Patent ID: 7041207

Claim:
A gas sensor including an electrochemical cell for detecting a gas concentration, comprising an oxygen-ion conductive solid electrolyte layer comprising stabilized or partially stabilized zirconia and alumina grains; metallic electrodes comprising a gas measuring electrode including a lead portion and an oxygen-reference electrode formed on the oxygen-ion conductive solid electrolyte layer; a ceramic substrate mainly comprising alumina laminated with the oxygen ion conductive solid electrolyte layer and including a heater and heater leads embedded in the substrate; and an intermediate ceramic layer comprising zirconia which may be stabilized in part or whole in an amount of 20% by weight or more and alumina, the intermediate layer being disposed between the oxygen ion-conductive solid electrolyte layer and the ceramic substrate and has a thickness of 5 μm to 200 μm, wherein the oxygen-ion conductive solid electrolyte layer contains 10% to 80% by weight of alumina grains, the amount of alumina contained in the intermediate ceramic layer is at least 10% by weight more than in the oxygen-ion conductive solid electrolyte layer, an average grain size of solid electrolyte ceramic grains of stabilized or partially stabilized zirconia contained in the oxygen-ion conductive solid electrolyte layer after firing is not greater than 2.5 μm, and an average grain size of the alumina grains contained in the oxygen-ion conductive solid electrolyte layer after firing is not greater than 1 μm, and wherein the oxygen-ion conductive solid electrolyte layer, the metallic electrodes, the ceramic substrate, and the intermediate layer are integrally co-fired at a sintering temperature of at least 1350° C. to form a laminate.