This means the safe water-based inks could be applied on delicate surfaces such as human skin or fruits to design electronic tattoos or sensing tags without incurring any damage.
“When people hear the term ‘printed electronics,’ the expectation is that a person loads a substrate and the designs for an electronic circuit into a printer and, some reasonable time later, removes a fully functional electronic circuit,” explains Aaron Franklin, the James L. and Elizabeth M. Vincent Associate Professor of Electrical and Computer Engineering at Duke.
“Over the years there have been a slew of research papers promising these kinds of ‘fully printed electronics,’ but the reality is that the process actually involves taking the sample out multiple times to bake it, wash it or spin-coat materials onto it,” Franklin adds. “Ours is the first where the reality matches the public perception.”
“For direct or additive printing to ever really be useful, you’re going to need to be able to print the entirety of whatever you’re printing in one step,” argues Franklin. “Some of the more exotic applications include intimately connected electronic tattoos that could be used for biological tagging or unique detection mechanisms, rapid prototyping for on-the-fly custom electronics, and paper-based diagnostics that could be integrated readily into customized bandages.”
In a first paper titled “Silver nanowire inks for direct-write electronic tattoo applications” appearing in the Nanoscale journal, Franklin’s lab describes a novel ink containing silver nanowires that can be printed onto any substrate at low temperatures with an aerosol printer. It yields a thin film that maintains its conductivity without any further processing. Once printed, the ink dries within two minutes and retains its high electrical performance even after enduring a 50 percent bending strain more than a thousand times.
A second paper published in the ACS Nano journal, “Flexible, Print-in-place 1D-2D Thin-film Transistors Using Aerosol Jet Printing” focuses on expanding the aerosol printing technique with other inks, including dispersed carbon nanotubes and hexagonal boron nitride flakes. Through precise ink formulations, the researchers were able to print 1D–2D thin-film transistors consisting of 1D CNT channels, a 2D hexagonal boron nitride (h-BN) gate dielectric and traces of silver nanowires as the conductive electrodes, all deposited using the same printer.
“Nobody thought the aerosolized ink, especially for boron nitride, would deliver the properties needed to make functional electronics without being baked for at least an hour and a half,” boasted Franklin, “but not only did we get it to work, we showed that baking it for two hours after printing doesn’t improve its performance. It was as good as it could get just using our fully print-in-place process.”
Franklin doesn’t see his printing method replacing large-scale manufacturing processes for wearable electronics. But he does see a potential value for applications such as rapid prototyping or situations where one size doesn’t fit all.
“Think about creating bespoke bandages that contain electronics like biosensors, where a nurse could just walk over to a work station and punch in what features were needed for a specific patient,” said Franklin. “This is the type of print-on-demand capability that could help drive that.”
Duke University – www.duke.edu