Programmable, electroforming-free TiOx/TaOx heterojunction-based non-volatile memory devices

Abstract

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 TiO_x and TaO_x 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 TaO_x film, serving as the switching matrix, with the TiO_x film serving as an additional oxygen vacancy source to reduce the overall resistivity of TaO_x 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.