JPH0394509A - Piezoelectric filter - Google Patents

Abstract

PURPOSE:To obtain an excellent characteristic in a capacitor part by using a dielectric material for a part of a piezoelectric board to which a capacitor electrode is to be formed. CONSTITUTION:A part formed with a capacitive electrode 24 in a mother board 26 made of a PZT is, e.g. punched to form plural holes 28. Then a dielectric substance 16 such as titanium oxide barrium group or lead composite perovskite group is packed in the holes 28. Then a filter electrode 18 of a prescribed pattern made of an Ag paste is formed on one major side of a mother board 26 baked integrally. In this case, since the characteristic of the capacitive part is improved, the filter characteristic is enhanced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a piezoelectric filter, in particular, for example, a piezoelectric filter made of PZT (
The present invention relates to a piezoelectric filter formed using a ceramic substrate exhibiting piezoelectric properties, such as lead zirconate titanate.

[Prior art]

Conventionally, PZT has generally been used as a piezoelectric substrate for, for example, a three-terminal piezoelectric filter. In a three-terminal piezoelectric filter, in order to add capacitance, it is necessary to form a portion that does not have piezoelectric characteristics on the piezoelectric substrate. Conventionally, partial polarization processing has been used as a method for this purpose.

[Problem to be solved by the invention]

However, although PZT has good characteristics as a piezoelectric substrate, it has a low dielectric constant and is inappropriate for forming a capacitor. Furthermore, since PZT has a large dielectric loss tan δ, there is a problem in that the insertion loss of the filter becomes large.

Therefore, the main object of the present invention is to provide a piezoelectric filter that uses a piezoelectric substrate and yet provides good characteristics in the capacitive portion.

[Means to solve the problem]

The present invention is a piezoelectric filter in which a vibrating electrode and a capacitive electrode are formed on a piezoelectric substrate, characterized in that a portion of the piezoelectric substrate on which the capacitive electrode is to be formed is made of a dielectric material. .

[Operation] A hole can be made in a green sheet made of a piezoelectric material such as PZT by a method such as punching at a portion where a capacitor electrode is to be formed. Then, powder of a dielectric material such as barium titanate or lead composite perovskite is filled into the hole. Then, by reciting this, the portion where the capacitor electrode is to be formed is formed of a dielectric material. Even if polarization treatment is applied afterwards,
Although the piezoelectric substrate as a whole is polarized, the portion formed of the dielectric material is hardly polarized, and that portion exhibits capacitive or optimal dielectric characteristics.

〔Effect of the invention〕

According to this invention, since a dielectric material can be used in the portion of the piezoelectric substrate where the capacitive electrode is to be formed, the characteristics of the capacitive portion are improved in a piezoelectric filter such as a three-terminal piezoelectric filter, so that the filter characteristics becomes good.

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

〔Example〕

As shown in FIG. 6, the three-terminal piezoelectric filter 10 of this embodiment includes a piezoelectric substrate 12 made of, for example, PZT, and a dotted circle 14 on which a capacitive electrode 24 (described later) is formed on the piezoelectric substrate 2. The area surrounded by is formed by a dielectric material 16 such as barium titanate or lead composite velocite.

A filter electrode l8 made of, for example, Ag is formed on one main surface of the piezoelectric substrate 12. The filter electrode 18 includes two pairs of opposing vibrating electrodes 20,
One electrode of the opposing vibrating electrodes 20 is connected to a connecting electrode 22, and the other electrode is commonly connected to a capacitive electrode 24 formed on the dielectric material 16. Further, although not shown, a predetermined ground electrode and a back electrode are formed on the other main surface of the piezoelectric substrate 12.

Such a three-terminal piezoelectric filter 10 is manufactured as follows.

First, as shown in FIG. 1, it is made of, for example, PZT,
A green sheet motherboard 26 that will later be cut out to become the piezoelectric substrate 12 described above is prepared.

Then, in the mother board 26, the capacitor electrode 2 is removed in a later process.
A plurality of holes 28 are formed by, for example, punching the portion where 4 is to be formed (the dotted circle 14 in FIG. 6).

Then, as shown in FIG. 2, these holes 28 are filled with a dielectric material 16 made of, for example, barium titanate or lead composite perovskite. At this time, if the dielectric material is made into powder, the embedding work will be easier. Thereafter, the mother board 26 in which the dielectric material 16 is embedded is integrally fired.

Next, as shown in FIG. 3, a filter electrode 18 of a predetermined pattern made of, for example, Ag paste is formed on one main surface of the integrally burned mother substrate 26. At this time, the capacitor electrode 24 is formed on the dielectric 16. Note that a predetermined pattern of ground electrodes and back electrodes are also formed on the other main surface of the motherboard 26.

Thereafter, as shown in FIG. 4, polarization electrodes 3Oa and 30b are applied to the entire surface of both main surfaces of the motherboard 26 using a conductive resin made of, for example, epoxy resin mixed with silver powder. Then, a DC voltage of a predetermined magnitude is applied between the polarization electrodes 30a and 30b to perform polarization processing. At this time, the portion formed by PZT is polarized, but the portion where the dielectric 16 is embedded is hardly polarized.

Here, the size of the hole 28, that is, the dielectric 16, is slightly larger than the capacitor electrode 24, and is made large enough to sufficiently cover the area necessary for the capacitor electrode 24.

By doing so, the capacitor electrode 2 is
Since the electrodes 30a and 30b include all edges of the electrodes 30a and 30b, the electric field concentration at that part during the polarization process is relaxed.After the polarization process is completed, the polarization electrodes 30a and 30b are connected to an organic material such as Freon. Etching is performed using an etchant consisting of a container. Thereafter, as shown in FIG. 5, the motherboard 26 is cut in the directions shown by dashed-dotted lines 32 and 34 to obtain the three-terminal piezoelectric filter 10 shown in FIG. 6.

In the above-described embodiment, the polarization treatment was performed after forming the filter electrode 18 on the mother substrate 26, but the filter electrode 18 may be formed after the polarization treatment of the mother substrate 26 is performed.

Further, in the above embodiments, a three-terminal piezoelectric filter has been described, but the present invention is applicable to any other piezoelectric filter that requires a capacitive electrode.

[Brief explanation of drawings]

1 to 6 are illustrative views showing the manufacturing process of an embodiment of the present invention. FIG. 1 is a perspective view showing a state in which a hole is formed in a mother board, and FIG. FIG. 3 is a perspective view showing a state in which a body material is embedded, FIG. 3 is a perspective view showing a state in which predetermined electrodes are formed, FIG. 4 is a perspective view showing a state in which polarization electrodes are formed, and FIG. FIG. 5 is a perspective view showing a state in which the motherboard is cut out, and FIG. 6 is a perspective view showing a completed three-terminal piezoelectric filter. In the figure, 10 is a three-terminal piezoelectric filter, 12 is a piezoelectric substrate, 14 is a dielectric material, and 24 is a capacitive electrode.

Claims (1)

[Claims] A piezoelectric filter in which a vibrating electrode and a capacitive electrode are formed on a piezoelectric substrate, characterized in that a portion of the piezoelectric substrate on which the capacitive electrode is formed is made of a dielectric material. Piezoelectric filter.