JPH0145771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystal resonator using a rectangular crystal plate. This crystal resonator uses an AT-cut crystal plate, has an oscillation frequency of 1 to 6MHz, and has dimensions of
Various types of small vibrators of about 10 x 2 mm have been introduced. In order to reduce the crystal impedance (hereinafter referred to as "CI") during oscillation and obtain stable oscillation, the crystal plate is formed into a bevel shape or a convex shape.

The bevel shape and the convex shape are such that, as shown in the plan view of FIG. The difference is that the thickness of the crystal plate 200 is gradually reduced with a constant radius of curvature, as shown in the plan view in FIG. The thickness is gradually reduced toward the sides. In addition, in FIG. 1 and FIG. 2, 101 and 201 are excitation electrodes to be subjected to thickness vibration.

By creating such a bevel shape or convex shape, it is possible to create a flat plate (with the same dimensions).
Although CI can be made smaller compared to
However, the limit was reached at about 150 Ω, and it was impossible to reduce the CI to several tens of Ω, which could be obtained with a circular crystal plate with a diameter of 8 mm.

The present invention exceeds the limits of conventional bevel and convex shapes and has a CI of several tens of ohms.
The object of the present invention is to provide a crystal resonator that can be made as small as possible, and the present invention will be described in detail below with reference to the drawings of the embodiments.

Figure 3 shows the shape of a crystal plate that is an embodiment of the present invention, where A is a plan view and B is a plan view of the same figure.
A ₃₁ - A ₃₁ cross-sectional view and C in the same figure is A ₃₂ - _{A 32} in A in the same figure.
FIG. 4 is a cross-sectional view, and FIG. ₄ shows a crystal resonator in which excitation electrodes and extraction electrodes are arranged on the crystal plate shown in the previous figure.
−A ₄ sectional view.

The crystal plate 300 of this example is a well-known AT-cut crystal plate (crystal coordinates (X, Y, Z) after rotating the crystal coordinates (X, Y, Z) of the crystal by a predetermined angle (34° to 36°) around the X axis. _A crystal plate cut parallel to the w ₀ = 2 mm) along the Z′ axis, and the thickness direction (thickness t ₀ =
0.34mm) is set as the Y′ axis. Note that the oscillation frequency f
is inversely proportional to the thickness t ₀ , and in this example f≒
It is 5MHz.

A flat surface 301 having an elliptical outline having a major axis (l ₁ = 3.6 mm) and a minor axis (w ₁ = 1.0 mm) is formed on both main surfaces of this crystal plate 300. Between the elliptical shape of the surface 301 and the rectangular outline of the crystal plate 300, the thickness ti of the crystal plate 300 is
A similar ellipse that gradually becomes smaller as it advances in the long side direction and the short side direction of 00, and the locus of points on both principal surfaces with the same thickness ti is approximately similar to the ellipse of the flat surface 301. A shape 302 and a portion 303 of its similar ellipse are formed sequentially toward the periphery.

Then, a metal such as Agg or Au is vacuum-deposited or sputtered on both main surfaces including the flat surface 301 of this crystal plate 300, and an excitation electrode 304 is formed in opposite directions from the excitation electrode 304 to both ends in the longitudinal direction. A crystal resonator is constructed by arranging the lead electrode 305 and the lead electrode 305 . Although electrical and mechanical connections of this crystal resonator are not shown, both ends of the extraction electrode 305 are fixed to predetermined supports.

Therefore, the elliptical shape of the crystal plate 300 (flat surface 30
1), that is, the relationship between each dimension of major axis l ₁ and minor axis w ₁ and CI, as a result of a detailed study and experiment, we found that the length of the crystal plate 300 in the long side direction is as shown in FIG. Ratio of major axis l ₁ of ellipse to l ₀ (l ₁ / l ₀ )
is 0.7 or less _{, the} ratio (w ₁ /
When w ₀ ) is 0.6 or less, CI becomes 70 Ω or less and decreases; conversely, when the ratio (l ₁ /l ₀ ) exceeds 0.7 and the ratio (w ₁ /w ₀ ) exceeds 0.6 was found to increase dramatically when CI exceeds 100Ω. Note that in the crystal resonator of this example, since l ₁ /l ₀ =0.45 and w ₁ /w ₀ =0.5, its CI is 40Ω.

Such ratios (l ₁ /l ₀ ) and ratios (w ₁ /w ₀ ) and CI
The relationship _between the It can be seen that the method can be implemented for a crystal oscillator.

Regarding the cutting angle of the crystal plate, AT cut is superior in terms of frequency-temperature characteristics when used at room temperature, but BT cut, FC cut, etc. may also be selected depending on individual usage conditions. .

As described above, according to the present invention, regarding CI,
It has the advantage of being significantly smaller than the limits of conventional small rectangular crystal resonators and providing stable oscillation. Also, within the allowable range of CI,
It is possible to achieve a size reduction corresponding to the CI reduction of the present invention.

[Brief explanation of drawings]

Figure 1 shows a conventional bevel-shaped crystal resonator, where A is a plan view and B is a top view of A ₁ - A of the same figure.
_A1 is a sectional view. FIG. 2 shows a conventional convex-shaped crystal resonator, and FIG _{. 2A} is a plan view, and FIG. FIG. 3 shows an embodiment of a crystal plate according to the present invention, in which A is a plan view, B is a sectional view taken along A ₃₁ - A ₃₁ in A, and C is a sectional view taken along A ₃₂ - A in A of the same figure. A ₃₂ sectional view. Fourth
The figure shows an embodiment of a crystal resonator using the crystal plate shown in FIG. 3, _{and FIG} . FIG. 5 shows the ratio (l ₁ /l 0 ) and the ratio (l 1 /l ₀ ) of each length in the long side direction and short side direction of the crystal oscillator according to the present invention and each length of the major axis and minor axis of the ellipse of the flat surface. FIG. 2 is a characteristic curve diagram showing the relationship between w ₁ /w ₀ ) and CI. 300...Crystal plate, 301...Flat surface, 302
...Similar ellipse, 303...Part of similar ellipse,
304...Excitation electrode, _l0 ...Length in the long side direction of the crystal plate, w0 _... Length in the short side direction of the crystal plate, _l1 ...Longer axis of the ellipse, w1 _... Length in the short side direction of the crystal plate Minor axis, ti...The thickness of the crystal plate between the oval and rectangle.

Claims (1)

[Claims] 1 The shape of both main surfaces of the AT-cut crystal plate is rectangular, excitation electrodes to be vibrated in thickness are arranged on both main surfaces, and the length of the crystal plate is set in the same direction as the long side direction of the crystal plate. The major axis has a length of 0.7 times or less,
Both main surfaces of the crystal plate are flat surfaces having an elliptical outline and a short axis having a length not more than 0.6 times the length in the short side direction in the same direction as the short side direction of the crystal plate. and the thickness of the crystal plate between the ellipse of the flat surface and the rectangle of the crystal plate gradually decreases as it advances in the long side direction and the short side direction of the crystal plate. , a locus of points where the thickness of the crystal plate is equal between the ellipse of the flat surface and the rectangle of the crystal plate is a similar ellipse that is similar to the ellipse, or a part of the similar ellipse. A crystal oscillator characterized by: