Polyimide capacitive humidity sensing element

• US 4,761,710 A
• Filed: 06/23/1987
• Issued: 08/02/1988
• Est. Priority Date: 06/23/1987
• Status: Expired due to Term

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Chen, Stephen G. L.
• Primary Examiner(s): Griffin, Donald A.
• Application Number:
  US07/065,830
• Time in Patent Office: 406 Days
• Field of Search: 361/286, 73/336.5
• US Class Current: 361/286
• CPC Class Codes: G01N 27/126 comprising organic polymers
• CPC Class Codes: G01N 27/225 by using hygroscopic materials

Abstract

The present invention relates to a humidity sensing element having a polyimide moisture sensing film. It is of a capacitive structure containing, without the use of adhesives, a polyimide film which is either sandwiched between a corrosion resisting metal substrate and a thin moisture permeable gold layer, or vapor deposited on both sides thereof with a moisture permeable thin gold layer.

Claims

1. A capacitive humidity sensing element comprising:

a corrosion resistant metal substrate;

a humidity sensitive polyimide film coated on the corrosion resistant metal substrate; and

a moisture permeable thin gold electrode on top of the humidity sensitive polyimide film, the humidity sensitive polyimide film being produced by reacting;

a dianhydride selected from the group consisting of pyromellitic dianhydride and 3,3'"'"'-4,4'"'"'-benzophenon tetracarboxylic acid dianhydride, with

a diamine selected from the group consisting of p-phenylene diamine, m-phenylene diamine, 4,4'"'"'-diamino-diphenyl methane, 4,4'"'"'-diamino-diphenyl ether, 3,4'"'"'-diamino-diphenyl ether and 4,4'"'"'-diamino-diphenyl sulfide.

2. A capacitive humidity sensing element according to claim 1, wherein the dianhydride and the diamine are reacted in a polar solvent.

3. A capacitive humidity sensing element according to claim 1, wherein the moisture permeable thin gold electrode is vapor deposited onto the humidity sensitive polyimide film.

4. A capacitive humidity sensing element according to claim 1, wherein the moisture permeable thin gold electrode is formed as a continuous layer.

5. A capacitive humidity sensing element according to claim 1, wherein the moisture permeable thin gold electrode is formed as a patterned layer.

6. A capacitive humidity sensing element according to claim 1, wherein the corrosion resistant metal substrate is made of a metal selected from the group consisting of stainless steel, gold, platinum and nickel.

7. A capacitive humidity sensing element according to claim 6, wherein the corrosion resistant metal substrate is further secured onto an insulating material.

8. A capacitive humidity sensing element according to claim 7, wherein the metal substrate is vapor deposited onto the moisture sensitive polyimide film.

9. A capacitive humidity sensing element according to claim 6, wherein the corrosion resistant metal substrate is made of gold and is moisture permeable.

10. A process for producing a capacitive humidity sensing element comprising the steps of:

(i) coating a solution of a dianhydride selected from the group consisting of pyromellitic dianhydride and 3,3'"'"'-4,4'"'"'-benzophenon tetracarboxylic acid dianhydride, and a diamine selected from the group consisting of p-phenylene diamine, m-phenylene diamine, 4,4'"'"'-diamino-diphenyl methane, 4,4'"'"'-diamino-phenylene diamine, 4,4'"'"'-diamino-diphenyl methane, 4,4'"'"'-diamino-diphenyl ether, 3,4'"'"'-diamino-diphenyl ether and 4,4'"'"'-diamino-diphenyl sulfide in a polar solvent onto a corrosion resistant metal substrate;

(ii) heating the coated substrate in stages to a temperature between 200° and

300 °

C. until a humidity sensitive polyimide film is formed on the substrate; and

(iii) coating a thin gold layer onto the humidity sensitive polyimide film.

11. A process according to claim 10, wherein the polar solvent is N-methyl-pyrrolidone.