Humidity sensor

• US 5,004,700 A
• Filed: 08/01/1990
• Issued: 04/02/1991
• Est. Priority Date: 08/19/1983
• Status: Expired due to Term

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.), EMI Ltd (Universal Music Group NV)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.), EMI Ltd (Universal Music Group NV)
• Inventors: Hijikigawa, Masaya, Prosser, Stephen J., Webb, Brian C., Pedley, Derek G., Furubayashi, Hisatoshi
• Primary Examiner(s): Chaudhuri, Olik
• Assistant Examiner(s): WILCZEWSKI, MARY A
• Application Number:
  US07/561,377
• Time in Patent Office: 244 Days
• Field of Search: 437/7, 437/40, 437/42, 437/228, 437/231, 437/235, 357/25, 338/34, 338/35, 427/412.1, 427/58, 430/311, 428/411.1, 525/60, 525/61
• US Class Current: 438/49
• CPC Class Codes: G01N 27/4141 specially adapted for gases
• CPC Class Codes: H01L 29/4966 the conductor material next to the insulator being a composite material, e.g. organic material, TiN, MoSi2 H01L29/4908, H01L29/4983 take precedence

Abstract

A method of making a humidity sensor comprises providing a host device constituted by a semi-conductor substrate (10) and a gate insulator (13) of an insulated gate field effect transistor, forming a layer (14) of poly (vinyl) alcohol (PVA) on the exposed surface of the insulator, heat treating the layer to crystallize and stabilize the PVA, and forming a gate electrode (15) on the PVA layer, so that the gate electrode is porous allowing ambient water vapor to be absorbed by the PVA which, in response, undergoes a change of bulk dielectric constant, thereby causing a change in gate capacitance of the transistor resulting in a detectable change of electrical conductivity in the drain source channel.

Claims

1. A method of fabricating a humidity sensor comprising the steps of:

providing a host device constituting a semi-conductor substrate and the gate insulator of an insulated gate field effect transistor, the gate insulator having an exposed surface;

forming a layer of an aqueous solution of polyvinyl alcohol on the exposed surface of the gate insulator;

subjecting said layer to heat treatment to cause crystallization and/or stabilization of the polyvinyl alcohol; and

forming a gate electrode on said layer so treated.

2. A method as claimed in claim 1 wherein said layer forming step comprises depositing said layer of an aqueous solution of polyvinyl alcohol by spin coating.

3. A method according to claim 2 wherein said heat treatment includes heating the host device, with said layer of aqueous solution of polyvinyl alcohol applied, at a temperature in the range from 120°

C. to 250°

C.

4. A method according to claim 2 including patterning said layer of polyvinyl alcohol after being subjected to said heat treatment.

5. A method according to claim 2 including patterning said gate electrode thereby to expose said layer of polyvinyl alcohol to ambient water vapor.

6. The method as claimed in claim 2 wherein said spin coating comprises depositing said layer of an aqueous solution of polyvinyl alcohol in a thickness in the range from 100 Å

to approximately 500 Å

to expose the layer of polyvinyl alcohol to ambient water vapor.

7. The method as claimed in claim 1 wherein said layer forming step comprises:

applying a silane coupling reagent adhesion promoter to said substrate by spin coating to cover said gate insulator;

drying said substrate in air at approximately 90°

C. for approximately one hour; and

depositing said layer to cover said gate insulator by spin coating at substantially 300 rpm for substantially fifteen seconds.

8. A method according to claim 1 wherein said heat treatment includes heating the host device, with said layer of aqueous solution of polyvinyl alcohol applied, at a temperature in the range from 120°

C. to 250°

C.

9. A method according to claim 8 including patterning said layer of polyvinyl alcohol after being subjected to heat treatment.

10. A method according to claim 8 including patterning said gate electrode thereby to expose said layer of polyvinyl alcohol to ambient water vapor.

11. A method according to claim 1 including patterning said layer of polyvinyl alcohol after being subjected to said heat treatment.

12. A method according to claim 11 including patterning said gate electrode thereby to expose said layer of polyvinyl alcohol water vapor.

13. A method according to claim 1 including patterning said gate electrode thereby to expose said layer of polyvinyl alcohol to ambient water vapor.