Electroforming-Free HfO2:CeO2 Vertically Aligned Nanocomposite Memristors with Anisotropic Dielectric Response

Resistive switching and anisotropic optical properties have been investigated in two-phase HfO2:CeO2 nanocomposite thin films of different HfO2:CeO2 ratios of 3:1, 1:1, and 1:3 on single-crystalline SrTiO3(001) substrates. Vertically aligned nanocomposite (VAN) thin films with CeO2 pillars embedded in a HfO2 matrix have been obtained using a one-step pulsed laser deposition technique. By adjusting the molar ratio of HfO2 and CeO2 in the films, the resistive switching effect and the anisotropic dielectric response were tuned and correlated with the density of the conducting vertical-phase boundaries. It is shown that only HfO2:CeO2 VAN films of 1:1 composition give rise to a forming-free switching system as they have clear vertical boundaries that guide oxygen vacancy channels. These films show strong promise for resistive switching memory devices.