Activation process of reversible Pd thin film hydrogen sensors

Abstract

Microcantilever-based thin film palladium hydrogen sensors have high selectivity and sensitivity. Reproducibility and accuracy of the sensor performance depend on the activation process of the polycrystalline palladium film deposited on the cantilever. When the hydrogen is in solid solution (α-phase), the cantilever bending is mostly governed by the residual film stress induced by the swelling at the grain boundaries in the film. When the palladium hydride (β-phase) starts to be formed, the cantilever undergoes a large deflection due to hydrogen absorption-induced film swelling (10% change in volume). Differences in the phase diagrams of the palladium hydride for two film thicknesses show that the cantilever bending is governed by hydrogen uptake as well as the release of the residual stress of the film through cyclic exposure and cycling number.