Improved Bipolar Resistive Switching of HfOx/TiN Stack with a Reactive Metal Layer and Post Metal Annealing

Improvement of a reactive metal layer (AlCu, Ti, or Ta) for the bipolar resistance switching (BRS) performance of HfOx based resistive memory (RM) with TiN as electrodes are studied in this work. After appropriate post metal annealing (PMA), the reactive metal layer with high oxygen content serves as an embedded resistor and modifies the insulator properties of theses stacked layers, which show stable repetitive switching through by the migration of oxygen ions in HfOx layer during operation. The Gibbs free energy for the oxidation of the reactive metal with respect to that of HfO2 dominates the optimal PMA temperature for the devices with stable BRS. Except for the reduction of forming voltage and leakage current, the AlCu layer with high resistance after PMA of 500 degrees C is beneficial for the devices with successive BRS and on/off ratio of 4. The forming voltage of the Ti devices seems insensitive on the PMA. Compared with the Ta device, the Ti/HfOx RM device after the PMA of 450 degrees C for 5 min exhibits a different current-voltage behavior during the first RESET voltage sweep and a higher resistance ratio (> 40). These results are attributed to the higher affinity of oxygen in the Ti capping layer. The combination of HfOx with a reactive metal and an enough PMA shows great potential for future nonvolatile memory application. (C) 2010 The Japan Society of Applied Physics