Reliable BiI₃-Based Resistive Random-Access Memory Devices with a High On/Off Ratio

In this paper, we report resistive random-access memory (RRAM) with bismuth iodide (BiI3) as the resistance switching layer, which exhibits an on/off ratio of the order of 108. The behaviors of the resistive switching performance of the BiI3 devices were systematically investigated. The chemical states and electronic structures of the resistance switching layer (BiI3) were studied via X-ray photoemission spectroscopy with depth profile. The spectroscopies demonstrate that the filament formation belongs to the metal bridge type, which is dominated by the presence of bismuth atoms resulting from the formation of silver iodide (AgI). X-ray diffraction, the cross section of transmission electron microscopy, scanning electron microscopy, and atomic force microscopy were employed to study the formation process of the metal filament in the BiI3-based RRAM. The results reveal that the upward diffusion of Ag cations will react with iodide anions, and bismuth cations will turn into the metallic state, which results in forming a conductive filament inside the resistance switching layer. Furthermore, the devices with the structure of Ag/polymethylmethacrylate (PMMA)/BiI3/PMMA/Au demonstrate low first reset voltage (approximately −0.66 V), a high retention larger than 5 × 104 s, and 6 × 103 switching cycles. This study not only demonstrates the excellent performance of BiI3-based RRAM devices but also provides fundamental insights into the mechanisms of the metallic filament first reset process in the BiI3 layers.