JP4784699B2 - AT cut crystal unit - Google Patents

Description

  The present invention relates to a piezoelectric vibrator, and more particularly to a piezoelectric vibrator that suppresses a thickness bending vibration mode coupled to thickness shear vibration.

Piezoelectric vibrators, for example, AT-cut quartz crystal vibrators, are widely used from communication devices to electronic devices because they are small in size and can easily obtain highly accurate and highly stable frequencies.
FIG. 4 is a perspective view showing a configuration of a conventional surface-mount type crystal resonator (SMD crystal resonator), and electrodes 12a facing both main surfaces of an AT-cut crystal substrate 11 cut out from a crystal crystal in a strip shape. , 12b are attached, and the lead electrodes 13a, 13b are extended from the electrodes 12a, 12b toward the end of the substrate 11 to form the crystal resonator element S. Next, the crystal resonator element S is accommodated in a ceramic package (not shown), and the lead electrodes 13a and 13b are conductively fixed to the terminal electrodes provided in the step portions inside the package using a conductive adhesive or the like. Further, the quartz crystal unit is put in a vacuum apparatus, finely adjusted to a desired frequency using means such as vapor deposition, and then the metal lid is resistance-welded to constitute the quartz crystal unit.

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

  For example, as means for avoiding coupling with outline vibration, a quartz crystal resonator in which the principal surface of a piezoelectric substrate is processed as shown in FIGS. 5A, 5B, and 5C is devised and used. I came. That is, FIG. 5A shows 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 shows a so-called convex vibrator (plano convex vibrator) in which the main surface is processed into a lens shape, and FIG. 5C shows a vibrator (mesa shape) in which a part of the main surface is processed into a convex shape. Vibrator). In either case, the vibration energy of the thickness shear vibration is concentrated at the center of the substrate and acts to weaken the coupling with the contour system vibration.

FIG. 6C shows the difference in vibration displacement distribution between the flat strip-like vibrator shown in FIG. 6A and the mesa-like vibrator shown in FIG. 6B by simulation using the finite element method. It is. That, 4800Myuemu a longitudinal dimension X ₀ of the substrate, 780 nm dimensions Z ₀ in the width direction, and a thickness of 128μm to Y _0, the size of the gold electrode D is 3600Myuemu, the quartz oscillator and 0.9μm thickness thereof The vibration energy distribution P is shown. Also, T represents the vibration energy distribution of the crystal resonator in which the amount corresponding to the frequency drop due to the electrode D is converted into the thickness of the mesa structure and the thickness t of the convex portion is 12.98 μm. At this time, it was assumed that a thin electrode film (an 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 portion. The vertical axis indicates 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 indicates the distance from the center of the substrate.
As apparent from FIG. 6 (c), in both cases, displacement due to higher-order thickness bending vibration occurs at the edge of the substrate, but the mesa-shaped vibrator (T) is more flat plate-shaped vibrator (P It can be seen that the vibration displacement is smaller.

However, the mesa-type crystal resonator can suppress the thickness bending vibration to some extent than the conventional flat plate-shaped crystal resonator, but it may not be able to suppress the vibration sufficiently. There has been a problem that the frequency temperature characteristic of the curve shifts from a smooth cubic curve or the CI-temperature characteristic fluctuates (CI dip).
The present invention has been made to solve the above problems, and an object thereof is to provide a crystal resonator that suppresses thickness bending vibration.

In order to achieve the above object, the AT-cut quartz crystal resonator according to the first embodiment of the present invention includes a crystal axis of quartz, an X axis as an electrical axis, a Y axis as a mechanical axis, and an optical axis. Centering on the X axis of the Cartesian coordinate system consisting of the Z axis, the Z axis is tilted in the −Y direction of the Y axis as the Z ′ axis, and the Y axis is tilted in the + Z direction of the Z axis An AT-cut quartz substrate having a Y′-axis, a plane parallel to the X-axis and the Z′-axis and having a thickness in a direction parallel to the Y′-axis, An excitation electrode provided so as to face each other on the main surface, and a lead electrode extending from the excitation electrode, and the AT-cut quartz substrate has a thick portion on which the excitation electrode is formed, A thin-walled portion formed around the thick-walled portion, the surface of the thick-walled portion is rectangular, and the rectangular A first pair of sides constituting the first pair of sides is parallel to the X-axis, a second pair of sides is parallel to the Z′-axis, and is located at a boundary between the thick portion and the thin portion, and the Z 'Having two boundary surfaces linearly extending in a direction parallel to the axis, and an elevation angle of the boundary surface with respect to the X axis is smaller than 90 ° over the entire direction of the Z' axis, The side surface parallel to the X axis and the side surface parallel to the X axis of the thin portion are in the same plane, and the dimension of the side parallel to the Z ′ axis of the AT-cut quartz substrate is W, The dimension of the side parallel to the X axis is L1, the thickness dimension of the thick part in the direction parallel to the Y ′ axis is H, and the dimension of the side of the thick part parallel to the X axis is L2. In this case, the relationship of W / H = 5.53 and L2 / L1 = 0.75 is satisfied .
The AT-cut crystal resonator according to the second aspect of the present invention is characterized in that an elevation angle of at least one of the two boundary surfaces is about 35 °.
The AT-cut quartz resonator according to the third aspect of the present invention is characterized in that an elevation angle of at least one of the two boundary surfaces is about 63 °.
In the AT-cut quartz crystal resonator according to the fourth aspect of the present invention, when the difference between the thickness of the thick part and the thickness of the thin part is t and the thickness of the thick part is H, (H− t) /H=0.9 is satisfied.
Application Example 1 A piezoelectric vibrator according to Application Example 1 has an XY ′ cross-sectional shape on a strip-shaped AT-cut quartz substrate with the longitudinal direction as the X axis, the width direction as the Z ′ axis, and the thickness direction as the Y ′ axis. The piezoelectric vibrator is characterized in that a convex portion having a trapezoidal shape is formed integrally with the quartz substrate, and a counter electrode is provided on the back surface of the substrate facing the upper surface of the convex portion.
Application Example 2 The piezoelectric vibrator according to Application Example 2 is characterized in that when the elevation angles between the slope of the convex portion and the substrate surface are θ1 and θ2, the elevation angles θ1 and θ2 are both smaller than 90 °. This is a piezoelectric vibrator.
Application Example 3 A piezoelectric vibrator according to Application Example 3 is characterized in that the elevation angles θ1 and θ2 are approximately 35 ° and 63 °, respectively.

FIG. 2A is a perspective view and FIG. 2B is a sectional view of a piezoelectric vibrator according to the present invention. (A), (b), (c) is sectional drawing which shows the process of forming the piezoelectric substrate based on this invention. (A) is sectional drawing of the piezoelectric substrate which has the trapezoidal convex part used for simulation, (b) is a figure which shows the energy distribution of the displacement which used elevation angle (alpha) as a parameter. It is a perspective view of the conventional strip-shaped crystal resonator. (A) is a chamfered substrate, (b) a convex processed substrate, and (c) is a cross-sectional view of a mesa processed substrate. (A) is a cross-sectional view of a strip-like vibrator, (b) is a cross-sectional view of a mesa-like vibrator, and (c) is a diagram showing a vibration displacement energy distribution according to the shape of a piezoelectric substrate.

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.
FIG. 1A is a perspective view showing the configuration of a piezoelectric vibrator according to the present invention, where the longitudinal direction of length L is the X axis, the width direction of length W is the Z ′ axis, and the thickness direction of thickness H is FIG. L2 is the length of the apex side in the X-axis direction at the substantially central portion of the piezoelectric substrate 1 with Y ′ axis, θ ₁ and θ ₂ are the elevation angles at which the apex L2 is desired, and the length of the apex side in the Z′-axis direction An XY ′ cross section with a thickness of W and a thickness of t forms a trapezoidal convex portion, and an upper surface of the trapezoidal convex portion and an electrode 2a facing the back surface of the piezoelectric substrate 1 facing the convex portion, 2b is attached, and lead electrodes 3a and 3b are extended from the electrodes 2a and 2b toward the ends of the piezoelectric substrate 1, respectively, to constitute a piezoelectric vibration element.

The feature of the present invention is not a mesa-shaped piezoelectric substrate in which both ends of the convex portion are perpendicular to each other as shown in FIG. 6C, but a trapezoidal top side as shown in a sectional view in FIG. The piezoelectric vibrator is configured using a piezoelectric substrate having a convex portion with elevation angles θ ₁ and θ ₂ as 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. 2 is applied and exposed and developed through a mask to form a strip electrode film 4 periodically arranged on the piezoelectric substrate 1 as shown in FIG. Next, when this is etched in an etching solution, for example, an ammonium fluoride solution, the wall surfaces on both sides of the etched groove are at a predetermined angle as shown in the cross-sectional view of FIG. The etching surface provided with this will be exhibited. When the metal film 4 is peeled off, as shown in FIG. 2C, the etching substrate becomes a piezoelectric substrate 1 in which the etching grooves are regularly arranged, and the elevation angle at which the top side of the trapezoidal convex portion is desired is θ ₁ = about A substrate with θ ₂ = about 63 ° is obtained in the direction of 35 ° and −X axis, and the substrate having trapezoidal convex portions according to the present invention is obtained by cutting the substrate with QQ. The thickness t of the convex portion can be controlled by the etching time.

FIG. 3A is a diagram showing a cross section of a piezoelectric substrate having a trapezoidal convex portion, where the elevation angle at which the apex is desired is set to α, the apex length is L2, the convex thickness is t, This is a substrate in which 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. 3B shows the length L2 of the top side of the trapezoidal convex portion, where the longitudinal dimension L1 of the substrate shown in FIG. 3A is 4800 μm, the width dimension W is 780 μm, the thickness H is 141 μm. Is the finite element method for the vibration energy distribution of a quartz crystal with a thin electrode film (an electrode film that has conductivity but no mass loading effect) attached to a quartz substrate with a thickness of 3600 μm and a thickness t of 12.98 μm It is the figure calculated | required by simulation using. Displacement distributions were compared by changing the elevation angle α as a parameter to 35 °, 63 °, and 90 °. As is clear from FIG. 3B, it has been found that the displacement of the thickness bending vibration generated at the peripheral edge of the substrate becomes smaller as the elevation angle α is made smaller than the conventional angle, rather than at a right angle.
The small displacement of the thickness flexural vibration means that the coupling between the thickness shear vibration and the thickness flexural vibration is small, and the frequency-temperature characteristic draws a smooth cubic curve, and the CI-temperature characteristic is flat. It will approach.

(The invention's effect)
Since the present invention is configured 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. If the piezoelectric vibrator according to the present invention is used in a temperature-compensated crystal oscillator or the like often used in a mobile phone or the like, an excellent effect of improving the yield is exhibited.

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

Claims (4)

Centering on the X axis of an orthogonal coordinate system consisting of an X axis as an electric axis, a Y axis as a mechanical axis, and a Z axis as an optical axis, which are crystal axes of quartz, the Z axis is the Y axis. The axis tilted in the −Y direction is the Z ′ axis, the Y axis is tilted in the + Z direction of the Z axis, the Y ′ axis, and is configured by planes parallel to the X axis and the Z ′ axis. An AT-cut quartz substrate having a thickness in a direction parallel to the Y ′ axis,
Excitation electrodes respectively provided to face the main surfaces of the front and back surfaces of the AT-cut quartz substrate;
A lead electrode extending from the excitation electrode;
With
The AT-cut quartz substrate has a thick part where the excitation electrode is formed, and a thin part formed around the thick part,
The surface of the thick part is rectangular,
The first pair of sides constituting the rectangle is parallel to the X axis, and the second pair of sides is parallel to the Z ′ axis,
Two boundary surfaces located at the boundary between the thick part and the thin part and extending linearly in a direction parallel to the Z ′ axis,
The elevation angle of the boundary surface with respect to the X axis is smaller than 90 ° over the entire direction of the Z ′ axis,
The side surface parallel to the X axis of the thick portion and the side surface parallel to the X axis of the thin portion are in the same plane,
The dimension of the side parallel to the Z ′ axis of the AT-cut quartz substrate is W, and the dimension of the side parallel to the X axis is L1.
When the thickness dimension in the direction parallel to the Y ′ axis of the thick part is H, and the dimension of the side parallel to the X axis of the thick part is L2,
W / H = 5.53 and L2 / L1 = 0.75
An AT-cut quartz crystal resonator that satisfies the above relationship . The AT-cut crystal resonator according to claim 1, wherein an elevation angle of at least one of the two boundary surfaces is about 35 ° . 2. The AT-cut crystal resonator according to claim 1, wherein an elevation angle of at least one of the two boundary surfaces is about 63 ° . The difference between the thickness of the thick part and the thickness of the thin part is t,
When the thickness of the thick part is H,
(H−t) /H=0.9
The AT-cut crystal resonator according to claim 1, wherein the AT-cut crystal resonator is satisfied .

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