Conductive Filament Localization Within Crossbar Resistive Memories by Scanning Joule Expansion Microscopy

Control of filament growth within conductive bridge random access memories (CBRAM) is of crucial interest in order to ensure the reliability of such emerging devices. Here, we demonstrate that Scanning Joule Expansion Microscopy (SJEM) can be used to detect and precisely localize conductive filaments within operating crossbar CBRAM devices. Flexible memory devices based on Pd/Al2O3/Ag stacks are first elaborated at low temperature on polyimide substrate. These devices show set and reset operations at low voltage (<2V) with ON/OFF ratios superior to 10(4). Under operation in the low resistance state, the SJEM amplitude images reveal a hot spot underlying the presence of a single conductive filament. An effective thermal diffusion length of 4.3 mu m is extracted at 50kHz and it is also demonstrated that the thermal expansion signal is proportional to the dissipated Joule power. We believe that the proposed procedure opens the way to reliability studies that can be applied to any family of memory device based on filamentary conduction.