The correlation between the electrodes and the properties of the BiI3 device is systematically investigated. The X‐ray and UV photoemission spectroscopies are carried out to study the chemical state and electronic structure of the metal/BiI3 interfaces formed by the in‐situ deposition of BiI3 on the metal. This revealed the upward diffusion of Ag and the self‐formation of a conductive filament; the latter is further confirmed via tunneling electron microscopy. By coating the Au substrate with Ag layers of various thicknesses as a buffer layer, the morphology, surface roughness, chemical states, and quantity of the filament in the BiI3 layer can be manipulated. The device with the structure of Au/10 nm Ag/BiI3/Au demonstrated an ultrahigh on/off ratio of 109, good retention of 104 s, and multistate data storage. This study provides not only a fundamental insight into the interaction of BiI3 with metal, which will be helpful to design resistive switching devices and optoelectronics based on BiI3 material, but also a facile method to control the quantity of conductive filament in the BiI3 layer.

In this paper, we report resistive random-access memory (RRAM) with bismuth iodide (BiI 3 ) as the resistance switching layer, which exhibits an on/off ratio of the order of 10 8 . The behaviors of the resistive switching performance of the BiI 3 devices were systematically investigated. The chemical states and electronic structures of the resistance switching layer (BiI 3 ) 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 BiI 3 -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)/BiI 3 /PMMA/Au demonstrate low first reset voltage (approximately −0.66 V), a high retention larger than 5 × 10 4 s, and 6 × 10 3 switching cycles. This study not only demonstrates the excellent performance of BiI 3 -based RRAM devices but also provides fundamental insights into the mechanisms of the metallic filament first reset process in the BiI 3 layers.