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 (
${V}_{\text {th}}{)}$
shift with hump and on-current (
${I}_{\text {on}}{)}$
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 (
${V}_{\text {g}}{)}$
is a sub-transistor effect caused by hole trapping at the IGZO/top gate insulator (TGI) interface. 2. The positive shift of
${V}_{\text {th}}$
is caused by the trapped photo-induced electrons at the IGZO/bottom gate insulator (BGI) interface. 3. The
${I}_{\text {on}}$
reduction occurred due to trapped photo-induced electrons at interface between
$\text{n}^{-}$
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
$\text{n}^{-}$
region of IGZO/BGI interface, which corresponds to a drop in effective gate and drain voltage, respectively. Thus, the positive
${V}_{\text {th}}$
shift and
${I}_{\text {on}}$
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.