JPS6012810B2 - Low phase distortion piezoelectric filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric filter using an energy confinement type thickness double vibration mode with improved group delay time characteristics (hereinafter abbreviated as DT characteristics).

Filters using the energy confinement type thickness double vibration mode are disclosed in Japanese Patent Publication No. 45-122384 and Utility Model Publication No. 1983-
This method is known from Japanese Utility Model Publication No. 3090y, Japanese Utility Model Publication No. 51-21634, and US Pat. No. 3,676,724. For example, the structure disclosed in US Pat. No. 3,676,724 is shown in FIG. 1 as an electrical circuit diagram. In the figure, 1 is a first energy confinement type dual mode filter element, 2 is a second energy confinement type dual mode filter element, and 3 is a capacitor for capacitance coupling between the filter elements 1 and 2. Note that 4, 5, and 6 are an input terminal, an output terminal, and a common ground terminal, respectively. FIG. 2 shows an example of the actual structure of the circuit shown in FIG. 1, and the packaging is done by the method disclosed in Japanese Patent Publication No. 45-122384. In the figure, 7 is a piezoelectric ceramic substrate, and 8 is an exterior resin made of an inelastic material. FIG. 3 shows a cross-sectional view taken along line A-A in FIG. 2. In Figures 2 and 3, 9 and 10 are
A cavity 11,1 for not disturbing the vibration of the filter element 1
2 is a cavity for not disturbing the vibration of the filter element 2. The cavity 9 exists on the piezoelectric ceramic plate 7 on the side where the divided electrodes 13 and 14 of the filter element 1 are provided, and the cavity 1
It exists on the piezoelectric ceramic plate 7 on the side where the common electrode 15 is provided on the opposite side. Similarly, the cavity 11 is present on the piezoelectric ceramic plate 7 on the side where the divided electrodes 16 and 17 of the filter element 2 are provided, and the cavity 12 is conversely present on the piezoelectric ceramic plate 7 on the side where the common electrode 18 is provided. exists above.
In this way, cavities were provided on both surfaces of the vibrating portion of the electric ceramic plate 7. This is because it was thought that normal operation would not occur if the exterior resin 8 was in close contact with the vibrating part since thickness vibration was used.

Furthermore, the passband characteristics of the conventional piezoelectric ceramic filter as described above, and the G.I. D. T. An example of the characteristics is shown in FIG. 6a.

In the figure, curve a shows the passing band characteristic, and curve b shows ○.
D. T. Show characteristics. G. D. T. The characteristic is a downward convex curve. G. D. T. It is preferable that the characteristics be as flat as possible because phase distortion of the passing signal is small. Therefore, the main object of this invention is that G. D. T. It is to improve the characteristics.

Another object of this invention is that G. D. T. The aim is to simplify the production process as well as improve properties.

Another object of this invention is that G. D. T. In addition to improving the characteristics, the goal is to lower the unit price of the product. Another object of this invention is that G. D. T. In addition to improving the properties, the goal is to improve the impact resistance of the product and increase the reliability of the product.

In summary, the present invention is directed to a piezoelectric filter using an energy confinement type thickness double vibration mode characterized in that one surface vibrating portion of a piezoelectric substrate is covered with an inelastic object. This is a piezoelectric filter in which an adhesive exterior resin is used as a non-elastic material on the vibrating portion of one surface side of the piezoelectric substrate covered with the piezoelectric substrate.

The above-mentioned objects and other objects and features of the present invention will become more apparent from the following description of embodiments with reference to the drawings.

In this embodiment of the present invention, parts having the same functions as those of the conventional example are given the same numbers and their explanations will be omitted.

FIG. 4 is an example in which the cavity 12 in FIG. 3 is eliminated.

In other words, in the case of the manufacturing method according to Japanese Patent Publication No. 45-22384, it is only necessary to leave the common electrode 18 and the entire vibrating part around it free of wax. The passband characteristics of a piezoelectric ceramic filter having such a structure, and G. D
．． T. An example of the characteristics is shown in FIG. 6b. The passband characteristic curve a is almost the same as a in the same figure, but the G. D. T. The characteristic curve b is flatter than that shown in FIG. 3b. Figure 5 is the third
This is an example in which both the cavities 10 and 12 in the figure are removed.

The manufacturing method for eliminating cavities is the same as the example shown in the fourth figure. Figure 6c
are the passband characteristics of the piezoelectric ceramic filter of this structure and G. D. T. An example of the characteristics is shown below. The passing band characteristic curve a is wider than the curves a and b in the same figure, and the G. D. T
．． The characteristic curve is slightly upwardly convex. Note that the surface of the piezoelectric substrate on which the cavity is left is not limited to the side on which the divided electrodes are provided.

In addition, when focusing on a single cavity provided on one side of the piezoelectric plate, it is possible to not only eliminate the cavity completely, that is, mechanically damp the entire vibration range with the exterior resin, but also use the exterior resin to dampen the vibrations. Examples in which the range is partially damped are also included in the present invention.

That is, in the case of the manufacturing method according to Hakama Kosho No. 45-22384, when wax is partially attached to the resonant electrode surface or the piezoelectric ceramic plate surface within the vibration range, a cavity is formed in that part, resulting in partial damping. The cavity forming method is not limited to the method disclosed in Japanese Patent Publication No. 45-122384, but any other known method can be applied to the present invention.

It goes without saying that the number of filter elements provided on the piezoelectric plate is not limited to two, but may be one, three or more.

As is clear from the above embodiments, according to the present invention, G.G. D. T. It can be freely controlled to improve the characteristics.

Further, while using a high-Q piezoelectric material, the same effect as when using a low-Q piezoelectric material can be obtained. Further, although conventionally a process for forming a cavity was required, according to the present invention, at least one process for forming a cavity is no longer necessary, thereby simplifying the production process. As a result, the unit price of the product becomes cheaper. Also, from a different perspective, G. D. T. In order to improve the properties compared to conventional ones, it would normally be necessary to add a process or material to the conventional process, but according to this invention, the amount of exterior resin is increased by at least one cavity volume (which is extremely small). It's easy to do and it's low cost. ○． T. It can be said that the characteristics can be improved. moreover,
Since the area where the exterior resin is in close contact with one surface of the piezoelectric substrate increases, the strength of the piezoelectric substrate is equivalently improved. In other words, the impact resistance of the product can be improved and the reliability of the product can be increased. In addition, outside of the data in Figure 6a, ■ Made by Murata Manufacturing Co., Ltd., product name S
FFEIO. The data of one product of 7MP, b and c of the same figure, were obtained from a product in which the present invention was implemented using the internal element of the product with the same product name.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a piezoelectric filter, Fig. 2 is a plan view showing the internal structure of the piezoelectric filter of the circuit shown in Fig. 1, and Fig. 3 is a sectional view taken along line A-A in Fig. FIG. 4 is a sectional view of the first embodiment of the present invention, FIG. 5 is a sectional view of the second embodiment, and FIG. 6 shows the passband characteristic curves a and G. of the piezoelectric ceramic filter.
D. T. A characteristic curve b is shown, where a shows the third illustrated structural example, b shows the fourth illustrated structural example, and c shows the fifth illustrated structural example. 1...First filter element, 2...Second filter element, 7...Piezoelectric ceramic substrate, 8
......Exterior resin, 9,10,11...Cavity, 13,14...Divided electrode, 15...Common electrode, 16,17...・Divided electrode, 18...
...Common electrode. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1 In a piezoelectric filter using an energy confinement type thickness double vibration mode characterized in that one surface-side vibrating part of the piezoelectric substrate is covered with an inelastic object, the inelastic object is covered with an adhesive exterior resin. A low phase distortion piezoelectric filter using an energy confinement type thickness double vibration mode, which is characterized by a partial thickness.