Patent ID: 7607339

Claim:
A gas sensor element comprising: a first ceramic sheet including a solid electrolyte body; a second ceramic sheet being made of material compositions different from those of the first ceramic sheet and including a chamber forming layer having one surface facing the solid electrolyte body and formed with a recessed portion defining a reference gas chamber; an intermediate bonding layer that bonds the first and second ceramic sheets to each other so as to form a closed hollow space between the first and second ceramic sheets and is formed only in an area between the solid electrolyte body and the chamber forming layer; wherein the intermediate bonding layer has a multilayer structure including first and second unit intermediate layers laminated on each other such that an innermost end portion of one of the first and second unit intermediate layers protrudes inward in the closed hollow space and is laterally offset from an innermost end portion of the other of the first and second unit intermediate layers, and wherein the first unit intermediate layer is formed on the solid electrolyte body and the second unit intermediate layer is formed on the chamber forming layer such that the first unit intermediate layer has the innermost end portion protruding toward the reference gas chamber to a further extent than the innermost end portion of the second unit intermediate layer, whereby the innermost end portions of the first and second unit intermediate layers define a stepped shape in cross section and the innermost end portions do not extend inward of a periphery of the reference gas chamber; a reference gas detecting electrode formed on one surface of the solid electrolyte body in face-to-face relation with the reference gas chamber; a measuring gas detecting electrode formed on the other surface of the solid electrolyte body and exposed in a measuring gas chamber; a diffusion resistance layer stacked on the other surface of the solid electrolyte body so as to define the measuring gas chamber in an area around the measuring gas detecting electrode and operative to permeate measuring gas to the measuring gas chamber; and a shielding layer laminated on the diffusion resistance layer.