Rapid Thermal Annealing under O₂ Ambient to Recover the Deterioration by Gamma-Ray Irradiation in a-IGZO TFTs

Amorphous indium-gallium-zinc-oxide (a-IGZO) has been attracting great attention as a channel material for dynamic random access memory (DRAM) cell transistors due to its superior characteristics including low leakage current, large area deposition, and back-end-of-line (BEOL) compatibility. It should be clearly taken into account that DRAM will also be used in harsh environments such as military surveillance, aerospace, and nuclear power plants. Especially, these situations can cause inevitable and persistent degradation in long-term operations. When the a-IGZO thin film transistors (TFTs) were irradiated by gamma-ray with total doses of 500 Gy, threshold voltage (V_T) was negatively shifted and hysteresis (delta of V_T between forward and backward sweeps) was increased by creating a positive charge in gate insulator. The extracted density-of-states (DOS) and fitted model were employed to investigate the behavior of oxygen vacancy (V_O) in a-IGZO thin film. Electrical performance degraded by gamma-ray irradiation such as changes in V_T, border trap, tail acceptor-like states (g_TA(E)), and shallow donor-like states (g_SD(E)) were recovered through rapid thermal annealing (RTA) under the O₂ ambient.