Scientists from Tokyo University have just revealed a reliable method to inkjet print dots of one micron on to flexible film. It is described in Proceedings of the National Academy of Sciences. This is needed to conserve the very expensive inks used in printed electronics and to improve the electronic properties of printed electronic devices by reducing key dimensions such as the channel length of transistors. These are being developed by 360 organisations, half of them academic, and they are likely to be the biggest printed electronics market, just as silicon chip logic dominates conventional electronics expenditure. Indeed, in conventional flat screen displays, higher processing temperatures, increased manufacturing costs, and a higher price for the consumer are being incurred in order to improve performance and the new form of inkjet printing is expected to help to reverse this malign trend.
Current printed electronics techniques are limited in their abilities to replicate the resolutions achieved by silicon-based devices and other lithographic techniques for several reasons, one being surface tension of the inks. Putting down hydrophobic/ hydrophilic patterns to self assemble the subsequently deposited layer may require something less efficient than printing. Acoustically focussed inkjets have limitations. Yet inkjet is the preferred way of printing photovoltaics, OLEDs, electrophoretic and electrochromic displays, transistors and memory because it conserves expensive ink and tolerates the uneven surfaces of reel to reel film processes and so on. This new printing technique allows droplet volumes of less than 1 femtolitre - a millionth of that which recent techniques allowed.
The prolific University of Tokyo
The University of Tokyo is one of the most prolific and respected developers of printed electronics, including work on transmitting electric power through water, a disposable plastic film scanner with no moving parts, large area sensors and reprogrammable Braille cards using electroactive polymers. At the IDTechEx conference Printed Electronics Europe 2007, Professor Takao Someya of the University of Tokyo spoke on "E-skins and power sheets using printed organic transistors and printed MEMS switches". At this year's event Printed Electronics Europe 2008 early next month, FUJIFILM Dimatix, Optomec Inc., Trident Industrial Inkjet, Seiko Epson Corp., Pixdro/OTB, MAN Roland and the Welsh Centre for Printing and Coating will announce their latest advances. There will be at least 600 delegates and 60 exhibitors.
The University of Tokyo has worked on organic transistors for many years, including the integration of sensors into printed transistors. Categories of appropriate work at the University include: Inks/ materials organic, inks/materials inorganic, logic organic, logic inorganic, conductor patterns, printing flexo, printing gravure, printing litho, printing ink jet, printing screen, sensors.
See Sekitani, T., Noguchi, Y., Zschieschang, U., Klauk, H., Someya, T. (2008). Organic transistors manufactured using inkjet technology with subfemtoliter accuracy. Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0708340105.