Simulations of threshold voltage instabilities in HfySiOx and SiO2/HfySiOx-based field-effect transistors

Threshold voltage shifts in metal-oxide-semiconductor field-effect transistors with HfySiOx gate layers and SiO2/HfySiOx gate stacks have been simulated, taking into account the generation of Si trivalent dangling bonds at the Si/dielectric interface, resulting from the injection of electrons through the structure. While the tunneling current flowing through devices with HfySiOx single layers is predicted to be lower compared to devices with SiO2/HfySiOx gate stacks (with equivalent electrical thickness), it is found that the transistor lifetime, based on threshold voltage shifts, is improved in SiO2/HfySiOx gate stacks. This finding is attributed to the beneficial presence of the SiO2 interfacial layer, which allows the relaxation of strain at the Si/dielectric interface.