Jan 7, 2016 | By Kira
Using their previously developed Nanodrip 3D printing method along with gold or silver nanoparticles, a team of researchers from ETH Zurich have developed a novel method for 3D printing ultra-thin ‘nanowalls’ that could improve the performance of the touchscreens used in our smartphones, tablets and other devices. The 3D printing process allows for some of the most transparent and conductive electrodes ever developed, resulting in better screen quality and more precise and responsive touchscreens.
From our smartphones to ATMs, we use touchscreens just about everyday of our lives, without giving much thought to just how it is that a mere swipe of our finger is able to open an entire app, send an email, or take a picture.
As ETH Zurich explains, touchscreen technology relies on microscopic transparent electrodes that coat the surface of the device with a barely visible nanowall made from a conductive material. The most common material used today is indium tin oxide, a material with high transparency (necessary for us to view the screens, of course) but relatively low conductivity.
The researcher’s groundbreaking development is to 3D print these nanowalls with gold or silver metal nanoparticles, which are much more conductive and transparent than indium tin oxide and thus provide a better touchscreen experience overall.
“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.
But, you might say, gold and silver aren’t transparent—at least not in the way we are used to seeing them. This is where the nano-based 3D printing process, also known as ‘electrohydrodynamic ink-jet printing’ came into play. In order to retain the metal materials’ conductivity while gaining the appearance of transparency, the researchers 3D printed the electrodes into ultra-thin layers, between 80 to 500 nanometers thick. However, this presented yet another problem:
“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, 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 solve this dilemma, the electrodes were 3D printed so as to be two to four times taller than they are wide, increasing the width of the cross-sectional area, and thus increasing the conductivity.
The Nanodrip 3D printing process was developed by Poulikakos and his colleagues three years ago—in fact, it is the same process that enabled ETH Zurich to create the world’s tiniest color picture ever printed, which was so small it could fit inside a human hair. In this process, inks made from metal nanoparticles (in this case, gold or silver) are put into a solvent and then dispersed into tiny droplets with the aid of an electrical field. The solvent evaporates quickly, leaving behind the 3D structure.
The main advantage of this drop-by-drop 3D printing process is that the droplets themselves are ten times smaller than the aperture they are dispersed from, allowing for extremely small structures to be printed. As Poulikakos puts it, “Imagine a water drop hanging from a tap that is turned off. And now imagine that another tiny droplet is hanging from this drop – we are only printing the tiny droplet.”
As ETH reports, this is the first time touchscreen nanowalls have been manufactured using 3D printing, and the benefits are already quite clear—literally. Not only are the nanowalls more transparent than those made from indium tin oxide, they are more conductive and even more cost-efficient. This is because the production of indium tin oxide requires a high-maintenance cleanroom environment, whereas production with gold and silver nanoparticles does not.
In addition to improving the screen quality and responsiveness of smartphones, these 3D printed electrodes are also likely to be better suited to large touchscreens due to their higher conductivity, or even curved displays that use OLED rather than LCD technology. Another potential use could be in solar cells, which also use transparent electrodes. By making these electrodes more transparent and conductive, solar cells could harness even more electricity.
The next steps for the ETH Zurich team will be to find a way to scale up the 3D printing process so that it can be industrialized and mass-produced. Luckily, ETCH is already working with their spin-off company Scrona (who was also behind the tiniest 3D printed picture ever) to accomplish that.
Posted in 3D Printing Application
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