Diagram of a curvature-adjustable imager built with stretchable electronics that use n-type semiconductors sandwiched between elastomers to limit the semiconductors’ typical brittleness. Image: Cunjiang Yu/Penn State.There’s a barrier preventing the advent of truly elastic electronic systems, the kind needed for advanced human-machine interfaces, artificial skins, smart healthcare and more, but a team led by researchers at Penn State may have found a way to stretch around it.
According to principal investigator Cunjiang Yu, associate professor of engineering science and mechanics and of biomedical engineering at Penn State, fully elastic electronic systems require flexibility and stretchability in every component. Researchers have achieved this characteristic in most electronic components, but not in one type of semiconductor that is notoriously brittle.
Now, Yu and his international team have developed an approach to compensate for this frail and breakable semiconductor to take the field closer to fully flexible systems. They report their advance in a paper in Nature Electronics.
“Such technology requires stretchy elastic semiconductors, the core material needed to enable integrated circuits that are critical to the technology enabling our computers, phones and so much more, but these semiconductors are mainly p-type,” said Yu. “However, complementary integrated electronics, optoelectronics, p-n junction devices and many others – also require an n-type semiconductor.”
N-type semiconductors conduct electricity primarily through the movement of negative electrons, whereas p-type semiconductors conduct electricity primarily through the movement of positively charged ‘holes’ where electrons are missing. In combination, these two types of semiconductor can act as a switch, causing current to flow in one direction. N-type semiconductors are often rigid, and strategies to make them more mechanically stretchy are needed to achieve completely stretchable transistors and circuits.
To address this issue, the researchers sandwiched an n-type semiconductor between two rubbery materials known as elastomers, which are polymers that can stretch and snap back to their original shape.
“We found that the stack architecture improves mechanical stretchability and suppresses the formation and propagation of microcracks in the intrinsically brittle n-type semiconductor,” Yu said, explaining that microcracks are tiny structural defects that appear when the n-type semiconductor is stretched. They can degrade electrical performance and lead to mechanical failure.
The team put the stack through a gauntlet of stress and stability tests, all of which it passed with flying colors. They also used the stack to fabricate stretchy transistors and integrated electronic systems.
“The elastic transistors retained high device performance even when stretched 50% in either direction,” Yu said. “The devices also exhibited long-term stable operation for over 100 days in an ambient environment.”
According to Yu, this stability in an ambient environment is particularly useful, because n-type semiconductors can lose efficiency on exposure to oxygen and moisture. Sandwiched between elastomers, however, the semiconductor is effectively encapsulated against the elements.
Next, Yu said, the team will continue to work to improve the performances of these stacked materials and optimize the layer configuration to further reduce the density of microcracks.?
“Now we have a stretchy n-type semiconductor, and we will soon have stretchy rubbery integrated circuits,” Yu said. “Isn’t it exciting?”
This story is adapted from material from Penn State, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.