Negative Bias Illumination Stress Instability Research Articles

Effect of hydrogen incorporation on the negative bias illumination stress instability in amorphous In-Ga-Zn-O thin-film-transistors

In amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors, negative shifts of the threshold voltage commonly occur under negative bias illumination stress (NBIS), and its origin is attributed to hole traps such as O-vacancy (VO) defects. We perform density functional calculations to investigate the effect of hydrogenation on the NBIS instability. We find that hydrogen passivates the electrical activity of VO in form of HO, in which H occupies the vacancy site. The activation energy for dissociating HO into VO and an interstitial H (Hi) is about 1.27 eV, much higher than the migration barrier of about 0.51 eV for Hi diffusion. Kinetic Monte Carlo simulations show that HO defects are quite stable upon post thermal annealing up to 200 °C. Thus, we propose that H incorporation into a-IGZO not only effectively reduces the density of VO defects but also mitigates the NBIS instability in devices fabricated at low temperatures.

Suppression in negative bias illumination stress instability of zinc tin oxide transistor by insertion of thermal TiOxfilms

This letter examined the insertion effect of thermal TiO2 films on the device performance and photo-bias instability of zinc tin oxide (ZTO) thin-film transistors (TFTs). A 5.0-nm-thick TiOx device inserted at the ZTO/silicon nitride (SiNx) interface exhibited slightly lower mobility (9.4 cm2/V·s ) compared with that (14.1 cm2/V·s ) of the reference device with a ZTO/SiNx stack. On the other hand, the negative gate-bias-illumination-stress-induced instability of the TiOx-inserted device was strongly suppressed from 11.0 V (reference device) to 3.0 V. This was attributed to the increase in valence band offset between TiOx and ZTO films, leading to the diminished injection of photo-induced hole carriers into the underlying SiNx bulk region.

Anomalous behavior of negative bias illumination stress instability in an indium zinc oxide transistor: A cation combinatorial approach

This study examined the effects of the indium fraction in indium zinc oxide (IZO) on the performance and stability of IZO thin film transistors (TFTs). The field-effect mobility and sub-threshold swing were much improved with increasing In fraction; 41.0 cm2/Vs and 0.2 V/decade, respectively, at 85 at. % In, compared to 1.1 cm2/Vs and 2.4 V/decade of ZnO TFTs. In contrast, a local minimum negative bias illumination stress instability was observed near 73–77 at. % In. This behavior was explained by a poly-crystalline to amorphous phase transition in IZO thin films.

O-vacancy as the origin of negative bias illumination stress instability in amorphous In–Ga–Zn–O thin film transistors

We find that O-vacancy (VO) acts as a hole trap and plays a role in negative bias illumination stress instability in amorphous In–Ga–Zn–O thin film transistors. Photoexcited holes drift toward the channel/dielectric interface due to small potential barriers and can be captured by VO in the dielectrics. While some of VO+2 defects are very stable at room temperature, their original deep states are recovered via electron capture upon annealing. We also find that VO+2 can diffuse in amorphous phase, inducing hole accumulation near the interface under negative gate bias.