3D printed nanowalls could improve touchscreens

Touchscreen technology relies on nanowalls of transparent electrodes on the surface of the glass to receive input from our fingers. Until now, these barely visible webs have been fabricated using indium tin oxide, a transparent material with relatively low conductivity. The team at ETH has designed a system that can 3D print nanowalls using gold or silver, which are more conductive and transparent than indium tin oxide, delivering better touchscreen performance.

“Indium tin oxide is used because the material has a relatively high degree of transparency and the production of thin layers has been well researched, but it is only moderately conductive,” said Patrik Rohner, a PhD student at ETH and a member of the research team.

Gold and silver are not naturally transparent, so in order to gain the appearance of transparency, the electrodes are printed between 80 and 500 nanometres thick. To retain the desired levels of conductivity, the nanowalls make use of three dimensions, and the electrodes are created two to four times taller than they are wide.

“If you want to achieve both high conductivity and transparency in wires made from these metals, you have a conflict of objectives,” said Dimos Poulikakos, a professor of thermodynamics at ETH and head of the research. “As the cross-sectional area of gold and silver wires grows, the conductivity increases, but the grid’s transparency decreases.”

To create these gold and silver nanowalls, the team used a 3D printing process called Nanodrip, which was developed by Poulikakos and his colleagues three years ago. It is a form of electrohydrodynamic ink-jet printing, where inks made from metal nanoparticles in a solvent are dispersed in tiny droplets with the aid of an electrical field. By carefully balancing the composition of metallic ink and the electromagnetic field used, Nanodrip is able to deposit droplets ten times smaller than the aperture they are dispersed from.

“Imagine a water drop hanging from a tap that is turned off,” explained Poulikakos. “And now imagine that another tiny droplet is hanging from this drop – we are only printing the tiny droplet.”

According to the ETH team, the Nanodrip process should be more cost-effective than using indium tin oxide, as it does not require a clean room. The next challenge is to develop the technology so that it can be applied on an industrial scale, and the researchers are working with colleagues from ETH spin-off company Scrona to achieve that.