Abstract
Room‐temperature conductivity of mobile Na+ ions in the SiO2 layer of a metal–silicon dioxide–silicon structure is directly shown to be interface limited by use of the photo IV technique. Na+ ions were found to be located within ?50 Å of the interfaces regardless of field stressing conditions (2–4.5 MV/cm), temperature (20–40 °C), number of ions drifted (up to 2.6×1012 cm−2), or number of temperature‐bias cycles used to move Na+ ions back and forth between the interfaces.