A pen with conductive silver ink that can write electrical circuits and interconnects on paper, wood and other surfaces is composing a whole new chapter in low-cost, flexible and disposable electronics. “Pen-based printing allows one to construct electronic devices ‘on the fly,’ ” said Jennifer Lewis, the Hans Thurnauer professor of materials science and engineering and director of the Frederick Seitz Materials Research Laboratory at the University of Illinois. “This is an important step toward enabling desktop manufacturing, or personal fabrication, using very low-cost, ubiquitous printing tools.” Flexible array of LEDs mounted on paper. Hand-drawn silver ink lines form the interconnects between the LEDs. (Images: Bok Yeop Ahn) The research team, which published its work in the journal Advanced Materials, also included Jennifer Bernhard, a professor of electrical and computer engineering at UI; graduate student Analisa Russo; and postdoctoral researchers Bok Yeop Ahn, Jacob Adams and Eric Duoss. Although it looks like a typical silver-colored roller-ball pen, this pen’s ink is a solution of real silver. After writing, the liquid in the ink dries, leaving conductive silver pathways — in essence, paper-mounted wires. The ink maintains its conductivity through multiple bends and folds of the paper, enabling devices with great flexibility and conformability. University of Illinois engineers have developed a pen with conductive silver ink that can write electric circuits and interconnects directly on paper and other surfaces. Metallic inks have been used in approaches using inkjet printers to fabricate electronic devices, but the 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, handheld writing tool,” said Lewis, who also is affiliated with the Beckman Institute for Advanced Science and Technology. A sketch of the painting “Sae-Han-Do” by Jung Hee Kim, drawn in conductive silver ink that powers an LED mounted on the paper. The ability to create freestyle conductive pathways enables new possibilities in art, disposable electronics and folded 3-D devices. For example, the researchers used the silver pen to sketch a copy of the painting “Sae-Han-Do” by Jung Hee Kim, which portrays a house, trees and Chinese text. The ink serves as wiring for an LED mounted on the roof of the house, powered by a 5-V battery connected to the edge of the painting. The researchers also have demonstrated a flexible LED display on paper, conductive text and 3-D radio-frequency antennas. Next, the researchers plan to expand the palette of inks to enable pen-on-paper writing of other electronic and ionically conductive materials. The US Department of Energy supported this work. For more information, visit: www.illinois.edu