Cu/Pd Thin-film Thermopile as a Temperature and Hydrogen Sensor

This paper illustrates the experimental performance of a thermopile made by five Cu/Pd thermocouples (junction area 200 × 200 ?m) which shows sensitivity to both temperature and hydrogen and has a relatively low Johnson noise. The thermoelectric power of the elementary thermocouple is a few ?V/K. The H2 responsivity in a H2 + N2 flux is found to be dependent on the temperature difference T2 - T1 between the two thermocouple junctions and on the H2 concentration. With T2 - T1 equal to 100 K, T2 equal to 373 K and a H2 concentration of 88 ppm in N2, the thermopile gives a responsivity of about 750 nV/(ppm of H2). Response times depend on the temperature of both junctions and the hydrogen concentration in the H2 + N2 mixture and are mainly related to the adsorption-desorption processes of the Pdfilm itself. Data on the responsivity dependence versus H2 concentration and versus T2 - T1 are given and discussed. Noise problems are finally taken into account in order to consider the noise equivalent H2 concentration NECH2.