Scalable CGeSbTe-based phase change memory devices employing U-shaped cells

Phase change memory (PCM) that is operated on resistance changes caused by joule heating has been suggested as the next-generation memory for scaling since its programming current scales linearly. We propose a U-shaped cell design to further reduce the reset current in PCM devices, which enables easier and more efficient scaling than conventional PCMs. Simulation studies of heat transfer demonstrated that our U-shaped design with a dashed heater has a higher thermal efficiency of 4.97 K/μA compared to 3.36 K/μA in a lance cell with a ring heater for the same storage node. The reset current can be better scaled proportionate to k^2.0 in which the exponent is higher than the lance cell of k^1.5 in non-isotropic scaling. This better scalability is attributed to the small programming volume of the U-shaped cell, which was verified by transmission electron microscopy analysis. Furthermore, the cyclic endurance of the U-shaped cell was enhanced by 1 order of magnitude compared to a lance cell and the thinner CGeSbTe films reduced the reset current further. Our results show that a U-shaped cell is a highly promising design to scale reset current in next-generation PCM devices.