Balancing the Source and Sink of Oxygen Vacancies for the Resistive Switching Memory

The high nonuniformity and low endurance of the resistive switching random access memory (RRAM) are the two major remaining hurdles at the device level for mass production. Incremental step pulse programming (ISPP) can be a viable solution to the former problem, but the latter problem requires material level innovation. In valence change RRAM, electrodes have usually been regarded as inert (e.g., Pt or TiN) or oxygen vacancy (V_O) sources (e.g., Ta), but different electrode materials can serve as a sink of V_O. In this work, an RRAM using a 1.5 nm-thick Ta₂O₅ switching layer is presented, where one of the electrodes was V_O-supplying Ta and the other was either inert TiN or V_O-sinking RuO₂. Whereas TiN could not remove the excessive V_O in the memory cell, RuO₂ absorbed the unnecessary V_O. By carefully tuning (balancing) the capabilities of V_O-supplying Ta and V_O-sinking RuO₂ electrodes, an almost invariant ISPP voltage and a greatly enhanced endurance performance can be achieved.