The key factors in touch-screen displays are conductivity and transparency. Touch-screen displays need electrodes that are excellent conductors so the electronics react quickly to a touch on the screen. The electrodes also need to be transparent so they they don’t detract from the clarity of the screen image.
The industry standard for producing these transparent electrodes has been indium tin oxide (ITO)—a relatively scarce resource with a price tag commensurate with its scarcity. As a result, a veritable cavalcade of nanomaterials have been experimented with as an alternative, including carbon nanotubes, graphene, and recently a material called correlated metals.
Now researchers at ETH Zurich in Switzerland have not only thrown new materials into the ring in the form of gold or silver nanoparticles, but they’ve also come up with a new way to produce the electrodes on touch-screens with a 3-D printer dubbed the Nanodrip.
In research published in the journal Advanced Functional Materials, the Swiss-based researchers have used 3-D printing technology to deposit silver or gold nanoparticles into nanowalls that taken together form a grid pattern across the glass surface of the display. The researchers claim that this nanowalled grid pattern offers higher conductivity and better transparency than ITO.
The researchers knew that the metal nanoparticles would offer better conductivity than the ITO, but the issue they feared was that by building up these structures that they would lose too much transparency.
“If you want to achieve both high conductivity and transparency in wires made from these metals, you have a conflict of objectives,” explained Dimos Poulikakos, a professor at ETH, in a press release. “As the cross-sectional area of gold and silver wires grows, the conductivity increases, but the grid’s transparency decreases.”
The key was to make the walls so thin—only 80 to 500 nanometers thick—that they would be essentially invisible to the naked eye. But how does one make the walls this thin?
The researchers employed a 3-D printing technique they had developed three years ago called Nanodrip. It’s basically ink-jet printing. The ink in this case is metal nanoparticles in a solvent. An electrical field is used to draw out ultra-small droplets of the metallic ink from a glass capillary. The solvent in the ink quickly evaporates leaving behind a 3-D metal structure, which in this case takes the form of a grid pattern.
Better conductivity and transparency sound great, but a drip-by-drip 3-D printing doesn’t sound like it could compete in terms of scalability with ITO-enabled touch screen displays.
The ETH researchers are not deterred by this challenge and have even gone so far as to partner with former ETH colleagues who have spun out a company called Scrona to tackle this scalability issue.