Plasma deposited thin films suitable as moisture sensors

Plasma polymerized thin films from a mixture of hexamethyldisiloxane (HMDSO) and ammonia (NH₃) deposited directly onto a microdielectrometer chip have been evaluated as moisture sensors. Microdielectrometry was chosen as the measuring technique because of its fast response and real time detection capability. The sheet resistance of the plasma polymerized film was found to decrease by eight orders of magnitude with an increase in relative humidity from 0 to 92%. The moisture effect on the sheet resistance was also found to be reversible. The composition and structure of the films deposited from various mixtures of HMDSO/NH₃ have been elucidated by Electron Spectroscopy for Chemical Analysis (ESCA) and infrared spectroscopy.