Degradation process by effect of water molecules during negative bias temperature stress in amorphous-InGaZnO thin-film transistor

We explained how H2O degrades amorphous-InGaZnO thin-film transistors. H2O caused serious degradation only during negative bias temperature stress (NBTS). Degradation was caused by molecules that were absorbed or diffused from the outside. We suggest that degradation under NBTS is caused by the migration of hydrogen ions among oxygen vacancies. Under illumination, the soaking time t(S) did not affect the threshold voltage shift Delta V-th. We consider that this independence occurred because illumination caused ionization from the oxygen vacancy V-O state to V-O(2+), which impeded hydrogen migration induced by electric field and thereby protected the device from degradation after exposure to water. (c) 2017 The Japan Society of Applied Physics