a self - aligned , nonvolatile memory structure based upon phase change materials , including chalcogenides , can be made with a very small area on an integrated circuit . the manufacturing process results in self - aligned memory cells requiring only two array - related masks defining the bit lines and word lines . memory cells are defined at intersections of bit lines and word lines , and have dimensions that are defined by the widths of the bit lines and word lines in a self - aligned process . the memory cells comprise structures including a selection device , a heating / barrier plate layer and a phase change memory element , vertically arranged at the intersections of the bit lines and word lines .