PURPOSE: To achieve the better protection of an oxygen concentration detecting section with the reduction in the separation of a protective layer by providing the layer covering it with such a shape of the end thereof that the thickness thereof decreases gradually on the surface of a substrate thereof.
CONSTITUTION: An oxygen sensor has an intermediate layer 5 on a substrate 1. A reference electrode 6, a solid electrolytic layer 7, a measuring electrode 8 and a second measuring electrode 9 are stacked sequentially thereon 5 to form an oxygen detecting section. In this case, a protective layer 20 is so formed that the thickness thereof decreases gradually at the end thereof on the substrate 1 thereof to hold the gradient within 45°. This can check possible separation of the protective layer at said end thereof so effectively as to prevent deterioration in characteristics of the oxygen concentration detecting section due to such a separation.
MATOBA KAZUO
AOKI HIROYUKI
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