A Penn State-led research team may have discovered a means to circumvent the obstacle inhibiting the development of genuinely elastic electronic systems, the type required for improved human-machine interfaces, artificial skins, smart health care, and more.
A diagram of a curvature-adjustable imager built with stretchable electronics that use n-type semiconductors sandwiched in between elastomers to limit the semiconductors’ typical brittleness. Image Credit: Cunjiang Yu/Penn State
Fully elastic electronic systems need flexibility and stretchability in every component, according to principal investigator Cunjiang Yu, the Dorothy Quiggle Career Development Associate Professor of Engineering Science and Mechanics and Biomedical Engineering at Penn State.
Except for one type of semiconductor that is notoriously fragile, researchers have successfully accomplished this property in the majority of the components. Yu and his international team have now found a strategy to make up for the fragile and breakable semiconductor and move the industry closer to completely flexible systems.
The study was published 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. However, complementary integrated electronics, optoelectronics, p-n junction devices and many others—also require an n-type semiconductor.
Cunjiang Yu, Study Principal Investigator and Dorothy Quiggle Career Development Associate Professor, Engineering Science and Mechanics and Biomedical Engineering, Pennsylvania State University
When combined with p-type semiconductors, N-type semiconductors can function as a switch, allowing current to flow in one way. N-type semiconductors transmit electricity primarily through negative electrons carrying the charge.
According to Yu, since they are frequently stiff, certain techniques to make them more physically stretchy are required to produce fully stretchable transistors and circuits with n-type semiconductors.
To solve this problem, scientists sandwiched an n-type semiconductor between two elastomers, flexible polymers that can be stretched and then returned to their original shape.
Yu added, “We found that the stack architecture improves mechanical stretchability and suppresses the formation and propagation of microcracks in the intrinsically brittle n-type semiconductor.”
According to him, when the n-type semiconductor is stretched, small structural flaws known as microcracks develop.
They could result in mechanical failure and diminished electrical performance.
The stack underwent a series of stress and stability tests, and Yu stated that it passed each one with flying colors. The stack was also utilized to create integrated electronic systems and stretchable transistors.
“The elastic transistors retained high device performance even when stretched 50% in either direction. The devices also exhibited long-term stable operation for over 100 days in an ambient environment,” Yu further stated.
According to Yu, stability in an ambient environment is especially helpful since n-type semiconductors can lose efficiency when exposed to oxygen and moisture. The semiconductor is protected from the elements by being sandwiched between elastomers.
Yu stated that the team would continue to strive to enhance the stack’s performance and optimize the layer arrangement to further lower the density of microcracks.
Yu concluded, “Now we have a stretchy n-type semiconductor, and we will soon have stretchy rubbery integrated circuits. Isn’t it exciting?”
Furthermore, Yu is associated with the Materials Research Institute at Penn State as well as the Materials Science and Engineering Department in the College of Earth and Mineral Sciences. Penn State Department of Engineering Science and Mechanics graduate students Shubham Patel and Seonmin Jang and former postdoctoral researcher Hyunseok Shim, now affiliated with Pusan National University in Korea, co-authored the study.
Other co-authors are Yu’s former students at the University of Houston Kyoseung Sim and Yongcao Zhang; Binghao Wang, Southeast University in China; and Torbin J. Marks and Antonio Facchetti, Northwestern University. Sim is currently associated with Korea’s Ulsan National Institute of Science and Technology. Facchetti is also affiliated with Flexterra Inc.
This study was funded by the National Science Foundation, the Office of Naval Research, the Air Force Office of Scientific Research, and the Materials Research Science and Engineering Center at Northwestern University.
Journal Reference:
Shim, H., et al. (2023) Elastic integrated electronics based on a stretchable n-type elastomer–semiconductor–elastomer stack. Nature Electronics. doi:10.1038/s41928-023-00966-4.
Source: https://www.psu.edu/