JPH0454717A - Frequency control method for ultra thin plate multiplex mode piezoelectric filter element - Google Patents

Abstract

PURPOSE:To ensure high production efficiency and a high yield by arranging a mask having a prescribed opening to a full face electrode at manufacturing, and applying additional vapor deposition to an electrode material while relatively moving between the mask and a filter element. CONSTITUTION:Additional vapor-deposition 29 is implemented till the resonance frequency between split electrodes 14 and 13 is coincident while the resonance frequency is measured between a full face electrode 4 and the split electrode 13 of the filter element and while a mask 31 having a prescribed opening 30 toward the full face electrode 4 provided with a annular surrounding part 3 is moved relatively with respect to the part 3. Thus, the dissidence of the resonance frequency occurred due to the dispersion in the thickness of the piezoelectric raw material plate between the split electrodes of the ultra thin ultra thin plate multiplex mode piezoelectric filter element is easily eliminated by the alignment between the mask and the filter element without need of high accuracy and the productivity and the yield of the filter element are enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to multi-mode, piezoelectric filters, especially piezoelectric J! The frequency JI of the multi-mode piezoelectric filter element allows the fundamental frequency of the plate, that is, the center frequency fI number, to be adjusted to several IO 00MHz without using the one-tone technique.
g method.

(Prior art) Conventionally, a pair of opposing split electrodes are formed close to each other on the front and back sides of a piezoelectric substrate, and when alternating electric fields with a huge 18° phase difference are applied to these split electrodes and excited, the sound generated between the two electrodes. The resonant frequencies called symmetric and antisymmetric motes generated due to R coupling are respectively [Using two modes of vibration S and ra, the center layer wave number is approximately ``a'' and the bandwidth is approximately 2.
A place with the characteristic of (fa-Is)! ! 421 mode piezoelectric filters are widely used in various communication devices.

Additionally, there are filters in which the electrode is divided into three or more parts, and these are generally called multi-mode piezoelectric filters, but in this type of filter element, the resonance frequency of each electrode section formed on the piezoelectric substrate E is set quite strictly. (within a few percent of the target bandwidth), so after fixing the filter element on which electrode formation has been completed to the base, the required additional deposition is performed on the electrode part through a mask. The resonant frequencies of the side electrode part phase ξ were made to match and sealing was performed in vain.

By the way, in recent years there has been a growing demand for downsizing, R-shape, and high frequency for each communication device, so the various piezoelectric devices used in these devices are also becoming ultra-miniaturized, as well as high frequency and high frequency stability. In order to meet this demand, conventionally, as shown in Fig. 2(a), the center part of the life surface of the piezoelectric block 1, which has good temperature-frequency characteristics like a crystal, is used as a mechanical stirrup. Alternatively, an extremely thin vibrating part 2 is formed by recessing it by etching or the like, and an annular surrounding part 3 on the periphery supports the vibrating part 2 to ensure its shape, and the surface including the inner wall of the recess on the side of the recess. An ultra-thin plate piezoelectric resonator in which a full-surface electrode 4 is formed and a facing JIi 5 is formed on the surface of the vibrating part 2 on the opposite surface thereof has been researched. In order to take advantage of its shape characteristics, this type of resonator is housed so that the concave side of the piezoelectric block 1 faces the bottom of a dish-shaped package 6 made of sintered ceramics, as shown in FIG. 1(b). Then, the entire surface electrode 4 and the conductor l[7 provided on the bottom surface of the package 6 are adhesively fixed with a conductive adhesive 8, and an external lead 9 is formed from the conductor 117 to pass through the package wall in an airtight manner and to be exposed on the outer wall of the package. Connecting.

Further, the counter electrode 5 of the entire surface electrode 4 is similarly configured to be connected to a pad 11 connected to another external lead 10 exposed inside the package by a bonding wire 12, and piezoelectric This is intended to minimize the effects of distortion on the resonator.

If this type of piezoelectric resonator is applied to a dual-mode piezoelectric filter, the electrode facing the entire surface electrode 4 is divided through slits of a required width to form divided electrodes 13 and 14, as shown in FIG. and pads I7 connected to electrode leads 15 and 16 and external leads exposed inside the package 6, respectively;
It would be common to connect the terminals I8 to each other with bonding wires 12.

However, as mentioned above, the ultra-thin multi-mode piezoelectric filter element as described above has a fundamental frequency dispersion of 10 to several 100M.
This method not only uses a raw plate with a resonant frequency of H2, but also is intended to be an ultra-small element (about 3 maw x 3 II 11 in base plate size), and a large number of element patterns are formed simultaneously on two piezoelectric wafers. Since the device is intended to be mass-produced by cutting and then cutting, local variations in the thickness of the two plates are preserved in each device hill, and this causes the resonant frequency between the divided electrode attachment portions to be ignored. It has become clear that this can lead to unnecessary inconsistencies. In addition, if the conventional frequency adjustment method described above is used to eliminate this interlayer, an extremely precise mask must be used and the phases of the electrodes formed must be precisely matched, which reduces production efficiency. There was a concern that not only would this result in a decrease in the manufacturing cost, but also a decrease in manufacturing yield due to short circuits between the divided electrodes.

(Object of the Invention) The present invention has been made in order to eliminate the manufacturing defects of ultra-thin multi-mode piezoelectric filter elements, which have been studied in the past, as described above. It is an object of the present invention to provide a frequency adjustment method that does not require close alignment, does not cause short circuits between divided electrodes, and can therefore ensure high production efficiency and yield.

(Summary of the Invention) In order to achieve the above-mentioned object, 1 the frequency adjustment method according to the present invention is such that, before a filter element is assembled into a package, an appropriate mask is placed on the side substantially corresponding to the divided electrodes of the entire surface electrode, and The required additional deposition is performed while moving the mask and the filter element relatively.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

Prior to describing the embodiments, a frequency adjustment method in a conventional multi-mode piezoelectric filter element will be briefly explained in order to facilitate understanding of the present invention.

FIG. 3(a) is a partially cutaway front view showing the structure of a conventionally manufactured dual mode piezoelectric filter. 3.14 and electrode leads 20.21 extending from these to the edge of the blank plate 19, respectively.
, and a common voltage [I22 and electrode lead 23] is connected to the opposite surface.
are formed by vacuum evaporation, and the ends of the leads 20.2J and 23 are connected and fixed to the tips of the hot leads 25, 26 and the ground lead 27, which pass through the base 24 in an airtight manner, respectively, with conductive adhesive. At the manufacturing stage, the resonance frequency of the divided electrodes 13 and 14 is measured, and the electrode material is additionally vapor-deposited through the mask 28 on the divided electrodes with higher frequencies (see FIG. 2(b)). Alternatively, additional vapor deposition may be performed on one half of the common electrode 22 (see FIG. 3(c)).
In any case, since the type of filter element that is rejected has a completely flat substrate, there is little variation in thickness between mass-produced substrates.1 There is virtually no local difference in thickness between individual substrates, and the substrate Since both the size and the electrode size are much larger than the ultra-thin plate multi-mode piezoelectric filter element according to the present invention, the frequency adjustment as described above can be carried out relatively easily.

However, in the ultra-thin multi-mode piezoelectric filter element according to the present invention, a large number of recesses are formed in alignment on a large-area piezoelectric wafer by etching or mechanical polishing, and then electrodes are placed on the entire surface of the recesses on the sides of the recesses. The required divided electrodes are formed on the opposing surfaces of the recesses, and each of these filter elements is cut after the required frequency adjustment is performed to obtain a large number of filter elements at once. Piezoelectric wafers inevitably have local variations in thickness, and these variations in thickness cause variations in the depth of the recesses, as shown in FIG. In addition to reflecting this, the uniform electrode formation edge initially performed in the wafer state also causes a considerable difference in the resonance frequency between the portions of the divided electrodes 13 and 14 because the variation in plate thickness is preserved.
As mentioned above, it has been difficult to solve this problem using the conventional additive deposition method as described above.

In order to solve this problem, the present invention takes the following method.

FIG. 1(a) shows the frequency a! of the ultra-thin multi-mode piezoelectric filter element according to the present invention. ! This is a cross-sectional view for explaining the concept of the method. First, the resonant frequencies of the divided electrodes 13 and I4 of the individual filter elements formed in alignment on the piezoelectric wafer are measured. ! 1
It is obvious that the frequency of the portion 3 is higher than that of the electrode 14.

This means that the thickness of the piezoelectric plate (including the thickness of the electrode) at the part where 113 of the vibrating part 2 is attached to the shell is electric! Since t14 means that it is thinner than that of the attached part, the thickness of the additional A# film 29 gradually decreases from the annular surrounding part 311 to the center 2 of the half surface of the wafer concave surface to which the electrode 13 is attached. It is necessary to perform the vapor deposition as follows. In order to make this possible, a mask 31 having an opening 30 of an appropriate size on the surface where additional vapor deposition is to be performed is used while measuring the resonance frequency between the electrode 13 and the electrode on the opposite surface (the entire surface electrode 4).
The mask 3I may be brought into contact with the wafer and moved relative to the wafer at a required speed.

By doing this, there is no restriction on the thickness of the raw plate of the vibrating section 2.
can be compensated for and Sl! The resonant frequencies of the portions W4 of the top layer 34 can be matched with each other with considerable accuracy.

Incidentally, since the mask 3 is moved relative to the wafer, it is sufficient to align each filter element with respect to the 1R electrode I3 or 14, so that the mask 3 is moved relative to the wafer. does not require precise alignment.

By the way, in order to carry out the above-mentioned frequency jl adjustment, it is sufficient to use a device as shown in FIG. A mask 31 and a drive mechanism 34 for moving the same at a predetermined speed are disposed, and a hood 35 that completely covers the mask 31 is provided below the mask 31.
A steamed food heating section 36 is disposed at the bottom of the chamber, and a shutter 37 is disposed between the mask 31 and the heating section 36, and these are housed in a vacuum chamber. In addition, the drive mechanism 34 of the mask 31
Generally, a nut 39 engaged with a precision screw 38 is fed by a motor.

The additional evaporation device for frequency adjustment described in 1.
2. Using a resonant frequency measuring device (not shown) for each of the above filter elements, the resonant frequency of the divided electrode 1314 portion was measured and stored, and the portions to be subjected to additional vapor deposition were determined. 33, which is also not shown, moves the filter element to be subjected to additional vapor deposition onto the hood 35, opens the shutter 37, and then moves the mask 31. Additional vapor deposition is performed while

The moving speed of the mask 3I may be determined according to the relationship with the amount of additional deposition that can be predicted based on the resonant frequency of the additional deposition portion measured in advance.

During the additive deposition process, the drop in the resonant frequency of the core may be measured and changes may be made midway based on the results. These operations can be performed using the C2 attached to the additive deposition equipment.
It is clear that the process can be implemented reliably by providing the required program to 0, so a more detailed explanation will be omitted to avoid complication of the specification.

1. Since the present invention uses the following method, the thin part of the piezoelectric plate of the filter element vibrating part is made thicker by the electrode material, and as a result, the vibrating part thickness is equivalently made uniform. This reduces the amount of electrode deposits on the front and back sides of the piezoelectric plate and suppresses the generation of spurious noise, compared to simply matching the resonant frequencies of the divided electrode parts by additional vapor deposition on one divided electrode. It should be noted that it also has the effect of

(Effects of the Invention) Since the present invention uses the method as explained above, it is possible to eliminate the problem caused by the variation in the thickness of the piezoelectric element between the divided electrode parts of the 8NN thin plate mode piezoelectric filter element. Since the mismatch in resonant frequency that occurs can be easily resolved by positioning the mask and filter element that does not require high precision, it is possible not only to improve the production efficiency of filter elements and reduce manufacturing costs, but also to improve the present invention. If such an additional vapor deposition method is used, the balance between the equivalent amounts of electrode deposits on the front and back surfaces of the piezoelectric element plate will not be disturbed, and therefore it is effective in suppressing the generation of spurious noise.

[Brief explanation of the drawing]

FIG. 1(a) shows the frequency j1! according to the present invention. ! FIG. 2(b) is a conceptual diagram illustrating the method; FIG.
b) is a perspective view showing the structure of an ultra-thin piezoelectric resonator and a sectional view showing its packaging method, and (c) is a package of an ultra-thin baking soda mode piezoelectric filter element to which the method of the present invention is applied. Figure 3 is a plan view showing the state in which it is stored in the
a) to (c) are front views showing the configuration of a conventional multi-mode piezoelectric filter element and a conceptual diagram showing one frequency adjustment method thereof, and FIG. 4 is an ultra-thin multi-mode piezoelectric filter element to which the present invention is applied. FIG. 3 is a cross-sectional view showing the state of the filter element before frequency adjustment. Symbol 1...Piezoelectric element plate, 2...Vibrating part, 3...Annular surrounding part, 4...Full surface electrode, 13.14...Divided electrode, 31...Mask patent applicant Toyo Tsushin Machine Co., Ltd.

Claims (1)

[Claims] An ultra-thin vibrating part and a thick annular surrounding part that supports the periphery of the vibrating part are integrally formed, and a divided electrode is provided close to one principal surface of the vibrating part of a piezoelectric element plate, and at least the divided electrode is connected to the opposite surface of the vibrating part. In an ultra-thin multi-mode piezoelectric filter element in which a full-surface electrode is formed on a corresponding surface, a mask having a predetermined opening is disposed on the full-surface electrode side, and while relative movement between the mask and the filter element is performed, the mask is removed. Frequency adjustment of an ultra-thin multi-mode piezoelectric filter element, characterized in that the resonant frequencies of the divided electrode forming portions of the filter element are adjusted to match by additionally depositing an electrode material through the filter element. Method.