A Tunable Palladium-based Capacitive MEMS Hydrogen Sensor Performing High Dynamics, High Selectivity and Ultra-low Power Sensing

AbstractWe developed an ultra-low power MEMS hydrogen (H2) sensor performing high dynamics together with high sensitivity up to the Lower Explosive Limit (LEL), i.e. 4% vol. H2 in dry air. The architecture consists of Al clamped-clamped beams (700 nm- thick, 800μm-total width, 140 or 240μm-length) with both ends made of a Pd/Al bimorph (200/700 nm-thick) on a quarter of its length, acting as actuators, released above a split-bottom electrode. The initial stress defines the initial deflection of the structure while the Pd-hydriding induces compressive stress variation in the Pd actuator layer and therefore the membrane deflection. A capacitive transduction is used to continuously measure the gap variation due to the H2 absorption and hydriding kinetic. Results show a fast response time of less than 5 s for an effective concentration of about 0.2% vol. H2 in dry air or N2 mixture, with no cross sensitivity