Programmable, electroforming-free TiO/TaO heterojunction-based non-volatile memory devices.

Electroforming-free resistive switching in memristors is essential to reliably achieving the performance of high switching speed, high endurance, good signal retention, and low power consumption expected for next-generation computing devices. Although there have been various approaches to resolve the issues observed with the electroforming process in oxide-based memory devices, most of them end up having high SET and RESET voltages and short lifetimes. We present a heterojunction interface of oxygen-vacancy-defect-rich ultrananocrystalline TiOx and TaOx films used as the switching matrix, which enables high-quality electroforming-free switching with a much lower programming voltage (+0.5-0.8 V), a high endurance of over 104 cycles and good retention performance with an estimated device lifetime of over 10 years. The electroforming-free switching behavior is governed by migration of oxygen vacancies driven by electric field localization that is imposed by the ultrananocrystalline nature of the TaOx film, serving as the switching matrix, with the TiOx film serving as an additional oxygen vacancy source to reduce the overall resistivity of TaOx and provide low-bias rectification. The ability to perform electroforming-free resistive switching along with excellent switching repeatability and retention capabilities for various digital and analog programmable voltages enables high scalability and large density integration of the cross-bar ReRAM framework.