Champaign, IL--Researchers at the University of Illinois have created a silver-nanoparticle-based ink that can be used in a rollerball pen to draw electrical connections for flexible LED displays and other devices (a rollerball pen is like a ball-point pen with a slightly larger roller often made of plastic).1
The key word is "flexible": while silver-particle-based conductive inks have been around for a long time, they are made for use on rigid substrates. In contrast, the new ink can be used on paper and the paper folded back and forth (to a bend radius of 0.5 mm) thousands of times before the ink fails. This makes the ink well-suited for rollable and flexible displays
When rolled on with a 12 micron thickness, the ink has a very low electrical resistivity of 1.99 x 10-4 ohm-cm, which can be lowered further to 4.34 x 10-6 ohm-cm by annealing it. The silver content is 45% to 55% by weight, the corresponding viscosity is 1 to 10 Pa-s, and the binder is hydroxyethyl cellulose, a material commonly used in cosmetics and other household products.
In comparison, a well-known conventional conductive pen, the CircuitWriter pen made by Caig Laboratories (Poway, CA), creates a film with similar thickness (between 10 and 25 microns), also contains silver, has an acrylic binder, and has a solids weight proportion of 51.5%. However, the manufacturer advises that although it is okay to use the ink on a slightly flexible circuit board, the ink is not meant for use on surfaces meant to be flexed. (The CircuitWriter conductive pen is the one commonly sold by RadioShack.)
Easy application: just draw it on
Metallic inks have also been used in approaches using inkjet printers to fabricate electronic devices, but the nanoparticle-based ink in a rollerball pen offers freedom and flexibility to apply ink directly to paper or other rough surfaces instantly, at low cost, and without programming.
"The key advantage of the pen is that the costly printers and printheads typically required for inkjet or other printing approaches are replaced with an inexpensive, hand-held writing tool," said Lewis, who is also affiliated with the Beckman Institute for Advanced Science and Technology.
Among other things, the U. of Illinois researchers have demonstrated a flexible LED display on paper, conductive text, and three-dimensional radio-frequency antennas.
REFERENCE:
1. Analisa Russo et al., Advanced Materials, article first published online: 20 June 2011; DOI: 10.1002/adma.201101328.
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