JPS6228610B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic filter and a method for manufacturing the same.

As is well known, ceramic filters such as energy-trapped piezoelectric ceramic resonators that utilize thickness vibration or the like are highly evaluated for their high performance in relatively high frequency bands, such as IMHz or higher, and are widely used.

The front view shown in Figure 1A is a resonator with a conventional structure, which is an example of a ceramic filter.
Both the front energy trapping electrode 10 and the back electrode 11 are provided to be exposed on the surface of the piezomagnetic element 15. FIG. 1B is also an example of a ceramic filter with a conventional structure, and is characterized in that the front energy trapping electrodes 12, 13 and the back electrode 14 are all exposed on the surface of the piezomagnetic element 16. .

Since the resonant frequency of a ceramic filter takes a specific value, it is necessary to adjust it to a predetermined value during the manufacturing process. In a ceramic filter with a conventional structure as shown in Fig. 1 A and B above, the shape and dimensions of the piezoelectric magnetic element, which are a major factor in determining the resonance frequency diagram, are determined based on empirical rules as much as possible before forming the electrodes. After carefully selecting the materials, electrodes were formed or the resonant frequencies of the completed products were measured to select those that met predetermined standards.

However, in such a method, it is natural that the frequency variation is large and the yield is extremely poor.

On the other hand, unlike when piezoelectric ceramic plates are used, in the case of high-grade crystal films for narrow bands, the resonant frequency decreases as the electrode thickness increases, so the resonant frequency of the actual product is monitored during the manufacturing process.
A method has been adopted in which the thickness of the electrode is adjusted by controlling the amount of evaporation to achieve a predetermined resonance frequency, and very good results have been achieved.

Therefore, it would be great if a method similar to the one used for quartz filters could be applied to ceramic filters to which the present invention relates, but unfortunately, it is difficult.
This is because piezoelectric ceramic plates are inherently highly coupled compared to quartz crystals, so the piezoelectric reaction accounts for a significant portion of the energy trapping, and the mass effect of the electrodes does not contribute much to the energy trapping. Even if the thickness of the electrode is slightly changed, the change in the resonant frequency due to the difference between the resonant and anti-resonant frequencies is so small that it is not practical. If ceramic filters were manufactured while monitoring the frequency in an evaporator like quartz filters, they would inevitably be expensive. There is a risk that you will not be able to take advantage of your unique qualities.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new structure of a ceramic filter and a method of manufacturing the same, which eliminates these drawbacks and facilitates reduction in manufacturing costs.

The novel structure proposed by the present invention is characterized in that the energy trapping electrode is formed by being embedded inside the piezoelectric ceramic body.

Hereinafter, an example of the energy trap type piezoelectric ceramic vibrator of the present invention will be explained using the drawings.
That is, as shown in the perspective view of FIG.
3, 24, 25 are formed, and the electrode extraction portion 2
The electrode portions other than 6, 27, and 28 are configured so as not to be exposed on the surface of the piezoelectric ceramic body.

With the structure of the present invention, frequency adjustment can be made easily and with high precision, and energy confinement, which is the essence of the filter function, can also be achieved sufficiently.

That is, in the structure of the present invention, since the energy trapping electrode is located inside the piezoelectric ceramic body, the frequency can be adjusted while polishing the thickness of the piezoelectric ceramic in the portion covering the outside of the electrode. Moreover, while obtaining these advantages, there are no disadvantages. In other words, as a result of the high coupling of piezoelectric ceramics, the cutoff frequency of the energy trapping electrode part is considerably lower than that of the non-electrode part. Covering the piezoelectric ceramic with a piezoelectric ceramic does not have any adverse effect on the original energy trapping effect.

Next, in order to obtain the structure of the present invention as described above, an energy trapping electrode is printed with a conductive paste on the surface of a raw ceramic sheet or a press-molded body made of piezoelectric ceramic powder and an organic binder, and then the piezoelectric ceramic A suitable method is to print a powder paste or to press a raw ceramic sheet and then sinter the whole.

Hereinafter, the manufacturing method of the present invention will be specifically explained using a typical example of implementation and using FIG. 3.

First, piezoelectric ceramic powder is dispersed in a solvent together with an organic binder to form a slurry.

Using the doctor blade method, 10μ ~
Make a uniform raw sheet of about 200μ.

This raw sheet is shown in Figure 3 as 31, 32, 33, 3.
4, 35, 36, for example, are punched out into rectangular shapes of 60 mm x 40 mm, and then printed with gold, platinum, palladium, silver, or an alloy of two or more of these by screen printing. Energy trapping electrodes 37, 3 using conductive paste
Print many numbers 8 and 39. Between the ceramic raw sheets 32 and 36 on which electrodes are printed, a predetermined number of raw ceramic sheets (33, 34, 35 in this example) on which no electrodes are printed are stacked and pressed to match a desired resonance frequency. Alternatively, instead of such a laminate, ceramic raw sheets 32, 3
It goes without saying that energy trapping electrodes 37, 38, and 39 may be printed on the front and back sides of the press-formed bodies corresponding to 3, 34, and 35.

Next, energy trapping electrodes 37, 38,
Ceramic raw sheets 31 and 36 are crimped to cover 39, and the whole is sintered. Of course, instead of the raw ceramic sheets 31 and 36, a paste made of piezoelectric ceramic may be printed. In any case, the present invention is characterized by embedding the energy trapping electrode inside the piezomagnetic element. This ceramic raw sheet 31,
The thickness equivalent to 36 mm should be designed to be necessary and sufficient for adjusting the resonance frequency, and the number of adjustment steps by polishing should be reduced as much as possible.

Among the manufacturing methods of the present invention, the method of stacking several thin raw ceramic sheets to a predetermined thickness as shown at 32, 33, 34, and 35 in Fig. 3 is as follows:
There are also advantages on a mass production scale, such as the ability to immediately respond to changes in design specifications.

Now, heat the laminate thus crimped to 950℃ to 1300℃.
It is sintered at a temperature of about 1 hour at 0.degree. C., and input/output electrodes are applied to the areas where the internal electrodes are exposed on the side surfaces, and polarization electrodes (not shown) are applied to both surfaces of the laminate and then baked.

After that, apply DC voltage to the polarization electrode at 120℃.
Polarize for 1 hour.

After dividing into individual filters with a scriber, the frequency is adjusted by polishing one or both of the upper and lower surfaces of the laminate while measuring the frequency with an energy trapping electrode. At this time, some or all of the previously formed polarization electrodes will be lost due to polishing, but this does not matter at all.

In this way, all the ceramic filters manufactured according to the present invention exhibit good filter characteristics,
Moreover, the center frequency of the filter could be adjusted to within ±0.1% of the target value.

As described above, by implementing the present invention,
It is possible to provide a high-performance ceramic filter at a low cost that allows simple and accurate frequency adjustment without requiring special equipment, and has great industrial value.

[Brief explanation of the drawing]

FIG. 1 shows a front view of an example of a conventional ceramic filter. A is an example of a resonator, and B is an example of a filter. In the figure, 10, 12, 13 are front energy trapping electrodes, 11, 14 indicated by dotted lines are back electrodes, and 15, 16 are piezomagnetic elements. FIG. 2 is a perspective view showing an example of the structure of the ceramic filter of the present invention.
2 shows a piezoelectric ceramic body, 23 and 24 electrodes on the input/output side, 25 a ground electrode, 26 and 27 an input/output terminal, and 28 a ground terminal, respectively. FIG. 3 is an exploded perspective view for explaining an example of the manufacturing method of the present invention. 31,3 in the figure
3, 34, and 35 indicate raw ceramic sheets to which no electrodes are applied, and 32, 36 indicate energy trapping electrodes 37, 3 as shown in the shaded area.
It shows a ceramic sheet with numbers 8 and 39 printed on it.

Claims (1)

[Claims] 1. An energy trapping electrode is embedded inside the piezoelectric ceramic body, and has a three-terminal configuration with an input/output electrode and a ground electrode, and the electrode is located at or near the center of the piezoelectric ceramic body. 1. A ceramic filter, wherein the outer surface of a piezoelectric ceramic body corresponding to the electrode can be polished into parallel planes. 2. Print an energy trapping electrode with a conductive paste on the surface of a raw ceramic sheet or press-molded body made of piezoelectric ceramic powder and an organic binder, and then print a paste made of piezoelectric ceramic powder on top of that, or print a raw ceramic sheet on top of that. A method for manufacturing a ceramic filter, which comprises crimping and then sintering the entire ceramic filter.