Researchers use polymers to make electronic devices such as diodes and transistors, but they have paid little attention to exploiting polymers as memory devices. Now, Forrest and colleagues have made a 'write-once read-many-times' (WORM) device by layering a conductive plastic called 'PEDOT' onto the surface of a thin-film silicon diode that has been deposited on a flexible metal foil. The data can only be written once because the write process causes permanent physical changes in the material. However, the data can be read and re-read indefinitely.

The Princeton-HP team discovered that PEDOT – which is used as a coating for photographic film and in video displays - conducts electricity at low voltages but becomes permanently non-conducting at higher voltages (of around 10 volts). It thus acts a fuse or circuit breaker.

In a memory device, data needs to be written as a string of ‘1s’ and ‘0’s. The new memory element would consist of a grid of circuits in which all the connections contained a PEDOT fuse. A large applied voltage would result in the fuse being blown and would close the circuit. This would be a '0'. At lower voltages, the fuse would remain intact, leaving the circuit open and would act as a '1'.

The researchers say that their technique could be used to make memory blocks as small as 1 square millimetre that were capable of storing 1 megabit of information. Although this is 100 times lower than the best magnetic memories, the device could find applications in ultra-low cost data archiving. Moreover, the memory would contain no moving parts - such as the laser and motor drives found in conventional magnetic and optical writers.

The team now hopes to turn their invention into a commercially viable product. “This could take as little as five years,” says Forrest.