Direct application voltage variable material, components thereof and devices employing same

• US 7,132,922 B2
• Filed: 12/23/2003
• Issued: 11/07/2006
• Est. Priority Date: 04/08/2002
• Status: Active Grant

• Current Assignee: Littelfuse Incorporated
• Original Assignee: Littelfuse Incorporated
• Inventors: Vyas, Tushar, Whitney, Stephen J., Harris, Edwin James
• Primary Examiner(s): HOANG, TU BA
• Application Number:
  US10/746,020
• Publication Number:
  US 20040201941A1
• Time in Patent Office: 1,050 Days
• Field of Search: 338/4, 338 20- 21, 338/22.R, 338/22.SD, 338/25, 737/21, 737/27, 252/301.4 R, 252/301.4 S, 252/500, 219/501, 219/553
• US Class Current: 338/22.0SD
• CPC Class Codes: H01C 17/06513 characterised by the resistive component
• CPC Class Codes: H01C 17/06553 composed of a combination of metals and oxides
• CPC Class Codes: H01C 17/0656 composed of silicides H01C17/0652 takes precedence
• CPC Class Codes: H01L 23/62 Protection against overvoltage, e.g. fuses, shunts
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/12044 OLED
• CPC Class Codes: H01L 2924/3011 Impedance
• CPC Class Codes: H02H 9/044 Physical layout, materials not provided for elsewhere varistors H01C7/12; spark-gaps H01T; Ovshinsky devices H10N70/00
• CPC Class Codes: H05K 1/0257 Overvoltage protection
• CPC Class Codes: H05K 1/0298 Multilayer circuits
• CPC Class Codes: H05K 1/167 incorporating printed resistors
• CPC Class Codes: H05K 2201/0224 Conductive particles having an insulating coating
• CPC Class Codes: H05K 2201/0272 Mixed conductive particles, i.e. using different conductive particles, e.g. differing in shape
• CPC Class Codes: H05K 2201/0738 Use of voltage responsive materials, e.g. voltage switchable dielectric or varistor materials

Abstract

A voltage variable material (“VVM”) including an insulative binder that is formulated to intrinsically adhere to conductive and non-conductive surfaces is provided. The binder and thus the VVM is self-curable and applicable in a spreadable form that dries before use. The binder eliminates the need to place the VVM in a separate device or to provide separate printed circuit board pads on which to electrically connect the VVM. The binder and thus the VVM can be directly applied to many different types of substrates, such as a rigid (FR-4) laminate, a polyimide or a polymer. The VVM can also be directly applied to different types of substrates that are placed inside a device. In one embodiment, the VVM includes doped semiconductive particles having a core, such which can be silicon, and an inert coating, which can be an oxide. The particles are mixed in the binder with conductive particles.

Claims

1. A composition for providing protection against electrical voltage overstress comprising:

an insulating binder;

semiconductor particles with each particle including a doped core and a insulating coating maintained on the core, the semiconductor particles suspended within the binder; and

conductive particles suspended within the binder;

wherein the conductive and semiconductive particles are dispersed within the insulating binder such that the interparticle spacing between each of the particles establishes a high resistance state, and wherein the particles suspended within the binder establish a low resistance state in response to an electrical voltage overstress condition.

2. The composition of claim 1, wherein the insulating binder includes a polymer resin.

3. The composition of claim 1, wherein the doped core includes silicon and a dopant material.

4. The composition of claim 3, wherein the dopant material includes at least one component selected from the group consisting of:

antimony, arsenic, phosphorous and boron.

5. The composition of claim 1, wherein the doped core has an average size of about five microns to about 100 microns.

6. The composition of claim 1, wherein the coating has an average thickness of about 100 to 10,000 Angstroms.

7. The composition of claim 1, wherein the coating includes at least one material selected from the group consisting of:

silicon dioxide, epitaxial silicon and glass.

8. The composition of claim 1, wherein the conductive particles consist essentially of a single material.

9. The composition of claim 1, wherein the conductive particles include an oxide coating.

10. The composition of claim 1, wherein the conductive particles include at least one material selected from the group consisting of:

aluminum, brass, carbon black, copper graphite, gold, iron, nickel, silver stainless steel, tin, zinc and any combination thereof.

11. The composition of claim 1, wherein the conductive particles have an average size of about five microns to about fifty microns.

12. The composition of claim 1, which includes at least one additional type of particle selected from the group consisting of:

insulative particles, semiconductive particles and tungsten powders.

13. A composition for protecting against electrical voltage overstress comprising:

an insulating binder, the insulating binder includes a resin defining a high dielectric breakdown strength;

doped semiconductive particles including a core and an insulating shell, the semiconductive particles suspended within the binder; and

conductive particles suspended within the binder, the conductive particles consisting essentially of a single material, and

wherein the wherein the conductive and semiconductive particles are dispersed within the insulating binder such that the high dielectric breakdown strength prevents conductivity during a normal condition and the establishes a low resistance state in response to an electrical voltage overstress condition, and wherein the binder, the semiconductive particles and the conductive particles are configured and arranged to be laminated into an electrode gap.

14. The composition of claim 13, wherein the conductive particles include at least one material selected from the group consisting of:

aluminum, brass, carbon black, copper graphite, gold, iron, nickel, silver stainless steel, tin, zinc and any combination thereof.

15. The composition of claim 13, which is configured and arranged to be applied directly to a use, without being encapsulated in a device.

16. The composition of claim 13, which is configured and arranged to be provided in a device.

17. The composition of claim 13, which includes at least one additional type of particle selected from the group consisting of:

an insulative particle, a semiconductive particle and tungsten powder.

18. A particle for use in an electrical voltage overstress composition comprising:

a doped semiconductive core, the doped semiconductive core includes

a core material;

a dopant; and

wherein the core material is selected from the group consisting of silicon carbide, germanium, gallium and arsenide, and the dopant is selected from the group consisting of antimony, arsenic, phosphorus and boron; and

an insulating coating surrounding the core material, the insulating coating cooperating with the core material to establish a high resistance state such that the particle is electrically insulating, and a low resistance state in response to an electrical voltage overstress condition such that the particle is electrically conductive.

19. The particle of claim 18, wherein the doped core includes silicon and a dopant material.

20. The particle of claim 19, wherein the dopant material includes at least one component selected from the group consisting of:

antimony, arsenic, phosphorous and boron.

21. The particle of claim 18, wherein the doped core has an average size of about five microns to about 100 microns.

22. The particle of claim 18, wherein the coating has an average thickness of about 100 to 10,000 Angstroms.

23. The particle of claim 18, wherein the coating includes at least one material selected from the group consisting of:

silicon dioxide, epitaxial silicon and glass.

24. A particle for use in an electrical overstress composition comprising:

an inner silicon portion, the inner silicon portion includes;

a core material;

a dopant, the dopant selected to change the electrical conductivity of the core material; and

an outer portion that includes a material selected from the group consisting of;

silicon dioxide, epitaxial silicon and glass, the outer portion defining and insulating coating around the inner silicon portion.

25. The particle of claim 24, wherein the outer portion is grown via a heat controlled environment.

26. The particle of claim 24, wherein the outer portion is applied using a fluidized plasma reactor.