Particle-free silver ink developed for printable electronics
By Ben Coxworth
January 16, 2012
There's no doubt that we will soon be seeing a lot more in the way of low-cost electronic circuits that have been printed onto common, flexible materials such as plastic, paper or fabric. One of the key technological innovations making this possible is silver ink, which is used to print these circuits' conductors. While such ink usually incorporates particles of silver suspended in a carrier liquid, a new type of ink created at the University of Illinois forgoes the particle approach, and is said to offer some distinct advantages as a result.
Developed by a team led by Prof. Jennifer Lewis, the new ink is a transparent solution of silver acetate dissolved in ammonia. When printed, its liquid component quickly evaporates, leaving behind lines of dry, conductive silver.
The ink can reportedly be made much more quickly than its particle-based counterpart - a batch can be whipped up within minutes, as opposed to the several hours and multiple steps required for traditional silver ink. Once created, the solution remains stable for several weeks, so it doesn't have to be used right away.
It can also squeeze its way through 100-nanometer printing nozzles, which is "an order of magnitude" smaller than what can be managed by particle-based inks. This makes it particularly well-suited to the printing of micro-electronics. Because it has a low viscosity, it can additionally be applied using inkjet printers or direct ink writing, or it can be airbrushed over a large area.
Yet one other advantage of the new ink is the fact that it has a low processing temperature. Other types of silver inks require quite a high temperature for their annealing process, a treatment in which they are heated and then allowed to cool. In some cases, that temperature is high enough to damage the material on which they're being printed. The U Illinois ink, however, has a relatively low annealing temperature of 90ºC (194ºF).
A paper on the research was recently published in the Journal of the American Chemical Society.
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