Phase change memory technology

We survey the current state of phase change memory (PCM), a non-volatile\nsolid-state memory technology built around the large electrical contrast\nbetween the highly-resistive amorphous and highly-conductive crystalline states\nin so-called phase change materials. PCM technology has made rapid progress in\na short time, having passed older technologies in terms of both sophisticated\ndemonstrations of scaling to small device dimensions, as well as integrated\nlarge-array demonstrators with impressive retention, endurance, performance and\nyield characteristics.\n We introduce the physics behind PCM technology, assess how its\ncharacteristics match up with various potential applications across the\nmemory-storage hierarchy, and discuss its strengths including scalability and\nrapid switching speed. We then address challenges for the technology, including\nthe design of PCM cells for low RESET current, the need to control\ndevice-to-device variability, and undesirable changes in the phase change\nmaterial that can be induced by the fabrication procedure. We then turn to\nissues related to operation of PCM devices, including retention,\ndevice-to-device thermal crosstalk, endurance, and bias-polarity effects.\nSeveral factors that can be expected to enhance PCM in the future are\naddressed, including Multi-Level Cell technology for PCM (which offers higher\ndensity through the use of intermediate resistance states), the role of coding,\nand possible routes to an ultra-high density PCM technology.\n