We correlate the concentration and configuration of electrical defects in ferroelectric Si -doped HfO 2 (FE- HfO 2 ) with the electrical device performance during wake-up and fatigue regimes. To this end, we combine time-to-breakdown (TDDB), Kelvin probe force microscopy (KPFM), conductive atomic force microcopy (C-AFM) and Scalpel SPM, probing for the first time, the nanoscopic material variations as a function of device's field cycling behavior.