The history of phase-change memory
The existence of materials that exhibit a controllable change in phase has been known for many years and has been in use for optical memory applications. Electronic memories based on these materials have recently experienced a resurgence of interest for use as a next-generation NVM for the reasons addressed in the previous section. Pioneering work conducted by Micron and others has moved the technology to the forefront of the memory industry R&D activity with a promise to alter the way NVM is used in memory systems.
The history of phase-change materials can be traced back to work starting in the 1950s by Dr. Stanford Ovshinsky who was researching the properties of a class of glassy materials that exhibited the ability to easily and stably change between two phases. By the late 1960s, he had reported that certain of these materials exhibited a reversible change in both resistively and reflectivity upon a change in phase between an ordered (poly-crystalline) state and a disordered (amorphous) state. It was recognized that this effect could be exploited for both optical memories as well as electronic memories. In a September 28th, 1970 issue of Electronics, Energy Conversion Devices (ECD), a company formed by Dr. Ovshinsky, in collaboration with Intel's Gordon Moore reported the world's first electronic phase-change memory array, a 256-bit semiconductor device.
Nearly 30 years later, Ovonyx, a joint venture between ECD and Tyler Lowery, the former CTO/COO of Micron Technology was formed. In February 2000, Intel and Ovonyx announced collaboration and licensing agreement that spawned the modern age of research and development in PCM. In December of 2000, STMicroelectronics ("ST") and Ovonyx also began a collaboration. By 2003, the three companies had joined forces to accelerate progress on the technology by avoiding duplication in basic, precompetitive R&D and through expanding the research scope. In 2005, ST and Intel agreed to codevelop a 90-nm PCM technology.
In 2008, ST and Intel combined their NOR, NAND (ST's NAND), and PCM business to form a new flash company called Numonyx (now part of Micron). The formation of what was Numonyx further accelerated progress in the development of PCM resulting in the first commercial PCM product at the end of 2008.
In the intervening years since that first significant work in 1970, much progress has been made in semiconductor manufacturing technology, enabling the practical development of PCM for both optical and electronic storage devices. Phase-change materials have been in use for many years for high-volume rewritable CDs and DVDs. With the start of production of phase-change materials for electronic memories by Numonyx and others, PCM begins to deliver on its promise to expand the usage of nonvolatile memory.