Direct Observation for Distinct Behaviors of Gamma-Ray Irradiation-Induced Subgap Density-of-States in Amorphous InGaZnO TFTs by Multiple-Wavelength Light Source

The amorphous In─Ga─Zn─O (a-IGZO) thin film transistors (TFTs) have attracted attention as a cell transistor for the next generation DRAM architecture because of its low leakage current, high mobility, and the back-end-of-line (BEOL) compatibility that enables monolithic 3D (M3D) integration. IGZO-based electronic devices used in harsh environments such as radiation exposure can be vulnerable, resulting in functional failure. Here, the behavior of subgap density-of-states (DOS) over full subgap range according to the impactful gamma-ray irradiation in a-IGZO TFTs is investigated by employing DC current–voltage (I−V) data with multiple-wavelength light sources. To understand the origins of the radiation effect, IGZO films have been also analyzed by x-ray photoelectron spectroscopy (XPS). Considering in-depth electrical and chemical analysis, the unexpected increase of subthreshold leakage current caused by total ionizing dose (TID) is strongly correlated with newly discovered deep-donor states ((Formula presented.)) at the specific energy level. In particular, oxygen vacancies caused by the gamma-ray irradiation give rise to undesirable electrical characteristics such as hysteresis effect and negative shift of threshold voltage (V_T). Furthermore, the TCAD simulation results based on DOS model parameters are found to exhibit good agreement with experimental data and plausible explanation including ((Formula presented.)).