Phase change memory (PCM) is an important storage-class memory technology and a promising candidate for neuromorphic applications. PCM is based on the reversible resistance change in chalcogenide glasses, like Ge2Sb2Te5 (GST), which can be induced with Joule heating pulses. However, PCM suffers from relatively large programming energy during the reset (amorphization) process which requires heating the PCM above its melting temperature (TM ~ 600°C in GST). Reductions in reset energy have so far been achieved mainly by scaling down cell dimensions. We study the fundamental limits of PCM technology by manipulating the cell structure, materials and programming scheme.