Paper-printed silicon breakthrough for micro-electronic transistors

A method that allows silicon to be produced directly on paper from liquid silicon ink with a single laser pulse could potentially oust existing materials in the production of micro-electric transistors.

In recent years, researchers have sought a replacement to silicon and have built fully flexible electronic circuits either from organic or metal-oxide ink materials. However, in most cases these materials can lack the favourable electronic properties of silicon, despite being easier to “print”.

A team of researchers at Delft University of Technology in the Netherlands have designed a new method of transforming the liquid silicon directly into poly-silicon. Traditionally, printing silicon ink on to substrates needs a 350C thermal heating step. The researchers’ new method bypassed this step.

“It was very simple,” said Ryoichi Ishihara, lead researcher on the project. “We coated liquid polysilane directly on paper by doctor-blading or skimming it by a blade directly in an oxygen-free environment. Then we heated the layer with an excimer-laser [a form of ultraviolet laser used in microelectronic manufacturing].”

The laser blast only lasted a few tens of nanoseconds, leaving the paper completely intact. Ishihara and his team found that thin-film transistors using the laser-printed layer exhibited mobility as high as conventional poly-silicon conductors after testing its conductive performance.

The immediate application of this printing capacity is in wearable electronics as it allows for the production of fast, cost-effective and flexible transistors, according to the researchers.

They intend to improve the production process of the thin-film transistors to include additional non-silicon layers. “The process can be expanded to biomedical sensor and solar-cell areas and will also realize stretchable electronics,” Ishihara said.

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