Liquid metal printing key to 2D electronics

Electronics engineers have been searching some time for a technology that will allow them to increase the processing power of electronic components. Researchers in Australia believe that the answer may lie in ultra-thin components made by a process that starts with printing with liquid metals.

"The fundamental technology of car engines has not progressed since 1920 and now the same is happening to electronics. Mobile phones and computers are no more powerful than five years ago,” said Prof Kourosh Kalantar-zadeh of RMIT University in Melbourne. “That is why this new 2D printing technique is so important - creating many layers of incredibly thin electronic chips on the same surface dramatically increases processing power and reduces costs.”

Techniques used to date have required very high temperatures for processing and have not been able to create homogeneous surfaces of semiconductors over a large area, said Benjamin Carey, another researcher on the project. The Melbourne team, working with the Australian research Council CSIRO, Monash University, North Carolina State University and the University of California developed a technique based on printing with the low melting point metals gallium or indium in a liquid state onto a solid substrate. "These metals produce an atomically thin layer of oxide on their surface that naturally protects them. It is this thin oxide which we use in our fabrication method,” Carey explained.

The oxide layer can be transferred onto an electronic wafer substrate with a specially prepared surface by rolling, the team explains in a paper in Nature Communications. The metal oxide is then sulphurised in a relatively simple low-temperature process, converting it to GaS or InS, which have semiconducting properties. The pre-treatment of the surface of the wafer forms individual transistors. “We have used this novel method to create transistors and photo-detectors of very high gain and very high fabrication reliability in large scale,” Carey said.

The component layer has a thickness of some 1.5nm, far thinner than is possible to fabricate by conventional electronic manufacturing methods. The resulting wafers are also flexible. “It will allow for the next revolution in electronics," claimed Kalantar-zadeh.