Liquid Silver Used to Print Electronic Circuits

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Printing electronics just got a boost from the University of Illinois, where the latest in electric inks has been made from silver.

Jennifer Lewis, a professor of materials science and engineering, and graduate student S. Brett Walker described the new ink in the Journal of the American Chemical Society. Most inks for printing electronics have metallic particles in them. This ink is all liquid — a solution of silver and ammonia. When printed, the liquid evaporates, leaving a trail of conductive material.

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There are several big advantages over more conventional electronic ink. One is the size of the inkjet nozzle that can be used. Inks using particles require bigger nozzles — on the order of a micrometer in size. The liquid silver ink requires much smaller nozzles — 100 nanometers. It’s also easier to make than other electronic ink and it sticks to a wide variety of materials, including plastic, paper or fabric.

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The other big selling point is temperature. A typical particle-based ink has to be printed at a relatively high temp in order to get good conductivity. That's why they aren't used on paper or some plastics. But the silver-based solution gets to its maximum conductivity at about 90 degrees Celsius, or about 194 degrees Fahrenheit. That’s warm, yes, but still cool enough to work most materials.

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Also, while silver may sound like an expensive material, it’s been between $26 and $48 per ounce over the last year, and an ounce of silver would supply a lot of printing ink. The cost per unit volume would be comparable to that of printer inks sold today.

Sure, scientists have printing electronics onto flexible surfaces to make antennas, for example, and there are now even pens that can “write” circuits. But the silver ink gets us all one step closer to printing circuits using a simple desktop machine.

Image: University of Illinois / S. Brett Walker

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