JP2021158423A - Crystal oscillator - Google Patents

Abstract

To provide a specific structure preferable at individual frequencies in an AT-cut crystal oscillator having a first excitation electrode 15 of uniform thickness and a second excitation electrode 17 having an inclined portion 17a near the outer periphery.SOLUTION: The thickness of a main pressure portion 17b of a second excitation electrode is thicker than that of a first excitation electrode. A crystal piece 11 has a crystal X-axis direction dimension L1 of 2.1 mm, a Z' direction dimension of 1.348 mm, and an oscillation frequency of 50 MHz as a fundamental wave. The ratio of the mass of the first and second excitation electrodes to the mass of the crystal piece is 5%, and the confinement coefficient of the crystal piece in the crystal Z' axis direction by the first and second excitation electrodes is 4.7 to 5.6, the width of the inclined portion is set to 1 to 2.5 times the wavelength λ of the vibration in the bending mode generated by the crystal piece, and each of the first and second excitation electrodes has an elliptical shape with the long side direction of the crystal piece as the long axis and the short side direction of the crystal piece as the short axis, and the long axis length/short axis length=1.265 is satisfied.SELECTED DRAWING: Figure 1

Description

The present invention relates to an AT-cut crystal unit in which an inclined portion is formed around an excitation electrode.

In a crystal oscillator that slides and vibrates in thickness, by using a so-called convex-shaped crystal piece having a thin outer circumference, vibration energy can be confined in the crystal piece and unnecessary vibration can be suppressed. However, in order to form the quartz piece into a convex shape, there is a problem that processing is troublesome and costly.

Therefore, in Patent Document 1, the crystal piece remains flat, and an inclined portion in which the thickness of the excitation electrode gradually decreases is formed on the edge of each of the excitation electrodes formed on both main surfaces, thereby achieving the effect of the convex shape. It has been shown to be generated to reduce the labor and cost of processing the quartz piece.

JP 2002-217675 JP-A-2018-98592

On the other hand, in Patent Document 2, the structure of the crystal oscillator disclosed in Patent Document 1, that is, the excitation electrodes provided on both sides of the crystal piece have inclined portions at the edges, and the frequency is adjusted. Therefore, it is described that the inclined portion may disappear when the excitation electrode is trimmed, resulting in a large loss of vibration energy (Patent Document 2, for example, FIG. 4, paragraph 26, etc.). In order to improve this, the first excitation electrode formed on one main surface of the quartz piece has a uniform thickness as a whole, and the second excitation electrode formed on the other main surface has a constant thickness. It is assumed that there is a main thick portion formed by and an inclined portion formed around the main thick portion and the thickness gradually decreases outward from the portion in contact with the main thick portion, and the main thick portion is the first excitation electrode. The structure to make it thicker than the thickness of is described.

The crystal oscillator disclosed in Patent Document 2 can reduce the degree of deterioration of vibration loss even if the frequency is adjusted by adjusting the frequency on the first excitation electrode side.
However, in Patent Document 2, reference to an appropriate structure relating to an AT-cut crystal unit having a specific frequency and size is not always satisfactory.
This application was made in view of the above points, and therefore, the purpose of this application is to have an AT having a first excitation electrode having a uniform thickness and a second excitation electrode having an inclined portion near the outer periphery. It is an object of the present invention to provide a specific structure preferable in individual frequencies in a cut crystal unit.

In order to achieve this object, according to the AT-cut crystal unit of the present invention, a package, an AT-cut crystal piece contained in the package, which is flat and has a rectangular planar shape, and a main crystal piece of the crystal piece. The first excitation electrode provided on one surface of the surface and having a uniform thickness, and the main surface provided on the other surface of the main surface and having an inclined portion near the outer periphery and having a uniform thickness other than the inclined portion. In a crystal oscillator that is thicker than the thickness of the first excitation electrode that is the pressing part,
The crystal piece is a crystal piece having a long side in the X-axis direction of the crystal, a short side in the Z'direction of the crystal, and an oscillation frequency of 50 MHz as a fundamental wave.
The mass ratio of the first excitation electrode and the second excitation electrode / the mass of the crystal is 5.0%, and the confinement coefficient of the crystal piece in the crystal Z'axis direction by the first excitation electrode and the second excitation electrode is set. Is it 4.7 to 5.6?
Alternatively, the mass ratio of the mass of the first excitation electrode and the second excitation electrode / the mass of the crystal is set to 5.4%, and the crystal piece is confined in the crystal Z'axis direction by the first excitation electrode and the second excitation electrode. Is the coefficient set to 4.9 to 5.5?
Alternatively, the mass ratio of the mass of the first excitation electrode and the second excitation electrode / the mass of the crystal is set to 5.9%, and the crystal piece is confined in the crystal Z'axis direction by the first excitation electrode and the second excitation electrode. The coefficient is set to 5.2 to 5.7,
The width of the inclined portion has a dimension of 1 to 2.5 λ with respect to the wavelength λ of the vibration in the bending mode generated in the crystal piece.
Each of the first excitation electrode and the second excitation electrode has an elliptical shape with the long side direction of the crystal piece as the major axis and the short side direction of the crystal piece as the minor axis, and has a major axis length / minor axis. The length is 1.265 ± 10%.

In carrying out the present invention, the crystal piece has L1 / t ≧ 65 and W1 when the dimension of the crystal in the X-axis direction is L1, the dimension of the crystal in the Z'axis direction is W1, and the thickness is t. It is preferable that the crystal piece satisfies / t ≧ 42. For example, a crystal piece having a long side dimension L1 of 2.1 ± 0.1 mm and a short side dimension W1 of 1.348 ± 0.1 mm has L1 / t = 65 and W1 / t = 42, and is used in the present invention. This is an example of a possible crystal piece.
Further, the oscillation frequency of the crystal piece is 50 MHz, which is a fundamental wave, and includes a frequency band of 50 MHz ± 5 MHz, more preferably a frequency band of 50 MHz ± 3 MHz. The design concept of the present invention can be applied to such a frequency band as well.
The confinement coefficient is a value determined by n (We / βz · tq) √Δ. Here, n is the vibration order of the crystal oscillator (for example, 1 for the fundamental wave), We is the dimension of the quartz crystal axis of the excitation electrode in the Z'direction, and βz is the anisotropy coefficient of the crystal crystal axis in the Z'direction. 1.538 and tq are the thickness of the crystal piece. Further, Δ is a value determined by the mass of the excitation electrode / the mass of the crystal, and specifically, is a value obtained by (2ρe · te / ρq · tq). Here, ρq is the density of the crystal, tq is the thickness of the crystal, ρe is the density of the excitation electrode, and te is the thickness of the excitation electrode.

In the above invention, the reason why the major axis length / minor axis length = 1.265 ± 10% is that the anisotropy coefficient ratio of the AT-cut crystal piece (X-axis direction: 1.945, Z'axis). Direction: 1.538 ratio = 1.945 / 1.538≈1.265) and its tolerance ± 10%. The anisotropy coefficient is described in, for example, the document "Elastic Wave Device Technology (Ohmsha 2014 Edition), pp. 183-185", and thus the description thereof will be omitted.
Further, in carrying out each of the above inventions, as the package, a ceramic package having a long side of 3.2 mm and a short side of 2.5 mm in terms of external dimensions, that is, a so-called 3225 size ceramic package is preferable. However, ± 0.2 mm, which is a general tolerance of the package, is allowed for both the long side and the short side.
Further, the above-mentioned value showing the mass ratio of the mass of the first excitation electrode and the mass of the second excitation electrode / the mass of the crystal is ± 0.1% with respect to each value, which is included in the present invention.

According to the crystal oscillator of the present invention, it is unnecessary in a crystal oscillator having a first excitation electrode having a frequency of around 50 MHz and a uniform thickness and a second excitation electrode having an inclined portion near the outer periphery. Vibration can be suppressed and loss of vibration energy during frequency adjustment can be prevented.

1 (A) is a plan view for explaining the crystal oscillator 10 of the embodiment, FIG. 1 (B) is a cross-sectional view for explaining the crystal oscillator 10 of the embodiment, and FIG. It is a cross-sectional view along the line. FIG. 2A is a cross-sectional view illustrating an inclined portion of the excitation electrode of the crystal unit 10 of the embodiment, and FIG. 2B is a plan view illustrating an elliptical electrode. It is a figure explaining the simulation result of Example 1. FIG. It is a figure explaining the simulation result of Example 2. FIG. It is a figure explaining the simulation result of Example 3. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the figures used in the description are merely schematic to the extent that these inventions can be understood. Further, in each of the figures used for explanation, similar constituent components may be indicated with the same number, and the description thereof may be omitted. Further, the shapes, dimensions, materials and the like described in the following embodiments are merely preferable examples within the scope of the present invention. Therefore, the present invention is not limited to the following embodiments.

1. 1. Structure of Crystal Oscillator First, the structure of the crystal oscillator 10 of the embodiment will be described with reference to FIGS. 1 (A) and 1 (B).
The crystal oscillator 10 of the embodiment includes a package 11, an AT-cut crystal piece 13, a first excitation electrode 15, and a second excitation electrode 17.
In the case of this example, the package 11 is a ceramic package and has a recess 11a for mounting an AT crystal piece. The circumference of the recess 11a is a bank portion 11b. In this ceramic package 11, the crystal piece 11 is sealed by joining a lid member (not shown) to the bank 11b by any suitable method such as seam sealing, glass sealing, and gold tin sealing. can. Considering the size of the crystal piece 13 used in the simulation described later, the external dimensions of the package 11 are preferably the so-called 3225 size, in which the long side L0 is about 3.2 mm and the short side W0 is about 2.5 mm.
The AT crystal piece 13 is a flat plate and a rectangular flat surface, and has a thickness corresponding to a frequency. Since the AT-cut quartz piece itself is known, the description thereof will be omitted.
A first excitation electrode 15 is provided on one main surface of the AT-cut crystal piece 11. A second excitation electrode 17 is provided on the other main surface. These electrodes 15 and 17 can be composed of, for example, a laminated film of a chromium film and a gold film.
The first excitation electrode 15 has a uniform thickness. As shown in FIG. 1 (B), the second excitation electrode 17 has an inclined portion 17a whose thickness decreases from the center side of the crystal piece toward the edge in the vicinity of the outer periphery thereof, except for the inclined portion 17a. Is a main pressure portion 17b having a uniform thickness. The thickness of the main thick portion 17b of the second excitation electrode 17 is thicker than the thickness of the first excitation electrode 15.
The crystal oscillator 10 of this embodiment has the following structure according to the frequency of the crystal piece 13.

The crystal piece 13 is a crystal piece having a long side in the X-axis direction of the crystal, a short side in the Z'direction of the crystal, and an oscillation frequency of 50 MHz as a fundamental wave.
Further, the mass ratio of the mass of the first excitation electrode 15 and the second excitation electrode 17 / the mass of the crystal piece 13 is set to 5.0%, and the crystal Z'axis direction of the crystal piece by the first excitation electrode and the second excitation electrode is used. The confinement coefficient is set to 4.7 to 5.6.
Alternatively, the mass ratio of the mass of the first excitation electrode 15 and the second excitation electrode 17 / the mass of the crystal is set to 5.4%, and the first excitation electrode 15 and the second excitation electrode 17 are used in the crystal Z'axis direction of the crystal piece. The confinement coefficient is set to 4.9 to 5.5.
Alternatively, the mass ratio of the mass of the first excitation electrode 15 and the second excitation electrode 17 / the mass of the crystal is set to 5.9%, and the first excitation electrode 15 and the second excitation electrode 17 are used in the crystal Z'axis direction of the crystal piece. The confinement coefficient is set to 5.2 to 5.7.
Further, the width Wk of the inclined portion 17 (see FIG. 2A) is set to have a dimension of 1 to 2.5 λ with respect to the wavelength λ of the vibration in the bending mode generated in the crystal piece 13.
Further, each of the first excitation electrode 15 and the second excitation electrode 17 has an elliptical shape with the long side direction of the crystal piece 13 as the major axis and the short side direction of the crystal piece 13 as the minor axis, and has a major axis length. La / minor axis length Wa = 1.265 ± 10%.
Here, the major axis length La and the minor axis length Wa are defined as the lengths connecting the midpoints of the inclined portions 17 in this example (see FIG. 2B).
The confinement coefficient and the major axis length La / minor axis length Wa = 1.265 ± 10% have been described in the above-mentioned "Means for Solving Problems".

2. Simulation and Results The crystal oscillator 10 of the above embodiment was simulated by the finite element method under various conditions shown in Examples 1 to 3 below. In these simulations, as shown in FIG. 2A, the inclined portion 17a has an inclined portion composed of three stepped portions of a first portion 17aa, a second portion 17ab, and a third portion 17ac. A model was used.
Further, the width Wk of the inclined portion 17a was set to 75 μm. This 75 μm is a dimension corresponding to 1.4 times the wavelength λ of the unnecessary signal in the bending mode generated in the crystal piece of 50 MHz.

Regarding the size of the crystal piece used in the simulation, the long side dimension L1 is 2.1 mm and the short side dimension W1 is 1.348 mm. Of course, the size of the crystal piece is not limited to these examples. For example, if the long side dimension L1 and the short side dimension W1 of the crystal piece are larger than the above, L1 / t and W1 / t with respect to the thickness t, that is, the side ratio is advantageous for the characteristics of the crystal oscillator. It may be larger.

Further, the width Wka of the first portion 17aa, the width Wkb of the second portion 17ab, and the width Wkc of the third portion 17ac (see FIG. 2A, respectively) of each of the models of Examples 1 to 3 are inclined. The size was set to one-third of the width Wk of the part.
The thickness t1 of the first portion 17aa, the thickness t2 of the second portion 17ab, and the thickness t3 of the third portion 17ac (see FIG. 2A, respectively) are four minutes of the thickness t of the main thickness portion 17b, respectively. It was set to 1.
Further, in the model of Example 1, the thickness of the main thickness portion 17b of the second excitation electrode 17 is 110 nm, and in the model of Example 2, the thickness of the main thickness portion 17b of the second excitation electrode 17 is 120 nm. In the model of Example 3, the thickness of the main thickness portion 17b of the second excitation electrode 17 was set to 130 nm.
In each of the models of Examples 1 to 3, the thickness of the first excitation electrode 15 was 30 nm thinner than the thickness of the main thick portion 17b of the second excitation electrode 17. The film thickness of the first excitation electrode and the film thickness of the second excitation electrode were set to the above values, because the ratio of the mass of the electrode to the mass of the crystal piece was 5.0% or 5.4% in the present application. This is to make it equal. The film thickness of the first excitation electrode was reduced by 30 nm from the film thickness of the second excitation electrode, but this is an example, and the degree of thinning is not limited to this. It may be further thinned to the extent that the first excitation electrode is formed as a film. However, if the frequency is so thin that the frequency cannot be adjusted, it is outside the scope of the present invention.

With respect to the simulation model of Example 1 above, by swinging the elliptical major axis and minor axis dimensions of the excitation electrode as shown in Table 1, six types of models having different confinement coefficients are constructed, and the first of these models The loss (1 / Q) in the crystal oscillator when the film thickness of the excitation electrode 15 is reduced, that is, when the first excitation electrode 15 is scraped by argon ions or the like by adjusting the frequency of the crystal oscillator, is determined. Calculated by the finite element method.

Further, with respect to the simulation model of the above-mentioned Example 2, six types of models having different confinement coefficients are constructed by oscillating the elliptical major axis and minor axis dimensions of the excitation electrode as shown in Table 2, and these models. Loss (1 / Q) in the crystal oscillator when the film thickness of the first excitation electrode 15 is reduced, that is, when the first excitation electrode 15 is scraped by argon ions or the like by adjusting the frequency of the crystal oscillator. Was calculated by the finite element method.

Further, with respect to the simulation model of the above-mentioned Example 3, six types of models having different confinement coefficients are constructed by oscillating the dimensions of the elliptical major axis and the minor axis of the excitation electrode as shown in Table 3. When the film thickness of the first excitation electrode 15 of the model is reduced, that is, when the first excitation electrode 15 is scraped by argon ions or the like by adjusting the frequency of the crystal oscillator, the loss (1 /) in the crystal oscillator. Q) was calculated by the finite element method.

In FIG. 3, for the six types of samples shown in Table 1, the horizontal axis represents the film thickness (nm) reduced by the frequency adjustment of the first excitation electrode 15, and the vertical axis represents the loss of the crystal oscillator (1). / Q) is taken to show the relationship between the two.
From FIG. 3 and Table 1, when the frequency is 50 MHz and the ratio of the mass of the excitation electrode to the mass of the crystal piece is 5.0%, the minor axis length W2 is 1.048 to 1.245 mm, that is, the confinement coefficient is set. When it is set to 4.7 to 5.6, it can be seen that the loss can be suppressed to a small value even if the film thickness of the first excitation electrode 15 is reduced by frequency adjustment.

In FIG. 4, for the six types of samples shown in Table 2, the horizontal axis represents the film thickness (nm) reduced by the frequency adjustment of the first excitation electrode 15, and the vertical axis represents the loss of the crystal oscillator (1). / Q) is taken to show the relationship between the two.
From FIG. 4 and Table 2, when the frequency is 50 MHz and the ratio of the mass of the excitation electrode to the mass of the crystal piece is 5.4%, the minor axis length W2 is 1.048 to 1.166 mm, that is, the confinement coefficient is set. When it is set to 4.9 to 5.5, it can be seen that the loss can be suppressed to a small value even if the film thickness of the first excitation electrode 15 is reduced by frequency adjustment.

In FIG. 5, for the six types of samples shown in Table 3, the horizontal axis represents the film thickness (nm) reduced by the frequency adjustment of the first excitation electrode 15, and the vertical axis represents the loss of the crystal oscillator (1). / Q) is taken to show the relationship between the two.
From FIG. 5 and Table 3, when the frequency is 50 MHz and the ratio of the mass of the excitation electrode to the mass of the crystal piece is 5.9%, the minor axis length W2 is 1.048 to 1.166 mm, that is, the confinement coefficient is When it is set to 5.2 to 5.7, it can be seen that the loss can be suppressed to a small value even if the film thickness of the first excitation electrode 15 is reduced by frequency adjustment.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above examples. For example, the step of the inclined portion in the above embodiment is four steps, but the step is not limited to four steps, and the step may be at least more than this. Moreover, the above-described embodiment may be implemented in various combinations.
Further, as an example by simulation, an example of a crystal piece having a frequency of 50 MHz, a long side dimension L1 of 2.1 mm, and a short side dimension W1 of 1.348 mm was given, but the package size can be stored in the so-called 3225 size. As a result, the same effect has been confirmed for crystal pieces having a long side dimension L1 of 2 to 2.4 mm and a short side dimension W1 of 1.2 to 1.5 mm.

10: Crystal oscillator of the embodiment 11: Package 13: AT cut crystal piece 15: First excitation electrode 17: Second excitation electrode 17a: Inclined portion 17aa: First part 17ab: Second part 17ac: Third part 17b: Main pressure part

Claims (4)

A package, an AT-cut crystal piece that is flat and has a rectangular planar shape, and a first excitation electrode that is provided on one surface of the main surface of the crystal piece and has a uniform thickness. A second excitation electrode provided on the other surface of the main surface and having an inclined portion near the outer periphery and a main pressure portion having a uniform thickness other than the inclined portion is provided, and the thickness of the main thick portion is provided. Is thicker than the thickness of the first excitation electrode,
The crystal piece is a crystal piece having a long side in the X-axis direction of the crystal, a short side in the Z'direction of the crystal, and an oscillation frequency of 50 MHz as a fundamental wave.
The mass of the first excitation electrode and the second excitation electrode / the mass of the crystal is 5.0%, and the confinement coefficient of the crystal piece in the crystal Z'axis direction by the first excitation electrode and the second excitation electrode is 4 It is set as .7 to 5.6.
The width of the inclined portion has a dimension of 1 to 2.5 λ with respect to the wavelength λ of the vibration in the bending mode generated in the crystal piece.
Each of the first excitation electrode and the second excitation electrode has an elliptical shape with the long side direction of the crystal piece as the major axis and the short side direction of the crystal piece as the minor axis, and has a major axis length / minor axis. A crystal oscillator characterized in that the length is 1.265 ± 10%. A package, an AT-cut crystal piece that is flat and has a rectangular planar shape, and a first excitation electrode that is provided on one surface of the main surface of the crystal piece and has a uniform thickness. A second excitation electrode provided on the other surface of the main surface and having an inclined portion near the outer periphery and a main pressure portion having a uniform thickness other than the inclined portion is provided, and the thickness of the main thick portion is provided. Is thicker than the thickness of the first excitation electrode,
The crystal piece is a crystal piece having a long side in the X-axis direction of the crystal, a short side in the Z'direction of the crystal, and an oscillation frequency of 50 MHz as a fundamental wave.
The mass of the first excitation electrode and the second excitation electrode / the mass of the crystal is 5.4%, and the confinement coefficient of the crystal piece in the crystal Z'axis direction by the first excitation electrode and the second excitation electrode is 4 It is set as .9 to 5.5,
The width of the inclined portion has a dimension of 1 to 2.5 λ with respect to the wavelength λ of the vibration in the bending mode generated in the crystal piece.
Each of the first excitation electrode and the second excitation electrode has an elliptical shape with the long side direction of the crystal piece as the major axis and the short side direction of the crystal piece as the minor axis, and has a major axis length / minor axis. A crystal oscillator characterized in that the length is 1.265 ± 10%. A package, an AT-cut crystal piece that is flat and has a rectangular planar shape, and a first excitation electrode that is provided on one surface of the main surface of the crystal piece and has a uniform thickness. A second excitation electrode provided on the other surface of the main surface and having an inclined portion near the outer periphery and a main pressure portion having a uniform thickness other than the inclined portion is provided, and the thickness of the main thick portion is provided. Is thicker than the thickness of the first excitation electrode,
The crystal piece is a crystal piece having a long side in the X-axis direction of the crystal, a short side in the Z'direction of the crystal, and an oscillation frequency of 50 MHz as a fundamental wave.
The mass of the first excitation electrode and the second excitation electrode / the mass of the crystal is 5.9%, and the confinement coefficient of the crystal piece in the crystal Z'axis direction by the first excitation electrode and the second excitation electrode is 5. It is as .2 to 5.7,
The width of the inclined portion has a dimension of 1 to 2.5 λ with respect to the wavelength λ of the vibration in the bending mode generated in the crystal piece.
Each of the first excitation electrode and the second excitation electrode has an elliptical shape with the long side direction of the crystal piece as the major axis and the short side direction of the crystal piece as the minor axis, and has a major axis length / minor axis. A crystal oscillator characterized in that the length is 1.265 ± 10%. The crystal piece has a long side dimension of 2 to 2.4 mm and a short side dimension W1 of 1.2 to 1.5 mm, and the package has an outer long side dimension of 3.2 ± 0. The crystal transducer according to any one of claims 1 to 3, wherein the crystal transducer has a short side dimension of 2.5 ± 0.2 mm and 2 mm.

Images