JPS62281319A - Variable capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a variable capacitor, and for example, to an element structure of a multilayer variable capacitor using a ferroelectric ceramic material as an insulator. .

[Conventional technology]

Conventionally, variable capacitors consist of (a) multiple metal plates called variable capacitors that are arranged facing each other, and the effective area can be changed by moving one of the plates. (b) Connect multiple ceramic capacitors etc. in parallel, and connect each capacitor with an IC for operation.
etc. are connected and operated individually to change the capacitance value in an electric circuit, ←J Utility Application No. 58-172 shown in Figure 6
No. 557, etc., a ferroelectric layer is formed on the outermost ferroelectric layer 10 of a multilayer ceramic capacitor, and a part of the comb blade-shaped electrode 4a is mechanically cut by laser trimming or the like. There are means for changing the effective area between the internal electrodes 4b which are arranged facing each other with the layer 10 interposed therebetween.

[Problem that the invention seeks to solve]

In the conventional variable capacitor (A) described above, the capacitor as a whole has a large shape and the capacitance is changed mechanically, so the capacitance cannot be changed by an electrical signal and requires an electrical response. It cannot be applied to circuits that

In (b), multiple capacitors are used in parallel, so
It is difficult to highly integrate electrical circuits, and since multiple capacitors are operated individually, the capacitance is output in steps.

Furthermore, (c) has the disadvantage that once a part of the electrode is cut off, the capacitance cannot be increased thereafter.

On the other hand, the inventor has already developed a device for drawing out the capacity as shown in FIG. A variable capacitor is proposed in which the poles are arranged at positions sandwiching the bias extraction electrodes.90 This variable capacitor has bias extraction electrodes 12a.
, 12bK DC voltage gold is applied to the polarization 11a for drawing out the capacitance.

The capacitance between 11b and 11b can be changed linearly. However, the variable capacitor shown in FIG. 5 has a ferroelectric layer 10a (10
b) The area where no DC bias is applied and the capacitance can be changed is the bias extraction 'electrode 17a, 12.
The ferroelectric layer 10c is sandwiched between the ferroelectric layer 10c and the ferroelectric layer 10c, so that a large capacitance change cannot be obtained. For this reason, its use must be limited to a narrow range.

[Means for solving problems]

SUMMARY OF THE INVENTION The object of the present invention is to eliminate such conventional drawbacks and provide a nine-variable capacitor.

According to the present invention, the end faces of the internal electrodes are exposed from the insulating layer using a ferroelectric material on the four opposing sides of the hexahedral element, and the external electrodes are attached to the end faces of the poles inside. In the variable capacitor, a pair of internal electrodes are used as capacitance extraction electrodes, and a pair of internal electrodes are used as bias extraction electrodes, and the bias extraction electrodes are arranged at positions where the capacitance extraction electrodes are sandwiched. A capacitor is obtained.

Next, the principle of operation of the variable capacitor of the present invention will be explained.

Generally, ferroelectric materials used in capacitors etc. have a g-electric constant due to a phase transition near the Curie point.

Abnormalities are observed in many physical properties such as elastic modulus and specific heat, but in particular, the dielectric constant C suddenly increases at the Curie point. This is because the crystalline state of the crystalline body is extremely unstable near the Curie point, and almost no internal stress is generated. When a DC bias is applied to the ferroelectric near this Curie point, internal stress is generated, and the dielectric constant ε becomes small.

As mentioned above, by intentionally controlling the external electric field of the ferroelectric material near the Curie point, it is possible to change the dielectric constant ε, so the bias extraction provided in the ferroelectric material near the Curie point When a DC bias is applied to the capacitance extraction electrode (hereinafter referred to as bias electrode), the capacitance extraction electrode (
It becomes possible to change the capacitance tTh between the electrodes (hereinafter abbreviated as capacitive electrodes).

〔Example〕

The present invention will be explained below with reference to FIGS. 1 to 4.
- FIG. 1 is an exploded perspective view of the variable capacitor of the present invention.

Reference number 1 in the figure is made by kneading ferroelectric ceramic powder with a synthetic resin binder such as polyvinyl alcohol (PVA),
The green sheet 2 is formed into a sheet by a doctor blade method or the like and cut into a desired shape.The green sheet 2 is an internal electrode in which a conductive paste such as palladium is applied to one side of the green sheet 10 and dried.

Next, the laminated structure of the valley sheet of the capacitor of the present invention will be explained.

Reference numerals 11a and 11b are exposed in the center with an end surface 2a which becomes an extraction electrode of a rectangular internal electrode 2 aligned with one end surface of the front edge or the rear edge of the green sheet 1, and then an upper capacitor electrode and a lower capacitor electrode.

12a and 12b are rectangular internal electrodes 2 on both side end surfaces of the green sheet 1 outside the capacitor electrodes 11a and llb.
The upper bias electrode and lower bias electrode 13a and 13b, which are aligned and exposed on the end surface 2bt, are a green notebook for a protective film without an internal electrode disposed in the outermost layer.

Next, each sheet is arranged in the configuration shown in Figure 1, and the stacked sheets are heat-processed from above and below using a heat press, etc., and after being made into a single sheet, it is heated in an electric furnace at a temperature of several hundred degrees to several hundred degrees. After firing, as shown in FIG. 3, external electrodes 21a are attached to the front and rear capacitance electrode end faces 2a, and external electrodes 21b are attached to the left and right bias electrode end faces 2b, thereby forming the variable capacitor of the present invention.

Next, a method for adjusting the capacitance of the variable capacitor of the present invention will be explained.

By applying a DC voltage to the external electrode 21b connected to the bias electrode 12a.

The IT ratio of the ferroelectric layer 10C sandwiched between the ferroelectric layers 12b changes to the negative side. The change characteristics are shown in FIG. 4, and when a full DC bias voltage of 50 V is applied to a strong conductor with a thickness of 45 μm, the capacitance changes significantly by -70%.

As described above, the variable capacitor of the present invention can linearly change the capacitance between the capacitance electrodes by using the electrodes as described above and applying a DC voltage to the bias electrode.

〔Effect of the invention〕

As explained above, the variable capacitor of the present invention has the following effects.

(i) The capacity can be obtained linearly by varying the capacity over a wide range.

(ill) The capacitance can be changed to ei by an external electrical signal.

(11D Small size, high reliability, suitable for !i,!.

In addition, the variable capacitor of the present invention can be used in a filter circuit, for example, to perform cutoff and pass operations at any frequency in one cycle, and also with other time constants.

It can be widely used in oscillation circuits, etc.

[Brief explanation of the drawing]

1, 2, and 3 are an exploded perspective view, a right sectional view, and a perspective view, respectively, of a variable capacitor according to an embodiment of the present invention;
Fig. 4 is a capacitance-bias voltage characteristic diagram of the variable capacitor of the present invention, Fig. 5 is a sectional view of a variable capacitor of the ninth embodiment previously proposed by the present inventor, and Fig. 6 is a diagram of a conventional variable capacitor. It is an exploded perspective view showing an example. 1...Green sheet, 2...Internal electrode, 11a11b...Capacitance electrode, 12a, 12b
...Bias [@, 2a...Capacitive electrode end surface, 2b...Bias electrode end surface, 2La, 2
1b...external electrode, 10...ferroelectric layer, 10a, 10b...capacitance electrode, ferroelectric layer between bias electrodes, 10C...bias Ferroelectric layer between electrodes, 4a, 4b... Capacity 1 is the pole. Figure 3 2) 7゜TO203040Sθ / phantom voltage (v) Moonlight thickness 45 m Section 4 Capacitance bias characteristic 1

Claims (1)

[Claims] In a variable capacitor in which the end faces of internal electrodes are exposed from an insulating layer made of a ferroelectric material on four opposing sides of a hexahedral element, and external electrodes are attached to the end faces of the internal electrodes,
A variable capacitor characterized in that one pair of the internal electrodes are used as capacitance extraction electrodes, the other pair are used as bias extraction electrodes, and the bias extraction electrodes are arranged at positions where the capacitance extraction electrodes are sandwiched.