Drain Current Stress-Induced Instability in Amorphous InGaZnO Thin-Film Transistors with Different Active Layer Thicknesses

In this study, the initial electrical properties, positive gate bias stress (PBS), and drain current stress (DCS)-induced instabilities of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with various active layer thicknesses (T(IGZO)) are investigated. As the T(IGZO) increased, the turn-on voltage (V(on)) decreased, while the subthreshold swing slightly increased. Furthermore, the mobility of over 13 cm(2)·V(−1)·s(−1) and the negligible hysteresis of ~0.5 V are obtained in all of the a-IGZO TFTs, regardless of the T(IGZO). The PBS results exhibit that the V(on) shift is aggravated as the T(IGZO) decreases. In addition, the DCS-induced instability in the a-IGZO TFTs with various T(IGZO) values is revealed using current–voltage and capacitance–voltage (C–V) measurements. An anomalous hump phenomenon is only observed in the off state of the gate-to-source (C(gs)) curve for all of the a-IGZO TFTs. This is due to the impact ionization that occurs near the drain side of the channel and the generated holes that flow towards the source side along the back-channel interface under the lateral electric field, which cause a lowered potential barrier near the source side. As the T(IGZO) value increased, the hump in the off state of the C(gs) curve was gradually weakened.