A detailed physical analysis of the conductive filament electrically formed in HfO2-based resistive switching memory devices with both Hf and Ti metal oxygen exchange layers is presented. The filament, observed by applying transmission electron microscopy (TEM), scanning TEM (STEM), and electron energy loss spectroscopy (EELS) techniques to 50 × 50 nm2 cells, is a cone-shaped metal-rich region in the HfO2 dielectric of the resistive switching device.