Phase-change Memory - 2000 and Later

2000 and Later

In August 2004, Nanochip licensed PRAM technology for use in MEMS (micro-electric-mechanical-systems) probe storage devices. These devices are not solid state. Instead, a very small platter coated in chalcogenide is dragged beneath many (thousands or even millions) of electrical probes that can read and write the chalcogenide. Hewlett-Packard's micro-mover technology can accurately position the platter to 3 nm so densities of more than 1 Tbit (125 GB) per square inch will be possible if the technology can be perfected. The basic idea is to reduce the amount of wiring needed on-chip; instead of wiring every cell, the cells are placed closer together and read by current passing through the MEMS probes, acting like wires. This approach bears much resemblance to IBM's Millipede technology.

In September 2006, Samsung announced a prototype 512 Mb (64 MB) device using diode switches. The announcement was something of a surprise, and it was especially notable for its fairly high density. The prototype featured a cell size of only 46.7 nm, smaller than commercial Flash devices available at the time. Although Flash devices of higher capacity were available (64 Gb, or 8 GB, was just coming to market), other technologies competing to replace Flash in general offered lower densities (larger cell sizes). The only production MRAM and FeRAM devices are only 4 Mb, for example. The high density of Samsung's prototype PRAM device suggested it could be a viable Flash competitor, and not limited to niche roles as other devices have been. PRAM appeared to be particularly attractive as a potential replacement for NOR Flash, where device capacities typically lag behind those of NAND Flash devices. (State-of-the-art capacities on NAND passed 512 Mb some time ago.) NOR Flash offers similar densities to Samsung's PRAM prototype and already offers bit addressability (unlike NAND where memory is accessed in banks of many bytes at a time).

Samsung's announcement was followed by one from Intel and STMicroelectronics, who demonstrated their own PRAM devices at the 2006 Intel Developer Forum in October. They showed a 128 Mb part that recently began manufacture at STMicroelectronics's research lab in Agrate, Italy. Intel stated that the devices were strictly proof-of-concept, but they expect to start sampling within months, and have widespread commercial production within a few years. Intel appears to be aiming their PRAM products at the same market as Samsung.

PRAM is also a promising technology in the military and aerospace industries where radiation effects make the use of standard non-volatile memories such as Flash impractical. PRAM memory devices have been introduced by BAE Systems, referred to as C-RAM, claiming excellent radiation tolerance (rad-hard) and latchup immunity. In addition, BAE claims a write cycle endurance of 108, which will allow it to be a contender for replacing PROMs and EEPROMs in space systems.

In February 2008, Intel engineers, in cooperation with STMicroelectronics, revealed the first multilevel (MLC) PRAM array prototype. The prototype stored two logical bits in each physical cell, in effect 256 Mb of memory stored in a 128 Mb physical array. This means that instead of the normal two states—fully amorphous and fully crystalline—an additional two distinct intermediate states represent different degrees of partial crystallization, allowing for twice as many bits to be stored in the same physical area on the chip.

Also in February 2008, Intel and STMicroelectronics began shipping prototype samples of their first PRAM product released to customers. The 90 nm, 128 Mb (16 MB) product is called Alverstone.

In June 2009, Samsung and Numonyx B.V. announced a collaborative effort in the development of PRAM market tailored hardware products that would revolutionise the memory industry in terms of design and efficiency in production.

In April 2010, Numonyx announced the Omneo line of 128-Mbit NOR-compatible phase-change memories and Samsung announced shipment of it 512 Mb phase-change RAM (PRAM) in a multi-chip package (MCP) for use in mobile handsets by Fall 2010.

In June 2011, IBM announced that they had created stable, reliable, multi-bit phase change memory with high performance and stability.