JP3552056B2 - Multi-mode piezoelectric filter element - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a structure of a multi-mode piezoelectric filter element using a piezoelectric element plate.
[0002]
[Prior art]
Conventionally, as shown in FIG. 4, opposing electrodes 2 are attached to the front and back of the main surface of a piezoelectric element such as an AT-cut quartz element (AT sheet) 1 so that one or both of the electrodes 2 have a predetermined gap. through by dividing by the acoustic coupling of the vibration mutually by the divided electrodes 2 result, symmetric mode generated in the AT plate surface - de and antisymmetric mode - de referred to as the resonance frequency is two composed f _s and f _a respectively vibration mode - using de, become so-called multi (dual) center frequency is substantially f _a pass bandwidth approximately 2 (f a _{-f s)} mode - de crystal filter element is in the fields such as communication equipment Widely used.
In the manufacture thereof, an electrode was generally formed on the surface of the AT plate processed to a predetermined size by vapor deposition using a metal mask having a hole having the same shape as the electrode. However, in this method, since the edge of the electrode is blurred, the electrode shape and the gap interval g of the divided electrode 2 vary, and there is a problem that the pass band width of the filter that changes with these dimensions as parameters varies. This is due to a well-known phenomenon that, for example, when the gap g becomes narrower, the acoustic coupling of the divided electrodes 2 becomes stronger and the pass bandwidth becomes wider, and in the opposite case, it becomes narrower.
[0003]
Therefore, paying attention to the fact that the pass bandwidth changes using the plateback amount of the divided electrode as a parameter, the above-described variation is adjusted by changing the electrode film thickness.
Here, the plate back amount refers to the amount of change in the natural frequency due to the attachment of the electrode to the surface of the quartz crystal plate, with no electrode on the surface as a reference. The plateback amount increases as the film thickness increases.
Actually, in the graph showing the well-known relationship between the plateback amount and the pass bandwidth as shown by the solid line in FIG. 5, when the plateback amount is selected in the vicinity of one of the circles where the slope becomes large, The electrode shape and the gap g were determined so as to obtain the target pass band width Δf given by the specifications or the like.
As is apparent from the above-mentioned reason, it is only necessary to use the fact that, for example, when the gap interval g is changed, the graph can be moved up and down as shown by the dotted line in FIG.
With this configuration, the pass band width can be easily changed depending on the plate back amount in the vicinity of the mark in FIG. 5. The width variation was adjusted.
[0004]
By the way, with the recent miniaturization of electronic devices and the like, in the multi-mode piezoelectric filter element as described above, a plurality of minute electrodes are simultaneously formed on the surface of one AT plate by photolithography. Is manufactured by a so-called batch process in which is cut into small units. This enables mass production and cost reduction. Of course, the use of photolithography makes the edges of the divided electrodes much sharper than before and greatly reduces variations in the gap g. Variations in the passband are extremely limited and no adjustment is needed.
[0005]
However, in such a multi-mode piezoelectric filter element, when the plateback amount is selected in the vicinity of one of the circles in FIG. 5 as described above, the target pass band width Δf given by the specification or the like is obtained. When the electrode shape of the split electrode and the gap interval g are determined, the pass band width variation due to the plate back amount, that is, the variation in the electrode film thickness, which has not conventionally been a problem, appears. There was a defect that it had to be adjusted despite the extreme limitations.
[0006]
[Object of the invention]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned defects of the conventional multi-mode piezoelectric filter element, and has a multi-mode in which the pass band width does not vary even if the thickness of the divided electrodes varies. An object is to provide a piezoelectric filter element.
[0007]
Summary of the Invention
In order to achieve the above object, a multi-mode piezoelectric filter element according to the present invention is a divided electrode obtained by dividing one or both of opposing electrodes attached to both opposing surfaces of a piezoelectric element with a predetermined gap. In the multi-mode piezoelectric filter element described above, the plateback amount is selected near an extreme point of a graph showing the relationship between the plateback amount of the divided electrode and the passband width, and the desired passband width is selected. The divided electrodes are configured to obtain the following.
[0008]
【Example】
Hereinafter, the present invention will be described in detail with reference to the drawings showing examples.
FIG. 1 is a graph showing the relationship between the plateback amount and the pass band width in a multimode quartz filter element having a center frequency of 90 MHz and having a divided electrode formed on the AT plate surface by photolithography. That is, by selecting the electrode shape of the divided electrodes and the gap interval g so that the desired passband width Δf is obtained when the electrode film thickness corresponding to the plate back amount p in the vicinity of the mark (● in the figure) is selected. As is evident, the pass band width hardly changes with the change in the amount of plate back, so that even if there is a variation in the manufacturing of the electrode film thickness, it is possible to manufacture without any adjustment. can do.
[0009]
By the way, in the multi-mode piezoelectric filter element, there is an increasing demand for higher frequency as well as miniaturization. However, a base plate of a piezoelectric resonator utilizing a thickness shear vibration such as an AT-cut crystal resonator is generally a flat plate. Since the resonance frequency is inversely proportional to the plate thickness, the fundamental vibration has a limit of about 40 MHz from the viewpoint of manufacturing technology and mechanical strength.
As one means for solving this problem, there has been proposed a multi-mode piezoelectric filter element using an ultra-thin piezoelectric resonator capable of exciting a fundamental vibration in a high frequency range of several tens to several hundreds MHz. . FIGS. 2A and 2B are a plan view and an AB sectional view, respectively, showing an example in which this ultra-thin plate piezoelectric resonator is used in a multi-mode piezoelectric filter element according to the present invention. One surface of the plate 1 is recessed by, for example, etching, and the bottom surface is formed as a thin plate-shaped vibrating portion 3 and a thick annular surrounding portion 4 supporting the periphery of the vibrating portion 3 is integrally formed with the vibrating portion 3. In the ultra-thin sheet crystal resonator formed and maintaining the mechanical strength of the vibrating part 3, a conductive film is vapor-deposited on the concave side to form the entire surface electrode 5, and the vibrating part 3 on the opposing flat surface is substantially formed. As described above, by forming the divided electrode 2 at the center in the vicinity of the extreme point of the graph showing the relationship between the plateback amount and the passband width, and selecting the plateback amount so as to obtain a desired passband, as described above. The same effect as in the embodiment can be obtained in the high frequency region. In can also be obtained.
[0010]
In the above-described multi-mode piezoelectric filter, when fine adjustment of the pass bandwidth is required after manufacture, a split electrode 2 of a type in which only one electrode is split as shown in FIG. By attaching a metal 6 by vapor deposition or the like to the electrode surface directly behind the undivided side by evaporation or the like, acoustic coupling in the vicinity of the gap between the divided electrodes 2 is increased, and as a result, a well-known technique that widens the pass bandwidth can be applied. Good.
As described above, the present invention has been described by using the multi-mode piezoelectric filter element using the AT-cut quartz plate as an example. However, the present invention is not limited to this. Although the description is omitted, other piezoelectric materials have the same relationship between the plateback amount and the pass band width, and it is obvious that the present invention may be applied to these.
[0011]
【The invention's effect】
Since the present invention is configured as described above, it has a remarkable effect in minimizing the manufacturing variation of the pass bandwidth without changing the shape of the divided electrodes, that is, changing the photolithographic mask, and without requiring an adjustment step. Present.
[0012]
[Brief description of the drawings]
FIG. 1 is a diagram showing a relationship between a plateback amount and a pass bandwidth of a multi-mode piezoelectric filter element according to the present invention.
FIGS. 2A and 2B are a plan view and a cross-sectional view taken along AB, respectively, showing an example of a multi-mode piezoelectric filter element using an ultra-thin plate piezoelectric resonator according to the present invention.
FIG. 3 is a view for explaining a method of adjusting the pass bandwidth of the multi-mode piezoelectric filter element according to the present invention.
FIG. 4 is a perspective view showing a basic configuration of a multi-mode piezoelectric filter element.
FIG. 5 is a diagram showing a relationship between a plateback amount and a pass bandwidth of a conventional multi-mode piezoelectric filter element.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... AT cut quartz crystal plate 2 ... Division electrode 3 ... Vibration part 4 ... Circular surrounding part

Claims (3)

In a multi-mode piezoelectric filter element in which one or both of the opposing electrodes adhering to both opposing surfaces of the piezoelectric element are divided electrodes separated by a predetermined gap,
The gap g of the gap between the divided electrodes is determined by the plate back of the divided electrodes. (back) The relationship between the amount and the pass band width is set so that a desired pass bandwidth can be obtained when the plate back amount of the divided electrode is selected near a value at which the relation between the pass electrode and the pass band is maximized. Is a multi-mode piezoelectric filter element characterized in that the relationship between the plateback amount of the split electrode and the pass bandwidth is set near a value at which a maximum is exhibited . The piezoelectric element has a structure in which a thin vibrating portion and a thick annular surrounding portion supporting the periphery of the vibrating portion are integrally formed, and the counter electrode is provided on the surface of the vibrating portion. The multi-mode piezoelectric filter element according to claim 1, wherein: Claim 1, characterized in that it is deposited the required amount of the metal at the position corresponding to the gap directly behind the desired a dividing not side electrode surface of the counter electrode so that the pass band width is obtained and the divided electrodes and 2 multi-mode piezoelectric filter element according.

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