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.