Total Ionizing Dose Response of Hafnium-Oxide Based MOS Devices to Low-Dose-Rate Gamma Ray Radiation Observed by Pulse CV and On-Site Measurements

This paper reports on the low-dose-rate radiation response of Al-HfO₂/SiO₂-Si MOS devices, where the gate dielectric was formed by atomic layer deposition with 4.7 nm equivalent oxide thickness. The degradation of the devices was characterized by a pulse capacitance-voltage (CV) and on-site radiation response techniques under continuous gamma (γ) ray exposure at a relatively low-dose-rate of 0.116 rad(HfO₂)/s. A significant variation of the flat-band voltage shift of up to ± 1.1 V under positive and negative biased irradiation, with the total dose of up to 40 krad (HfO₂) and the electric field of ∼0.5 MV/cm, has been measured on the HfO₂-based MOS devices using the proposed techniques, not apparent by conventional CV measurements. The large flat-b and voltage shift is mainly attributed to the radiation-induced oxide trapped charges, which are not readily compensated by bias-induced charges produced over the measurement timescales of less than 5 ms. Analysis of the experimental results suggest that both hole and electron trapping can dominate the radiation response performance of the HfO₂-based MOS devices depending on the applied bias. No distinct loop width variation has been found with irradiation in all cases.