Patent ID: 8377274

Claim:
A gas sensor including a gas sensor element extending in a longitudinal direction thereof, the gas sensor element comprising; a first measurement chamber interposed between two solid electrolyte layers stacked with an interval therebetween and into which a gas to be measured is introduced from outside the sensor; a first pumping cell having a first inner pump electrode facing the first measurement chamber and a first counterpart electrode for the first inner pump electrode, the first inner pump electrode being configured to control oxygen partial pressure in the first measurement chamber; a second measurement chamber in mutual communication with the first measurement chamber, that is partitioned from surroundings and into which a gas to be measured having a controlled oxygen partial pressure is introduced from the first measurement chamber; and a second pumping cell having a second inner pump electrode disposed within the second measurement chamber and a second counterpart electrode for the second inner pump electrode, the second pumping cell being configured to detect a specific gas component in the gas to be measured within the second measurement chamber, wherein the second inner pump electrode is made of an aggregate that contains Pt as a principal ingredient consisting of a plurality of Pt particles, in a cutting plane of the gas sensor element taken along its stacking direction, when a reflection electron image including an interface between the second inner pump electrode and a solid electrolyte layer in contact with the second inner pump electrode is observed, a surface of the Pt particle making up the outermost surface of the second inner pump electrode is defined as a surface to be measured, the maximum height and the minimum height between the surface to be measured of individual ones of the Pt particles and the interface are determined from a direct distance perpendicular to the interface, and the relationships T 1 −T 2 ≧5 and T 2 /T 1 ≦0.75 are satisfied, wherein T 1 (μm) is an average of the three largest values among the maximum heights arranged in a decreasing order from the largest value and T 2 (μm) is an average of the three smallest values among the minimum heights arranged in an increasing order from the smallest value.