Investigations on charge storage and transport in plasma-deposited inorganic electrets

The storage and transport of charges in plasma deposited inorganic electrets with low mechanical stress were investigated under different conditions. Silicon dioxide, nitride and oxynitride were chemically deposited on Si substrates by means of a radio frequency (13.56 MHz) plasma system. The samples were negatively charged by the constant voltage corona method. The surface potential was observed during aging at room temperature, at elevated temperatures of 200, 250 and 300°C and at a relative humidity of 95% at 60°C. The thermal activation process was examined by thermally stimulated discharge (TSC) measurements. Silicon oxynitride possessed the highest charge stability during the different experiments, correlating with the current maximum located at ~400°C. The charge transport in silicon dioxide, with a current maximum located at ~330°C, was described by a theoretical model which considered the drift and the partial retrapping of free charges in the bulk. Despite treatment with hexamethyldisilazane, it was not possible to stabilize the surface potential of silicon nitride samples even at room temperature