Reduction of Negative Bias and Light Instability of a-IGZO TFTs by Dual-Gate Driving

Stability under negative-bias-illumination-stress (NBIS) of dual-gate (top- and bottom-gate) amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors is investigated. It is found that the negative threshold-voltage shift (ΔV TH ) induced by NBIS is much smaller under dual-gate driving (when the two gates are electrically tied together) compared with single-gate driving. For a 20 nm-thick a-IGZO active layer, this is attributed to bulk accumulation, where electrons are accumulated across the entire depth of the active layer, which is responsible for the small negative ΔV TH after NBIS. Due to bulk accumulation, the Fermi level can be easily shifted by dual-gate driving as compared with the conventional single-gate driving, even after NBIS.