Polymer Memory

While microchip makers continue to wring more and more from silicon, the most dramatic improvements in the electronics industry could come from an entirely different material: plastic. Labs around the world are working on integrated circuits, displays for handheld devices and even solar cells that rely on electrically conducting polymers-not silicon-for cheap and flexible electronic components. Now two of the world’s leading chip makers are racing to develop new stock for this plastic microelectronic arsenal: polymer memory.

Advanced Micro Devices of Sunnyvale, CA, is working with Coatue, a startup in Woburn, MA, to develop chips that store data in polymers rather than silicon. The technology, according to Coatue CEO Andrew Perlman, could lead to a cheaper and denser alternative to flash memory chips-the type of memory used in digital cameras and MP3 players.Meanwhile, Intel is collaborating with Thin Film Technologies in Linkping, Sweden, on a similar highcapacity polymer memory.

Polymer microelectronics are potentially far less expensive to make than silicon devices. Instead of multibillion-dollar fabrication equipment that etches circuitry onto a silicon wafer, manufacturers could eventually use ink-jet printers to spray liquid-polymer circuits onto a surface. Polymer memory comes with an added bonus: unlike the memory in your PC, it retains information even after the power is shut off. Such nonvolatile memory offers potential advantages- not the least of which is the prospect of never having to wait around for a PC to boot up-and a number of researchers are working on various approaches (see “Magnetic Random-Access Memory,” TR July/August 2002). But polymer memory could potentially store far more data than other nonvolatile alternatives.

Polymer memory stores information in an entirely different manner than silicon devices. Rather than encoding zeroes and ones as the amount of charge stored in a cell, Coatue’s chips store data based on the polymer’s electrical resistance. Using technology licensed from the University of California, Los Angeles, and the Russian Academy of Sciences in Novosibirsk, Coatue fabricates each memory cell as a polymer sandwiched between two electrodes. Application of an electric field to a cell lowers the polymer’s resistance, thus increasing its ability to conduct current; the polymer maintains its state until a field of opposite polarity is applied to raise its resistance back to its original level. The different conductivity states represent bits of information.

Coatue’s polymer memory cells are about one-quarter the size of conventional silicon cells. And unlike silicon devices, the polymer cells can be stacked to produce a three-dimensional structure. That architecture could translate into memory chips with several times the storage capacity of flash memory. By 2004, Coatue hopes to have memory chips on the market that can store 32 gigabits, outperforming flash memory, which should hold about two gigabits by then.

But turning polymer memory into a commercial product won’t be easy. Memory technologies compete not only on storage capacity but on speed, energy consumption and reliability. “The difficulty is in meeting all the requirements of current silicon memory chips,” says Thomas Theis, director of physical sciences at IBM’s Watson Research Center in Yorktown Heights, NY. Until new memory materials are able to compete with the high performance of silicon, Theis notes, they are likely to be limited to niche applications.

One likely use is in disposable electronics, where cost, rather than performance, is the deciding factor. Researchers at Lucent Technologies’ Bell Laboratories are working on polymer memory devices for use in identification tags. The polymer memory made at Bell Labs is still relatively slow by silicon standards, and anticipated capacity is only on the order of a kilobit. But, says Bell Labs chemist Howard Katz, the flexible and low-cost polymer memory devices could be “very attractive” for, say, identification tags meant to be thrown away after a few uses.

As polymer memory technology advances, it could pave the way to computers made entirely of plastic electronic components, from the display to the logic chip. That may be decades off, but as researchers push the bounds of polymers, the vision seems less far-fetched. And in the short term, Coatue says its polymer memory could be integrated into the existing silicon infrastructure. “The revolution has already begun,” says MIT chemist Tim Swager, a scientific advisor to Coatue.