Scaling of resistive random access memory devices beyond 100 nm²: influence of grain boundaries studied using scanning tunneling microscopy

Resistive Random Access Memory (ReRAM) has emerged as the successor to FLASH in memory technology due to its multi-level fabrication possibilities and prospects of scaling down virtually to atomic dimensions. However, as we report here, when polycrystalline switching materials are used, the ReRAM devices scaled down to the sub-5 nm² area show complete randomness due to inhomogeneous conductance values of grains and grain boundaries. By measuring the switching properties of grains and grain boundaries individually using a scanning tunneling microscope, we demonstrate that the doublet and triplet grain boundaries behave like degenerate semiconductors and act as conduction channels that bypass the resistive switching of the devices. Fabricating virtual devices using gold clusters deposited on top, we show that the random distribution of such highly conducting grain boundaries reduces the reliability of nano-scale ReRAM devices when scaled down to the sub-10 nm scale. (paper)