You can add another crazy characteristic to graphene’s ever-expanding list of “wonder material” properties: It can now be used to create flexible, transparent thin-film transistors… using an inkjet printer.
The discovery comes from researchers at the University of Cambridge, UK, who were trying to ameliorate the lackluster performance of existing inkjet-printed electronics. As we covered last month, it’s possible to print standard CMOS transistors using different ferroelectric polymer inks, but the resultant circuit is so slow that it can’t actually function as a computer. If graphene could replace or augment the interconnects or transistors, these circuits would be a lot faster — and that’s what these Cambridge engineers have done.
The actual meat of the discovery is that graphene has been successfully chipped off a block of graphite using a chemical solvent. These flakes are then filtered to remove any larger, print head-clogging chunks, and then turned into a polymer ink. Despite its amazing properties, graphene hasn’t yet found a way into our computers is because it’s currently very hard and expensive to produce, isolate, and use in silicon circuits. Cambridge’s discovery probably won’t help IBM bring 100GHz graphene circuits to market, though — but it could enable, quite literally, wearable computers.
So far, the results are promising: the graphene-based inks are comparable to existing printed circuits, or a little bit faster — and for a first attempt, that’s not bad. The researchers seem very positive about the long-term prospects of the discovery, too: “This paves the way to all-printed, flexible and transparent graphene devices on arbitrary substrates.” In this case, substrates means everything from thin films that can be applied to clothing, all the way through to e-paper and/or flexible TFT displays. Graphene-based inks are transparent, too, incidentally — by virtue of being incredibly thin, and because of graphene’s regular, honeycomb arrangement (see above).
Did anyone think, when they saw their first inkjet printer in the ’80s or ’90s, that they would one day be capable of printing computer circuits? Even more outlandishly, some 3D printers also use inkjet technology — one nozzle places the resin, and an inkjet then fires out a binder to stick it all together. It provides a very interesting counterpoint to standard chip fab processes, too — a silicon wafer might go through five, multi-million-dollar machines to turn into a chip, while all you need to make a graphene chip is a very accurate stepping motor, a pot of graphene ink, and a piezoelectric actuator to propel the ink in minute quantities.