JP3407575B2 - Monolithic crystal filter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic crystal filter using a thickness system vibration used in communication equipment and the like, and more particularly, to the effect of suppressing spurious effects due to a contour system vibration. And a monolithic crystal filter. 2. Description of the Related Art A prior art will be described with reference to FIGS. FIG. 2 is a plan view showing an electrode configuration of a conventional monolithic crystal filter. The monolithic crystal filter has electrodes for excitation formed on the front and back surfaces of the crystal plate 8. The quartz plate 8 is an AT-cut quartz plate, and an input electrode 81, an output electrode 82, and lead electrodes 81a, 82a for leading these electrodes to the outer peripheral edge of the quartz plate are provided on one main surface as thin film forming means such as a vacuum evaporation method. The other main surface is provided with common electrodes 83 and 84 (not shown) and extraction electrodes 83a and 84a for guiding these electrodes to the outer peripheral edge of the quartz plate by the same means.
Although not shown, the input / output electrodes 81 and 82 are respectively connected to input / output terminals provided on a base, and the common electrodes 83 and 84 are connected in common and connected to a ground terminal also provided on the base. Hermetically sealed in this state. Further, as shown in FIG. 3, a configuration in which a shield electrode 85 is disposed between an input electrode 81 and an output electrode 82 in addition to the configuration of the monolithic quartz crystal filter has been devised. (See Japanese Patent Application Laid-Open No. 5-327402) The shield electrode is led out to the end of the quartz plate by extraction electrodes 85a and 85a. A monolithic crystal filter having such a configuration has a symmetric mode oscillation (f) with a common electrode portion and an input / output electrode formed opposite to each other with a quartz plate interposed therebetween as a resonance region.
s) and the obliquely symmetric mode vibration (fa) are confined in these electrode portions, and they are acoustically coupled to form a multimode main vibration, thereby forming a crystal filter having a predetermined pass band. I have. Generally, in the manufacture of a piezoelectric vibrator such as a monolithic crystal filter, a design is made to minimize the generation of unnecessary spurious components other than the main vibration. This design is optimally designed in consideration of various parameters such as the external dimensions of the quartz plate, electrode dimensions, and electrode thickness. However, when a quartz plate is attached to a base with a bonding material or the like, the frequency may fluctuate or spurious may occur. Further, there is a case where it is unavoidable that the external dimensions of the quartz plate cannot be set to an optimum size due to circumstances of the manufacturing apparatus and the like, and in such a case, spurious may occur. Suppression of such spurious and the like,
As adjustment means, a metal material was added by partial vapor deposition on the excitation electrode, and fine adjustment by weighting was used. However, since partial vapor deposition on the excitation electrode changes the frequency of the main vibration, it is not very effective in suppressing spurious, and is not particularly effective in suppressing spurious in a contour system. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. Even if the outer shape of a quartz plate cannot be optimized due to a limitation of a manufacturing apparatus, spurious and the like are suppressed to a level that causes no practical problem. It is an object of the present invention to provide a monolithic crystal filter capable of performing the following. SUMMARY OF THE INVENTION The present invention has been made by focusing on the fact that spurious can be suppressed by unbalance of the extraction electrode as a whole quartz plate, which has not been considered in the past. Each lead electrode led out to the edge of the quartz plate from the formed input / output electrode, common electrode, etc., is unbalanced in an asymmetric shape as a whole, and the weight of the quartz plate is determined by the unbalanced arrangement of the lead electrodes The above problem has been solved by changing. According to a first aspect of the present invention, there is provided a monolithic crystal filter in which an input electrode and an output electrode are formed on one main surface of a rectangular crystal plate so as to be close to each other at a predetermined interval, and the input electrode is formed on the other main surface. A common electrode corresponding to each output electrode is provided, and the input electrode, the output electrode, and the common electrode are provided with extraction electrodes derived from electrodes at the corners of the quartz plate, and at least a shield passing between the input and output electrodes is provided. An electrode is provided, and an extraction electrode of the shield electrode is formed only on one end side of the quartz plate of the shield electrode, and the weight is increased by a configuration in which the extraction electrode is extended to a corner end of the quartz plate. I have. With this configuration, the extraction electrode is formed only on one side of the shield electrode, and the extraction electrode can be extended to the corner of the quartz plate. Is spoiled, so that spurious components that are originally likely to occur with a combination of a specific frequency and external dimensions are suppressed. Next, verification data for explaining the effect of the present invention are shown in FIGS. FIG. 4 is a graph showing the frequency characteristics of the conventional product, and FIG. 5 is a diagram showing the frequency characteristics of the product of the present invention. As the present invention, a monolithic crystal filter having the same electrode configuration as shown in the embodiment shown in FIG. 1 was used, and a conventional product having the same electrode configuration as that of the conventional example shown in FIG. 3 was used. Each of the quartz plates has a rectangular shape of 3 mm in length and 4 mm in width, and has a center frequency of 29.25 M for fundamental vibration.
Hz. As is clear from FIGS. 4 and 5, spurs appear on the right side of the center frequency in the conventional product. However, by making the extraction electrode unbalanced as in the case of the present invention, the spurious response becomes practical. It can be understood that it is suppressed to a level that does not cause a problem. Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing an embodiment of the present invention. Quartz plate 1 is an AT cut quartz plate,
It is processed into a rectangular shape. An input electrode 51 and an output electrode 52 are provided in the central portion of one main surface side by side at predetermined intervals in the Z′-axis direction, and lead electrodes 51a and 52a are provided on the end faces of the quartz plate from the respective electrodes. Is derived. On the other main surface, the input electrode and the output electrodes 51 and 52 are provided.
Are provided, and the extraction electrodes 53a and 54a are electrically extracted, respectively. A resonance region is formed by these input / output electrodes and the common electrode, and functions as a monolithic crystal filter. The common electrodes are commonly connected and grounded. A narrow shield electrode 61 is provided between the input and output electrodes.
Are formed. The shield electrode 61 plays a role of preventing an electric signal input to the input electrode from directly reaching the output electrode as an electromagnetic wave, and the shield electrode 61 is formed by an extraction electrode 61a. And finally connected to the common electrode and grounded. The extraction electrode 61a is configured to extend to the lower end of the quartz plate, and the weight of the portion where the extraction electrode 61a is formed is increased, so that the entire quartz plate is unbalanced and has a specific frequency and outer shape. In the combination of dimensions, spurious components that are likely to occur are suppressed. The monolithic crystal filter is not shown, but, for example, a base having lead terminals connected to the support is prepared, and the quartz plate 1 having the above-described electrode configuration is supported by the support joined to the lead terminals. It may be hermetically sealed with a cap, or may be mounted on a surface mounting package having external lead-out electrode pads and hermetically sealed. In each of the embodiments described above, a rectangular quartz plate is mainly used as an example. However, the present invention is not limited to a rectangular shape, and may be another shape such as a partially arcuate shape. . Further, the present invention can be applied to an extraction electrode configuration of a 4-pole monolithic crystal filter in which two sets of multimode filters are formed on the same crystal plate. Further, the spurious suppression effect may be enhanced by adding a configuration in which the electrode area and the electrode thickness are different for the input electrode, the output electrode, and the extraction electrode extending from the common electrode. According to the present invention, the extraction electrode is formed only on one side of the shield electrode, and the extraction electrode is extended to the corner of the quartz plate. Since the balance of the weights is in an unbalanced state, it is possible to suppress spurious that is likely to occur with a combination of a specific frequency and an external dimension. Therefore, even when the outer shape of the quartz plate cannot be made to the optimum shape due to the limitation of the manufacturing apparatus, a monolithic quartz filter capable of suppressing spurious and the like to a practically acceptable level can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of an embodiment. FIG. 2 is a plan view showing a conventional example. FIG. 3 is a plan view showing a conventional example. FIG. 4 is a diagram showing comparison data. FIG. 5 is a diagram showing comparison data. Explanation of reference numerals 1,8 Quartz plate 51, 81 Input electrode 52, 82 Output electrodes 53, 54, 83, 84 Common electrodes 51a, 52a , 53a, 54a, 81a, 82a, 8
3a, 84a Extraction electrode

   ────────────────────────────────────────────────── ─── Continuation of front page       (56) References JP-A-7-170148 (JP, A)                 JP-A-5-335880 (JP, A)                 JP-A-5-327402 (JP, A)                 JP-A-4-259108 (JP, A)                 JP-A-62-230108 (JP, A)                 JP-A-3-272206 (JP, A)                 Shokai 55-18811 (JP, U)

Claims (1)

(57) [Claims 1] An input electrode is provided on one main surface of a rectangular quartz plate.
Output electrodes are formed close to each other at predetermined intervals, and common electrodes respectively corresponding to the input electrode and the output electrode are provided on the other main surface, and the input electrode, the output electrode, and the common electrode are connected to the corners of the quartz plate. In a monolithic crystal filter having an extraction electrode with an electrode led out to a portion, a shield electrode that passes at least between the input and output electrodes is provided, and an extraction electrode of the shield electrode is formed only on one end of the quartz plate of the shield electrode. The weight is increased by a configuration in which the extraction electrode is extracted to the corner of the quartz plate ,
If the balance between left and right is different due to the asymmetric shape when viewed over the entire crystal plate
Monolithic crystal filter, characterized in that it is caused.