JP4003302B2 - Piezoelectric vibrator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric vibrator, and more particularly to a piezoelectric vibrator having excellent spurious characteristics.
[0002]
[Prior art]
Conventionally, for example, a crystal resonator as a piezoelectric resonator can control the frequency with high accuracy and high stability by its high Q value.
A typical AT-cut quartz substrate as a crystal resonator has a thickness-shear vibration as a main vibration. Normally, a finite AT-cut quartz substrate has a thickness-shear vibration as a vibration mode that appears when excited. Many other secondary vibration modes occur. The presence of these sub-vibrations (hereinafter referred to as spurious) causes the frequency selectivity and frequency stability of the crystal unit to deteriorate, so suppressing spurious in improving the frequency stability of the crystal unit is not possible. is important.
Conventionally, as shown in FIG. 4, for example, there is a quartz crystal resonator in consideration of spurious suppression.
As shown in the figure, an excitation electrode 102 that also serves as a vibration part is provided at the center of the front and back surfaces of the quartz substrate 101, and the excitation electrode 102 is extended to the end of the quartz substrate 101 by a lead electrode 103. In a crystal unit having a portion fixed to a land pattern 105 provided in a package using a conductive adhesive 104, as a means for suppressing spurious generated near the main vibration mode, other than the main vibration region on the surface of the crystal substrate 101 For example, the absorber 106 is formed by applying, for example, a silicon-based adhesive or the like in the form of dots or lines.
With such a configuration, the vibration energy of the spurious mode generated in the quartz substrate 101 is attenuated by the mass addition of the absorber 106, so that it is possible to obtain a quartz resonator having excellent spurious characteristics.
[0003]
[Problems to be solved by the present invention]
However, the spurious suppression method described with reference to FIG. 4 is effective in suppressing the higher-order mode (hereinafter referred to as inharmonic) of the main vibration among the spurious modes, but the bending is different from the high thickness shear vibration that is the main vibration. A sufficient effect cannot be obtained for suppressing the vibration mode.
Therefore, a crystal oscillator using a crystal resonator in which the main vibration mode and the bending vibration mode are likely to be coupled has a problem that sufficient frequency stability cannot be obtained.
For example, the frequency of the main vibration mode that is the thickness-shear vibration of the crystal resonator changes so as to become a smooth cubic curve with a temperature change, but the flexural vibration mode that is a spurious mode at a certain temperature point When coupled, the frequency may change suddenly, resulting in a frequency jump. As a result, the frequency temperature characteristic of the crystal resonator becomes discontinuous, and there is a problem that sufficient frequency stability cannot be obtained.
For example, it is only necessary to change the conductance value of the temperature compensation circuit so as to cancel the cubic function temperature characteristic of the crystal resonator, and also change the frequency jump due to the bending vibration mode. However, it has been difficult and difficult to change the conductance value rapidly.
Therefore, the crystal resonator that causes the frequency jump has to be discarded, which causes a problem that the yield of the crystal resonator is deteriorated and the cost is not sufficiently reduced.
Also, even if a frequency jump does not occur immediately after manufacturing, it may occur due to secular change, and when a crystal unit that generates such a malfunction is used in a mobile communication device, the communication state is suddenly disconnected. Had a problem.
The present invention has been made in order to solve the above-described problem, and a piezoelectric vibrator that can obtain good frequency-temperature characteristics by suppressing a flexural vibration mode that is easily coupled with the main vibration mode of the vibrator. Provide in.
[0004]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the piezoelectric vibrator according to claim 1 according to the present invention has a thickness-shear mode in which a notch portion is formed substantially at the center of a short side of a rectangular piezoelectric substrate as a main vibration. a is, and set the size of the notch so as to suppress the occurrence of unnecessary vibration mode other than the main vibration upon and adhere the protruding portions located on opposite sides of the notch in the package, the The depth L of the notch is 0 <L ≦ λ / 4 with respect to the wavelength λ of the unnecessary vibration mode .
[0006]
The piezoelectric vibrator according to claim 2, to the billing in addition to the serial mounting of the invention in claim 1, the notch width W0 of the short sides of each said piezoelectric substrate width W of the protruding portions located on both sides It is characterized by W0 / 4 or less.
[0007]
[Embodiments of the Invention]
Hereinafter, the present invention will be described in detail based on illustrated embodiments.
FIG. 1 shows a structural diagram of an embodiment of a quartz substrate 1 according to the present invention.
FIG. 2A shows an external perspective view, and FIG. 2B shows a top view.
As shown in the figure, when the longitudinal direction is X, the AT-cut quartz crystal resonator 1 is a rectangular quartz substrate, and is formed with a notch 2 at substantially the center of both ends in the X direction.
The inventor of the present application performs detailed finite element analysis on the AT-cut quartz crystal having the above-described configuration as described above, and the quartz crystal 1 is located in the central portion of the quartz crystal substrate 1 as shown in FIG. By obtaining the knowledge that the aspect of reflection of the vibration wave in the flexural vibration mode is different at the end of each area when it is divided into A and the area B located on both sides of the area. The inventors have found that it is possible to concentrate the vibration energy of the bending vibration mode in the region B.
That is, as described above, a large number of vibration modes are generated in a piezoelectric substrate such as a quartz substrate, and each of these vibration modes has a different wavelength. Will be different.
Therefore, depending on the difference in wavelength between the main vibration mode and the bending vibration mode which is a spurious mode, the dimension of the depth L of the notch 2 and the width of the protrusions located on both sides of the notch 2 are described. By appropriately setting the dimension of W, the vibration energy of the bending vibration wave can be concentrated in the region B.
Furthermore, the vibration energy in the bending mode can be suppressed by fixing the protrusions located on both sides of the notch 2 as a support to the ceramic container as will be described later.
On the other hand, since the vibration energy of the thickness shear vibration which is the main vibration remains in the region A, it is possible to obtain a desired signal by arranging the excitation electrode in the region A.
[0008]
Hereinafter, the analysis result of the quartz resonator having the configuration shown in FIG. 1 using the finite element method will be described in detail while comparing with the analysis result of the conventional quartz substrate.
FIG. 2 is an analysis result showing a distribution of vibration energy of the bending vibration mode generated in the quartz substrate 1.
FIG. 5 shows the analysis results for the conventional quartz substrate 101 shown in FIG. FIG. 2A and FIG. 5A show displacement diagrams in the bending vibration mode as seen from the Y-axis direction.
FIG. 2B and FIG. 5B show displacement diagrams in the bending vibration mode as seen from the X-axis direction.
In any of the above figures, the propagation of vibration energy is represented by the density of the lines in the figure, indicating that the more dense the lines are drawn, the more concentrated the vibration energy is. Yes.
As for the dimensions of the quartz substrate used for the analysis, the quartz substrate 101 has an X dimension of 400 μm, a Y dimension of 100 μm, and a Z dimension of 400 μm. In addition to the above dimensions, the quartz substrate 1 has bending vibration at the end in the ± Z direction. A protrusion having a length of λ / 8 is provided in the X-axis direction with respect to the mode wavelength λ.
[0009]
As shown in FIG. 2A, it can be seen that the vibration energy of the bending vibration mode distributed on the Z-X plane of the quartz crystal substrate 1 is concentrated and propagated in the regions B located at both ends in the Z-axis direction of the substrate.
Further, as shown in FIG. 2B, the vibration energy distributed in the ZY plane is also concentrated in the region B located at both ends of the substrate, and the displacement amount in the Y-axis direction is large.
On the other hand, as shown in FIG. 5A, in the quartz substrate 101 in which the notch 2 is not provided at the end, the vibration energy of the bending vibration mode is uniformly propagated to the entire Z-X plane. At the same time, as shown in FIG. 5B, the amount of displacement of the substrate in the Y direction occurs uniformly over the entire area.
In other words, from these results, the bending wave propagation mode of the bending vibration mode generated in the quartz substrate 1 is affected and changed by the reflection of the bending wave by the notch 2, and accordingly, the bending vibration in the region B is changed. It is estimated that the vibration energy of the mode is concentrated.
Accordingly, as shown in FIG. 3A or 3B, the conductive adhesive 5 is applied to the stepped portion 4 of the ceramic container 3 with the protruding portions on both sides of the cutout portion 2 of the crystal substrate 1 as supporting portions. By using and fixing, the vibration energy of the bending vibration mode concentrated in the region B is diffused to the container 2 through the adhesive 4, so that the bending vibration mode can be selectively attenuated. is there.
The ceramic container 3 shown in the figure includes a step portion 4 and a land pattern 6 on the surface of the step portion 4, and the quartz substrate 1 has excitation electrodes on the front and back surfaces thereof. 7 and a lead electrode 8 extending from the excitation electrode 7 to the protruding portion.
[0010]
Further, as a result of examining the optimum value of the depth L of the notch 2, it is located on both sides of the notch 2 when L> λ / 4 with respect to the wavelength λ of the bending vibration wave. Since the bending vibration mode exists independently in the regions A and B even if the protruding portion is a support portion, the bending vibration mode is difficult to be suppressed.
Accordingly, it is desirable to select the depth of the notch 2 in the range where the optimum value of L is 0 <L ≦ λ / 4.
Further, regarding the optimum value of the width W of the projecting portion located on both sides of the notch 2, the width in the Z-axis direction of the quartz substrate 1 is W0, and the width is W> W0 / 4. The vibration mode exists in the central part of the region A, and the main vibration mode and the spurious mode cannot be sufficiently separated.
Therefore, it is desirable that the width W of the protrusion is in the range of W ≦ W0 / 4.
Further, in one embodiment, the description has been made using quartz as a piezoelectric substrate, but the present invention is not limited to this, and a piezoelectric vibrator using a piezoelectric substrate made of a piezoelectric material such as lithium niobate or lithium tantalate. Even if it exists, it cannot be overemphasized that the function equivalent to one Example is acquired by using this invention.
[0011]
[Effect of the present invention]
As described above, according to the invention, the notch portion at the end portion of the piezoelectric substrate has a depth λ / 4 or less with respect to the frequency λ of the unnecessary mode vibration wave, and the protruding portions located on both sides thereof. The width W of the notch is set to be equal to or less than W0 / 4 with respect to the width W0 of the end where the notch is provided. Further, when the piezoelectric substrate is fixed to the package, both sides of the notch are provided. By bonding and fixing the projecting part located at the center, it is possible to suppress the generation of unnecessary modes other than the thickness-shear vibration mode, which is the main vibration, so that a piezoelectric vibrator with high frequency stability can be easily obtained. In addition, there is an effect that it is possible to provide a low-cost piezoelectric vibrator accompanying the improvement of the yield of the piezoelectric vibrator due to the above effect.
[Brief description of the drawings]
FIG. 1 is an external structural view of a quartz crystal substrate according to the present invention.
(A) Side surface inclination structure figure of quartz substrate based on this invention is shown.
(B) The top view of the quartz substrate based on this invention is shown.
FIG. 2 is a vibration energy distribution diagram showing an analysis result of a finite element method for a bending vibration mode of a quartz crystal substrate according to the present invention.
(A) The distribution map of the bending vibration energy of the ZX plane of the quartz crystal substrate based on this invention is shown.
(B) The distribution diagram of the bending vibration energy of the ZY plane of the quartz substrate based on this invention, and the figure which shows the displacement amount of a Y direction.
FIG. 3 is a top structural view of a crystal resonator according to the present invention.
(A) A structural view in the case of holding a quartz substrate on one side is shown.
(B) A structural diagram when the Wednesday substrate is held on both sides is shown.
FIG. 4 is a top structural view of a crystal resonator using a conventional spurious mode suppressing method.
FIG. 5 is a vibration energy distribution diagram showing an analysis result of a finite element method with respect to a bending vibration mode of a conventional conventional quartz crystal substrate.
(A) The distribution map of the bending vibration energy of the ZX plane of the conventional quartz substrate is shown.
(B) A distribution diagram of flexural vibration energy on the ZY plane of a conventional quartz substrate and a diagram showing the amount of displacement in the Y direction.
[Explanation of symbols]
1, 101 crystal substrate, 2 notch, 3 ceramic container, 4 steps, 5, 104 conductive adhesive, 6, 105 land pattern, 7, 102 excitation electrode, 8, 103 lead electrode, 106 absorber

Claims (2)

A piezoelectric vibrator whose main vibration is a thickness-slip mode in which a notch is formed in the approximate center of the short side of a rectangular piezoelectric substrate, and the protrusions located on both sides of the notch are bonded and fixed to the package The size of the notch is set so as to suppress the occurrence of unnecessary vibration modes other than the main vibration, and the depth L of the notch is set to 0 <L ≦ with respect to the wavelength λ of the unnecessary vibration mode. A piezoelectric vibrator characterized by having λ / 4 . The notch of the piezoelectric vibrator mounting serial to claim 1, each of the width W of the protruding portion, characterized in that the W0 / 4 or less with respect to the width W0 of the short side of the piezoelectric substrate located on both sides .

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