Stretchable rubber diode opens up possibilities for medical and electronic devices

Fully rubbery Schottky diode. (A) An illustration of the morphology of the rubbery semiconductor composed of P3HT-NF and PU. (B) An optical image and a microscopic image of the P3HT-NFs/PU composite film. (C) Schematic illustration in an exploded view of the fully Schottky diode. (D) Optical images of the diode under the mechanical stress of 0 and 30%. (E) An optical microscopic image of the diode. (F) IV characteristics of the rubbery Schottky diode under the mechanical stress of 0, 10, 20 and 30%. (G) Energy levels of AgNW, AuNP, P3HT-NF and liquid metal. (H) Illustration of the energy band diagram of the Schottky junction based on metal (liquid metal) and p-type semiconductor (P3HT). LUMO, the lowest unoccupied molecular orbital; HOMO, the highest occupied molecular orbital. Credit: Scientists progress (2022). DOI: 10.1126/sciadv.ade4284

If you’re reading this article on your computer or phone, it’s partly thanks to diodes. Diodes – typically rigid electrical components that easily conduct electrical current in one direction – are used for a variety of critical electronic functions, from converting AC to DC current and converting mechanical energy to electrical for service switching component that enables digital displays and more. Electronic devices, such as robotics or medical devices, are becoming more flexible as technology advances, so Penn State researchers have developed an all-rubber stretch diode that maintains performance.

The team published their results in Scientists progress.

“This diode is made entirely from stretchable rubber materials – this rubber material strategy is key,” said corresponding author Cunjiang Yu, Dorothy Quiggle Career Development Associate Professor of Engineering Science and Mechanics and Associate Professor biomedical engineering and materials science and engineering. . His group has already developed other rubbery electronic materials, such as transistors. “By creating a rubbery diode, we have added to our rubbery electronics library so that we can get closer to making circuits and integrated electrical systems entirely from rubbery materials.”

More flexible devices may behave more like biological tissue, allowing for better bio-integrated devices, according to Yu. An example may be a flexible patch device that could be implanted over the heart.

“A heartbeat will generate electrical signals,” he said. “With a rubbery diode, a device could convert alternating current to direct current in the body, which is currently not possible.”

To achieve such electrical performance while mechanically stretched, Yu said, the researchers rationally considered the device’s architecture, vertical structures and layout. In addition to the benefits for more flexible medical devices, the development also has implications for power management systems from these medical devices to standalone systems.

“Energy harvested from harvesters always needs to be rectified before the energy is stored for use – and that’s important in many emerging fields,” Yu said.

Yu gave the everyday example of light-up sneakers, which contain a piezoelectric energy harvester to convert mechanical energy – one step – into electrical energy to light the LEDs. A rectifier circuit converts the harvested AC electricity into useful DC current.

“Researchers and industry are using conventional diodes, but they want something that can be stretched, like what we report in the paper,” he said. “Such rubbery diodes open up many possibilities.”

Yu said the next steps are to further optimize the diode and integrate it into more complex systems.

“We seek to improve diode architectures and performance and achieve unperturbed operations even under very large mechanical stretching or deformation ranges,” he said. “We want to use these diodes to meet critical device needs in various emerging applications such as robotics and biomedical devices.”