Abstract: A gas concentration detector using solid electrolyte layers laminated measures a concentration of gas constituents in measuring gas such as exhaust gas of an internal combustion engine without being influenced by oxygen concentration in the measuring gas. The measuring gas is introduced into an inner cavity of the detector and outside air as a reference gas is introduced into an air passage in the detector. Oxygen concentration in the measuring gas in the inner cavity is maintained at a predetermined level by operation of an oxygen pumping cell constituted by an ion conductive solid electrolyte layer and a pair of electrodes formed on both surfaces of the layer. The oxygen concentration in the inner cavity is measured by an oxygen sensor cell having one electrode exposed to the inner cavity and the other electrode exposed to the reference gas.

Abstract: An air-fuel ratio detecting element is composed of an oxygen pump portion and an oxygen sensor portion which are provided on a single solid electrolyte sheet, a heating element, and a spacer. The oxygen pump portion is composed of a pair first of electrodes provided on opposite sides of the solid electrolyte sheet, and a communication hole which is formed through the solid electrolyte sheet and the electrodes. Electrodes are disposed on the solid electrolyte sheet on the same side as the second electrode, whereby the oxygen sensor portion is formed. The spacer has an opening and a slit-like opening. The heating element 4, the spacer, and the solid electrolyte sheet are stacked from bottom to top, and then the stacked assembly is baked. In this case, they are stacked such that the opening faces the first electrodes and the second electrode.