THE FUTURE IS ORGANIC

Dick Pountain/11 October 2010 15:08/Idealog 195

If you use a modern touch-screen smartphone or watch a newish flat-screen telly then you've probably marvelled at the sharp and bright display quality, which is thanks to Active Matrix Organic Light Emitting Diode (AMOLED) technology. You might not, however, have thought further about the implications of this technology for the future of IT, the clue to which lies in that "O" for Organic.

AMOLED displays contain a layer of organic LEDs (one per pixel) fabricated from light-emitting organic polymers like poly(p-phenylene vinylene) or doped poly(n-vinylcarbazole), printed onto a plastic sheet which is then sandwiched with another thin film containing the transistor switches that turn each pixel on and off. At the moment the only materials suitable for making this substrate layer are still inorganic, silicon-based ones like polycrystalline silicon or amorphous silicon - so AMOLED  is still a hybrid technology in this sense. It's likely that soon we'll see displays in which amorphous silicon transistors are created using cold vapour deposition methods so that the whole display can become flexible, but the ideal would be if the transistors themselves could be fabricated in some organic, plastic technology. That would revolutionise the electronics business in ways we can barely imagine yet.

I've written in this magazine before about how the computing revolution was basically driven forward by the benign scaling properties of the Complementary Metal-Oxide-Semiconductor (CMOS) fabrication process, which is what gave rise to Moore's Law. Not every chip in your phone or PC is made in CMOS, but almost all of them are made from *some* combination of silicon, silicon dioxide and metal layers and for that reason they're all very hard and brittle. Indeed they're so fragile that they have to be encased in plastic, with metal pins sticking out to make contact with their circuits. It's these packages that determine the shape and size of what we think of as an electronic device. A motherboard consists of metal tracks on a plastic substrate, connecting together the pins of chip packages like so many railway lines connecting cities. In a mobile phone this board will be thin and bendy to some extent, but you can't bend the chip  packages.

If we had a wholly organic system for making electronic circuits, then intelligence could be distributed throughout what at present is merely the protective casing of a device. Just about anything that can be fabricated from plastic could be made smart, and that means just about anything. So what are the prospects for a wholly organic electronics? Well, this year's Nobel Prize for physics reveals one very promising avenue: Andre Geim and Konstantin Novoselov, two Russian expatriate scientists working at Manchester University shared the prize for their work on graphenes, which might be the key to whole new ways of making electronic circuits.

You may remember from school chemistry that graphite, the form of carbon used in pencil leads and lubricating greases, is slippery because it's made up of piles of one-atom-thick sheets whose the carbon atoms are connected hexagonally like molecular chicken wire. These sheets are phenomenally strong in themselves, but very weakly connected to their neighbours so they can slip over each other like a pack of cards. A graphene is a single one of these sheets, and Geim and Novoselov pioneered methods for extracting and manipulating such sheets. (Every time you write with a lead pencil, you leave a smear of graphenes across the paper).

The electronic properties of graphenes are as interesting as their mechanical ones: in their plane they conduct electricity and heat better than silver, and they display semiconduction of a potentially useful kind. Their conduction properties can be modified by electrical and magnetic fields perpendicular to their plane, and Field Effect Transistors (FETs), albeit rather inefficient ones, have already been made from them. You can oxidise graphenes and dope them with other elements to further modify their properties. They're closely related to fullerenes and carbon nanotubes, whose mechanical properties have been under intense scrutiny for years, and it's not too far fetched to imagine layers of doped graphene deposited on plastic with individual components connected by nanotube conductors.

It's recently been demonstrated that you can inject spin-polarised electrons into graphene lattices, opening up the possibility of "spintronic" memory devices based on reading electron spins rather than charges. Graphenes also have optical properties that make them potentially useful in displays and in photonic circuits. And because graphenes conduct very poorly indeed perpendicular to their plane, when appropriately layered they form the thinnest capacitor imaginable, so it's equally possible to imagine a hypercapacitor formed within the actual plastic case of a gadget replacing a battery: it might only power the device for a few minutes but would take only seconds to recharge from some wireless inductive source. In fact I might just rewrite that famous scene from the movie "The Graduate":

Mr. McGuire: "I want to say one word to you. Just one word".
Benjamin: "Yes, sir".
Mr. McGuire: "Are you listening?"
Benjamin: "Yes, I am".
Mr. McGuire: "Graphenes".

In the movie the word was of course "Plastics" but that was back in 1967. The two words may one day be seen as marking the frontier between technological epochs.