Scalability of valence change memory: From devices to tip-induced filaments

Since the early days of the investigation on resistive switching (RS), the independence of the ON-state resistance with actual cell area has been a trademark of filamentary-switching. However, with the continuous downscaling of the memory cell down to 10 x 10 nm2 and below, the persistence of this phenomena raises intriguing questions on the conductive filaments (CFs) and its dimensions. Particularly, the cell functionality demonstrated at relatively high switching current (> 100 μA) implies a high current density (> 106 A/cm2) inside a CF supposedly confined in few hundreds on nm3. We previously demonstrated a methodology for the direct observation of CFs in integrated devices namely scalpel SPM, which overcomes most of the characterization challenges imposed by the device structure and the small CF lateral dimensions. In this letter, we use scalpel SPM to clarify the scaling potential of HfO2-based valence change memory (VCM) by characterization of CFs programmed at relatively high switching current and by AFM tip-induced RS experiments. Besides the demonstration of a remarkable scaling potential for the VCM technology, our results are also used to clarify the present understanding on the AFM-based experiments.