fabrication of different types of oxygen sensors and their improvement by using one- or two-sided semiconductor oxide references

we report the development of different types of oxygen sensors based on yittria-stabilized zirconia (ysz) as a solid electrolyte. the conventional oxygen sensor is a concentration cell with two porous pt electrodes, one of which is exposed to air as a constant (reference) oxygen concentration and the other is exposed to automobile exhaust gas of variable oxygen concentration, depending on the air-to-fuel (atf) ratio injected into engine. the conventional sensor is miniaturized by using an oxide semiconductor instead of the reference air. this the response time and the sensitivity of the sensor significantly improved. also the light-off time, during which most of large city pollutant are dramatically reduced. the transition response of above sensors occur at the stoichiometric atf ratio, while recently lean-burn engines working at atf ratios higher than that of stoichiometric are proffered. in addition to the above sensors, we have developed a new type of ysz- based oxygen sensor, in which two oxides (e.g. tio2, sno2 and ceo2) with different semi conductive characteristics are applied on the tow pt electrodes. this way the transition response of the sensor is shifted toward atf ratios higher than the stoichiometric ones, suitable for lean-burn engines.