JPH0519969B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a variable capacitor, and particularly to an element structure of a multilayer variable capacitor using a ferroelectric ceramic material for an insulating layer.

[Conventional technology]

Conventionally, variable capacitors have been constructed by (a) having multiple metal plates called variable capacitors arranged facing each other and moving one side to change the effective area, and (b) having multiple ceramic capacitors connected in parallel. (c) A type in which an IC or the like is connected to each capacitor and operated individually to change the capacitance value using an electric circuit. A part of the comb-shaped electrode 4a formed on the outermost ferroelectric layer 10 of the capacitor is mechanically cut by laser trimming or the like, and the electrodes are placed facing each other with the ferroelectric layer 10 interposed therebetween. Something that changes the effective area between internal electrodes 4b,
There are other means such as

[Problem that the invention seeks to solve]

Among the conventional variable capacitors mentioned above, in the variable capacitor of method (a), the overall shape of the capacitor is large and the capacitance changes mechanically, so it is not possible to obtain a means to change the capacitance by an electrical signal, and the electrical response is cannot be applied to the required circuit. In the method (b), since multiple capacitors are used in parallel, it is difficult to achieve high integration of the electric circuit, and since multiple capacitors are operated individually, the capacitance is output in a stepped manner. Furthermore, the method (c) has the disadvantage that once a portion of the electrode is cut off, the capacitance cannot be increased thereafter.

The purpose of the present invention is to eliminate the drawbacks of the conventional technology, provide a variable capacitor that outputs capacitance linearly over a wide range, can change the capacitance by an external electrical signal, is small, highly reliable, and has excellent mass production. It's about doing.

[Means for solving problems]

The variable capacitor of the present invention has a variable capacitor in which the end faces of internal electrodes are exposed from an insulating layer made of a ferroelectric material, and external electrodes are attached to the end faces of the internal electrodes on four opposing sides of a hexahedral element. In capacitors,
By using one pair of capacitance extraction electrodes (hereinafter abbreviated as capacitance electrodes) of the internal electrodes and the other pair as bias extraction electrodes (hereinafter abbreviated as bias electrodes), and by arranging the capacitance electrodes at positions sandwiching the bias electrodes. configured.

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

Generally, ferroelectric materials used in capacitors etc. exhibit abnormalities in many physical properties such as permittivity, elastic modulus, and specific heat due to phase transition near the Curie point. becomes larger. This is because the crystalline state of the ferroelectric is extremely unstable near the Curie point, and an electric dipole is easily generated by an external electric field. ) becomes larger. When a DC bias is applied to a ferroelectric material near this Curie point, a state occurs in which a large number of electric dipoles are generated as described above, and in this state, the response of the electric dipoles becomes slower in response to a small AC voltage. Therefore, the dielectric constant ε
becomes smaller. As mentioned above, by intentionally controlling the external electric field of the ferroelectric near the Curie point, it is possible to change the dielectric constant ε. Applying a DC bias makes it possible to change the capacitance.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1, FIG. 2, and FIG. 3 are an exploded perspective view, a sectional view, and a perspective view, respectively, of one embodiment of the variable capacitor of the present invention. First, in Fig. 1, 1 is a green sheet made by kneading ferroelectric ceramic powder with a synthetic resin such as polyvinyl alcohol (PVA) as a binder, forming it into a sheet by means such as a doctor blade method, and cutting it into a desired shape. ,
Reference numeral 2 designates an internal electrode in which a conductive paste made by adding butyl carbitol or the like to an alloy such as silver-palladium is coated on one side of the green sheet 1 and dried.

Furthermore, the laminated structure of each sheet of the capacitor of the present invention will be explained. Reference numerals 11a and 11b indicate upper bias electrodes and lower bias electrodes 12a and 12b, which are exposed at the center with end surfaces 2a, which serve as extraction electrodes of rectangular internal electrodes 2, aligned with one end surface of the front edge or rear edge of the green sheet 1. is the aforementioned bias electrode 1
An upper capacitor electrode and a lower capacitor electrode 13 are exposed on the outside of 1a and 11b with the end surfaces 2b of the rectangular internal electrodes 2 aligned with both end surfaces of the green sheet 1.
A and 13b are protective film green sheets without internal electrodes disposed on the outermost layer.

Next, the laminate of each sheet arranged in the configuration shown in Fig. 1 is heated and pressed from above and below using a heat press or the like to form a second layer.
After forming an integrated laminate as shown in the figure, it is fired in an electric furnace at a temperature of several hundred degrees to several thousand degrees, and external electrodes 21a are attached to the front and rear bias electrode end faces 2a as shown in FIG. The left and right capacitive electrode end faces 2b
An external electrode 21b is applied to the capacitor to form a variable capacitor of the present invention.

Next, the variable capacitor capacity adjustment method of the present invention will be explained. By applying a DC voltage to the external electrode 21a connected to the bias electrode, the dielectric constant of the ferroelectric layer 10 sandwiched between the bias electrodes 11a and 11b changes to the negative side. Figure 4 shows the change characteristics, and when the ferroelectric thickness is 45 μm
When a DC bias voltage of 50V is applied, the capacitance becomes -
A large change of 70%.

The variable capacitor according to one embodiment of the present invention described above is
By applying a DC voltage to the bias electrode using the electrode structure as described above, the capacitance between the capacitor electrodes can be linearly changed.

〔Effect of the invention〕

As explained above, the variable capacitor of the present invention is
One pair of internal electrodes are used as capacitance extraction electrodes, the other pair are used as bias extraction electrodes, and the capacitance extraction electrodes are arranged in positions that sandwich the bias extraction electrodes, and a DC voltage is applied to the bias electrodes. (1) Capacity can be obtained linearly over a wide range. (2)Capacitance can be changed by external electrical signals. (3) Compact, highly reliable, and suitable for mass production. Effects such as this can be obtained.

The variable capacitor of the present invention can be used in a filter circuit to perform cutoff and pass operations at any frequency with a single chip, and can be widely used in time constant oscillation circuits and the like.

[Brief explanation of drawings]

1, 2, and 3 are exploded perspective views, sectional views, and perspective views of a variable capacitor according to an embodiment of the present invention, and FIG. 4 is a capacitance-bias diagram of a variable capacitor according to an embodiment of the present invention. A voltage characteristic diagram, FIG. 5, is an exploded perspective view of an example of a conventional variable capacitor. 1... Green sheet, 2... Internal electrode, 2a
...Bias electrode end surface, 2b...Capacitance electrode end surface,
4a, 4b... Capacitive electrode, 10... Ferroelectric layer,
11a, 11b...bias electrode, 12a, 12
b... Capacitive electrode, 13a, 13b... Green sheet for protective film, 21a, 21b... External electrode.

Claims (1)

[Claims] 1. Exposing the end surfaces of the internal electrodes on the four opposing sides of the hexahedral element from the insulator layer using a ferroelectric material,
and in a variable capacitor in which an external electrode is attached to an end face of an internal electrode, one pair of the internal electrodes is used as a capacitance extraction electrode, and the other pair is used as a bias extraction electrode, and the capacitance extraction electrode is located at a position where the bias extraction electrode is sandwiched. A variable capacitor characterized by being arranged in.