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.

Relationship between Detrapping of Electrons and Negative Gate Bias during Recovery Process in a‐InGaZnO Thin Film Transistors

“…a‐IGZO TFTs with inverted staggered and back‐channel‐etched structure were fabricated on glass substrate; their structure has been described in detail elsewhere . The TFTs used in the experiment had widths W 90, 100, 240, or 500 μm and lengths L 4.0, 4.5, or 5.0 μm.…”

“…Because of these merits, a‐IGZO is considered as a promising channel material for switching/driving TFTs in advanced display devices. Its reliability is a main concern for practical applications, and threatened by stresses such as gate bias, temperature, ambient effects, and illumination …”