November 27, 2012
Researchers Create Flexible Nano-Sized Electronic Circuits
Michael Harper for redOrbit.com — Your Universe Online
Scientists have been finding ways to shrink electronic circuits ever since they were first invented. But no matter how small these circuits get, they´ve been largely confined to rigid surfaces, typically silicon.Now, one University of Pennsylvania team have set out to free the electronic circuit from its stiff and rigid existence and, just as many other researchers have been doing in recent years, they looked to nanomaterials to do it.
A flexible circuit could open up a world of electronic possibilities, allowing for even more applications and more opportunities.
Opting to use nanocrystals, the University of Pennsylvania team were able to “print” the important elements of a circuit on a thin, flexible piece of plastic. What´s more, this new process even allows these circuits to be made at room temperature, as opposed to using high heat to form these electronics.
David Kim, a doctoral student in the Department of Materials Science and Engineering and Cherie Kagan, who studies in both the Electrical and Systems Engineering department, as well as the arts and sciences department, led this research with the help of their team.
“We have a performance benchmark in amorphous silicon, which is the material that runs the display in your laptop, among other devices,” explained Kagan in a statement.
“Here, we show that these cadmium selenide nanocrystal devices can move electrons 22 times faster than in amorphous silicon."
These nanocrystal devices aren´t just faster; being able to imprint them at room temperature is also significant, as it means they can be used on heat-sensitive plastics, making even more surfaces a potential candidate to become a circuit.
By opening up the possibility of flexible plastics, Kagan, Kim and colleagues also found they could use a different chemical, or ligand, to facilitate connectivity once these nanocrystals are placed on a surface.
“There have been a lot of electron transport studies on cadmium selenide, but until recently we haven´t been able to get good performance out of them,” said David Kim.
“The new aspect of our research was that we used ligands that we can translate very easily onto the flexible plastic; other ligands are so caustic that the plastic actually melts.”
The team also had some options when implanting these nanocrystals on plastics. According to Kagan, these crystals are suspended in an ink-like liquid. The team used spin-coating--which uses centrifugal force--to apply the inky crystals onto the plastic, though they noted these crystals could also be applied through dipping, spraying or even printed through an ink-jet printer.
These circuits were built in steps, first by placing electrodes on the bottom of the plastic. Then, the team defined where on the circuit gold should be used to conduct electricity between the bottom and top layers. Aluminum oxide is then applied as an insulter with a thin layer of the nanocrystals. More electrodes were placed on top to finally form the circuits.
“The more complex circuits are like buildings with multiple floors,” Kagan said. “The gold acts like staircases that the electrons can use to travel between those floors.”
The team built three kinds of circuits using these nanocrystals; an amplifier, an inverter and a ring oscillator.
“All of these circuits operate with a couple of volts,” said Kagan. “If you want electronics for portable devices that are going to work with batteries, they have to operate at low voltage or they won´t be useful.”