Direct Thermoelectric Hydrocarbon Gas Sensors Based on ${\rm SnO}_{2}$

Direct thermoelectric gas sensors offer a promising measurement principle. Similar to the conductivity, the measurand Seebeck coefficient depends on the ambient gas atmosphere. Moreover, and unlike the conductivity, it is independent from the geometry of the gas sensitive film. This behavior is clearly demonstrated in a comparison of a fresh sensor and a sensor that was deliberately milled out. As an exemplary material for a gas sensitive film, tin dioxide was chosen. Direct thermoelectric gas sensors, therefore, promise better long-term stability, since in contrast to conductometric sensors aging phenomena-like cracks and abrasions do not affect the Seebeck coefficient. Thermoelectric gas sensors are difficult to measure, not only because a voltage and a temperature difference have to be measured, but also with respect to problems that occur, if one measures small thermovoltages on high-ohmic films. Hence, we optimized the design of the direct thermoelectric gas-sensing device, with special respect to low internal film resistances. The result of this optimization is a thermoelectric gas sensor with an accuracy comparable to conductometric gas sensors.