Effect of Bilayer CeO/ZnO and ZnO/CeO Heterostructures and Electroforming Polarity on Switching Properties of Non-volatile Memory.

Memory devices with bilayer CeO/ZnO and ZnO/CeO heterostructures sandwiched between Ti top and Pt bottom electrodes were fabricated by RF-magnetron sputtering at room temperature. N-type semiconductor materials were used in both device heterostructures, but interestingly, change in heterostructure and electroforming polarity caused significant variations in resistive switching (RS) properties. Results have revealed that the electroforming polarity has great influence on both CeO/ZnO and ZnO/CeO heterostructure performance such as electroforming voltage, good switching cycle-to-cycle endurance (~ 10), and ON/OFF ratio.

Endurance and Cycle-to-cycle Uniformity Improvement in Tri-Layered CeO/Ti/CeO Resistive Switching Devices by Changing Top Electrode Material.

Resistance switching characteristics of CeO/Ti/CeO tri-layered films sandwiched between Pt bottom electrode and two different top electrodes (Ti and TaN) with different work functions have been investigated. RRAM memory cells composed of TaN/CeO/Ti/CeO/Pt reveal better resistive switching performance instead of Ti/CeO/Ti/CeO/Pt memory stacks. As compared to the Ti/CeO interface, much better ability of TaN/CeO interface to store and exchange plays a key role in the RS performance improvement, including lower forming/SET voltages, large memory window (~10) and no significant data degradation during endurance test of >10 switching cycles.

Forming-free bipolar resistive switching in nonstoichiometric ceria films.

The mechanism of forming-free bipolar resistive switching in a Zr/CeOx/Pt device was investigated. High-resolution transmission electron microscopy and energy-dispersive spectroscopy analysis indicated the formation of a ZrOy layer at the Zr/CeOx interface. X-ray diffraction studies of CeOx films revealed that they consist of nano-polycrystals embedded in a disordered lattice.