JP5661506B2 - Crystal oscillator - Google Patents

Description

  The present invention relates to a GT-cut crystal resonator.

  Quartz resonators used as frequency and time reference sources are divided into several types of “cuts” according to the crystallographic orientation of the crystal plates that make up the crystal units, that is, when the crystal plates are cut from a single crystal of crystal. being classified. As such cuts, for example, AT cuts, SC cuts, and the like are widely known. Among them, the GT-cut quartz plate has excellent frequency temperature characteristics, and the change in the resonance frequency when the ambient temperature changes is very small. Therefore, it is expected to be applied to a highly accurate and stable crystal oscillator. .

  As is well known, quartz crystal has three crystal axes, X-axis, Y-axis, and Z-axis, which are crystallographically defined. A crystal plate cut along a plane perpendicular to the Y axis (that is, a plane parallel to the X axis and the Z axis) is called a Y plate, but the Y plate is rotated by + 51.5 ° around the X axis (that is, φ = + 51.5 °) and a cut made of a quartz plate formed by rotating the plate by + 45 ° in the plane of the plate (that is, θ = + 45 °) is a GT cut. φ and θ are parameters that are commonly used to specify the cut orientation in quartz. FIG. 1 shows a cutting orientation 12 when a GT-cut quartz plate is cut out from a single crystal of quartz (raw stone 11). For reference, FIG. 1 also shows a cutting direction of a typical cut other than the GT cut. In order to specify the orientation of the GT cut crystal plate, the X, Y, and Z axes are obtained by rotating the X, Y, and Z axes around the X axis by + 51.5 °, respectively. And the Z ′ axis. Since the rotation is about the X axis, the X ′ axis naturally coincides with the X axis. The axes obtained by rotating the X ′ axis and the Z ′ axis by 45 ° around the Y ′ axis in the direction from the Z ′ axis to the X ′ axis are defined as an X ″ axis and a Z ″ axis, respectively.

  Here, the vibration mode in the GT-cut quartz plate will be described. As shown in FIG. 2, the vibration mode of the GT-cut quartz plate 21 is a vibration mode (width / length) in which a longitudinal vibration (extension / contraction vibration) mode in the X ″ axis direction and a longitudinal vibration mode in the Z ″ axis direction are combined. Also referred to as a longitudinally coupled vibration mode). In the figure, the direction of the stretching vibration is indicated by an arrow, and the contour displaced by the vibration is indicated by a broken line. However, for the sake of explanation, the displaced contour is drawn as a displacement much larger than the actual displacement amount in the quartz plate 21. Conventionally, a GT-cut quartz plate has a rectangular shape in which one pair of sides is parallel to the X ″ axis and the other pair is parallel to the Z ″ axis because the two longitudinal vibration modes are combined. Alternatively, it has a rectangular shape and is used as a diaphragm in a crystal unit, that is, a crystal piece. Excitation electrodes for exciting the crystal plate as the vibration plate are respectively provided on both main surfaces of the crystal plate.

  When a GT-cut quartz plate is used as the diaphragm constituting the quartz resonator, that is, the quartz piece, it is necessary to hold the quartz plate in the container so as not to contact the wall surface of the quartz resonator container. Therefore, as shown in Patent Document 1 and Non-Patent Document 2, by using a photolithography technique, the main body portion (vibrating portion) of the vibration plate and the support portion for the vibration plate are integrally formed from a plate member of crystal. It has been proposed to do so. In this case, as shown in FIG. 3, the support portion 22 is connected to the midpoint position of each of a pair of opposing sides in the rectangular main body portion of the quartz plate 21 as the vibration plate. Further, by using a method such as the finite element method, the shape of the support portion 22 is set so that the resonance frequency of the vibration portion alone and the resonance frequency of the entire resonance system including the support portion 22 are substantially the same. To design.

  Note that the vibration mode of the quartz plate is different for each cut. For example, in the case of an AT-cut quartz plate that has been widely used conventionally, the vibration mode is a thickness-shear vibration mode, and the resonance frequency is determined only by the thickness. Therefore, in the AT-cut quartz plate, the planar shape can be arbitrarily set. For example, as shown in Patent Document 2, the planar shape can be a circle or an ellipse, or it becomes a fixed point in thickness-shear vibration. The crystal piece can be supported at the position. However, in the case of a GT-cut crystal piece, the vibration mode is the width / length longitudinally coupled vibration mode, the resonance frequency changes according to the planar shape and size such as width and length, and the two coupled to each other. Since it is necessary to ensure that both vibrations in the vibration mode occur, the planar shape cannot be arbitrarily set, and the support portion cannot be arranged at any position. In particular, there is generally no fixed point for vibration displacement on the outer periphery of a rectangular GT-cut quartz plate.

JP-A-9-246898 JP 2007-158486 A JP-A-2-207615

Hirofumi Kawashima, Koichi Hirama, Naoya Saito, Mitsuaki Koyama, "Crystal Resonator and its Applied Devices", IEICE Transactions CI, Vol. J82-CI, No. 12, pp. 667-682, 1999 December Hirofumi Kawashima, Osamu Ochiai, Akihito Kudo, Yasunori Nakajima, “About Small GT-Cut Quartz Crystals”, Journal of the Japan Watch Association, No. 104, pp. 36-48, 1983

  As described above, the GT-cut quartz plate has excellent frequency temperature characteristics and is suitable for constituting a highly stable and accurate quartz crystal oscillator. However, a conventional GT-cut crystal piece has a rectangular planar shape, and a support portion is connected to the midpoint of each of a pair of opposing sides. Since the vibration mode of the GT-cut quartz plate is the width / length longitudinally coupled vibration mode, the connection position of such a support portion is a position where the quartz plate is subjected to vibration displacement. There is a risk that the vibration of the plate is hindered. Attempts have also been made to design support parts using the finite element method so that they do not adversely affect the vibration of the quartz plate, but such support parts have complex shapes, Manufacturing is difficult. Further, since the size of the support portion itself cannot be ignored as compared with the main body portion of the vibration plate, the dimensional variation in the support portion has a great influence on the vibration characteristics of the crystal plate and inhibits the miniaturization of the crystal resonator.

  An object of the present invention is to provide a GT-cut quartz crystal resonator that can be provided with a support portion having a small and simple structure without adversely affecting vibration characteristics.

  The crystal resonator of the present invention is a GT-cut crystal resonator, and is an elliptical crystal plate having a major axis and a minor axis as vibration directions of two orthogonal longitudinal vibration modes in GT cut, And a support portion that supports the quartz plate by connecting to a position where the vibration displacement is minimized on the outer periphery of the quartz plate when the two longitudinal vibration modes are combined.

  In the present invention, a GT-cut quartz plate, which has conventionally been rectangular, is elliptical. By using the oval shape, as will be described later, four points on the outer peripheral portion of the crystal plate have points where the vibration displacement is minimized, so that a support portion for supporting the crystal plate with respect to such a point is provided. Connecting. As a result, according to the present invention, the quartz plate can be supported at a position that is substantially a fixed point with respect to vibration displacement, and the support portion has a small and simple structure without affecting vibration characteristics. Can be used, and a crystal resonator having good temperature characteristics and high stability can be obtained.

It is a figure explaining the cutting azimuth | direction of the crystal plate of GT cut. It is a top view explaining the vibration mode of a quartz plate of GT cut. It is a top view explaining the conventional square-shaped GT cut crystal resonator provided with the support part. It is a figure which shows the fundamental structure of the crystal oscillator of one Embodiment of this invention. It is a top view which shows an example of the specific structure of the crystal oscillator of one Embodiment of this invention. FIG. 6 is a cross-sectional view taken along line A-A ′ of FIG. 5. It is a figure explaining the axial direction in a quartz plate. It is a graph which shows the relationship between the primary temperature coefficient (alpha) in the aspect ratio and frequency temperature characteristic in an elliptical-shaped GT cut quartz crystal resonator.

  FIG. 4 is a diagram showing a basic configuration of the crystal resonator according to the embodiment of the present invention. The crystal resonator of the present embodiment is the same as the above-described conventional one in that a GT-cut crystal plate 31 is used, but differs from the conventional one in that the planar shape of the crystal plate 31 is an ellipse.

The elliptical crystal plate 31 has a plate surface orthogonal to the Y ′ axis in the GT cut, the long axis as an ellipse matches the X ″ axis in the GT cut, and the short axis matches the Z ″ axis. As a result, the quartz plate 31 has a vibration mode in which the longitudinal vibration mode in the X ″ -axis direction and the longitudinal vibration mode in the Z ″ -axis direction are coupled, as in the quartz plate 21 shown in FIG. It has a width-length longitudinally coupled vibration mode that alternately expands and contracts in the direction and the Z ″ axis direction. In FIG. 4, the outline of the quartz plate 31 displaced by vibration is drawn with emphasis by a broken line. I don't mean. In the figure, the magnitude of the vibration displacement is minimal at each point indicated by P _{1 to} P ₄ . Since the elliptical crystal plate 31 is alternately expanded and contracted in the X ″ axis direction which is the long axis and the Z ″ axis direction which is the short axis, the point where the magnitude of the vibration displacement is minimized is the outer periphery of the crystal plate 31, that is, There will always be four on the ellipse. Assuming that the amplitude of vibration in each longitudinal vibration mode is sufficiently small compared to the size of the quartz plate 31, the points P _{1 to} P ₄ are substantially fixed points with respect to the vibration displacement in the width / length longitudinally coupled vibration mode. Become. Which position on the outer periphery of the quartz plate 31 formed into an ellipse is the fixed point is the ratio of the length a of the major axis to the length b of the minor axis in the quartz plate 31, that is, the aspect ratio (b / It depends on a). For example, when the aspect ratio is 0.855, each fixed point is a direction that forms an angle of 57.5 ° from the major axis to the minor axis direction when viewed from the center of the quartz plate 31, that is, the center of the ellipse. Located in.

In the crystal resonator of the present embodiment, the crystal unit 31 can be connected to one or more of the fixed points P _{1 to} P ₄ of the crystal plate 31 without affecting the vibration characteristics of the crystal plate 31. The plate 31 can be supported. Since the support portion is connected to the fixed point in the vibration mode, it is not necessary to make the resonance frequency coincide with the resonance frequency of the quartz plate 31, and the support portion can have a simple configuration. For example, the support portion can be configured by a simple rod-shaped member or beam member connected to the outer periphery of the crystal plate 31. In addition, since the GT-cut quartz plate 31 is used, good frequency-temperature characteristics can be obtained, and a high-accuracy and stable crystal oscillator can be obtained by combining this quartz crystal resonator and an oscillation circuit.

  5 and 6 show an example of a specific configuration of the crystal resonator according to the present embodiment configured as described above.

This crystal unit includes a frame 33 formed in a substantially rectangular shape, and an elliptical GT-cut crystal plate 31 is held in an opening of the frame 33. 5 and 6, the elliptical quartz plate 31 has a plate surface that is orthogonal to the Y ′ axis in the GT cut, and the long axis as the ellipse coincides with the X ″ axis in the GT cut. , The short axis coincides with the Z ″ axis. The crystal plate 31 is supported by two rod-shaped support portions 32 extending from the inner wall of the frame 33. The two support portions 32 are mechanically connected to the crystal plate 31 at two of the _four fixed points P _{1 to} P ₄ described above on the outer periphery of the elliptical crystal plate 31. Here, the support portion 32 is connected to a pair of fixed points P ₂ and P ₄ (see FIG. 4) sandwiching the center of the quartz plate 31 (the center of the ellipse). The thickness of the frame 33 is sufficiently thicker than the thickness of the crystal plate 31. Accordingly, for example, when the lid member is disposed on the upper surface and the lower surface of the frame 33 so that the quartz plate 31 is stored in the space surrounded by the frame 33 and the lid member, the lid of the quartz plate 31 is provided. Contact to the member is prevented.

  Such a quartz crystal resonator uses, for example, a quartz plate-like member corresponding to a GT cut, and the quartz plate 31, the support portion 32, and the portion that becomes the frame 33 remain, and the other portions are removed. It can be formed by applying a photolithography technique to the member. When a crystal resonator is formed on a crystal plate-like member using a photolithography technique, the support portion 32 and the frame 33 are also made of crystal and are configured integrally with the crystal plate 31.

  Further, an excitation electrode 34 is formed on almost the entire main surface of the quartz plate 31, and an extraction electrode 36 for realizing electrical connection to the excitation electrode 34 is formed on the surface of the one support portion 32. Thus, it extends to the connection pad 37 formed on the upper surface of the frame 33. Similarly, an excitation electrode 35 is formed on almost the entire other main surface of the crystal plate 32, and this excitation electrode 35 supports the other of the connection pads (not shown) formed on the lower surface of the frame 33. They are electrically connected via an extraction electrode (not shown) formed on the surface of the part.

5 and 6, the crystal plate 31 is supported at two points. As long as the crystal plate 31 is supported at the above-described fixed points P _{1 to} P ₄ , which part is supported? Whether to support at a fixed point can be arbitrarily determined.

  FIG. 7 shows the orientation of each axis in an elliptical GT-cut quartz crystal plate 31.

For crystal plate of GT-cut, X since the "axial modulus C _'11 and Z" axis direction of the elastic coefficient C' ₃₃ are equal, interchanging the X "axial dimension and Z" axial dimension Shows the same vibration characteristics. That is, in the above description, in the elliptical quartz plate, the major axis is the X ″ axis direction and the minor axis is the Z ″ axis direction, but the major axis is the Z ″ axis direction and the minor axis is the X ″ axis direction. The same effect as described above can be obtained.

  Next, regarding the crystal resonator of this embodiment, a change in frequency temperature characteristics when the aspect ratio (b / a) in the elliptical crystal plate 31 is changed will be described. FIG. 8 is a graph showing the results of examining the relationship between the aspect ratio and the primary temperature coefficient α. It can be seen that if the aspect ratio is in the range of 0.75 to 0.90, good temperature characteristics (primary temperature coefficient is approximately in the range of ± 10 ppm / ° C.) can be obtained.

As described above, the crystal resonator according to one aspect of the present invention has been described, but as another aspect of the crystal resonator according to the present invention,
A quartz plate cut out from the quartz crystal along a plane obtained by rotating a plane perpendicular to the Y axis of the quartz crystal around the X axis by + 51.5 °;
A support portion for supporting the crystal plate,
The quartz plate is formed in an ellipse having a major axis and a minor axis in directions inclined ± 45 ° with respect to the X axis in the plane of the quartz plate, respectively.
In the position of the outer periphery of the quartz plate, the support portion is the position where the vibration displacement in the combined vibration mode in which the longitudinal vibration mode in the major axis direction and the longitudinal vibration mode in the minor axis direction are coupled is minimized. There is a crystal resonator connected to a crystal plate. Even in such a crystal resonator, the support portion can be made of quartz, and the crystal plate and the support portion can be formed integrally. Moreover, it is preferable that the length of the short axis with respect to the length of the long axis is in the range of 0.75 or more and 0.90 or less. Furthermore, an excitation electrode can be formed on each main surface of the quartz plate.

    11 rough stone; 12 GT cut cutting orientation; 21, 31 GT cut quartz plate; 22, 32 support; 33 frame (frame); 34, 35 excitation electrode; 36 extraction electrode; 37 connection pad.

Claims (4)

A GT-cut crystal resonator that vibrates in the width / length longitudinally coupled vibration mode ,
A crystal plate formed in an elliptical shape having a major axis and a minor axis as vibration directions of two orthogonal longitudinal vibration modes in GT cut;
A support portion for supporting the crystal plate by connecting to a position where vibration displacement is minimized on the outer periphery of the crystal plate when the two longitudinal vibration modes are combined;
A crystal unit having   The crystal unit according to claim 1, wherein the support portion is made of crystal and is formed integrally with the crystal plate.   3. The crystal resonator according to claim 1, wherein a length of the short axis with respect to a length of the long axis is in a range of 0.75 to 0.90.   4. The crystal resonator according to claim 1, further comprising an excitation electrode formed on each main surface of the crystal plate. 5.

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