Microfabrication of MOS H2 sensors based on Pd-gate deposited by pulsed laser ablation

A Nd:YAG high power 532 nm pulsed laser was employed to deposit, a thin layer (30 nm) of palladium on the gate of a microfabricated gas sensor (MOS capacitor). The functional performances of the MOS device were investigated by characterizing the capacitance (C–t, C–V) variations occurring upon H2 exposure, as a function of the gas concentration. A comparison in terms of sensor response versus concentration and recovery time was also performed with sensors in which the Pd layer was deposited by metal evaporation, maintaining all the parameters of the microfabrication process constant and by changing the operative working temperature. An improved performance was observed for the laser deposited Pd layer with respect to the evaporated one, an effect ascribed to the presence of Pd atoms into the underlying silicon oxide layer.