A highly selective MEMS transducer for hydrogen sensing based on stress modification in palladium thin films

We developed and integrated a MEMS capacitive transducer based on aluminium/palladium bimorph configured as clamped-clamped beams, performing fast and highly selective hydrogen detection. The bimorph is obtained by combining evaporation and sputtering deposition techniques and acts as actuator of the structure. The stress control in the beams has been investigated in order to gain control over the sensing dynamics. The transducer response time is less than 4 s at 0.2 % vol. H2/N2 concentration. The related kinetic shows good correlations to previous in situ experiments of stress modifications in palladium thin films with controlled initial stress. The device is interfaced by an AD774x capacitance-to-digital converter and a CC253x microcontroller within a dedicated housing including a Porex® microporous polymer membrane for IP66 compatibility. Finally, the ultra-low power consumption (<; 10 μW) of such devices is very promising to ease their integration in emerging interconnected sensor nodes within the Internet-of-Things vision.