness and t is the thickness, forms a trapezoidal convex portion, and the upper surface of the trapezoidal convex portion and the electrode 2a facing the back surface of the piezoelectric substrate 1 facing the convex portion. 2b, and lead electrodes 3a, 2b from the electrodes 2a, 2b toward the end of the piezoelectric substrate 1, respectively.
3b is extended to form a piezoelectric vibration element.

A feature of the present invention is not a mesa-shaped piezoelectric substrate in which both ends of a convex portion are at right angles as shown in FIG. 6C, but a trapezoidal shape as shown in a sectional view in FIG. Is that a piezoelectric vibrator is configured using a piezoelectric substrate having a convex portion having elevation angles θ ₁ and θ _{2 at} which the top sides are desired. A method for forming a piezoelectric substrate according to the present invention will be described with reference to the drawing shown in FIG. First, a metal film 4, for example, a gold (Au) film is attached to the AT-cut substrate 1 having a thickness for obtaining a desired frequency by means of vapor deposition or the like, and a photoresist film is formed on the film 4. Is applied, exposed through a mask, and developed to form a strip-shaped electrode film 4 periodically arranged on the piezoelectric substrate 1 as shown in FIG. Next, this is an etchant,
For example, when etching is performed in an ammonium fluoride solution, the wall surfaces on both sides of the etched groove exhibit an etching surface having a predetermined angle as shown in a cross-sectional view of FIG. become. When the metal film 4 is peeled off, as shown in FIG. 2C, the piezoelectric substrate 1 in which the etching grooves are regularly arranged is obtained. The elevation angle at which the top of the trapezoidal convex portion is desired is θ ₁ = approximately in the + X axis direction. A substrate having θ ₂ = approximately 63 ° is obtained in the direction of 35 ° and the −X axis, and the substrate having the trapezoidal convex portion according to the present invention is obtained by cutting the substrate along QQ. The thickness t of the projection can be controlled by the etching time.

FIG. 3 (a) is a view showing a cross section of a piezoelectric substrate having a trapezoidal convex portion, where the elevation angle at which the top side is desired is set to α, the length of the top side is L2, and the thickness of the convex portion. Is t, the dimension in the X-axis direction is L1, the thickness of the substrate is H, and the width in the Z ′ direction is W (not shown). FIG. 3 (b) shows that the dimension L1 in the longitudinal direction of the substrate shown in FIG. 3 (a) is 4800 μm, the dimension W in the width direction is 780 μm, the thickness H is 141 μm, and the length L2 of the top of the trapezoidal projection is L2. The vibration energy distribution of a crystal resonator with a thin electrode film (electrode film that is conductive but has no mass load effect) attached to a quartz substrate with a thickness of 3.600 μm and a thickness t of 12.98 μm is determined by the finite element method. FIG. 6 is a diagram obtained by simulation using Using the elevation angle α as a parameter, 35
変 位, 63 ゜, and 90 ゜, and the displacement distributions were compared.
As is clear from FIG. 3B, it has been found that the displacement of the thickness bending vibration generated at the peripheral portion of the substrate becomes smaller as the elevation angle α becomes smaller than the conventional case where the elevation angle α is made a right angle. The small displacement of the thickness bending vibration means that the coupling between the thickness shear vibration and the thickness bending vibration is small, and the frequency temperature characteristic draws a smooth cubic curve.
-The temperature characteristic approaches flat.

[0011]

According to the present invention, as described above, the coupling between the thickness vibration and the thickness bending vibration can be suppressed, and a piezoelectric vibrator having a smooth frequency-temperature characteristic and a small CI dip can be realized. When the piezoelectric vibrator according to the present invention is used for a temperature-compensated crystal oscillator or the like which is widely used in mobile phones and the like, an excellent effect that the yield is improved is exhibited.

[Brief description of the drawings]

1A is a perspective view of a piezoelectric vibrator according to the present invention, FIG.
(B) is a sectional view thereof.

FIGS. 2A, 2B, and 2C are cross-sectional views showing a process for forming a piezoelectric substrate according to the present invention.

3A is a cross-sectional view of a piezoelectric substrate having a trapezoidal convex portion used in a simulation, and FIG. 3B is a diagram illustrating an energy distribution of displacement with an elevation angle α as a parameter.

FIG. 4 is a perspective view of a conventional strip-shaped crystal resonator.

5A is a cross-sectional view of a chamfered substrate, FIG. 5B is a convex-processed substrate, and FIG. 5C is a cross-sectional view of a mesa-shaped substrate.

6A is a cross-sectional view of a strip-shaped vibrator, FIG. 6B is a cross-sectional view of a mesa-shaped vibrator, and FIG. 6C is a diagram showing a vibration displacement energy distribution depending on the shape of a piezoelectric substrate.

[Explanation of symbols]

1. Piezoelectric substrate 2a, 2b Electrode 3a, 3b Lead electrode 4. Metal film for etching L1 Dimension in X-axis direction Dimension in W'Z 'direction H Thickness of substrate L2 X-axis dimension of the convex part t ··· Thickness of the convex part θ ₁ , θ ₂ ··· Elevation angle Q ··· Cutting surface α ··· Elevation angle

Claims (3)

[Claims] 1. A rectangular AT-cut quartz substrate having an X axis in a longitudinal direction, a Z 'axis in a width direction, and a Y' axis in a thickness direction.
A piezoelectric vibrator, wherein a projection having a trapezoidal Y ′ cross-section is formed integrally with the quartz substrate, and an opposing electrode is provided on the upper surface of the projection and on the back surface of the substrate facing the projection. 2. An elevation angle between an inclined surface of the projection and a substrate surface is θ.
1 and θ2, the elevation angles θ1 and θ2 are all 9
A piezoelectric vibrator characterized by being smaller than 0 °. 3. The elevation angles θ1 and θ2 are set to approximately 35, respectively.
A piezoelectric vibrator characterized by {63}.