New Scientist reports ink drops sliding down a microscopic ridge, like water running off a roof, can boost the speed of printed transistors for flexible electronics The new technique cut the overlap in the final transistor to just 0.78 micrometres, a 10-fold improvement on the previous all-printed techniques and comparable to the figures obtained by using photolithography to clean up after printing.
Without final tuning printed electronic transistors tend to perform poorly, says Huai-Yuan Tseng at the University of California, Berkeley, who with colleague Vivek Subramanian has developed a more accurate way of printing transistors, without resorting to extra processing. Tseng says their method is the first to abandon traditional etching altogether.
The problem is that ink cannot be squirted accurately enough to prevent the three electrodes in a field-effect transistor from being too close together. The source and drain are arranged in a line and printed on one layer while the third, the gate, is printed on a different layer, separated by a nanoscale insulator.
In printed transistors the source and drain can vertically overlap the gate by 10 micrometres or more, allowing electric fields from the gate electrode to couple with the other electrodes and impair performance. The larger the overlap between gate and the source and drain, the larger the parasitic capacitance, and hence the slower the transistors are.