Smaller, simpler way to archive data

Engineers at Princeton University and Hewlett-Packard have invented a combination of materials that could lead to inexpensive, compact electronic memory devices for archiving digital images or other data.

The invention could result in a single-use memory card that permanently stores data and is faster and easier to use than a compact disk. The device could be very small because it would not involve moving parts such as the laser and motor drive required by CDs.

The researchers achieved the result by discovering a previously unrecognised property of a commonly used conductive polymer plastic coating. Their memory device combines this polymer with thin-film, silicon-based electronics.

"We are hybridising," says Princeton professor of electrical engineering Stephen Forrest, who led the research group. "We are making a device that is organic (the plastic polymer) and inorganic (the thin-film silicon) at the same time.

As a result, the device would be like a CD in that writing data onto it makes permanent physical changes in the plastic and can be done only once. But it also would be like a conventional electronic memory chip because it would plug directly into an electronic circuit and would have no moving parts." Forrest said.

The research was done in Forrest's lab by former postdoctoral researcher Sven Moller, who is now at HP in Corvallis, Ore.

Moller made the basic discovery behind the device by experimenting with polymer material called Pedot, which is clear and conducts electricity. It has been used for years as an antistatic coating on photographic film, and more recently as an electrical contact on video displays that require light to pass through the circuitry. Moller found that Pedot conducts electricity at low voltages, but permanently loses its conductivity when exposed to high voltages (and thus higher currents), making it act like a fuse or circuit breaker.

This finding led the researchers to use Pedot as a way of storing digital information. Digital images and all computerised data are stored as numbers that are written as long strings of ones and zeroes. A Pedot-based memory device would have a grid of circuits in which all the connections contain a Pedot fuse. A high voltage could be applied to any of the contact points, blowing that particular fuse and leaving a mix of working and non-working circuits. These open or closed connections would represent zeros and ones and would become permanently encoded in the device. A blown fuse would block current and be read as a zero, while an unblown one would let current pass and act as a one.

This grid of memory circuits could be made so small that, based on the test junctions the researchers made, 1 million bits of information could fit in a square millimetre of paper-thin material. If formed as a block, the device could store more than one gigabyte of information, or about 1000 high quality images, in one cubic centimetre, which is about the size of a fingertip.

Developing the invention into a commercially viable product would require additional work on creating a large-scale manufacturing process and ensuring compatibility with existing electronic hardware, a process that might take five years, Forrest said.