Phase-change Memory

Phase-change memory (also known as PCM,PCME, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and C-RAM) is a type of non-volatile random-access memory. PRAMs exploit the unique behavior of chalcogenide glass. In the older generation of PCM heat produced by the passage of an electric current through a heating element generally made of TiN would be used to either quickly heat and quench the glass, making it amorphous, or to hold it in its crystallization temperature range for some time, thereby switching it to a crystalline state. PCM also has the ability to achieve a number of distinct intermediary states, thereby having the ability to hold multiple bits in a single cell, but the difficulties in programming cells in this way has prevented these capabilities from being implemented in other technologies (most notably flash memory) with the same capability. Newer PCM technology has been trending in a couple different directions. Some groups have been directing a lot of research towards attempting to find viable material alternatives to Ge₂Sb₂Te₅ (GST), with mixed success, while others have developed the idea of using a GeTe - Sb₂Te₃ superlattice in order to achieve non thermal phase changes by simply changing the coordination state of the Germanium atoms with a laser pulse, and this new Interfacial phase change memory (IPCM) has had many successes and continues to be the site of much active research.

Leon Chua, who is considered to be the father of non-linear circuit theory, has argued that all 2-terminal non-volatile memory devices including phase change memory should be considered memristors. Stan Williams of HP Labs has also argued that phase change memory should be considered to be a memristor.