Resistive switching memristors: structures, materials, fabrication techniques, and process challenges for VLSI integration.

Memristors have gained popularity in being used as nanodevices to be used as nonvolatile memory devices, neuromorphic computing systems, and even compute-in-memory systems due to their property of nonvolatile resistive switching, power savings, scalability, and simple metal-insulator-metal structures. These memristive switching operations can occur due to different phenomena like oxygen vacancy movement, electrochemical metallization, valence change operations, phase change, and ferroelectric polarization operations. Performance of such devices greatly depends on materials and processing, hence knowing their relationship is very important. This review presents an extensive discussion about various memristor structures, materials used, fabrication processes, testing procedures, and the problems encountered in VLSI scaling down. Special attention has been paid to the switching phenomenon, defect management, interfaces, the movement of conductive filaments, and fabrication variability that considerably influence the performance, endurance, and reliability of memristors. In addition, the importance of the processes used for fabricating memristor devices such as photolithography, chemical vapor deposition, sputtering, electron-beam deposition, and atomic layer deposition has been highlighted. Through the use of improvements in materials science, device architectures, fabrication processes, and system integration techniques, this review outlines the potentials and open issues involved in memristor research. The findings outlined in the discussion offer a basis for furthering the progress of reliable and scalable memristor technology compatible with CMOS circuits.