Patent ID: 8152979

Claim:
An ammonia gas sensor comprising: a solid electrolyte member which extends in an axial direction and contains zirconia as a predominant component; a detection portion provided on a front surface of the solid electrolyte member; a reference electrode provided on a back surface of the solid electrolyte member; a detection lead provided directly, or via another member, on the front surface of the solid electrolyte member so as to establish electrical connection between the detection portion and an external circuit, and an insulating portion provided at least on a surface of the detection lead or between the detection lead and the solid electrolyte member, wherein the detection portion includes a detection electrode formed of a noble metal, and a selective reaction layer formed of a metal oxide having selectivity for ammonia gas, wherein the detection electrode is provided directly, or via another member, on the solid electrolyte member; and the selective reaction layer is provided directly, or via another member, on the detection electrode, and wherein the insulating portion is formed on the surface of the detection lead, and includes a first insulating portion which extends in the axial direction onto the surface of the detection electrode to shield the detection lead from exposure to a gas under measurement through the detection electrode, wherein the first insulating portion extends to the detection electrode so as to be provided at an interface between the selective reaction layer and the detection electrode, wherein the metal oxide is vanadium oxide, bismuth oxide, or a composite oxide of vanadium oxide and bismuth oxide, and wherein the selective reaction layer overlaps the first insulating portion.