The role of interface and exchange processes in forming and switching of ZrO2 based ReRAM devices

Redox-based resistive random access memories (ReRAM) have many promising features like high scalability, low energy consumption and fast read and write times, making it a promising candidate for future non-volatile memories as well as for new computing concepts like neuromorphic computing. To date, the understanding of these devices is not deep enough to predict the behaviour of a device based on its specifications like geometry and material properties. In this work, correlations between the stack parameters and the properties of ReRAM devices are investigated to help overcoming this problem.
Initially, a model picture describing the forming process is introduced, which allows to separate the forming voltage into an oxide thickness dependent and an interface dependent part. The oxide thickness dependent part is dominated by the oxide properties, the interface dependent part is dominated by the electrode properties. It was shown that the interface voltage can be reduced by using ohmic electrode materials with high oxygen affinity like Hf. Additionally, it could be proven that several nanometres of the electrode at the oxide/electrode interface are oxidized, which was found to have an influence on the pristine resistance and capacitance.
In another part of this work, the processes happening during switching could be revealed by hard x-ray photo emission electron microscopy (HAXPEEM) experiments. These measurements could show that the oxide layer is actually reduced and that an oxygen exchange at the ohmic electrode layer is happening in these devices. A closer investigation revealed that this exchange must be due to an interaction with the surrounding.