Radiation effects, negative-bias-temperature instability, and low-frequency 1/f noise in SiGe/SiO2/HfO2 pMOS devices
The total ionizing dose (TID) response of HfO2-SiO2/SiGe pMOS FinFETs under different irradiation biases has been evaluated. Negative bias irradiation leads to the worst-case degradation. We attribute this result to an increase in density of additional radiation-induced holes that become trapped in the HfO2 under negative bias, and additional electron trapping under positive bias in the HfO2, as compared with the 0 V irradiation case. When devices are exposed to negative bias-temperature stress, we find similar values of Ea for oxide-trap charge buildup, and a reduced Ea for interface-trap buildup, for Si0.55Ge0.45 pMOSFETs with high-k gate stacks, compared to control Si devices with SiO2 gate dielectrics. The low-frequency 1/f noise of these devices was also investigated. The magnitude of noise is unaffected by negative-bias-temperature stress (NBTS) for temperatures below ~ 250 K, but increases significantly at higher temperatures. The noise is described well by the Dutta-Horn model before and after NBTS. The noise is attributed to oxygen-vacancy and hydrogen-related defects in the SiO2 and HfO2 (especially at the higher measuring temperatures) and/or hydrogen-dopant interactions in the SiGe layer of the device (especially for lower measuring temperature).