Thin film gas sensor configuration
A gas sensor for sensing a gas stream constituent includes, mounted a substrate, a first gas-sensing element capable of sensing the constituent in a first concentration range, a reference element insensitive to the constituent and having electrical properties congruent with the first gas-sensing element, a heating element substantially circumscribing the first gas-sensing element and the reference element, a temperature-sensing element circumscribing the first gas-sensing element and the reference element, and a second gas-sensing element capable of sensing the constituent in a second concentration range. The first gas-sensing element and the reference element are preferably metal-gated metal-oxide semiconductor (MOS) solid-state devices. The gas sensor is particularly configured to sense hydrogen concentration in a gas stream.
1. A gas sensor for sensing a gas stream constituent, the gas sensor comprising:
(a) a thermally conductive, electrically insulative substrate;
(b) a first gas-sensing element mounted on said substrate, said first gas-sensing element capable of sensing said constituent in a first concentration range;
(c) a reference element mounted on said substrate, said reference element and said first gas-sensing element having congruent electrical properties, said reference element insensitive to said constituent;
(d) a heating element mounted on said substrate such that a uniform temperature environment is effected around said first gas-sensing element and said reference element;
(e) a temperature-sensing element mounted on said substrate and in thermal connection with said first gas-sensing element and said reference element;
(f) a second gas-sensing element mounted on said substrate capable of sensing said constituent in a second concentration range such that said heating element imparts at least some heat to said second gas-sensing element;
wherein said temperature-sensing element is thermally connected to said heating element and wherein said first gas-sensing element, said reference element, said heating element, said temperature-sensing element and said second gas-sensing element are arranged in a nested geometric configuration on said substrate.
2. The gas sensor of claim 1 wherein said second gas-sensing element is mounted on said substrate such that a uniform temperature environment is effected around said first gas-sensing element, said second gas-sensing element and said reference element.
3. A method of fabricating a gas sensor for sensing a gas stream constituent, the fabricating method comprising:
(a) mounting a first gas-sensing element on a thermally conductive, electrically insulative substrate, said first gas-sensing element capable of sensing said constituent in a first concentration range;
(b) mounting a reference element on said substrate, said reference element and said first gas-sensing element having congruent electrical properties, said reference element insensitive to said constituent;
(c) mounting a heating element on said substrate such that a uniform temperature environment is effected around said first gas-sensing element and said reference element;
(d) mounting a temperature-sensing element on said substrate such that said temperature-sensing element is in thermal connection with said first gas-sensing element and said reference element;
(e) mounting a second gas-sensing element on said substrate, said second gas-sensing element capable of sensing said constituent in a second concentration range, such that at least some heat from said heating element is imparted to said second gas-sensing element;
wherein said temperature-sensing element is thermally connected to said heating element and wherein said first gas-sensing element, said reference element, said heating element, said temperature-sensing element and said second gas-sensing element form a geometric configuration that minimizes area occupied on said substrate.
4. The fabricating method of claim 3 wherein said second gas-sensing element is mounted on said substrate such that a uniform temperature environment is effected around said first gas-sensing element, said second gas-sensing element and said reference element.