In this work we will provide the results of an investigation into electron and hole mobility at high inversion charge density (6 to 8x1012 cm-2) in TiN/HfO2/SiOx/Si MOSFETs. We examine the influence of oxide charge on carrier mobility by using temperature bias stress to deliberately increase the density of oxide charge in the HfO2/SiOx gate stack. The temperature dependence of the electron mobility (50 K to 350 K) and hole mobility (218 K to 373 K) is determined before and after the various levels of oxide and interface degradation to allow an experimental determination of the Coulomb scattering term (α) as a function of temperature for various oxide charge levels. Based on the temperature dependant α determined for a 3nm HfO2 gate thickness n channel MOSFET, an empirical model has been developed which accurately predicts the measured electron mobility for the 2.4, 2.0 and 1.6nm HfO2 gate thicknesses.