Oxygen sensor

Claim 1

An oxygen sensor for detecting the concentration of oxygen contained in a subject gas comprising: a solid electrolytic element made of an oxygen ion-conducting metal oxide having a first surface adapted to be exposed to the subject gas and a second surface adapted to be exposed to a reference gas; a porous first electrode fixed on said first surface of said element; a porous second electrode fixed on said second surface of said element; an electrically-insulating layer made of a heat-resisting ceramic material formed on said first surface of said element except where said first electrode is fixed on said first surface; a metal lead formed on said insulating layer, this metal lead being made of film material and being electrically connected to said first electrode; an electrically-conductive retaining element formed on said metal lead, this retaining element being electrically connected to said first electrode and constituted by a densely sintered mixture of a conducting metal material and a binding material; and a gas diffusion-resisting layer made of a porous, electrically-insulating ceramic material, this layer covering said first electrode, said metal lead and said retaining element, this oxygen sensor thereby being adapted such that at least within a predetermined range of oxygen concentration, if said first electrode is electrically connected via said metal lead to an anode of a source of electrical power, and said second electrode is electrically connected to a cathode of said source of electrical power and a voltage applied across said electrodes thereby while said first surface is exposed to said subject gas and said second surface is exposed to said reference gas, a current will flow between said electrodes, which current is proportional to the difference between the concentration of oxygen in said subject gas and said reference gas.