Particle-free silver ink prints small, high-performance electronics

January 17, 2012
Silver Ink

Reactive silver ink is airbrushed onto a thin, stretchy plastic film to make a flexible silver electrode (credit: S. Brett Walker)

University of Illinois materials scientists have developed a new silver ink for printing high-performance electronics on ubiquitous, low-cost materials such as flexible plastic, paper or fabric substrates.

Electronics printed on low-cost, flexible materials hold promise for antennas, batteries, sensors, solar energy, wearable devices and more. Most conductive inks rely on tiny metal particles suspended in the ink. The new ink is a transparent solution of silver acetate and ammonia. The silver remains dissolved in the solution until it is printed, and the liquid dries quickly, yielding conductive features.

The new ink has several advantages over particle-based inks:

  • Much faster to make: a batch takes minutes to mix, whereas particle-based inks take several hours and multiple steps to prepare.
  • Stable storage of the ink for several weeks.
  • Can print through 100-nanometer nozzles an order of magnitude smaller than particle-based inks, an important feature for printed microelectronics.
  • The ink’s low viscosity makes it suitable for inkjet printing, direct ink writing, or airbrush spraying over large, conformal areas.
  • Low processing temperature. Metallic inks typically need to be heated to achieve bulk conductivity through a process called annealing. The annealing temperatures for many particle-based inks are too high for many inexpensive plastics or paper. By contrast, the reactive silver ink exhibits an electrical conductivity approaching that of pure silver upon annealing at .90 degrees Celsius (194 degrees F).

Ref.: S. Brett Walker and Jennifer A. Lewis, Reactive Silver Inks for Patterning High-Conductivity Features at Mild Temperatures, Journal of the American Chemical Society, 2012; [DOI: 10.1021/ja209267c]