An optimized preparation process of stainless-steel substrates and their application to thin-film high pressure sensors

An optimized preparation process of 17.4 PH stainless-steel substrates for thin-film pressure sensors (with an SiO₂ insulator interlayer) has been established. It includes a precipitation heat treatment, polishing and cleaning processes, and a chemical surface preparation. Several cleaning steps have been studied: decreasing (both ultrasonical and vapour phase), alkaline cleaning (both ultrasonical and electrolytical), and acid cleaning (passivation). Chloride particles (with alkaline metals and sulfur) have been identified as the first dielectric failure cause. They are eliminated mainly during alkaline cleaning steps. Although chloride particles are eliminated, their previously corrosion-induced holes in the stainless-steel surface act as a secondary-less critical-dielectric failure cause. With the established substrate preparation and SiO₂ sputtering deposition processes, films 2.4 μm thick resist breakdown voltages up to 50 V, with negligible leakage currents (less than 10 nA).