Flexible electronics are vital for monitoring various physiological parameters. At present, manufacturing flexible electronics requires chemical baths, hardening methods, and baking in high temperature to purify the material. Now, engineers at Duke University have devised a fully print-in-place technique for electronics that is gentle enough to work on delicate surfaces including paper and human skin. The advance could enable technologies such as high-adhesion, embedded electronic tattoos and bandages tricked out with patient-specific biosensors, Pratt School of Engineering at Duke.
The researchers described their methods in a series of papers published online in the journals Nanoscale and ACS Nano.
“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,” said 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 said. “Ours is the first where the reality matches the public perception.”
In the first paper, Franklin’s lab and the laboratory of Benjamin Wiley, professor of chemistry at Duke, developed a novel ink containing silver nanowires that can be printed onto any substrate at low temperatures with an aerosol printer. It produces a thin film that maintains its conductivity and after being printed, the ink is dry in less than two minutes and retains its high electrical performance even after enduring a 50 percent bending strain more than a thousand times.
In the second paper, this technology is taken a step further. The ink is combined with two other printable components to create functional transistors. The printer first puts down a semiconducting strip of carbon nanotubes. Once it dries, and without removing the plastic or paper substrate from the printer, two silver nanowire leads that extend several centimeters from either side are printed. A non-conducting dielectric layer of a two-dimensional material, hexagonal boron nitride, is then printed on top of the original semiconductor strip, followed by a final silver nanowire gate electrode, said the Duke University report.