A study on OTS-PCM pillar cell for 3-d stackable memory
High endurance ovonic threshold switch (OTS, here, TeAsGeSiSe-based) is integrated with phase change memory (PCM, here, doped Ge2Sb2Te5) to form a 3-D stackable pillar-type device. With the help of an etch buffer layer and a damage-free pillar reactive-ion etching process, we successfully demonstrate one-selector (OTS)/one-resistor (PCM) (1S1R OTS-PCM) pillar device without OTS/PCM composition modification. High temperature 400 °C annealing tests show this 1S1R OTS-PCM pillar device is back end of line compatible. We report the fundamental behavior of the OTS and the operation scheme of the 1S1R OTS-PCM device. The new Vth read scheme is proposed and excellent electrical performance is demonstrated. It provides the fast turn ON/OFF speed which enables 10-ns fast RESET speed. Program endurance greater than 109 cycles is achieved, and read endurance is higher than 1011 cycles.