Oxygen Tracer Diffusion in Amorphous Hafnium Oxide for Memristors

Hafnium oxide is a promising material for memristors, offering key advantages such as high endurance and retention. The non-volatility of resistive memory is commonly ascribed to the dissolution of sub-stoichiometric conducting filaments due to oxygen ion diffusion. However, the diffusion rates reported for hafnium oxide are too high to explain the actual retention times observed in these memory devices. In this study, we explore this discrepancy by performing oxygen tracer diffusion measurements in amorphous hafnium oxide thin films. Our findings indicate that the oxygen tracer diffusion in amorphous films is notably lower than in monoclinic hafnium oxide. Moreover, oxygen diffusion decreases by two orders of magnitude in the denser films produced by atomic layer deposition (ALD), as opposed to those created by sputtering. The diffusion times for oxygen in ALD films correspond with the experimental retention times, thus reconciling the differences between the reported diffusion rates and the observed retention performance. This study highlights the significant impact that processing conditions have on the oxygen transport properties in amorphous materials, offering valuable insights for refining resistive memory devices.