A comprehensive investigation of the underlying mechanism for total-ionizing-dose effects in a-InGaZnO TFTs with varied channel thicknesses

Abstract

This study systematically investigates the role of channel thickness (tIGZO) in the total-ionizing-dose (TID) response of a-IGZO thin-film transistors (TFTs). During irradiation, positive charges trapped in the gate dielectric and passivation layer, along with the mobile hydrogen (H) ions induced in the a-IGZO channel, collectively contribute to a decrease in the threshold voltage (Vth). The radiation-induced negative threshold voltage shift (ΔVth) amplifies with increasing tIGZO. This critical trend is mechanistically linked to a higher density of H ions incorporated into thicker a-IGZO layers during irradiation, which act as shallow donors. It also leads to an increase in the field-effect mobility (μFE). X-ray photoelectron spectroscopy analysis directly confirms the tIGZO-dependent increase in H concentration in the irradiated a-IGZO film. Thus, the TFT with the lowest tIGZO of 15 nm achieves the best radiation hardness. Furthermore, the radiation-induced traps are illustrated to exhibit a double-exponential energy distribution via C–V characterization, with the shallow traps being dominant. The damage is effectively recoverable through annealing at a low temperature of 200 °C, as a direct result of the shallow defects' low activation energy. This demonstrates an excellent radiation hardness of a-IGZO TFTs under TID conditions.