A team at MIT has developed a high-tech stamping process that involves a “forest” of carbon nanotubes, capable of printing electronic inks onto almost any surface, whether rigid or flexible. Think of an inkjet, only imagine that the nozzle is the size of a nanotube. When densely packed, nanotubes can act as nanoscale print heads for electronic inks. They make tiny, tiny traces, like the tiniest quill pen. Because the nanotubes are porous, though, the nano-nozzles can provide a uniform flow rate, crucial for accurate printing with the solutions of conductive nanoparticles that the team tested out as conductive inks.
What makes this particular application noteworthy is the “coffee ring” problem. It’s difficult to print conductive inks that don’t make little cracks when they’re flexed, or manage to bleed over onto places they shouldn’t. Electronics are only as good as their components, and perhaps the most important component is the conductive wires. Having tiny little nozzles can go a long way toward the precise application of the right conductive inks for a given substrate and its intended use.
Kim, Hart et al, 2016
The researchers’ own expectation is that the new nano-nozzles will be used in turn to develop transparent but sensor-rich panels, labels, stickers, and even food packaging. We’ve already isolated some of the specific molecular signatures of food spoilage bacteria; such a membrane could be used to detect these telltale molecules before the human nose can possibly perceive them. But the possible uses don’t stop there. The authors envision windowpanes that would tell you the day’s forecast based on hyper-local weather monitoring and forecasting. I for one see this contributing to a next-level HUD for a car windshield.
“There is a huge need for printing of electronic devices that are extremely inexpensive but provide simple computations and interactive functions,” says A. John Hart, senior author. “Our new printing process is an enabling technology for high-performance, fully printed electronics, including transistors, optically functional surfaces, and ubiquitous sensors.”
To understand the coffee ring problem in greater detail, it’s useful to consider modern semiconductor lithography. While the degree of complexity in a CPU is vastly larger than what you’d find on simple flexible electronics, the principles are the same. The more difficult it is to align each circuit or path with precisely where you want it to be, the less complex any given circuit design can be. One of the key problems that has held up the production of circuit printing in these kinds of markets is cost — we have technologies that allow for simple circuit printing at a high degree of precision, but they aren’t cheap enough for the kinds of projects that the MIT team envisions. Projects like this could be one way to bridge this gap going forward, because they combine a lower-cost manufacturing process with higher precision than has previously been available.
