Inkjet printers could be the chip factories of the future, squirting out circuits made from layers of organic semiconducting ink. Experiments at the University of Arizona, Tucson, have demonstrated moving images made out of organic LEDs and power generating arrays of plastic solar cells, but show potential for many more kinds of output.
The technology relies on two separate fields: the production of hyper-accurate inkjet printers, which now routinely deposit minuscule droplets of liquid only picolitres in volume at accuracies of more than a thousandth of an inch, and of organic liquids that form semiconducting polymers. The researchers -- professor Ghassan Jabbour and assistant Yuka Yoshioka -- say that by using standard inkjet printers and using different chemicals in place of the normal different colour inks, they can mix up a wide variety of components and print out complete circuits much as they would a full-colour picture, using standard printer drivers. Different resistances and other circuit features can be programmed by changes in the image file.
Unlike silicon circuits, no high temperatures, vacuum environments or million-dollar machinery is required, and as the chemicals are transparent the resultant images can be placed on clear plastic substrates and remain invisible until activated. However, Jabbour says, the system is still in the research stage and years away from being commercialised.
Inkjets are already being used in a number of non-standard ways as very precise liquid delivery systems, including DNA analysis, and investigation into their use as devices to inject individual cells in medical research is underway. On a more fragrant note, Kodak has recently been awarded patents for inkjet-based scent mixing.
The Arizona researchers are not the only people working on plastic electronics through inkjet printers. UK company Plastic Logic, a spin-off from the Cavendish Laboratories in Cambridge, is using similar techniques to produce active-matrix backplanes for organic light-emitting displays, and 'smart' labels as successors for product barcodes. Although the company says that performance will never approach that of silicon circuits -- inkjet resolution is of the order of 200 times larger than silicon chip features -- it says that the ability to change details of the circuit on the fly is very useful. Inkjet-printed circuit designs could be changed more quickly and inexpensively in software. "We could conceivably alter the circuitry with every pass of the inkjet, or run multiple small batches or variations on a product," marketing manager Tracey Stephens told the nanotech industry magazine Small Times.
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