Controllable extrinsic ion transport in two-dimensional perovskite films for reproducible, low-voltage resistive switching

Organic-inorganic halide perovskite has attracted significant interest in being switching medium for resistive random access memory (RRAM), yet the in-depth understanding of ion spatial distribution and transport kinetics—which is responsible for the filament formation and normally suffers from a paradox between stochasticity and dynamics—remains limited. Herein, we show evidence of space-confined, fast extrinsic ion transport within grain boundaries (GBs) of two-dimensional perovskite films through systematic ex-situ and in-situ studies. The filament growth can be dominated by the geometrical feature of GBs that act as the channel for cation transport in the dielectric film. By tailoring the structure of perovskite GBs, electroforming-free RRAM devices are fabricated with an ultralow set voltage of 0.09 V (1.8kVcm −1 ) and small temporal/spatial variations (<10%). The devices can also be integrated with flexible substrates for multifunctional applications, including multilevel writing and light erasing. Our work may open new perspectives for regulating filament formation kinetics in RRAMs and provides a reliable building block for future applications in electronic and photonic circuits.