New materials and heater geometry for high performance micromachined thermally insulated structures in gas sensor applications

A fabrication technology suitable for the realization of a substrate for thin film gas sensors operating at high temperature is presented. compared to previously reported Si microstructure with a thin membrane as physical support of the entire sensor stack, innovations constituted by the membrane material (non stoichiometric silicon nitride), adhesion layer (25 nm of TiN) between the Pt and the substrate to rise up to 800 °C the maximum operating temperature, a new design of the heater resistor and of the temperature sensor for an improved temperature uniformity over the device active area have been implememnted. Furthermore, a new passivation layer structure constituted by a sandwich of spin-on-glass and LTO offersa high degree of step coverage and, at the same time, very good electrical passivation efficiency. The results of computer simulation using FE program and experimental investigations carried out on the realized microstructures are presented.