Possibility of Freely Achievable Multilevel Storage of Phase-Change Memory by Staircase-Shaped Pulse Programming

We investigate the effect of the staircase-shaped pulse with two subpulses on programming characteristics in the double-layered phase-change memory for freely achievable multilevel storage. Phase-change material is melted during the first subpulse and the second one is used for controlling the total crystallinity after melting because it generally acts as crystallization time. Our finite-element analysis shows that the shorter the second subpulse is, the lower the crystallinity is. It is experimentally demonstrated that the device resistance increases with decreasing the width of the second subpulse owing to the decreasing crystallinity. This implies that any resistance levels are expected to be freely achieved by staircase-shaped pulse programming.