But such applications will require more than just plastic processors, says Wei Zhang, who works on organic electronics at the University of Minnesota. At the same conference where the organic processor was unveiled, Zhang and colleagues presented the first printed organic memory of a type known as DRAM, which works alongside the processor in most computers for short-term data storage. The 24-millimeter-square memory array was made by building up several layers of organic “ink” squirted from a nozzle like an aerosol. It can store 64 bits of information.
Previous printed memory has been nonvolatile, meaning it holds data even when the power is off and isn’t suitable for short-term storage involving frequent writing, reading, and rewriting, says Zhang. The Minnesota group was able to print DRAM because it devised a form of printed, organic transistor that uses an ion-rich gel for the insulating material that separates its electrodes.
The ions inside enable the gel layer to store more charge than a conventional, ion-free insulator. That addresses two problems that have limited organic memory development. The gel’s charge-storing ability reduces the power needed to operate the transistor and memory built from it; it also enables the levels of charge used to represent 1 and 0 in the memory to be very distinct and to persist for as long as a minute without the need for the memory to be refreshed.
Organic, printed DRAM could be used for short-term storage of image frames in displays that are today made with printed organic LEDs, says Zhang. That would enable more devices to be made using printing methods and eliminate some silicon components, reducing costs.
Finding a way to combine organic microprocessors and memory could cut prices further, although Zhang says the two are not yet ready to connect. “These efforts are new techniques, so we cannot guarantee that they will be built and work together,” says Zhang. “But in the future, it would make sense.”