QuickStudy: Phase-Change Memory

To read the recorded information, a probe measures the electrical resistance of the spot. The amorphous state's high resistance is read as a binary 0; the lower-resistance, crystalline state is a 1.

Speed Potential

PRAM enables the rewriting of data without a separate erase step, giving the memory the potential to be 30 times faster than flash, but its access, or read, speeds don't yet match those of flash.

Once they do, PRAM-based end-user devices should quickly become available, including bigger and faster USB drives and solid-state disks. PRAM is also expected to last at least 10 times as long as flash, both in terms of the number of write/rewrite cycles and the length of data retention. Ultimately, PRAM speeds will match or exceed those of dynamic RAM but will be produced at lower cost and won't need DRAM's constant, power-consuming refreshing.

PRAM also holds out the possibility of newer, faster computer designs that eliminate the use of multiple tiers of system memory. PRAM is expected to substitute for flash, DRAM and static RAM, which will simplify and speed up memory processing.

A person using a computer with PRAM could turn it off and back on and pick up right where he left off -- and he could do so immediately or 10 years later. Such computers would not lose critical data in a system crash or when the power went out unexpectedly. 'Instant-on' would become a reality, and users would no longer have to wait for a system to boot up and load DRAM. PRAM memory could also significantly increase battery life for portable devices.

History

Interest in chalcogenide materials began with discoveries made by Stanford R. Ovshinsky of Energy Conversion Devices Inc., now known as ECD Ovonics, in Rochester Hills, Mich. His work revealed the potential for using those materials in both electronic and optical data storage. In 1966, he filed his first patent on phase-change technology.

In 1999, the company formed Ovonyx Inc. to commercialize PRAM, which it calls Ovonic Universal Memory. ECD licensed all of its intellectual property in this area to Ovonyx, which has since licensed the technology to Lockheed Martin Corp., Intel Corp., Samsung Electronics Co., IBM, Sony Corp., Matsushita Electric Industrial Co.'sPanasonic unit and others. Ovonyx's licenses center around the use of a specific alloy of germanium, antimony and tellurium.