A study on mobility degradation in nMOSFETs with HfO2 based gate oxide

In this paper, we investigate the causes for electron mobility reduction inside the conduction channel of nMOSFETs with TiN/HfO2/SiO2 gate stack. The use of such a high-k gate dielectric stack induces new interactions compared to conventional SiO2 gate oxide, modifying the electrons momentum during their transport along the channel. Experimental results, obtained by split-CV at different temperatures and charge pumping techniques, allow us to separate the contribution of each known interaction in the mobility degradation. Remote interactions are found to be the main phenomena at stake, specifically remote coulomb scattering, which modifies the screened potential seen by electrons in the channel. We finally discuss about the nature and the localization of such an interaction within the gate stack.