Temperature Dependent Leakage Current Characteristics of an IrO <sub>2</sub>/TiO <sub>2</sub>/IrO <sub>2</sub> Redox Based Memristor and the Role of Aqueous Oxygen Evolution

Abstract

Among materials that exhibit so-called memristive effects, high permittivity oxide-based capacitors are in the main focus in electronics research, as they tend to show a resistance that is dependent on the electrical history of the material. Since memristive effects were discovered in TiO2 thin films in the early 2000s there has been much effort to integrate memristive materials into next-generation resistive switching based random-access memories. In this study, we investigate the leakage current behaviour of high-k IrO2/TiO2/IrO2 capacitors with temperature dependent static current/voltage measurements and time dependent long-term leakage current measurements. We explain the highly complex leakage current characteristics of such high-k oxide capacitors with an existing leakage current model that incorporates redox processes between insulator and electrode. We conclude that due to the highly asymmetric leakage current behaviour of our symmetric IrO2/TiO2/IrO2 capacitors the oxygen vacancy density in the insulating TiO2 is most decisive and is dominated by the oxygen storage capacity of the electrode. There is strong evidence for an aqueous oxygen evolution of water incorporated in the IrO2 top electrode, which provides the oxygen that changes the vacancy density with temperature and bias condition. Finally, we expand the existing model with a qualitative description of how the redox processes influence the electrical performance of the capacitors as a function of time.