A silver ink for printing high-performance electrical circuits on flexible substrates has been developed by a team at the University of Illinois. Electronics printed on flexible substrates are gaining popularity with the rising desire for thinner electronic gadgets, wearable devices, and the nascent market for flexible screens.
The team was led by Jennifer Lewis, Hans Thurnauer professor of materials science and engineering, and Jennifer Bernhard, a professor of electrical and computer engineering. Lewis and graduate team member Brett Walker have published the work in the Journal of the American Chemical Society.
The ink comprises silver acetate dissolved in ammonia to give a clear solution that is better than other inks which are particle based and less predictable. In the reactive ink developed by the team, the silver remains in solution until the solvent evaporates, leaving a conductive silver deposit.
Because it is a solution, the ink can be used in inkjet heads or airbrushes with nozzles that are only 100 nanometres in diameter – far smaller than is possible with particle inks. It is also feasible to use it in a pen for direct application to a surface.
“For printed electronics applications, you need to be able to store the ink for several months because silver is expensive,” said Walker. “Since silver particles don’t actually form until the ink exits the nozzle and the ammonia evaporates, our ink remains stable for very long periods. For fine-scale nozzle printing, that’s a rarity.”
Being a solution, the ink is easily made and takes only a few minutes, making it much easier to prepare than its counterpart which requires high temperatures and multi-step processes. Once the reactive ink has been deposited, it exhibits a conductivity close to pure silver, once it has been annealed at 90°C.
“We are now focused on patterning large-area transparent conductive surfaces using this reactive ink,” said Lewis
The use of the ink to create mobile phone aerials could greatly enhance reception in lower signal areas and there are also applications for RFID technology. Flexible connectors are also of use for batteries, sensors, and solar energy arrays.