Direct thermoelectric gas sensors: Design aspects and first gas sensors

Design aspects for novel direct thermoelectric gas sensors are discussed. Such sensors are based on materials that directly change their material property Seebeck coefficient with the ambient gas atmosphere. Since the measurement principle is a potentiometric one, a very good stability in harsh environments is expected, especially when compared to resistive gas sensors. In contrast to the potentiometric lambda sensor, no reference atmosphere is needed.A setup in multilayer thick film technology was chosen. In order to detect accurately the Seebeck coefficient of the material, a sinusoidally varying temperature difference was applied on the sensitive film with a modulation heater. With the initial sensor design a crosstalk from the modulation voltage to the measured thermovoltage of the gas sensitive layer was observed. The origin of this behavior could be explained by the Fourier analyzed signals of the thermovoltage of the gas sensitive layer and the temperature difference. An additional equipotential layer was considered to be an adequate mean to prevent this crosstalk. As a first example, a thermoelectric oxygen sensor utilizing SrTi0.6Fe0.4O3 as a gas sensitive material was manufactured. It could be shown that the oxygen sensitivity of this direct thermoelectric gas sensor is comparable to resistive SrTi0.6Fe0.4O3-gas sensors. A high accuracy was found.