JP5625432B2 - Piezoelectric vibration element and piezoelectric vibrator - Google Patents

Description

The present invention relates to a piezoelectric vibration element and a piezoelectric vibrator, and in particular, a piezoelectric vibration element in which a plurality of substantially elliptical protrusions are provided on a main surface of a piezoelectric substrate and an excitation electrode is formed thereon, and the piezoelectric vibration element The present invention relates to a piezoelectric vibrator housed in a package.

Piezoelectric vibrators are widely used as reference frequency sources for industrial equipment and consumer equipment because of their small size, small secular change, and easy high-accuracy frequency. In recent years, there has been a demand for further downsizing and higher performance of surface mount piezoelectric vibrators.
Patent Document 1 discloses a piezoelectric vibrator in which a vibrating portion and a supporting portion are integrated using a lithium tantalate X plate and a lithium niobate Z plate, and the cross-sectional shape of the vibrating portion is a bevel shape or a convex shape. Has been. When the longitudinal cross section of the vibrator is formed into a convex shape, the magnitude of the relative displacement at the end in the longitudinal direction is about 1/100 that in the case where the longitudinal cross section is rectangular.
It becomes.
A vibrator having a convex cross-sectional shape can be approximately replaced by changing the cross-sectional shape of the vibrator to a staircase shape. It is disclosed that if the cross-sectional shape of the staircase is a slope, the degree of approximation is further increased and disconnection of the excitation electrode at the stepped portion of the staircase can be prevented.
Patent Document 2 discloses a piezoelectric vibrator using a so-called mesa-type piezoelectric substrate in which convex portions are provided at opposite positions of both main surfaces. The excitation electrode formed on the mesa-type piezoelectric substrate extends to a partial area of the convex part and the flat part surrounding the convex part. It is disclosed that by enlarging the excitation electrode, it is possible to obtain a piezoelectric vibrator having increased strength at the stepped portion of the projection of the excitation electrode without causing a problem even if the electrode is slightly displaced when forming the excitation electrode. ing.

Patent Document 3 discloses a mesa crystal unit. FIG. 13A is a plan view and FIG.
b) is a cross-sectional view at PP, FIG. 10C is a cross-sectional view at Q-Q, and FIGS.
These are figures which show the vibration displacement distribution seen from the longitudinal direction and the transversal direction, respectively. The outer contour in the longitudinal direction (X-axis direction) of the quartz substrate 81 is processed into a semi-elliptical shape at both ends, and the ratio of the major axis / minor axis (major axis / minor axis) of the ellipse is 1.26. Both main surfaces of the quartz substrate 81 are shown in FIGS.
, (C), the central portion 82 is processed into a so-called mesa shape protruding in the thickness direction from the peripheral portion, and the shape of both end portions in the longitudinal direction of the central portion 82 is the outer contour shape of the quartz substrate 81. Similarly, it is processed into a semi-elliptical shape. The ratio of major axis / minor axis (major axis / minor axis) of this ellipse is also 1.26.
Further, the electrodes 82 a and 82 b attached to both surfaces of the central portion 82 are formed in a similar shape to the central portion 82. The vibration displacement distribution of the crystal resonator element configured as described above is shown in FIG.
The solid line 84 in (d) and that in the short direction are distributed as shown by the solid line 85 shown in FIG. In the longitudinal direction of the quartz plate 81, the vibration displacement distributions 94 and 95 in the longitudinal direction and the transverse direction of the rectangular quartz resonator element are distributed as indicated by broken lines in FIGS. 13 (d) and 13 (e). By comparing these, it can be seen that the vibration displacement distribution of the mesa-type crystal resonator element is concentrated in the central portion. That is, the degree of energy confinement becomes deeper, and a part of the vibration energy leaks to the support part or is converted into another contour vibration, so that the amount lost is reduced. Therefore, it is disclosed that a crystal resonator in which the series resonance resistance R1 is improved (Q value is improved) and unnecessary modes are suppressed can be obtained.

Japanese Patent Laid-Open No. 11-355094 JP 2005-94410 A JP 2007-158486 A

However, Patent Document 1 describes lithium tantalate and lithium niobate, but does not describe the convex shape and the vibration characteristics of quartz. Also, neither substrate processing considering the anisotropy of the piezoelectric substrate nor excitation electrode shape is described.
The crystal resonator disclosed in Patent Document 2 discloses that an excitation electrode larger than the mesa portion is formed, but energy confinement is insufficient with only one mesa portion, and a high Q value that satisfies the requirements There may be a problem that a crystal resonator having a low CI value cannot be obtained.
Further, although the crystal resonator disclosed in Patent Document 3 has a larger Q value than the crystal resonator disclosed in Patent Document 2, the yield is too high to satisfy the recently required Q value and spurious. There was a problem of being low.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a piezoelectric vibrator that is downsized, has a high Q value, and has reduced spurious, at low cost.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1] A piezoelectric vibration element according to the present invention is a piezoelectric vibration element using an AT-cut quartz crystal substrate, and includes a rectangular piezoelectric vibration substrate having a vibration region and having a longitudinal direction, and front and back surfaces of the piezoelectric vibration substrate. A first excitation electrode and a second excitation electrode respectively formed in a vibration region on the main surface, and in the vibration region of at least one main surface, the first excitation electrode is positioned at least on the outer diameter side. And a protrusion that is located on the inner diameter side of the first flat portion and protrudes outward in the thickness direction, and the protrusion is in the thickness direction relative to the first flat portion. a second flat portion which protrudes outward, and a third planar portion which protrudes into and thickness outwardly located inside of the second planar portion has a contour of said second planar portion In the plan view, the piezoelectric elements in which the two outer contour lines facing each other in the minor axis direction of the substantially elliptical shape are in corresponding positions, respectively. The piezoelectric vibration element is characterized in that it has a shape missing along the long side of the vibration substrate, and the outer shape of the third planar portion is substantially elliptical in plan view .

Application Example 2] The piezoelectric vibrating element, said piezoelectric vibrating board, the longitudinal direction Ri X-axis direction der, major axis versus the ratio of the shorter diameter of the second and third planar portions each elliptical respectively The piezoelectric vibration element according to Application Example 1, which satisfies a relationship of 1.26 to 1.00.

When a quartz crystal substrate is used as the piezoelectric vibration substrate, it is necessary to consider the anisotropy of the elastic constant of the quartz crystal. The elastic constant changes depending on the cutting angle. In AT-cut quartz substrates, the X direction and Z ′
The propagation constant differs from the direction, and the cross-sectional shape of the vibration displacement distribution is elliptical. Therefore, based on the vibration displacement distribution, a piezoelectric vibrator having a large Q value can be realized by forming a piezoelectric vibration substrate such that an elliptical shape in which a major axis and a minor axis are gradually reduced is laminated. In the case of an AT-cut quartz substrate, the ratio of the major axis to the minor axis of this elliptical shape is 1.26. When a piezoelectric vibrating substrate is constructed using this numerical value, the Q value of the piezoelectric vibrating element increases, and the spurious of the contour system is reduced. There is an effect that it can be reduced.

Application Example 3 In the piezoelectric vibration element, the midpoint of the line segment connecting the two focal points of the third plane portion is located at the center of the vibration region. 2. The piezoelectric vibration element according to 2.

Application Example 4 In the piezoelectric vibration element, the midpoint of the line segment connecting the two focal points of the third plane portion is decentered from the longitudinal center of the piezoelectric vibration substrate. The piezoelectric vibration element according to any one of Examples 1 and 2 .

A center line in the width direction orthogonal to the longitudinal direction of the piezoelectric vibration substrate and a center line in the width direction orthogonal to the longitudinal direction of the vibration region, that is, between the two substantially elliptical focal points that are the outer contour lines of the third plane portion. The piezoelectric vibration substrate is formed so as to be eccentric with respect to the center line in the width direction passing through the midpoint of the line segment connecting the two. When the piezoelectric vibration substrate is formed in this way, the distribution of vibration displacement is symmetric with respect to the center of the vibration region without being affected by the support portion, and the Q value of the piezoelectric vibration element can be increased and higher-order contours can be obtained. There is an effect that the mode can be reduced.

Application Example 5 In the piezoelectric vibration element, the piezoelectric vibration substrate has a support portion formed at least at one end in the longitudinal direction, and the thickness of the support portion is equal to or greater than the thickness of the third plane portion. The piezoelectric vibration element according to any one of Application Examples 1 to 4, wherein the piezoelectric vibration element is provided.

When a piezoelectric vibration element is configured using a piezoelectric vibration substrate having a support portion formed at least at one end in the longitudinal direction of the piezoelectric vibration substrate, the piezoelectric vibration substrate can be obtained by fixing the support portion of the piezoelectric vibration element to the inner bottom portion of the package. Since the influence of the support is not exerted on the vibration region, the Q value can be prevented from deteriorating.
Application Example 6 In the piezoelectric vibration element, when the thickness of the third plane portion is h and the thickness of the support portion is H, the relationship of H / h ≧ 1.1 is satisfied. The piezoelectric vibration element according to Application Example 5 which is characterized.
Application Example 7 In the piezoelectric vibration element, when the thickness of the third plane portion is h and the width of the support portion along the longitudinal direction is w, w / h ≧ 3.0 The piezoelectric vibration element according to Application Example 5 or 6, wherein the piezoelectric vibration element is satisfied.

Application Example 8 In the piezoelectric vibration element according to any one of Application Examples 5 to 7 , wherein the longitudinal depth of the support portion is larger than the thickness of the third plane portion. It is a piezoelectric vibration element of description.

Increasing the depth dimension in the longitudinal direction relative to the thickness dimension of the third plane has the effect that energy confinement becomes complete and a piezoelectric vibration element having a large Q value can be obtained.

Application Example 9 In the piezoelectric vibration element, an excitation electrode is formed across the second plane portion and the third plane portion, and the excitation electrode is rectangular when viewed from above the main surface. The piezoelectric vibration element according to any one of Application Examples 1 to 8, wherein

Considering the capacitance ratio, the electrode shape along the vibration displacement distribution is desirable, but the CI of the piezoelectric vibration element
When the value is made smaller, there is an effect that a small CI value can be obtained by using a rectangular electrode as large as possible.

[Application Example 10] A piezoelectric vibrator according to the present invention is the first planar portion, the second planar portion, and the third planar portion of the piezoelectric vibration element according to any one of Application Examples 1 to 9. Is accommodated in a state of facing the inner bottom surface of the package having a side wall on the peripheral edge of the substrate.

When a piezoelectric vibrator including the piezoelectric vibration element according to any one of Application Examples 1 to 8 and a package is configured, a piezoelectric vibrator having a large Q value and a reduced high-order contour mode can be obtained. There is an effect.

It is the schematic which showed the structure of the piezoelectric vibration element which concerns on this invention, (a) is a top view, (b) is sectional drawing. It is the figure which showed the structure of the piezoelectric vibration element of 2nd Example, (a) is a top view, (b) is sectional drawing. Cross-sectional view of the piezoelectric vibration substrate and dimensions of the main part. It is the figure which showed the displacement of a longitudinal direction (X-axis direction) and the displacement of a thickness direction (Y'-axis direction), (a) is 0.85, (b) is 1. 0, simulation results with support thickness fixed at 0.2 mm. It is the figure which showed the displacement of a longitudinal direction (X-axis direction) and the displacement of a thickness direction (Y'-axis direction), (a) is 1.16, (b) is 1. 47, Simulation results with support thickness fixed at 0.2 mm. The figure which showed the displacement component sum of the Y'-axis direction with respect to thickness ratio H / h. It is the figure which showed the displacement of a longitudinal direction (X-axis direction) and the displacement of a thickness direction (Y'-axis direction), (a) is 0.77, (b) is thickness / width ratio w / h. Simulation results with 1.55, (c) fixed at 1.93, and thickness ratio H / h fixed at 1.1. The figure shows the displacement in the longitudinal direction (X-axis direction) and the displacement in the thickness direction (Y′-axis direction). The thickness-to-width ratio w / h is 3.86, and the thickness ratio H / h is 1. Simulation result fixed at 1. The figure which showed the displacement component per unit of the Y'-axis direction with respect to thickness to width ratio w / h. It is the figure which showed the structure of the piezoelectric vibration element of 3rd Example, (a) is a top view, (b) is sectional drawing. It is the figure which showed the structure of the piezoelectric vibration element of a 4th Example, (a) is a top view, (b) is sectional drawing. Sectional drawing which showed the structure of the piezoelectric vibrator of this invention. It is the figure which showed the structure of the conventional quartz-crystal vibration element, (a) is a top view, (b), (c) is sectional drawing, (d), (e) is a figure which shows displacement distribution.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a configuration of a piezoelectric vibration element 1 according to an embodiment of the present invention. FIG. 1 (a) is a plan view and FIG. 1 (b).
These are sectional views in QQ. The piezoelectric vibration element 1 is an energy confinement type piezoelectric vibration element that vibrates in thickness, and has a rectangular piezoelectric vibration substrate (hereinafter referred to as a piezoelectric substrate) 5 having a vibration region, and on both front and back main surfaces of the piezoelectric substrate 5. The first excitation electrode 11a formed in each vibration region
And a second excitation electrode 11b.
At least one main surface of the piezoelectric substrate 5 is provided with at least a first flat portion 5a located near both ends in the longitudinal direction of the piezoelectric substrate 5, and an inner side (vibration region) of the piezoelectric substrate 5 with respect to the first flat portion 5a. And a step-like protrusion 5A protruding outward so as to increase in thickness toward the center of the vibration region.
The protrusion 5A is located on the inner side (near the center of the vibration region) of the piezoelectric substrate 5 than the first flat portion 5a, protrudes in the thickness direction from the first flat portion 5a, and extends in the longitudinal direction of the piezoelectric substrate 5. A substantially elliptical second plane part 5b having a major axis extending in the direction, and the inside of the piezoelectric substrate 5 from the second plane part 5b (
A third plane portion 5c having a substantially elliptical shape located in the center of the vibration region and projecting in the thickness direction from the second plane portion 5b and extending in the longitudinal direction of the piezoelectric substrate 5; Have. In other words, if the protrusion 5A is described in a state where the integrated structure is disassembled, the first protrusion 5A-1 having a substantially elliptical shape (substantially elliptic cylinder shape) having the second flat surface part 5b will be described. In the center of the upper surface, a step shape is formed such that the second protrusion 5A-2 having the upper surface of the third flat surface portion 5c having a substantially elliptic shape (substantially elliptic column shape) is laminated. Note that the substantially elliptical columnar shape is different from an ideal elliptical shape due to an error due to processing accuracy that occurs when the piezoelectric substrate 5 is formed and the characteristics of the material of the piezoelectric substrate 5 such as anisotropic characteristics of the etching amount. Including those with a shape that collapsed on the side.

The outer shapes of the second flat surface portion 5b and the third flat surface portion 5c have at least a part of an elliptical contour line, respectively, and the midpoints of the line segments connecting the respective focal points are respectively in the center of the vibration region. positioned. In the example of the piezoelectric vibration element 1 shown in FIG. 1, a shape in which the first flat surface portion 5 a and the protrusion 5 A are formed on the front and back main surfaces of the piezoelectric substrate 5 is shown. The front and back surfaces are formed substantially symmetrically with respect to the line. It should be noted that the target substantially ignores an error due to processing accuracy that occurs when the piezoelectric substrate 5 is formed, and an asymmetric shape caused by the influence of, for example, an anisotropic characteristic of the etching amount as a material characteristic of the piezoelectric substrate 5. It means that it is a target.
The piezoelectric substrate 5 includes a midpoint of the substantially elliptical outline of the second plane portion 5b (the center of a line segment connecting the two focal points) and a midpoint of the substantially elliptical outline of the third plane portion 5c. Are formed to match. Here, the substantially elliptical outer shape includes an elliptical shape or a shape in which at least a part of the elliptical shape is missing.

In the example shown in FIG. 1, the outline of the outer shape of the third plane part 5 c has an elliptical shape, but the outline of the outline of the second plane part 5 b has an outline in the minor axis direction of the elliptical shape. Some are missing. In other words, the outer shape of the second flat portion 5 b is such that a part of the circumference of the circumference of the ellipse shape (elliptical column shape) from the long side of the piezoelectric substrate 5 is located in the extending direction of the short axis along the longitudinal direction of the piezoelectric substrate 5. In the case of FIG. 1, the side of the linearly cut portion coincides with the long side of the piezoelectric substrate 5. In addition, the contour of the outer shape of the third plane portion 5c is
For example, as in the case of the first flat portion 5b, an oval-shaped portion with a part missing in the major axis direction (major axis direction) is also included in the present invention.
Further, a support portion 8 is integrally formed at one end portion of the piezoelectric substrate 5 in the longitudinal direction, and the thickness t of the support portion 8, that is, the thickness orthogonal to the longitudinal direction of the piezoelectric substrate 5 is piezoelectric. Central portion of the vibration region of the substrate 5 (thickness with the second flat surface portion 5c on the front surface and the second flat surface portion 5c on the back surface in FIG. 1B)
It is more than the thickness.
Further, the center line C ₁ of the vibration region in the width direction orthogonal to the longitudinal direction of the piezoelectric substrate 5 is separated from the support portion 8 with respect to the center line C ₀ of the piezoelectric substrate 5 in the width direction orthogonal to the longitudinal direction of the piezoelectric substrate 5. It is eccentric by α in the direction away from it.

On the front and back main surfaces of the piezoelectric substrate 5, a first excitation electrode 11a and a second excitation electrode 11b are respectively provided.
And are formed. The first excitation electrode 11a and the second excitation electrode 11b are both elliptical and face each other. The midpoint between the respective focal points of the elliptical first and second excitation electrodes 11a and 11b substantially coincides with the midpoint of the third plane portion 5c having a substantially elliptical shape, and the first
In addition, the first and second excitation electrodes 11a are arranged so that the extending direction of the major axis (major axis) of the second excitation electrodes 11a and 11b coincides with the extending direction of the major axis (major axis) of the third plane portion 5c. 11b, and in the case of FIG. 1, the contour shape of the third plane portion 5c and the first and second excitation electrodes 11a, 11 are formed.
The outline shape of b is almost similar.
The first and second excitation electrodes 11a and 11b are directed toward the support portion 8 of the piezoelectric substrate 5, respectively, and the extraction electrodes 11c are insulated from each other on the surfaces of the second plane portion 5b and the first plane portion 5a. , 11
d extends.
As electrode materials used for the first and second excitation electrodes 11a and 11b and the extraction electrodes 11c and 11d, chromium Cr + gold Au, nickel Ni + gold Au, or the like having a predetermined thickness is used.

In the case of thickness vibration, the frequency of the main vibration depends on the thickness of the piezoelectric substrate 5 (thickness between the third planar portions 5c), and does not depend on the longitudinal and lateral dimensions of the piezoelectric substrate 5. The dimensions in the longitudinal direction and the short direction are related to higher-order contours (width slip, etc.) that occur in the vicinity of the main vibration, so that the contour dimensions (long) prevent these contour vibrations from coupling with the main vibration in the operating temperature range. Width).
The stepwise mesa structure in the thickness direction of the piezoelectric substrate 5 confines the vibration energy of the main vibration to the center of the vibration region on the substrate, and leaks vibration energy to the substrate end and leaked thickness vibration. This is because it is converted to another mode to reduce the occurrence of spurious.
The cross-sectional shapes exhibited by the first flat surface portion 5a, the second flat surface portion 5b, and the third flat surface portion 5c shown in FIG. 1B are based on the desired frequency and the dimensions of the piezoelectric substrate 5, using the finite element method. The plane shape and cross-sectional shape which avoids a high-order contour vibration are determined by simulating.
An example in which an AT-cut quartz substrate is used as the piezoelectric substrate will be described. As is well known, an AT-cut quartz substrate is obtained by rotating a quartz plate (Y plate) perpendicular to the crystal axis Y (mechanical axis) about 35 degrees 15 minutes around the crystal axis X (electric axis). It is. The longitudinal direction of the rectangular AT-cut quartz substrate is the X axis, the short direction is the Z ′ axis, and the thickness direction is the Y ′ axis. 2nd plane part 5b shown in FIG.
, And the ratio of the major axis to minor axis (major axis to minor axis) of the substantially elliptical shape formed by the respective outer contours of the third plane part 5c is about 1.26.

The reason why the ratio of the major axis to the minor axis (major axis to minor axis) is 1.26 will be described. In the vibration equation of the energy confinement theory, when the propagation constants of the electrodeless portion and the electrode portion used in the equation representing the vibration displacement u are k and ke, respectively, k and ke can be represented by the following equations.
k = μ (mπ / h) (1− (f / (mfs)) ² ) ^1/2 (1)
ke = μ (mπ / h) ((f / (mfe)) ² −1) ^1/2 (2)
Here, the constant μ is a value determined from the elastic constant and the cutting angle, m is the harmonic order, h is the thickness of the quartz substrate, fs is the cutoff frequency of the electrodeless portion, and fe is the frequency of the electrode portion.
Since quartz is a crystal belonging to the trigonal system, it has anisotropy, and its elastic constant varies depending on the crystal axis direction. In the case of an AT-cut quartz plate, the elastic constant of the wave propagating in the X-axis direction is different from the elastic constant of the wave propagating in the Z′-axis direction. For this reason, the propagation constants k and ke
The constant μ used in the above is also μx for X-axis propagation and μz for Z′-axis propagation, and μx / μ
The ratio of z is about 1.26. For this reason, the vibration displacement distribution of the AT-cut quartz resonator differs in the X-axis direction and the Z′-axis direction in the spread of the displacement distribution, and the cross-sectional shape in the direction parallel to the quartz substrate is
The shape is elliptical with the major axis (major axis) in the X axis direction and the minor axis (minor axis) in the Z ′ axis direction, and the ratio μx / μz of the major axis / minor axis is about 1.26.

FIG. 1 shows an example of the piezoelectric vibration element 1 using the mesa-type piezoelectric substrate 5 having a two-stage structure including the first to third plane portions 5a, 5b, and 5c, but has more plane portions. It is desirable to use a multi-stage mesa structure piezoelectric substrate. However, when the shape dimension (length × width) of the piezoelectric substrate 5 is reduced to, for example, 1 mm × 0.6 mm, it becomes difficult to manufacture a multi-stage mesa piezoelectric substrate. Therefore, the number of stages that satisfies electrical characteristics such as a required Q value (CI value) and suppresses spurious near the main vibration to a standard value or less is selected.
In addition, the envelope connecting the corners of the first to third plane portions 5a, 5b, and 5c in the longitudinal direction of the piezoelectric substrate 5 may be designed by analogy from a proven convex-shaped piezoelectric substrate. However, it may be calculated using a finite element method. The same applies to the multistage mesa piezoelectric substrate.
In order to increase the thickness of the support portion, a thick film made of a material instead of quartz may be used.

2A and 2B are schematic views illustrating the configuration of the piezoelectric vibration element 2 according to the second embodiment, where FIG. 2A is a plan view and FIG. 2B is a cross-sectional view taken along the line QQ. 1 differs from the piezoelectric vibration element 1 shown in FIG. 1 in that groove portions 9 are provided on the front and back surfaces of the support portion 8 of the piezoelectric substrate 5, and excitation electrodes 11a,
That is, the shape of 11b is a rectangular shape and is extended not only to the third plane portion 5c but also to a part of the second plane portion 5b. If the piezoelectric vibration element 2 is not necessary, the groove 9 may be omitted.
The grooves 9 are provided on the front and back surfaces of the support portion 8, respectively, because the conductive adhesive is used to bond and fix the support portion 8 to the bottom of the package. This is to alleviate the distortion of the substrate 5 and to suppress the vibration region during application of the conductive adhesive or the spread to the other extraction electrode by the groove 9.
The reason why the excitation electrodes 11a and 11b are made larger than that of the piezoelectric vibration element 1 in FIG. 1 is that the CI value (equivalent resistance value) is reduced and it is easier to oscillate when used in an oscillator (the negative resistance value of the oscillation circuit is smaller). Because it was good).

As shown in FIG. 3, the dimensions of the main part of the piezoelectric vibration substrate 5 shown in FIGS.
The thickness of the central portion of the vibration region is h, the thickness of the support portion 8 is H, the width of the support portion 8 in the longitudinal direction of the piezoelectric vibration substrate 5 is w, and the upper or lower surface of the support portion 8 (the upper or lower surface of the groove portion 9). And the difference thickness between the upper surface or the lower surface of the longitudinal end portion of the piezoelectric vibration substrate 5 is defined as d. The ratio w / L of the width w of the support portion 8 to the length L in the longitudinal direction of the piezoelectric vibration substrate 5 is 0.2, and the ratio of the thickness H of the support portion 8 to the thickness h of the central portion of the vibration region (hereinafter referred to as The thickness displacement (referred to as the thickness ratio) is changed, and the vibration displacement in the longitudinal direction (X-axis direction) of the thickness-shear vibration excited by the piezoelectric substrate 5 and the vibration displacement in the thickness direction (Y′-axis direction) Are simulated using the finite element method.
FIG. 4A shows the vibration displacement excited by the piezoelectric vibration substrate 5 when the difference thickness d is zero, that is, when the thickness of the longitudinal end portion of the piezoelectric vibration substrate 5 is equal to the thickness H of the support portion 8. In the longitudinal direction (X
The displacement in the axial direction) and the displacement in the thickness direction (Y′-axis direction) are normalized positions of the piezoelectric vibration substrate 5 (the position of one end in the longitudinal direction of the piezoelectric vibration substrate 5 is 0, the other The edge position is 1)
Against. High-order bending vibration is superimposed on the displacement distribution in the longitudinal direction (X-axis direction), and the displacement in the thickness direction (Y′-axis direction) is also large.
FIG. 4B shows the displacement distribution in the longitudinal direction (X-axis direction) and the displacement distribution in the thickness direction (Y′-axis direction) when the thickness ratio H / h is 1.0. FIG. By increasing the thickness ratio H / h of the support portion 8, the amplitude of the higher-order contour vibration superimposed on the displacement distribution in the longitudinal direction (X-axis direction) becomes smaller than the amplitude shown in FIG. Thickness direction (Y 'axis direction)
It has been found that the amplitude of the vibration displacement is smaller than the amplitude of FIG.

FIG. 5A shows the displacement distribution in the longitudinal direction (X-axis direction) and the displacement distribution in the thickness direction (Y′-axis direction) when the thickness ratio H / h is 1.16. FIG. By further increasing the thickness ratio H / h of the support portion 8 of the support portion 8, the amplitude of the higher-order contour vibration superimposed on the displacement distribution in the longitudinal direction (X-axis direction) is the amplitude shown in FIG. It is getting smaller. The thickness direction (Y
It has been found that the amplitude of the vibration displacement in the “axial direction” is also smaller than the amplitude of FIG.
FIG. 5B shows the displacement distribution in the longitudinal direction (X-axis direction) and the displacement distribution in the thickness direction (Y′-axis direction) when the thickness ratio H / h is 1.47. FIG. Thickness ratio H / h of support 8
Is further increased, the amplitude of the higher-order contour vibration superimposed on the displacement distribution in the longitudinal direction (X-axis direction) is larger than the amplitude shown in FIG. Further, it was found that the amplitude of the vibration displacement in the thickness direction (Y′-axis direction) is also larger than the amplitude of FIG.
FIG. 6 shows the Y′-axis direction displacement component with respect to the change of the thickness ratio H / h, where the thickness ratio H / h is the horizontal axis and the thickness direction (Y′-axis direction) displacement component is the vertical axis. FIG. From this figure, the thickness ratio H
By setting / h to 1.1 or more, the Y′-axis direction displacement component can be kept small.
It is possible to form the thickness ratio H / h of the piezoelectric substrate 5 to 1.1 or more by etching using a photolithography technique, but it takes time and steps for etching. Therefore, the piezoelectric substrate 5 having a thickness ratio H / h of 1.0 is manufactured, and a metal having a specific gravity greater than the specific gravity (2.65) of quartz, for example, gold (specific gravity) is formed on the upper and lower surfaces of the support portion 8 of the piezoelectric substrate 5. 19.3) or the like is formed into a thin film by means of vapor deposition or the like, so that the equivalent thickness ratio H / h of the piezoelectric substrate 5 of 1.1 or more is obtained.
Can be realized.

Next, the ratio of the width w in the longitudinal direction (X-axis direction) of the support portion 8 to the thickness h at the center of the vibration region (hereinafter referred to as the thickness to width ratio) w / h is changed to change the piezoelectric substrate 5. The vibration displacement in the longitudinal direction (X-axis direction) and the vibration displacement in the thickness direction (Y′-axis direction) were simulated using the finite element method.
FIG. 7A shows the vibration displacement distribution in the longitudinal direction (X-axis direction) of the piezoelectric substrate 5 and the thickness direction (Y′-axis direction) when the thickness-to-width ratio w / h is 0.77. It is a figure which shows a vibration displacement part. When the thickness-to-width ratio w / h of the support portion 8 is small, the amplitude of higher-order contour vibration superimposed on the displacement distribution in the longitudinal direction (X-axis direction) is considerably large, and in the thickness direction (Y′-axis direction). It can be seen that the amplitude of the higher-order contour vibration superimposed on the vibration displacement distribution is also large.
FIG. 7B shows the vibration displacement distribution in the longitudinal direction (X-axis direction) of the piezoelectric substrate 5 and the thickness direction (Y′-axis direction) when the thickness-to-width ratio w / h is 1.55. It is a figure which shows a vibration displacement part. When the thickness / width ratio w / h of the support portion 8 is increased, the amplitude of the higher-order contour vibration superimposed on the displacement distribution in the longitudinal direction (X-axis direction) is smaller than that of FIG. Still big. Further, it can be seen that the amplitude of the higher-order contour vibration superimposed on the vibration displacement distribution in the thickness direction (Y′-axis direction) is smaller than that of FIG.
FIG. 7C shows the vibration displacement distribution in the longitudinal direction (X-axis direction) of the piezoelectric substrate 5 and the thickness direction (Y′-axis direction) when the thickness-to-width ratio w / h is 1.99. It is a figure which shows a vibration displacement part. When the thickness / width ratio w / h of the support 8 is further increased, the amplitude of the higher-order contour vibration superimposed on the displacement distribution in the longitudinal direction (X-axis direction) is considerably smaller than that of FIG. . In the thickness direction (
It can be seen that the amplitude of the higher-order contour vibration superimposed on the vibration displacement distribution in the Y′-axis direction) is considerably smaller than that of FIG.

FIG. 8 shows the longitudinal direction (X-axis direction) of the piezoelectric substrate 5 when the thickness to width ratio w / h is 3.86.
It is a figure which shows vibration displacement distribution of this, and the vibration displacement part of thickness direction (Y'-axis direction). When the thickness / width ratio w / h of the support 8 is further increased, the amplitude of the higher-order contour vibration superimposed on the displacement distribution in the longitudinal direction (X-axis direction) becomes larger than that of FIG. It can be seen that the amplitude of the higher-order contour vibration superimposed on the vibration displacement distribution in the thickness direction (Y′-axis direction) is larger than that in FIG.
FIG. 9 shows the change of the thickness-to-width ratio w / h when the thickness-to-width ratio w / h is on the horizontal axis and the displacement component per unit in the thickness direction (Y′-axis direction) is on the vertical axis. It is a figure which shows the displacement component per unit of the Y'-axis direction with respect to. From this figure, by setting the thickness to width ratio w / h in the vicinity of 1.9, it is possible to suppress the influence of higher-order contour vibration, but there is little margin in the thickness to width ratio w / h. . If the thickness-to-width ratio w / h is 3.0 or more, the influence of higher-order contour vibration can be suppressed, and the vibration displacement component in the thickness direction (Y′-axis direction) can be reduced.
FIG. 10 is a schematic diagram showing the configuration of the piezoelectric vibration element 3 according to the third embodiment.
Is a plan view, and FIG. 4B is a cross-sectional view taken along the line Q-Q. A difference from the piezoelectric vibration elements 1 and 2 shown in FIGS. 1 and 2 is a cross-sectional shape of the piezoelectric substrate 5. That is, the second and third plane portions 5
The points b and 5c are formed only on one main surface of the piezoelectric substrate 5. As with the conventional plano-convex piezoelectric substrate, the cutting angle is maintained as it is, so it is suitable for a piezoelectric vibration element that emphasizes temperature characteristics.

FIG. 11 is a schematic diagram showing the configuration of the piezoelectric vibration element 3 according to the fourth embodiment.
Is a plan view, and FIG. 4B is a cross-sectional view taken along the line Q-Q. The difference from the piezoelectric vibration elements 1 and 2 shown in FIGS. 1 and 2 is that support portions 8 a and 8 b are integrally formed at both ends in the longitudinal direction of the piezoelectric substrate 5. In the example shown in FIG. 4, an example of a double-supported structure in which the extraction electrode 11 c extends to the support portion 8 a and the extraction electrode 11 d extends to the support portion 8 b is shown, but only one of the support portions 8 a and 8 b is shown. A cantilever structure in which the extraction electrode is extended may be used.
A feature of the piezoelectric substrate 5 shown in FIG. 11 is that the substrate is symmetrical with respect to the longitudinal direction of the piezoelectric substrate 5 and is also symmetrical with respect to the thickness direction. By forming the piezoelectric substrate 5 in a symmetrical structure, generation of unnecessary vibration can be suppressed. Further, by adopting a structure in which the support portions 8a and 8b thicker than the vibration region are provided at the end of the piezoelectric substrate 5, it is possible to reduce the vibration in the inharmonic mode (non-harmonic high-order mode) and the high-order contour vibration mode. it can. This has been demonstrated with a high-frequency vibrator in which the central portion of the AT-cut quartz substrate is thinned by etching and a thick annular surrounding portion is formed on the periphery.
In addition, by attaching heavy metal to the upper and lower surfaces of the support portions 8a and 8b and lowering the cutoff frequency of the support portions 8a and 8b, it is possible to reduce high-order contour vibration and spurious due to the inharmonic mode. It becomes.

The example of the method for manufacturing the piezoelectric substrate 5 shown in FIGS. 1, 2, 10 and 11 can be easily manufactured by processing a wafer (large piezoelectric substrate) by applying a photolithography technique and an etching technique. In this case, the thickness of the central portion of the vibration region is equal to the thickness of the support portions 8a and 8b. However, the thickness of the support portion 8 is equivalently increased by the above-described means, and the thickness ratio of the thickness ratio is increased. H /
It is possible to set h to 1.1 or more.
Although an example of a quartz substrate has been shown, it goes without saying that the present invention can be applied to other piezoelectric substrates such as langasite, lithium tantalate, lithium niobate, and the like. However, since the vibration displacement distribution varies depending on the elastic constant, it is necessary to determine the ratio of the major axis to the minor axis of the elliptical shape according to the elastic constant of the piezoelectric substrate to be used.
Although the example which processes the piezoelectric substrate 5 and forms the 1st thru | or 3rd plane parts 5a, 5b, 5c was demonstrated, the 1st thru | or 3rd plane parts 5a, 5b, 5c are other than a plate-shaped piezoelectric substrate. Materials such as Cr
, Ni, gold and other metals may be used.

The piezoelectric vibration substrate 5 is provided with first to third plane portions 5a, 5b, and 5c, and the outline shape of the second and third plane portions 5b and 5c is substantially elliptical. Is configured so as to substantially coincide with the center of the vibration region of the piezoelectric substrate 5. As a result, the vibration displacement becomes a distribution near the center of the vibration region, and the vibration displacement becomes extremely small at the periphery of the piezoelectric substrate 5,
As the Q value of the piezoelectric vibration element is increased, vibration energy converted into higher order contour vibration at the end of the piezoelectric substrate 5 is reduced, and the occurrence of higher order contour vibration is reduced.
When a quartz substrate is used as the piezoelectric substrate 5, it is necessary to consider the anisotropy of the elastic constant of the quartz crystal. The elastic constant changes depending on the cutting angle. In the AT-cut quartz substrate, the propagation constants in the X direction and the Z ′ direction are different, and the cross-sectional shape of the vibration displacement distribution is an elliptical shape. Therefore, based on the vibration displacement distribution, a large Q value can be realized by forming the piezoelectric vibration substrate so that the elliptical shape in which the major axis and the minor axis are gradually reduced is laminated. In the case of an AT-cut quartz substrate, the ratio of the major axis to the minor axis of this elliptical shape is 1.26, and this value is used to calculate the piezoelectric substrate 5
If this is configured, the Q value of the piezoelectric vibration element is increased, and there is an effect that the spurious of the contour system can be reduced.

The shape of the piezoelectric substrate 5 in plan view from the main surface is formed by stacking elliptical shapes in which the major axis and minor axis of the elliptical shape are gradually reduced, and the midpoint of the line segment connecting the respective focal points, and the center of the vibration region It is desirable to configure so as to match. However, the planar shape of the piezoelectric substrate 5 is, for example, 1.0 m.
When it becomes small as m × 0.6 mm, it is difficult to form the contour shape of the second plane part into a perfect ellipse shape, and a part of two opposing contour lines in the minor axis direction is missing. Thus, there is an effect that it is possible to realize a piezoelectric vibration element having a large Q value even with the piezoelectric substrate 5 from which a part of the outline is missing.
When the planar shape of the piezoelectric substrate 5 is further reduced, a part of the outer contour line that opposes the minor axis direction of the third planar portion may be lost. When a piezoelectric vibration element is configured using such a piezoelectric substrate 5, a larger Q value can be obtained as compared with the Q value of a piezoelectric vibration element configured using a conventional flat piezoelectric substrate 5. There is.

The center line C ₀ in the width direction orthogonal to the longitudinal direction of the piezoelectric substrate 5 and the center line C _{1 in} the width direction of the vibration region orthogonal to the longitudinal direction, that is, a substantially elliptical shape that is the outline of the third plane portion. The piezoelectric substrate 5 is formed so as to be eccentric with the center line in the width direction passing through the midpoint of the line segment connecting the two focal points.
When formed in this way, the distribution of vibration displacement is symmetric with respect to the center of the vibration region without being affected by the support portion, so that the Q value of the piezoelectric vibration element can be increased and the high-order contour mode can be reduced. There is an effect that becomes possible.
When a piezoelectric vibration element is configured using the piezoelectric substrate 5 having a support portion formed at least at one end in the longitudinal direction of the piezoelectric substrate 5, the vibration region of the piezoelectric substrate 5 is fixed when the piezoelectric vibration element is fixed to the inner bottom portion of the package. Therefore, the Q value can be prevented from deteriorating.
Considering the capacitance ratio, the electrode shape along the vibration displacement distribution is desirable, but the CI of the piezoelectric vibration element
In order to make the value smaller, it is desirable to form electrodes not only on the third plane part 5c but also on the second plane part 5b. For example, by using as large a rectangular electrode shape as possible, a small CI value can be obtained. There is an effect that can be obtained.

FIG. 5 is a cross-sectional view showing an embodiment of the piezoelectric vibrator 15 according to the present invention, and the piezoelectric vibrator 15 includes any one of the above-described piezoelectric vibration elements 1 to 4 and a package. The package includes a package body 20 and a lid member 21 made of metal or glass. The package body 20 is formed by stacking, for example, green sheets, a space is provided inside, and external terminals 22 for connection are formed on the outer bottom surface of the package body 20. The pad electrode formed on the bottom surface inside the package body 20 and the external terminal 22 are electrically connected by an internal conductor.
A conductive adhesive is applied to the pad electrode formed on the bottom surface inside the package body 20, the piezoelectric vibration element 1 is placed thereon, and the conductive adhesive is cured, and then the inside of the package body 20 is inert gas. Then, the lid member 21 is hermetically sealed. Instead of filling the inert gas, the inside may be vacuum-sealed. Alternatively, the internal pad electrode of the package body and the piezoelectric vibration element 1 may be bonded using gold bumps or the like instead of the conductive adhesive.
When a piezoelectric vibrator including the above-described piezoelectric vibration element and a package is configured, there is an effect that a piezoelectric vibrator having a large Q value and a reduced high-order contour mode can be obtained.

1, 2, 3, 4... Piezoelectric vibration element, 5... Piezoelectric vibration substrate, 5a... First plane portion, 5b... Second plane portion, 5c ... Third plane portion, 8, 8a, 8b. , 9 ... Groove, 11a ... First excitation electrode, 11b ... Second excitation electrode, 11c, 11d ... Extraction electrode, 15 ... Piezoelectric vibrator, 20 package body, 21 lid member, 22 external terminal, 23 internal conductor, t: thickness of the support portion, C0: center line of the piezoelectric substrate, C1: center line of the vibration region, L: length in the longitudinal direction of the piezoelectric substrate, h: thickness of the center portion of the vibration region, H: support portion Thickness, w ... width of support

Claims (10)

A piezoelectric vibration element using an AT-cut quartz substrate,
A rectangular piezoelectric vibration substrate having a vibration region and having a longitudinal direction;
A first excitation electrode formed in a vibration region on the front and back main surfaces of the piezoelectric vibration substrate, respectively, and a second excitation electrode,
In the vibration region of at least one main surface, at least a first flat portion located on the outer diameter side, and a protrusion located on the inner diameter side of the first flat portion and projecting outward in the thickness direction Have
The protrusion includes a second flat surface portion protruding outward in the thickness direction from the first flat surface portion, and a third flat surface located inside the second flat surface portion and protruding outward in the thickness direction. And
The outer shape of the second planar portion is a shape that is missing along the long side of the piezoelectric vibration substrate in which the two outer contour lines facing each other in the minor axis direction in an elliptical shape correspond to each other in plan view. Yes,
The piezoelectric vibration element according to claim 3, wherein an outer shape of the third plane portion is substantially elliptical in plan view. In the piezoelectric vibration substrate, the longitudinal direction is the X-axis direction,
2. The piezoelectric vibration element according to claim 1, wherein a ratio of a major axis to a minor axis of the second and third plane portions each having an elliptical shape satisfies a relationship of 1.26 to 1.00, respectively.   3. The piezoelectric vibration element according to claim 1, wherein a midpoint of a line segment connecting the two focal points of the third plane portion is located at the center of the vibration region.   3. The piezoelectric vibration element according to claim 1, wherein a midpoint of a line segment connecting the two focal points of the third plane portion is eccentric from a center in a longitudinal direction of the piezoelectric vibration substrate. 5. The piezoelectric vibration substrate has a support portion formed at least at one end in the longitudinal direction, and the thickness of the support portion is equal to or greater than the thickness of the third plane portion. The piezoelectric vibration element according to any one of the above.   6. The piezoelectric vibration according to claim 5, wherein a relationship of H / h ≧ 1.1 is satisfied, where h is a thickness of the third plane portion and H is a thickness of the support portion. element.   6. The relationship of w / h ≧ 3.0 is satisfied, where h is a thickness of the third plane portion and w is a width along the longitudinal direction of the support portion. Or the piezoelectric vibration element of 6.   8. The piezoelectric vibration element according to claim 5, wherein a depth of the support portion in a longitudinal direction is larger than a thickness of the third plane portion.   The excitation electrode is formed across the second plane part and the third plane part, and the excitation electrode is rectangular when viewed from above the main surface. The piezoelectric vibration element according to claim 1.   The internal bottom surface of the package in which the first plane portion, the second plane portion, and the third plane portion of the piezoelectric vibration element according to any one of claims 1 to 9 have side walls on the periphery of the substrate. A piezoelectric vibrator characterized in that the piezoelectric vibrator is housed in a state of facing to each other.

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