(January 6, 2015) Researchers
at ETH Zurich have manufactured transparent electrodes for use in touchscreens
using a novel nanoprinting process. The new electrodes are some of the most
transparent and conductive that have ever been developed.
From smartphones to the operating interfaces of ticket
machines and cash dispensers, every touchscreen we use requires transparent
electrodes: The devices’ glass surface is coated with a barely visible pattern
made of conductive material. It is because of this that the devices recognise
whether and where exactly a finger is touching the surface.
Researchers under the direction of Dimos Poulikakos,
Professor of Thermodynamics, have now used 3D print technology to create a new
type of transparent electrode, which takes the form of a grid made of gold or
silver “nanowalls” on a glass surface. The walls are so thin that they can
hardly be seen with the naked eye. It is the first time that scientists have
created nanowalls like these using 3D printing. The new electrodes have a
higher conductivity and are more transparent than those made of indium tin
oxide, the standard material used in smartphones and tablets today. This is a
clear advantage: The more transparent the electrodes, the better the screen
quality. And the more conductive they are, the more quickly and precisely the
touchscreen will work.
This grid printed
in gold has walls only 300 nanometres thick.
(Photo: Schneider
J et al. Advanced Functional Materials 2015)
Third dimension
“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,” says Patrik
Rohner, a PhD student in Poulikakos’ team. In order to produce more conductive
electrodes, the ETH researchers opted for gold and silver, which conduct
electricity much better. But because these metals are not transparent, the
scientists had to make use of the third dimension. ETH professor Poulikakos
explains: “If you want to achieve both high conductivity and transparency in
wires made from these metals, you have a conflict of objectives. As the
cross-sectional area of gold and silver wires grows, the conductivity
increases, but the grid’s transparency decreases.”