Patent ID: 8419915

Claim:
A gas sensor comprising: A plate-shaped detection element configured to detect a specified gas component contained in a gas to be detected, said detection element having a symmetrical, stacked structure and comprising: A sensing portion configured to detect a specified gas component and having a first surface and a second surface opposite the first surface, the sensing portion comprising first and second solid electrolyte layers containing a first material as a main component; A first portion stacked on the first surface of the sensing portion and comprising one or more first base layers containing a second material as a main component different from the first material; and A second portion stacked on the second surface of the sensing portion and comprising one or more second base layers containing the second material as a main component, Wherein the total thickness of one or more second base layers, in a stacking direction of the sensing portion, the first portion and the second portion, is not less than 80% but not more than 120% of a total thickness of one or more first base layers, and Wherein the first and second portions are stacked on the first and second solid electrolyte layers, respectively, so as to extend over the first and second solid electrolyte layers in a direction orthogonal to the stacking direction, so that the symmetrical stacked structure of the detection element is disposed in the recited order of the first portion, the sensing portion, and the second portion, Wherein the sensing portion further includes an insulating layer, containing the second material, disposed between the first and second solid electrolyte layers, and Wherein the thickness of the insulating layer is less than a thickness of each of the first and second solid electrolyte layers and each of the first and second portions, and Both the first and second portions consist of dense layers.