Role and Optimization of the Active Oxide Layer in TiO2-Based RRAM

TiO 2 is commonly used as the active switching layer in resistive random access memory. The electrical characteristics of these devices are directly related to the fundamental conditions inside the TiO 2 layer and at the interfaces between it and the surrounding electrodes. However, it is complex to disentangle the effects of fi lm "bulk" properties and interface phenomena. The present work uses hard X-ray photoemission spectroscopy (HAXPES) at different excitation energies to distinguish between these regimes. Changes are found to affect the entire thin fi lm, but the most dramatic effects are confi ned to an interface. These changes are connected to oxygen ions moving and redistributing within the fi lm. Based on the HAXPES results, post-deposition annealing of the TiO 2 thin fi lm was investigated as an optimisation pathway in order to reach an ideal compromise between device resistivity and lifetime. The structural and chemical changes upon annealing are investigated using X-ray absorption spectroscopy and are further supported by a range of bulk and surface sensitive characterisation methods. In summary, it is shown that the management of oxygen content and interface quality is intrinsically important to device behavior and that careful annealing procedures are a powerful device optimisation technique.