Probing resistive switching in HfO₂/Al₂O₃ bilayer oxides using in-situ transmission electron microscopy

In this work, we investigate the resistive switching in hafnium dioxide (HfO₂) and aluminum oxide (Al₂O₃) bilayered stacks using in-situ transmission electron microscopy and X-ray energy dispersive spectroscopy. Conductance of the HfO₂/Al₂O₃ stack changes gradually upon electrical stressing which is related to the formation of extended nanoscale physical defects at the HfO₂/Al₂O₃ interface and the migration and re-crystallization of Al into the oxide bulk. The results suggest two competing physical mechanisms including the redistribution of oxygen ions and the migration of Al species from the Al electrode during the switching process. While the HfO₂/Al₂O₃ bilayered stack appears to be a good candidate for RRAM technology, the low diffusion barrier of the active Al electrode causes severe Al migration in the bi-layered oxides leading to the device to fail in resetting, and thereby, largely limiting the overall switching performance and material reliability.