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

Abstract

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.