Cu/Pd thin-film thermopile as a temperature and hydrogen sensor

Abstract This paper illustrates the experimental performance of a thermopile made by five Cu/Pd thermocouples (junction area 200 × 200 μm) 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 μV/K. The H 2 responsivity in a H 2 + N 2 flux is found to be dependent on the temperature difference T 2 - T 1 between the two thermocouple junctions and on the H 2 concentration. With T 2 - T 1 equal to 100 K, T 2 equal to 373 K and a H 2 concentration of 88 ppm in N 2 , the thermopile gives a responsivity of about 750 nV/(ppm of H 2 ). Response times depend on the temperature of both junctions and the hydrogen concentration in the H 2 + N 2 mixture and are mainly related to the adsorption-desorption processes of the Pd film itself. Data on the responsivity dependence versus H 2 concentration and versus T 2 - T 1 are given and discussed. Noise problems are finally taken into account in order to consider the noise equivalent H 2 concentration NEC H2 .