Solid electrolyte oxygen sensor and method of making same

A method of making an oxygen sensing device comprising the steps of:

• forming a sintered wafer of stabilized solid electrolyte ceramic;
• applying a first, porous, continuous electrode coating to the major portion of the sensing side of said wafer and to a narrow first band portion along the axial length of a first side edge portion of said wafer while leaving said sensing side of said wafer devoid of said electrode coating in the area thereof which is immediately adjacent a second side edge portion which is circumferentially spaced from said first band of coating;
• applying a second, porous, continuous electrode coating to the major portion of the reference side of said wafer and to a narrow second band portion along the axial length of said second side edge portion while leaving said reference side of said wafer devoid of said electrode coating in the area thereof which is immediately adjacent said first narrow band portion;
• applying first and second spaced conductive stripes internally along at least a portion of the length of an unfired ceramic tube having an inner diameter greater than the outer diameter of said wafer and a temperature coefficient of expansion which is compatible with said wafer after firing but will cause said tube to shrink into a hermetic sealing relationship with said wafer during firing, said stripes being applied at a circumferential spacing corresponding to the spacing between said first and second bands of coating;
• positioning said wafer internally of said unfired ceramic tube so that its first and second bands of coating are aligned with and overlie said first and second conductive stripes;
• and
• firing said tube and wafer assembly to shrink said tube onto said wafer and mechanically force said bands of coating into intimate contact with said conductive stripes.