Polysilicon mesoscopic wires coated by Pd as high sensitivity H2 sensors

In this paper, a new class of H2 sensors made up of mesoscopic polysilicon wires coated by palladium is presented. Using surface micromachining combined with an usual microelectronic planar process, polysilicon wires of the following dimensions have been constructed: from 0.25 up to 3.7 μm wide, from 100 up to 140 μm long, about 600 nm thick. Because of their high surface/volume ratio, these wires have shown a very high resistance percentage variation under hydrogen absorption. Experimental measurements have been performed in 100 ppm H2 flux at room temperature and atmospheric pressure. In order to reach transducers with an enhanced resolution, laser annealing experiments have been performed with the aim of oxidising the polysilicon and obtaining a consequent further reduction of the wire cross-section.