Low power gas detector

• US 4,580,439 A
• Filed: 02/07/1984
• Issued: 04/08/1986
• Est. Priority Date: 02/07/1983
• Status: Expired due to Term

• Current Assignee: Ricoh Seiki Co. Ltd. (Ricoh Company Limited)
• Original Assignee: Ricoh Seiki Co. Ltd. (Ricoh Company Limited)
• Inventors: Manaka, Junji
• Primary Examiner(s): Miles, Tim
• Application Number:
  US06/577,858
• Time in Patent Office: 791 Days
• Field of Search: 338/34, 73/23
• US Class Current: 73/31.06
• CPC Class Codes: 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
• CPC Class Codes: H01J 2217/49207 Electrodes

Abstract

A gas detector includes a gas detecting element comprised of a metal oxide semiconductor material which changes its value of electrical resistance at an elevated temperature when it absorbs a gas. In one form, the gas detecting element is supported in the form of a bridge so as to increase its response speed by making thermal capacity as small as possible. In another form, the gas detecting element is supported in the form of a cantilever, more preferably in the form of a ring as formed along the periphery of a overhang portion of a disc-shaped layer of electrically insulating material. Also provided is a process for manufacturing a thin film of metal oxide, which may be advantageously used as a gas detecting element of a gas detector or a transparent electrode, for example, in a liquid crystal panel.

Claims

1. A gas detector comprising:

a substrate;

an insulating layer formed on said substrate and having a projection which extends into the air;

at least two electrically conductive heater strips formed on said projection as spaced apart from each other;

means for applying a driving signal to said heater strips;

a gas detecting layer formed as extending between said heater strips, said gas detecting layer changing its electrical resistance when it absorbs a gas; and

means for detecting changes in the electrical resistance of said gas detecting layer.

2. A gas detector of claim 1 wherein said gas detecting layer comprises a metal oxide semiconductor.

3. A gas detector of claim 2 wherein said projection is in the form of a bridge.

4. A gas detector of claim 2 wherein said projection is in the form of a cantilever.

5. A gas detector of claim 3 wherein said projection is defined in an elongated manner whose longitudinal direction is in a particular relation to a crystal orientation of said substrate.

6. A gas detector of claim 5 wherein said substrate is provided with a void space in its top surface and said bridge-formed projection extends above said void space.

7. A gas detector of claim 1 wherein said means for detecting includes a detector strip of electrically conductive material formed on said projection as sandwiched between said heater strips.

8. A gas detector of claim 7 further comprising electrode pads formed on said insulating layer and each connected to one end of said heater and detector strips.

9. A gas detector comprising:

a substrate having a ridge which is generally circular in cross section;

an electrically insulating layer formed on said ridge having an overhang portion which is also generally circular and extending beyond the periphery of said ridge into the air over a predetermined amount;

at least two strips of electrically conductive material formed on said overhang portion as spaced apart from one another;

means for applying electrical current to at least one of said strips;

a gas detecting layer formed in contact with at least one of said strips, said gas detecting layer changing its electrical resistance when it absorbs a gas; and

means for detecting changes in the electrical resistance of said gas detecting layer.

10. A gas detector of claim 9 wherein said strips are formed circularly on said overhang portion.

11. A gas detector comprising:

a substrate provided with a recess circular in shape at its top surface;

an electrically insulating layer formed on said top surface having an overhang portion extending into said recess over a predetermined amount;

at least two ring-shaped strips of electrically conductive material formed on said overhang portion as spaced apart from one another;

means for applying electrical current to at least one of said strips;

a gas detecting layer formed in contact with at least one of said strips, said gas detecting layer changing its electrical resistance when it absorbs a gas; and

means for detecting changes in the electrical resistance of said gas detecting layer.

12. A gas detector comprising:

an electrically insulating layer;

at least two electrodes formed on said insulating layer as spaced apart from each other;

a gas detecting layer capable of being self-heated to a predetermined temperature when current is passed therethrough formed on said insulating layer as extending between said two electrodes, said gas detecting layer changing its electrical resistance when it absorbs a gas;

means for applying electrical current between said two electrodes for passing said current through said gas detecting layer thereby causing said gas detecting layer to be self-heated to a predetermined temperature; and

means for detecting changes in the electrical resistance of said gas detecting layer.

13. A gas detector of claim 12 wherein said insulating layer includes a projection which extends into the air and said gas detecting layer is formed on said projection.

14. A gas detector of claim 13 wherein each of said electrodes includes a lead-out portion which extends partly along said projection whereby the connections between said gas detecting layer and each of said lead-out portions are located on said projection.

15. A gas detector of claim 13 further comprising a support having a pair of ridges and wherein said projection is supported as extending between said ridges in the form of a bridge.

16. A gas detector of claim 15 wherein said bridge-formed projection becomes wider toward its center between its base ends which are supported on said ridges.