Patent ID: 8795492

Claim:
A gas sensor element comprising: a solid electrolyte body having oxygen ion conductivity and an opposite pair of first and second surfaces; a measurement electrode provided on the first surface of the solid electrolyte body so as to be exposed to a measurement gas; a reference electrode provided on the second surface of the solid electrolyte body so as to be exposed to a reference gas; and a porous diffusion-resistant layer through which the measurement gas is introduced to the measurement electrode, the porous diffusion-resistant layer having an outer surface through which the measurement gas flows into the diffusion-resistant layer, characterized in that the gas sensor element further comprises a protective layer that is provided to cover at least the outer surface of the porous diffusion-resistant layer, the protective layer being hydrophilic at room temperature and water-repellent at high temperatures at which the solid electrolyte body can be activated; and wherein the protective layer has a surface roughness Ra lower than or equal to 3.0 μm; wherein the protective layer is made of a ceramic comprising at least one of α-alumina, titania, zirconia, silicon carbide, silicon nitride, and zinc oxide; and further comprising a trap layer that is interposed between the outer surface of the porous diffusion-resistant layer and the protective layer to trap poisoning substances contained in the measurement gas.