PTC thermistor material

• US 6,218,928 B1
• Filed: 05/08/1998
• Issued: 04/17/2001
• Est. Priority Date: 09/13/1996
• Status: Expired due to Fees

• Current Assignee: Masuo Okada, TDK Corporation
• Original Assignee: Masuo Okada, TDK Corporation
• Inventors: Matsuoka, Dai, Okada, Masuo, Sawaguchi, Takahiro, Yodogawa, Masatada
• Primary Examiner(s): Gellner, Michael L.
• Assistant Examiner(s): LEE, KYUNG S
• Application Number:
  US09/068,337
• Time in Patent Office: 1,075 Days
• Field of Search: 338/22.R, 338/25, 338/225.D, 338/308, 338/309, 338/225, 338/322, 338/328, 252/520, 252/521
• US Class Current: 338/22.00R
• CPC Class Codes: C01G 29/00 Compounds of bismuth
• CPC Class Codes: C01G 29/006 Compounds containing, besides bismuth, two or more other elements, with the exception of oxygen or hydrogen
• CPC Class Codes: C01P 2002/54 one element only
• CPC Class Codes: C01P 2006/40 Electric properties
• CPC Class Codes: C04B 2235/3208 Calcium oxide or oxide-forming salts thereof, e.g. lime
• CPC Class Codes: C04B 2235/3213 Strontium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3215 Barium oxides or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3251 Niobium oxides, niobates, tantalum oxides, tantalates, or oxide-forming salts thereof
• CPC Class Codes: C04B 2235/3294 Antimony oxides, antimonates, antimonites or oxide forming salts thereof, indium antimonate
• CPC Class Codes: C04B 35/475 based on bismuth titanates
• CPC Class Codes: C22C 29/04 based on carbonitrides
• CPC Class Codes: C22C 29/12 based on oxides
• CPC Class Codes: C22C 29/16 based on nitrides containing cubic BN or wurtzitic BN and diamond C22C26/00
• CPC Class Codes: H01C 17/06553 composed of a combination of metals and oxides
• CPC Class Codes: H01C 7/022 mainly consisting of non-metallic substances H01C7/021 takes precedence
• CPC Class Codes: H01C 7/023 containing oxides or oxidic compounds, e.g. ferrites

Abstract

The PTC thermistor material of the invention comprises a matrix phase and electrically conductive phases substantially uniformly dispersed in the matrix phase, said conductive phases having a resistivity lower than that of the matrix phase, and has a resistivity changing sharply in the vicinity of the melting point of the conductive phases. The matrix phase is made up of any one of a polycrystalline ceramic material, a glass-polycrystalline ceramic composite material, a glass, a crystallized glass, and a polymer material, and the conductive phases are made up of a metal containing bismuth as a main component. It is thus possible to achieve a PTC thermistor material which can be controlled in terms of various properties such as the temperature at which PTCR property becomes available and the rate of resistivity change and so can be applied to circuit parts through which large currents pass in a normal operation state. Further, the PTC thermistor material can be easily manufactured with the stable PTCR property maintained. Furthermore, the PTC thermistor material can be operated with an increased rated current albeit being of small size, and has a high degree of shape freedom.

Claims

1. A PTC thermistor material comprising

(A) a matrix phase;

and

(B) electrically conductive phase uniformly dispersed in said matrix phase,

wherein said conductive phase has a resistivity lower than that of said matrix phase;

wherein a resistivity of said PTC thermistor material changes sharply at the melting point of said conductive phases; and

wherein said conductive phase is comprises of metal bismuth or a metal bismuth alloy; and

wherein said melting point is in the range of from 50 to 1,200°

C.;

wherein said bismuth alloy comprises bismuth and at least one additional metal selected from the group consisting of indium, gallium, silver, lead, copper, antimony, arsenic and germanium.

2. The PTC thermistor material of claim 1, wherein said bismuth alloy comprises bismuth in an amount of at least 40 wt %.

3. The PTC thermistor material of claim 1, wherein the resistivity of said conductive phase is up to 1×

10<sup>−

4</sup> Ω

m and the resistivity of said matrix phase is more than 1×

10³ Ω

m.

4. The PTC thermistor material of claim 1, wherein said matrix phase comprises an oxide comprising bismuth and titanium.

5. The PTC thermistor material of claim 4, wherein said oxide has the formula:

6. The PTC thermistor material of claim 4, wherein said oxide has the formula:

7. The PTC thermistor material of claim 1, wherein said resistivity changes at a rate of at least 1×

10².

8. The PTC thermistor material of claim 1, wherein the average grain diameter of the conductive phase is between 1 and 100 μ

m.

9. The PTC thermistor material of claim 1, wherein the average spacing between conductive phases is between 1 to 100 μ

m.