Total dose effects and bias instabilities of (NH₄)₂S passivated Ge MOS capacitors with Hf_xZr_1-xO_y thin films

The effects of biased irradiation on Ge MOS capacitors with Hf_xZr_1-xO_y(0.43 < x < 1) gate dielectrics have been investigated. These devices were irradiated by a 662-KeV Cs137γ-ray radiation source with 0.5 or-0.5 V gate bias. Prior to irradiation exposure, leakage behavior and bias-instability of Hf_xZr_1-xO_y films were also examined. Gate leakage current density increases with the increasing of Zr composition in gate oxide. In addition, Zr-containing dielectrics under positive bias (PB) exhibited more oxide negative trapped charges than that of HfO₂, which suggested that the oxygen-vacancy concentration in Hf_xZr_1-xO_y was increased by the addition of Zr. Larger flat-band voltage shifts (ΔVFB) were extracted under positive biased irradiation than the bias only results. The results indicate that radiation-induced interface traps (ΔNit) are the dominant factor for ΔVFB in HfO₂ thin films, whereas the radiation response for Zr-containing dielectrics under PB was mainly due to oxide traps. Under negative biased irradiation, ΔVFB was attributed to the combined effect of the net oxide trapped charges and the passivation of Ge dangling bonds at the Ge/high-k interface. Additionally, both bias-induced and radiation-induced charge trapping have a crucial effect on radiation response of Hf_xZr_1-xO_y at each dose level. Hf_xZr_1-xO_y is identified as a promising gate dielectric for advanced complementary metal-oxide-semiconductor technologies.