Degradation Due to Photo-Induced Electron in Top-Gate In-Ga-Zn-O Thin Film Transistors With n- Region Under Negative Bias Stress and Light Irradiation

We investigated the positive threshold voltage (Vth) shift with hump and on-current (Ion) reduction in top-gate In-Ga-Zn-O (IGZO) thin film transistors (TFTs) after negative gate bias of -20 V at 60?C and light irradiation stress (NBTIS). This degradation can be classified into three types of mechanism. 1. The hump at low gate voltage (Vg) is a sub-transistor effect caused by hole trapping at the IGZO/top gate insulator (TGI) interface. 2. The positive shift of Vth is caused by the trapped photo-induced electrons at the IGZO/bottom gate insulator (BGI) interface. 3. The Ion reduction occurred due to trapped photo-induced electrons at interface between n- region of IGZO/BGI interface. The electric field induced by trapped electron promotes depletion of the channel region at the IGZO/BGI and IGZO/TGI interface and n- region of IGZO/BGI interface, which corresponds to a drop in effective gate and drain voltage, respectively. Thus, the positive Vth shift and Ion reduction occurred due to trapping of photo-induced electron under NBTIS. Based on our proposed mechanism, this degradation was suppressed by the dual-gate structure.

Automated summary

We studied the degradation of top-gate In-Ga-Zn-O (IGZO) thin film transistors (TFTs) with hump formation, positive threshold voltage (Vth) shift, and reduction in on-current (Ion) after negative gate bias and light irradiation stress. This degradation can be attributed to hole trapping at the IGZO/top gate insulator (TGI) interface causing the hump effect, trapped photo-induced electrons at the IGZO/bottom gate insulator (BGI) interface leading to the positive Vth shift, and trapped photo-induced electrons at the n-region of IGZO/BGI interface causing Ion reduction. The presence of trapped electrons induces electric field, resulting in depletion of the channel region and drop in effective gate and drain voltage. The degradation was effectively suppressed by the dual-gate structure.