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

Abstract

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 tS did not affect the threshold voltage shift ΔVth. We consider that this independence occurred because illumination caused ionization from the oxygen vacancy VO state to VO2+, which impeded hydrogen migration induced by electric field and thereby protected the device from degradation after exposure to water.