Science

Delft researchers printed silicon on paper

Delft researchers have developed a technique to make chips with silicon ink. Ultimately they hope to make transistors for wearable electronics.

In seeking to develop the next generation of micro-electronic transistors, researchers have long sought to find the next best thing to replace silicon. To this end, a wealth of recent research into fully flexible electronic circuitry has focused on various organic and metal-oxide ink materials, which often lack all the favorable electronic properties of silicon but offer superior ‘printability’.

Recently, a group of researchers of TU Delft and the Japan Advanced Institute of Science and Technology in Nomi, Japan, has pioneered a method that allows silicon itself, in the polycrystalline form used in circuitry, to be produced directly on a substrate from liquid silicon ink with a single laser pulse — potentially ousting its pale usurpers.The research was published online on April 21, 2015 in the journal Applied Physics Letters.

It was possible before to print silicon ink onto substrates but only with a 350 degrees Celsius thermal annealing step, which is much too hot for many flexible surfaces. Lower temperatures resulted in insufficient cross-linking and led to oxidation of the ink.

The new technique, developed amongst others professor in micro electronics Ryoichi Ishihara (EEMCS faculty), takes on a completely different approach. “It was very simple. We coated liquid polysilane directly on paper by doctor-blading, or skimming it by a blade directly in an oxygen-free environment. Then we annealed the layer with an excimer-laser, a conventional tool used for manufacturing smartphone displays. And it worked.” Or so Ishihara said in a press release by the American Institute of Physics, the publisher of the journal Applied Physics Letters.

The laser blast only lasted a few tens of nanoseconds, leaving the paper completely intact. In testing its conductive performance, the scientists found that thin-film transistors using the laser-printed layer exhibited electron mobilities as high as those of conventional poly-silicon conductors.

The most immediate application of this printing capacity is in wearable electronics, as it should allow for the production of fast, low-power and flexible transistors at a low cost. “The process can be expanded to biomedical sensor and solar-cell areas,” Ishihara said, “and will also realize stretchable — and even edible – electronics.”

M. Trifunovic, et. al., Solution-processed polycrystalline silicon on paper, Applied Physics Letters. April 2015. doi:10.1063/1.4916998

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