Room Temperature Instabilities Observed on Silicon Gate Devices

A room temperature ionic instability has been observed on p-channel silicon gate MOS devices processed in a specific manner. This instability appears as a rapid and substantial change of threshold voltage at room temperature consistent with a fast moving ionic species in the gate oxide region. The diffusion constant of this species, measured over the temperature range from 0°C to 75°C is consistent with extrapolated data for H+ ions in SiO2. The magnitude of the room temperature threshold shift is voltage dependent and exists independently of any Na+ contamination. Correctly processed silicon gate devices are completely stable.