Hydrogen and ammonia response of metal-silicon dioxide-silicon structures with thin platinum gates

Abstract

The hydrogen and ammonia sensitivity of metal‐oxide‐semiconductor (MOS) structures with platinum gates between 3 and 70 nm thick was investigated. The response to these gases was measured as a shift in the capacitance‐voltage (C‐V) curve of the MOS structure along the voltage axis. The measurements were made at an elevated temperature, mainly at 150 °C, where chemical reactions take place on the surface of the catalytic metal. The main purpose of the investigation was to determine if hydrogen and ammonia are detected by similar mechanisms. It is concluded that hydrogen molecules are dissociated and hydrogen atoms give rise to a dipole layer at the metal‐oxide interface, similar to the behavior of hydrogen in hydrogen sensitive MOS structures with thick catalytic metal, normally Pd, gates. Ammonia, on the other hand, appears to be detected through surface potential changes of the Pt film, which are capacitively coupled to the semiconductor surface through voids in the thin metal film.