Forming-Free, Nonvolatile, and Flexible Resistive Random-Access Memory Using Bismuth Iodide/van der Waals Materials Heterostructures

Resistive switching devices based on halide perovskites exhibit promising potential in flexible resistive random-access memory (RRAM) owing to low fabrication cost and low processing temperature. However, the toxicity of these materials hinders their commercialization. Herein, bismuth iodide (BiI3) is employed as an insulator in RRAM. A monolayer of graphene or hexagonal boron nitride (h-BN) is employed as a buffer layer to achieve van der Waals epitaxy of BiI3 and meanwhile to prevent the intrusion of copper atoms. Thus, the film quality of the BiI(3)layer is greatly improved. Resistive-switching devices with the structure of copper foil/h-BN/BiI3/Au exhibited forming-free characteristics, high on/off ratio, excellent data-retention capability, and high endurance to 2500 sweep cycles. The forming-free behavior in the devices is studied using X-ray and ultraviolet photoemission spectroscopies, where a self-formed conductive filament composed of metallic bismuth is observed. The formation and rupture of the conductive filament in the BiI(3)layer, which serves as the in-gap channel, causes the switchable resistance of the devices. In addition, the devices exhibit excellent tolerance to bending, thus demonstrating high stability to at least 5000 bending cycles at a bending radius of 8.75 mm. This study demonstrates the promising potential of BiI3-based flexible resistive-switching memories.