Gas sensor

• US 20060185420A1
• Filed: 02/21/2006
• Published: 08/24/2006
• Est. Priority Date: 02/22/2005
• Status: Active Grant

• Current Assignee: Niterra Co., Ltd.
• Original Assignee: NGK Spark PLUG Company Limited (Niterra Co., Ltd.)
• Inventors: Nakagawa, Shinichi, Nakano, Yoshihiro, Kojima, Takio, Kida, Masahito
• Granted Patent: US 7,276,745 B2
• Time in Patent Office: Days
• US Class Current: 73/31.60
• CPC Class Codes: G01N 27/125 Composition of the body, e.g. the composition of its sensitive layer

Abstract

The present invention provides a gas sensor having excellent humidity resistance even if used in a high temperature and high humidity atmosphere. According to the present invention, a gas sensor is comprised of: a silicon substrate; a metal-oxide semiconductor portion comprised mainly of SnO₂ and formed on the substrate; and a catalytic portion comprised of Pd and dispersed on a surface of the metal-oxide semiconductor portion, wherein the metal-oxide semiconductor portion and the catalytic portion constitute a gas sensing portion. Furthermore, an insulating portion comprised mainly of SiO₂ is formed dispersedly on a surface of the gas sensing portion. Further, the catalytic portion and the insulating portion are formed on the surface of the metal-oxide semiconductor portion so that the surface additive rate, which is expressed by Si/(Pd+Si) representing the ratio in the number of atoms of Si to Pd, of the gas sensing portion having the insulating portion may be 65% or more to 97% or less, and so that the surface additive rate, which is expressed by Si/(Sn+Si) representing the ratio in the number of atoms of Si to Sn, of the gas sensing portion may be 75% or more to 97% or less.

Claims

1. A gas sensor comprising:

a gas sensing portion formed by a metal-oxide semiconductor portion whose electrical characteristic varies according to a gas to be detected and a catalytic portion dispersed on a surface of the metal-oxide semiconductor portion; and

an insulating portion formed on a surface of the gas sensing portion so that a part of the gas sensing portion may be exposed;

wherein the metal-oxide semiconductor portion is comprised mainly of SnO₂, the catalytic portion is comprised of a noble metal M and the insulating portion is comprised mainly of SiO₂,

wherein a first surface additive rate, which is expressed by Si/(M+Si) representing the ratio in the number of atoms of Si to M, of the gas sensing portion having the insulating portion is determined to be 65% or more to 97% or less, and a second surface additive rate, which is expressed by Si/(Sn+Si) representing the ratio in the number of atoms of Si to Sn, of the gas sensing portion is determined to be 75% or more to 97% or less.

2. A gas sensor as claimed in claim 1, wherein the noble metal M is Pd or Pt.

3. A gas sensor as claimed in claim 1,

wherein the metal-oxide semiconductor portion, the catalytic portion and the insulating portion assume a form of a thin film, respectively.

4. A gas sensor as claimed in claim 2,

wherein the metal-oxide semiconductor portion, the catalytic portion and the insulating portion assume a form of a thin film, respectively.

5. A gas sensor as claimed in claim 1, further comprises:

a silicon substrate; and

an insulating layer formed on the silicon substrate and in which a heating element for heating the metal-oxide semiconductor portion is buried therein,

wherein the silicon substrate includes an open space formed at a position directly below the heating element, and

wherein the metal-oxide semiconductor portion is formed on the insulating layer so as to be directly above the heating element.

6. A gas sensor as claimed in claim 2, further comprises:

a silicon substrate; and

an insulating layer formed on the silicon substrate and in which a heating element for heating the metal-oxide semiconductor portion is buried therein,

wherein the silicon substrate includes an open space formed at a position directly below the heating element, and

wherein the metal-oxide semiconductor portion is formed on the insulating layer so as to be directly above the heating element.

7. A gas sensor as claimed in claim 3, further comprises:

a silicon substrate; and

an insulating layer formed on the silicon substrate and in which a heating element for heating the metal-oxide semiconductor portion is buried therein,

wherein the silicon substrate includes an open space formed at a position directly below the heating element, and

wherein the metal-oxide semiconductor portion is formed on the insulating layer so as to be directly above the heating element.