# US 4,399,424 A · Gas sensor

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- Number: US 4,399,424 A
- Document ID: US4399424A
- Status: Granted
- Kind: A
- Application number: 06/308,290
- Filed: 1981-10-05
- Granted: 1983-08-16
- Earliest claimed: 1980-10-07
- Assignees: ITT Industries, Inc.
- Inventors: Leslie J. Rigby
- Web page: https://patentgrep.com/patent/US4399424A

## CPC

- G01N 27/12: of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid {, for detecting components in the fluid}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

A semiconductor gas sensor comprises an insulating substrate (11) on which a resistive heater track (15) coupled to a pair of electrodes (12, 14) is deposited. A film (16) of a semiconductive metal oxide, typically a doped oxide, is ion-plated on to the assembly so as to contact the resistive track (15) and a further electrode (13). Exposure of the device to a particular gas, e.g. hydrogen sulphide, reduces the resistivity of the semiconductive film (16), this change being detected via an amplifier circuit (not shown). In an alternative version of the sensor (FIGS. 5a, 5b and 6) the heater is disposed under a dielectric layer, the semiconductive film being ion-plated onto the dielectric layer and electrodes therein.

## Claims

### Claim 1

A hydrogen sulphide gas sensor comprising: a substrate insulator; first and second parallel conductive strips forming electrodes affixed to said substrate insulator in spaced relation to each other; a layer of a resistive heater material affixed to said substrate insulator and to said first and second strips; a dielectric film having obverse and reverse sides, said dielectric film having said reverse side thereof covering and fixed relative to said resistive heater material; third and fourth conductive strips forming electrodes, said third and fourth conductive strips being fixed to the obverse side of said dielectric film, said third and fourth conductive strips being long and thin in comparison to their widths, said third conductive strip being straight, said fourth conductive strip being U-shaped and straddling said third conductive strip, said fourth conductive strip having one leg on each side of and parallel to said third conductive strip, said legs being connected by a bight portion, each of said legs being uniformly spaced from said third conductive strip; and a semiconductive film fixed to said dielectric film between and in contact with said third and fourth conductive strips in a position to be heated by said heater means, said semiconductive film having a resistivity which decreases with an increase of hydrogen sulphide concentration in a gas contacting the same, said semiconductive film comprising tin oxide doped with alumina.

### Claim 2 (depends on 1)

The invention as defined in claim 1, wherein a fifth conductive strip is affixed to said dielectric film, said fifth conductive strip being U-shaped and surrounding said fourth conductive strip.

### Claim 3

A gas sensor comprising: a substrate insulator; a dielectric film having obverse and reverse sides; heater means fixed relative to and on said reverse side to supply heat to the vicinity of said obverse side; first and second conductive strips forming electrodes, said first and second conductive strips being fixed to the obverse side of said dielectric film, said first and second conductive strips being long and thin in comparison to their widths, said first conductive strip being straight, said second conductive strip being U-shaped and straddling said third conductive strip, said second conductive strip having one leg on each side of said first conductive strip, said legs being connected by a bight portion, each of said legs being uniformly spaced from said third conductive strip; and a semiconductive film fixed to said dielectric film between and in contact with said first and second conductive strips in a position to be heated by said heater means, said semiconductive film having a resistivity which decreases with an increase of hydrogen sulphide concentration in a gas contacting the same.