Binary metal oxide-based resistive switching memory devices: A status review

Semiconductor memories are essential ingredients of modern electronic devices. Resistive Random-Access Memories (RRAMs) have emerged as better alternatives for conventional charge-based flash memories due to their distinct features like high speed, ultra-low power consumption, and small footprint. RRAMs can be fabricated in a three-layer metal-insulator-metal configuration that uses various materials, viz., oxides, chalcogenides, biomaterials, ferrites, and perovskites, as an active switching layer. Among the different materials, binary metal oxides are prominently used for device fabrication, owing to their superior chemical composition, multistate switching ability, and compatibility with the complementary metal-oxide-semiconductor (CMOS) fabrication process. The present review critically discusses RRAM devices based on various binary metal oxides. In particular, we tried to review the resistive switching (RS) mechanisms of titanium oxide (TiO2), zinc oxide (ZnO), nickel oxide (NiO), tungsten trioxide (WO3) copper oxide (CuxO), tantalum oxide (TaOx or Ta2O5), and hafnium oxide (HfO2) based devices. In addition to this, various non-volatile memory performance parameters were discussed comprehensively. The review sets the tone of explorations with an introductory discussion regarding the background of RS mechanisms. After that, various materials used to develop memory devices were dealt with in-depth. Multiple aspects and factors responsible for the improved performance of memory devices based on different oxides have been deliberated critically. Lastly, the review concludes with significant vital insights regarding the mechanism, usefulness, superior materials used so far, and future scope of exploring these metal oxides in the current memory technology and bio-inspired neuromorphic computing.