JP2010129817A - Nonlinear resistance change element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To configure a nonlinear resistance change element whose low varistor voltage characteristics are compatible with the low capacitance characteristics. <P>SOLUTION: A varistor 102 has: a cylindrical nonlinear resistor 21 made from ceramic materials having nonlinear resistance change characteristics; a supporting member 20 surrounding a lateral part of the nonlinear resistor 21; a first electrode 22 conducting to a first surface of the nonlinear resistor 21; and a second electrode 23 conducting to a second surface of the nonlinear resistor. In addition, the varistor has low dielectric constant insulating members 24 and 25 which are provided between the first electrode 22 and the supporting member 20 and between the second electrode 23 and the supporting member 20, respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nonlinear resistance change element having a nonlinear resistance change characteristic such as a varistor.

  A typical example of a non-linear resistance change element having a non-linear resistance change characteristic is a varistor. Varistors are used to absorb and suppress external surges and noise caused by static electricity and other abnormal voltages.

  One field of application of varistors is countermeasures against static electricity in high-speed signal lines. In such varistors, the characteristics of low varistor voltage and low capacitance are desired. Patent Document 1 discloses a non-linear resistor composition having a reduced dielectric constant for the purpose of reducing the capacitance.

Here, the structure of a general conventional varistor will be described with reference to FIG.
1A and 1B are cross-sectional views of the element portion of the varistor. In the example of FIG. 1A, a laminated body of the nonlinear resistor layer 10 and the internal electrodes 11 and 12 is formed. External electrodes 13 and 14 are formed on the side surfaces. In the example of FIG. 1 (A), the internal electrodes 11 and 12 are alternately laminated, and in the example of FIG. 1 (B), the tips of the internal electrodes 11 and 12 are arranged in abutted state at a constant distance.
Japanese Patent No. 3710062

  As the varistor material, sintered ZnO is mainly used. This ZnO has a crystal grain size of about 3 μm to 30 μm. ZnO itself has a low resistance, but a boundary layer (grain boundary) between grains exists as a high resistance barrier. The resistance value and capacitance of the varistor are determined by the number of boundary layers formed by crystal grain boundaries connected in series between the electrodes. When the distance between the electrodes is the same, the number of crystal grain boundaries and the number of boundary layers decrease as the crystal grains increase, so that the varistor voltage (voltage necessary for the current to flow 1 mA) decreases. Further, since the number of equivalent series capacitors is reduced, the capacitance is increased. Therefore, the only way to make a varistor with a low varistor voltage and low capacitance is to reduce the dielectric constant of the ZnO material itself.

  Generally, it is better that the varistor voltage is low as ESD / surge countermeasure parts. In particular, the capacitance of the varistor must be small when it is put in parallel with a high-speed signal line. For example, it is required to be less than 1 pF in the several GHz band. Therefore, in the example shown in Patent Document 1, glass is mixed with ZnO to reduce the relative dielectric constant of the nonlinear resistor to about 80. In general, since Pr-based ZnO has a large particle size, the relative dielectric constant is about 400 to 1200. Bi-based ZnO can have a dielectric constant of about 200 depending on the sintering conditions. However, if only the dielectric constant of the material is lowered, the limit is about 1.1 pF. Moreover, when the dielectric constant is lowered as described above, the varistor voltage increases and becomes impractical.

  The situation described above is not limited to the multilayer varistor as shown in FIG. 1, but the same applies to a case where a nonlinear resistor is filled in the via so that the varistor characteristics are provided between the upper and lower electrodes of the via.

  Thus, it has been difficult in the past to achieve both a reduction in varistor voltage and a reduction in capacitance.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a non-linear resistance change element that has both a low varistor voltage characteristic and a low capacitance characteristic that are in a trade-off relationship.

In order to solve the above problems, the nonlinear resistance change element of the present invention is configured as follows.
(1) A columnar conductive portion made of a ceramic material having nonlinear resistance change characteristics, a support member made of an insulating material having a dielectric constant lower than the dielectric constant of the ceramic material surrounding the periphery of the side of the conductive portion, It is characterized by comprising a first electrode and a second electrode respectively conducting to the first surface and the second surface of the conductive portion.

(2) An insulator member having a dielectric constant lower than that of the conductive portion and the support member may be provided between the electrode and the support member.

  According to the present invention, a nonlinear variable resistance element having a low varistor voltage and a small capacitance can be obtained.

<< First Embodiment >>
The configuration and manufacturing method of the nonlinear variable resistance element according to the first embodiment will be described with reference to FIGS.
FIG. 2A is a cross-sectional view of the varistor 101 which is a nonlinear resistance change element according to the first embodiment, and FIG. 2B is a perspective view thereof. The varistor 101 includes a cylindrical non-linear resistor portion 21 made of a ceramic material having non-linear resistance change characteristics, a support member 20 surrounding the side of the non-linear resistor portion 21, and a first non-linear resistor portion 21. A first electrode 22 conducting to one surface and a second electrode 23 conducting to a second surface are provided.

The material and dimensions of each part are as follows.
[Nonlinear resistor 21]
Material: ZnO
Dielectric constant: 1200
Diameter D1: 100 μm
Height H: 400 μm
[Supporting member 20]
Material: Alumina ceramics Dielectric constant: 10
Height H: 400 μm
[Electrodes 22, 23]
Width W: 200 μm
Thus, since the dielectric constant of the support member 20 around the nonlinear resistor portion 21 is low, the capacitance between the first electrode 22 and the second electrode 23 is small. In this example, the capacitance between the electrodes 22-23 is about 0.15 pF.

  On the other hand, since the crystal grain size is about 20 μm, the number of crystal grain boundaries is about 400/20 = 20. Since the varistor voltage per crystal grain boundary is about 3V, the varistor voltage of the varistor 101 is about 60V.

FIG. 3 is a diagram showing a manufacturing process of the varistor 101 shown in FIG.
First, as shown in FIG. 3 (A), a plurality of holes H are formed in the support member 20B in the alumina ceramic mother board state, and inside the holes H as shown in FIGS. 3 (B) and 3 (C). Is filled with a ZnO slurry. This ZnO slurry is obtained by dispersing ZnO powder in water or an organic solvent under desired conditions.

Subsequently, as shown in FIG. 3D, the upper and lower surfaces of the support member 20B in the mother board state are lapped to flatten the upper and lower surfaces of the nonlinear resistor portion 21. Thereafter, as shown in FIG. 3E, a paste to be the electrodes of the first electrode 22 and the second electrode 23 is applied to the entire upper and lower surfaces and dried.
Thereafter, the ZnO is fired.

Next, as shown in FIG. 3F, the varistor 101 is configured by dividing the supporting member 20B in the mother board state into individual pieces at the element portion.
The ZnO may be fired after the support member 20B in the mother board state is divided into individual pieces at the element portion.
Alternatively, the motherboard-like support member 20B may be diced first and then filled with the ZnO slurry.

The division into pieces is performed using a dicing saw. At that time, if a scratch (notch groove) is put in advance at a position that becomes a separation line of the element of the support member 20B, and then dicing along that, the workability is improved. Moreover, when not using a dicing saw, you may break along the said scratch.
The scratch may be formed in any state before or after the ceramic sintering of the support member 20B.

<< Second Embodiment >>
FIG. 4 is a cross-sectional view of a varistor 102 according to the second embodiment. The varistor 102 includes a cylindrical non-linear resistor portion 21 made of a ceramic material having non-linear resistance change characteristics, a support member 20 surrounding the side of the non-linear resistor portion 21, and a first non-linear resistor portion 21. A first electrode 22 conducting to one surface and a second electrode 23 conducting to a second surface are provided. Unlike the varistor 101 shown in FIG. 2, a high dielectric constant dielectric material is used as the support member 20, and between the first electrode 22 and the support member 20, and between the second electrode 23 and the support member 20. Insulating members 24 and 25 having a low dielectric constant are formed. Moreover, the center part of the insulator members 24 and 25 is opened, and the first electrode 22 and the second electrode 23 are conducted to both ends of the nonlinear resistor part 21 through the openings 22P and 23P. I have to.

  As described above, the opening area of the insulator members 24 and 25 is made smaller than the cross-sectional area of the nonlinear resistor portion 21, so that the ZnO crystals arranged in series between the first electrode 22 and the second electrode 23 are arranged. The equivalent capacitor electrode area due to the boundary layer of the grain boundary decreases, and the capacitance decreases accordingly.

The material and dimensions of each part are as follows.
[Nonlinear resistor 21]
Material: ZnO
Dielectric constant: 1200
Diameter D1: 100 μm
Height H: 400 μm
[Supporting member 20]
Material: Zinc titanate Relative dielectric constant: 2000
Height H: 400 μm
[Electrodes 22, 23]
Width W: 200 μm
[Insulator members 24 and 25]
Material: Glass Relative permittivity: 4
Thickness T: 5μm
Through hole inner diameter D2: 25 μm
Thus, by interposing the low dielectric constant insulator members 24 and 25, the capacitance between the first electrode 22 and the second electrode 23 is small. In this example, the capacitance between the electrodes 22-23 is about 0.34 pF.
If the thickness dimension of the insulator members 24 and 25 is 10 μm and other conditions are the same as described above, the capacitance is 0.31 pF.

  By providing the low dielectric constant insulator members 24 and 25 as described above, a varistor having a sufficiently low capacitance can be configured even if the material of the support member 20 is a high dielectric constant dielectric material such as zinc titanate.

FIG. 5 is a diagram showing a manufacturing process of the varistor 102 shown in FIG.
First, as shown in FIG. 5 (A), a plurality of holes H are formed in the support member 20B of the zinc titanate mother board state, and as shown in FIGS. 5 (B) and 5 (C), the holes H Inside, a ZnO slurry is filled. This ZnO slurry is obtained by dispersing ZnO powder in water or an organic solvent under desired conditions.

  Subsequently, as shown in FIG. 5D, the upper and lower surfaces of the support member 20B in the mother board state are lapped to flatten the upper and lower surfaces of the nonlinear resistor portion 21. Thereafter, as shown in FIG. 5E, insulator members 24 and 25 having upper and lower surfaces of the nonlinear resistor 21 partially opened are formed on the entire upper and lower surfaces. Specifically, it is formed by thick film printing and baking of glass glaze.

Thereafter, as shown in FIG. 5 (F), a paste to be the electrodes of the first electrode 22 and the second electrode 23 is applied to the surfaces of the insulator members 24 and 25 and dried.
Thereafter, the ZnO is fired.

Next, as shown in FIG. 5G, the varistor 102 is formed by dividing the supporting member 20B in the mother board state into individual pieces at the element portion.
The ZnO may be fired after the support member 20B in the mother board state is divided into individual pieces at the element portion.
The method described in the first embodiment is applied to the method of dividing into pieces.

<< Third Embodiment >>
FIG. 6 is a cross-sectional view of a varistor 103 according to the third embodiment. In this example, the inner diameter of the opening formed in the insulator members 24 and 25 is made equal to the diameter D1 of the nonlinear resistor portion 21. As described above, the insulator members 24 and 25 may be disposed only between the support member 20 and the electrodes 22 and 23.
Other configurations and manufacturing methods are the same as those shown in the first and second embodiments.

The material and dimensions of each part are as follows.
[Nonlinear resistor 21]
Material: ZnO
Dielectric constant: 200
Diameter D1: 100 μm
Height H: 300 μm
[Supporting member 20]
Material: Zinc titanate Relative dielectric constant: 2000
Height H: 300 μm
[Electrodes 22, 23]
Width W: 300 μm
[Insulator members 24 and 25]
Material: Glass Relative permittivity: 4
Thickness T: 10μm
Through hole inner diameter D1: 100 μm
According to this configuration, the capacitance between the electrodes is 0.27 pF.

  In the structure shown in FIG. 6, since the joint surface between the electrodes 22 and 23 and the nonlinear resistor portion 21 can be widened, the voltage drop between the electrodes 22 and 23 when a voltage higher than the varistor voltage is applied between the electrodes and is conducted. The voltage can be further reduced.

<< Fourth Embodiment >>
FIG. 7 is a view showing a method for manufacturing the varistor 104. The basic structure of the varistor 104 is the same as that of the varistor 101 shown in FIG.
First, as shown in FIG. 7A, a nonlinear resistor material is formed into a shape in which a plurality of protrusions 21A protrude from a base portion 21B that spreads in a plate shape.
Subsequently, as shown in FIG. 7B, glass powder (glaze or slurry) is applied to the upper surface of the base portion 21B to form a motherboard-like support member 20B.
Thereafter, as shown in FIG. 7C, after the support member 20B is baked and vitrified, the upper and lower surfaces of the support member 20 are ground or etched to remove the tip portions of the base portion 21B and the protruding portion 21A. To do.

Subsequently, as shown in FIG. 7D, the first electrode 22 and the second electrode 23 are applied and cured on the upper and lower surfaces of the support member 20B, and then, as shown in FIG. Cut.
Thereafter, the individual pieces are fired to form the varistor 104 shown in FIG.

  In this way, the nonlinear resistor 21 may be formed by press molding. In addition, the part which will finally become the non-linear resistor part 21 is formed into a conical shape, so that the mold release at the time of pressing becomes easy.

<< Fifth Embodiment >>
FIG. 8 is a diagram showing a method for manufacturing the varistor 105 according to the fifth embodiment.
FIG. 8A is a cross-sectional view of a member in the middle of the manufacturing process. First, as the non-linear resistor portion 21 shown in FIG. 8A, a ceramic groove is filled with ZnO and sintered to form needle-shaped ZnO having a diameter of 150 μm. This is dipped in molten glass or resin, pulled up, and cured to form a cylindrical member as shown in FIG.

  Thereafter, as shown in FIG. 8 (B), it is cut to a length of 400 μm, and electrodes 22 and 23 are formed at both ends of the cut surface. Thereby, the varistor 105 similar to the varistor 101 shown in the first embodiment is configured.

  According to the manufacturing method shown in FIG. 8, glass or resin having a low dielectric constant can be used as the support member, so that a varistor with low capacitance can be realized. Further, a plurality of columnar members shown in FIG. 8A can be arranged in parallel and cut into individual pieces at the same time, thereby reducing the manufacturing cost.

1A and 1B are cross-sectional views of the element portion of a general conventional varistor. FIG. 2A is a cross-sectional view of the varistor 101 which is a nonlinear resistance change element according to the first embodiment, and FIG. 2B is a perspective view thereof. It is a figure shown about the manufacturing process of the varistor 101 shown in FIG. It is sectional drawing of the varistor 102 which concerns on 2nd Embodiment. It is a figure which shows the manufacturing process of the varistor 102 shown in FIG. It is sectional drawing of the varistor 103 which concerns on 3rd Embodiment. It is a manufacturing method of the varistor which concerns on 4th Embodiment, Comprising: It is a figure which shows another manufacturing method of the varistor 101 shown in FIG. It is a figure shown about the manufacturing method of the varistor 105 which concerns on 5th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Nonlinear resistor layer 20 ... Support member 20B ... Motherboard-like support member 21 ... Nonlinear resistor part 21A ... Protrusion part 21B ... Base part 22 ... First electrode 23 ... Second electrode 24, 25 ... Insulator member 22P, 23P ... Insulator member openings 101-105 ... Varistors

Claims (2)

A columnar nonlinear resistor portion made of a ceramic material having a nonlinear resistance change characteristic;
A support member made of an insulating material having a dielectric constant lower than the dielectric constant of the ceramic material, surrounding the periphery of the side of the nonlinear resistor portion;
A first electrode and a second electrode respectively conducting to the first surface and the second surface of the nonlinear resistor section;
A non-linear variable resistance element.   The nonlinear resistance change element according to claim 1, further comprising an insulator member having a dielectric constant lower than that of the nonlinear resistor portion and the support member, which is disposed between the electrode and the support member.

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