US3795048A

US3795048A - Method for manufacturing non-linear resistors

Info

Publication number: US3795048A
Application number: US00327177A
Authority: US
Inventors: K Tachibana; M Nishioka; M Ono
Original assignee: Mitsubishi Mining and Cement Co Ltd
Current assignee: Mitsubishi Mining and Cement Co Ltd
Priority date: 1972-02-16
Filing date: 1973-01-26
Publication date: 1974-03-05
Anticipated expiration: 1991-03-05
Also published as: FR2172134B1; DE2307322C3; FR2172134A1; DE2307322A1; DE2307322B2; JPS549294B2; JPS4941891A

Abstract

A method for manufacturing non-linear resistors comprising superposing several sintered wafers and applying silver electrodes to opposite surfaces of the sintered wafers superposed respectively is disclosed. The sintered wafer, consisting essentially of iron oxide and copper oxide has negative resistance and also possesses such thermister constant B*K and specific resistance R0 K Omega at 273* K as satisfy the relation B X R0 < OR = 104K Omega .*K. The non-linear resistors manufactured by this method, based on utilization of the property of the contact surfaces between the sintered wafers superposed, have remarkably stable volt-ampere characteristics and are inexpensive in cost.

Description

' United States Patent 11 1 Tachibana et al.

METHOD FOR MANUFACTURING NON-LINEAR RESISTORS lnventors:- Kan-ichi Tachibana; Michihiro Nishioka; Mikiya Ono, all of Kitakyushu, Japan Mitsubishi Mining & Cement Company, Ltd., Tokyo, Japan Filed: Jan. 26, 1973 Appl. No.: 327,177

[73] Assignee:

[30] Foreign Application Priority Data Feb.l6, 1972 Japan... 47-16305 US. Cl 29/621,-29/6l0, 338/204,

. 1m. c|.....' H010 1/14, HOlc 17/00 Field of seal-611,. 29/621,:610, 612; 338/22, 20, 338/204, 333

References Cited 7 UNITED STATES PATENTS 2,720,573 10/1955- Lundquist' 338/22 R- 3,l24,772 .3/1964 Newkirk 29/6l0 X Mar. 5,- 1974 3,343,114 9 1967 Rice 338/22 R 3,503,029 3/1970 Matsuoka 3,689,863 9/1972 Matsuoka 338/20 FOREIGN PATENTS 0R APPLICATIONS 1,446,249 6/1966 France 333 22 R Primary Examiner-Charles W. Lanham Assistant Examiner-Victor A. DiPalma Attorney, Agent, or Firm-Brenner & Wray ABSTRACT A method for manufacturing non linear resistors comprising superposing several sintered wafers and applying silver electrodes to opposite surfaces of the sintered wafers superposed respectively is disclosed. The sintered wafer, consisting essentially of iron oxide and copper oxide has negative resistance and also possesses such thermister constant BK a nd s pe i tic res i stance R0 K!) at 273 K as satisfy the relation B X R0 5 10KQK. The non-linear resistors manufactured by this method, based on utilization of the property of the contact surfaces between the sintered wafers superposed, have remarkably stable volt-ampere I characteristics and are inexpensive in cost,

2 Claims, 3 Drawing Figures METHOD FOR MANUFACTURING NON-LINEAR RESISTORS BACKGROUND OF THE INVENTION This invention relates to a novel method for manufacturing non-linear resistors comprising superposing several sintered wafers, said sintered wafer having negative resistance and also possessing the thermistor constant BK and the specific resistance R KQ at 273 K Hastin s/"afaintingremiss (T):

, and applying electrodes to opposite surfaces of said sintered wafers superposed respectively in a conventional manner. j

In general, the relation between the resistance RKQ at TK and the above mentioned R KQ, BK of an oxide semiconductor is expressed by the following equation R R eXp [B(l/T l/273)] The volt-ampere characteristic of such a varistor is given by the following equation (3):

'I=I,, v/v,, a..........

. I (3) where I is the current flowing through the varistor, V is the voltage across the varistor, V is the voltage applied to the opposite surfaces of the varistor at I=I mA, that is, a threshhold voltage, and exponent a, an index representing non-linearity is a numerical value greater missus y 3 s Silicon carbide varistors, when made to be smaller in size, deteriorate the characteristics and exhibit a values less than Silicon varistors and barium titanate varistors are both able to be small-sized, but are limited in uses because V value is only 0.5 -l .2V. Moreover, in such a varistor which is based on utilization of the mutual contact between internal particles of a sintered body as silicon carbidevaristors, it is difficult to completely control the state of said mutual contact between the internal particles even under the same manufacturing condition, consequently the product is inevitably .variable in the characteristic.

We have found that the defects of the conventional varistors as described hereinabove is able to be overcome by processing conventional thermister materials (the term sintered oxide material is hereinafter referred to as thermister) so as to limit the product of the thermister constant B K and the specific resistance R,,KQ at 273 K thereof within a certain range.

SUMMARY OF THE INVENTION A primary object of this invention is to provide a method for manufacturing a varistor which has'a remarkably stable volt-ampere characteristic;

Another object of thisinvention is to provide a method for manufacturing a varistor which is able to be small-sized.

Still another object of this invention is to provide a method for manufacturing a varistor which is inexpensive in cost.

According to this invention, there is provided a method for manufacturing a non-linear resister comprising superposing several sintered wafers, said sintered wafer having negativeresistance and also possessing the thermister constant BK and the specific resistiiiiEFRbKIYflT/FKYBM satisfy the relation PIXRo 10,000 K!) K, and applying electrodes to opposite surfaces of said sintered wafers superposed respectively.

This invention isnow explained in detail with reference to the attached drawings.

BRIEF DESCRIPTION OF THE ATTACHED DRAWINGS FIG. 1 is a sectional view of a varistor manufactured by the method of this invention. I

FIG. 2 shows a volt-ampere characteristic suitable for a varistor.

FIG. 3 shows a volt-ampere characteristic unsuitable for a varistor.

In FIG. 2 and Flg. 3, voltage E is plotted as abscissa and current as ordinate.

DETAILED DESCRIPTION OF THE INVENTION This invention, as described hereinabove, is based on the new information obtained from our studies that in case a thermister materialpossesses the thermister constant BK and the specific resistance R KO. at 273 K that satisfy the relation BXR 10,000 KO 9 K, a resistor manufactured by superposing several plates of such thermister material shows a stable volt-ampere characteristic as shown in FIG. 2, thus proviing to have an aptitude for a varistor, whereas in case a thermistor material possesses the thermistor constant BK and the specific resistance R KQ at 273 K that satisfy BXR IO,OOOKQ' K, a resistor manufactured by superposingseveral plates of such thermistor material shows a unstable voltampere characteristic as shown in FIG. 3, thus providing to have no aptitude for a varistOI'.

Therefore, this invention provides a method for manufacturing a varistor comprising, for example, superposing two sintered wafers 1, 1, each sintered wafer obtained by processing and sintering a thermister material so as to make the product of BK and R KQ and thereof be not more than l0,000KQ- K, applying electrodes, for example silver electrodes 2, 2 to opposite surfaces of the sintered wafers 1, l superposed respectively in a conventional manner, attaching lead wires 5,

5 to the silver electrodes 2, 2 respectively by using 501- der 4 and coating over the whole with suitable insulating coating material 6. I The wafer l is a sintered plate having any one of various shapes such as circular, square, rectangular, etc.

In this case, no surface barrier exists at the surface of the sintered wafer 1, which the electrode 2 is applied to, but at the contact surface 3, which no electrode is applied to, exists a surface barrier. Therefore, when volt-ampere characteristic as shown in FIG. 2 is. ob-

tained.

This invention also provides a method for manufacturing a non-linear resistor comprising superposing more than three plates of said sintered wafers and applying electrodes to opposite surfaces of said sintered wafers superposed in the same manner. The thus manufactured resistors have remarkably stable volt-ampere characteristics as shown in H6. 2, thus providing to be suitable for a'varistor. 7

As the varistors of this invention have, asrExample shows, remarkably stable volt-ampere characteristics, their yield rate is much higher, as compared with the conventional methods. Moreover, as the varistors of this invention utilize iron oxide, copper oxide, etc. as the main raw materials, they are. also advantageous in cost. This invention, as described hereinabove, provides a method for manufacturing varistors having remarkably stable characteristics at much higher yield rate and at quite lower cost, therefore it is industrially of great value.

The invention will be understood'more readily withv to be construed to limit the scope of the invention.

EXAMPLE The sintered body is prepared byaconventional technique. The starting material in the composite de fined in Table 1 is respectively mixed in a potmill so as to produce a homogeneous mixture. The mixture is dried in a dryer, pressed in a mold at a pressure of about IOOOkg/cm into a disc of 15mm in diameter and 2mm in thickness. The pressed disc is sintered in air at about 1,000. C, thus the sintered disc 1 is obtained. A varistor is manufactured by superposing the sintered disc 1 upon the other, applying silver electrodes 2, 2 to opposite surfaces of the sintered discs ll, 1 superposed, asttaching

lead wires

5, 5 to the silver electrodes 2, 2 by using solder 4 and coating over the whole with epoxy resin 6. As described hereinabove, a surface barrier exists at the contact surface between the sintered discs 1, 1 which no silver electrode is applied to. Therefore, when the sintered disc 1 is superposed upon the other, there generates a high resistance R KQ. The measured values of R V 0: of the thus manufactured varistor is respectively shown in Table 1. InTable l, the V -value is a voltage at 1=1mA. Further, theresistance R KQ and the thermisterconstant B K of the sintered disc 1 are measured in a conventional manner, and the values-of R E and BXR are also shown in Table 1.

TABLE 1 I Composition of Sintered Body Fe 0 (mol%) 66 40 34 CuO (m0l%) 34 50 60 66 R, (KO) 0.5 0.1 0.04 0.01 B ("K) 2l00 .1900 H00 1500 R (K9) I30 125 I25 125 'V (V) l9 l9 l9 -l9 As Table l shows, thevalue sofl'i 50% of Mastered stable volt-ampere characteristic as shown in FIG. 2,

thus proving to have an aptitude for varistor. The measured values of the varistors manufactured by superposing two-four plates of the sintered body consisting of Fe O (50mol percent) and CuO(50mol percent) as anaemia Table 1 are shownin Table 2T Table 2:

Number ofplates 2' 3 '4 12 mm 125 250. 376 v 19.5 33.5 48.0 0z(--) I 5 4 4 Table 2 shows that varistors of good quality having different V values can be manufactured by superpos ing more than'three plates of such sintered bodies having the product of B and R not more than 10,000KQ' Kas shown in Tablei. I

Next, comparison with Example, the sintered bodies are prepared in the same manner as Example from the starting materials in the compositions defined in Table B, R BXR are also shown in 3. The values of R Table 3.

TABLE 3 Composition of Sintered Body Fe,o,, (mom i 70 o 0 50' MnO, (mul'7l) 0 70 66 0 COO (mol'Ya) 30 30 34 50 R (Kfl) 20 20 l0 6 B (K) 4,500 4,500 6,000 3,500 R (KQ) I40 I40 30 50 R XB (Kn' K) 90,000 90,000 60,000 2 l 000 As Table 3 shows, the values of BXR of the sintered bodies are all larger than 10,000KQ' K. The resistor manufactured by superposing two plates of each of these sintered bodies shows respectively a unstable volt-ampere characteristic as shown in FIG. 3, thus proving to be unsuitable for a varistor..

We claim:

1. A method for manufacturing a non-linear resistor comprising superposing several sintered wafers, said sintered wafers having negative resistance and also pos- 10,000KQ" K, and applying electrodes to op-

Claims

2. A method for manufacturing a non-linear resistor as described in claim 1, wherein said sintered wafers comprise 66*34 percent of iron oxide (Fe2O3) and 34*66 mol percent of copper oxide (CuO).