Thin, transparent electronic devices small and flexible enough to wrap around a human hair could help lead to smart contact lenses and many other applications on or in the body, researchers say.
Scientists would like the breakthroughs made in electronics over the past century to go into new devices that could improve human health. That’s why research teams around the world are now working on extremely thin electronics that, unlike conventional microchips, are bendable and compatible with the flexible nature of the human body.
Electrical engineer Giovanni Salvatore and his colleagues at the Swiss Federal Institute of Technology in Zurich have developed a simple method for transferring such electronics onto nearly any surface.
(The use of transparent materials enable the realization of transparent devices that can be transferred on to plastic contact lenses and used to monitor intraocular pressure for glaucoma. Photo courtesy Salvatore et al.)
The new technique first involves building thin circuitry onto a 1-micron-thick elastic layer of a polymer known as parylene, whose thinness ensures extreme flexibility. This parylene layer in turn rests on soluble films that sit on a 2-inch-thick silicon wafer used as the rigid support needed during fabrication.
After fabricating the electronics, the entire combination is set floating on water. This dissolves the soluble films, letting the silicon wafer sink and leaving the parylene membrane sitting on top with the circuits embedded on top of it. In experiments, the researchers showed this membrane could then be transferred onto many surfaces, including biological tissues such as human skin and plant leaves.
"We use materials that can be all deposited at large scales and at the same time provide good electrical performance," Salvatore tells Txchnologist. "Large-scale manufacturing combined with a relatively easy fabrication process could be of great interest for industry."
The researchers first started with non-transparent electronics roughly 145 nanometers, or billionths of a meter, thick, making them thinner than any wavelength of visible light. They next moved to slightly thicker transparent electronics some 175 nanometers thick. In both cases, transistors continued to work even when wrapped around human hairs 100,000 nanometers thick.
Wearable and implantable flexible devices could provide details on the health status of patients in real time. “Other applications could be lightweight solar cells, energy scavengers or smart textiles,” Salvatore says.
One initial application might be smart plastic contact lenses covered with light, transparent and flexible electronics that can monitor the pressure inside the eye to keep track of glaucoma. This disease is the second leading cause of blindness globally. Glaucoma is estimated to afflict more than 2.2 million people in the United States.
Salvatore noted that many other research groups in the United States, Japan, Korea and elsewhere are working on the field of thin, flexible electronics, albeit with different materials or fabrication schemes.
"Flexible electronics for wearable or implantable devices is a very promising research field," said he says.
The researchers are now working on ways to improve the electrical performance of the devices — for instance, with new materials and transistors possessing even smaller features. Salvatore and his colleagues detailed their findings online Jan. 7 in the journal Nature Communications.
Top Image: Ultraflexible electronics substrate wrapped around hair. Photo courtesy Salvatore et al.