Semiconductor type gas sensor having two terminals

Claim 1

A gas sensor having two terminals and comprising: a heater having a positive temperature coefficient of resistance, and a gas sensitive semiconductor covering the heater at least at their opposite ends and having a negative temperature coefficient of resistance, the heater being an alloy composed of a principal ingredient and an auxiliary ingredient, the principal ingredient being platinum, the semiconductor being a sintered metal oxide composed of a principal ingredient and an auxiliary ingredient, the principal ingredient being tin oxide, wherein the kinds and contents of the auxiliary ingredients in the alloy and the sintered metal oxide are so selected that a combined resistance of said heater and said semiconductor are substantially constant corresponding to an offset of the temperature coefficient of resistance of the heater to the temperature coefficient of resistance of the semiconductor at operating temperatures, and wherein the auxiliary ingredient of the alloy is about 2 to 13 weight percent of rhodium and the auxiliary ingredient of the sintered metal oxide is about 0.01 to 0.10 atomic ratio percent of antimony pentoxide, the atomic ratio being based on the number of tin atoms and antimony atoms.