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Virtually imperceptible, light-as-a-feather electronic systems could next be hosted on human skin. New advances in electronic foils have yielded products that are virtually unbreakable and conformable to any shape, including wrinkles in the skin. Electronic devices will no longer need to be carried along but, instead, will be rendered as an indistinguishable layer on the skin.
This is a far cry from our hefty and hulking electronic origins, like wood-cabinet, RCA console televisions. Electronics are now smart, of course, and highly mobile appliances. However, in the abyss of high technology, good is never good enough. Today’s devices are not yet extremely mobile because they remain rigid, keeping them from what will be a delight for some and abhorrent to others – a truly intimate integration of electronics onto, and into, our bodies.
Electronic foils are quickly moving toward the mainstream, a technology not only envisioned for mobile, wearable devices but also with biomedical applications. The foils consist of organic transistors, which have an added possibility of being biodegradable. Once deposited on very lightweight plastic film, the overall thickness is just two micrometers, or about one-fifth the thickness of household plastic wrap. Researchers say that electronic foils may one day be just as common.
The sheets are thirty times lighter than office paper and can be crumpled tightly without harming the circuits. Moreover, given that the plastic films come in huge rolls, they can be fabricated on a large scale and inexpensively. Electronic foils conform to dynamic environments, taking repeated and severe stretching and bending, working at elevated temperatures and likely under water.
In February 2013, researchers at Northwestern University and the University of Illinois at Urbana-Champaign published the report “Stretchable batteries with self-similar serpentine interconnects and integrated wireless recharging systems,” detailing their development of stretchable batteries. This paved the way for the newly-announced generation of flexible electronics. Stretchable electronic devices could now be available for use anywhere, including inside the human body, where they could help monitor brain waves or heart activity.
Enter engineer Martin Kaltenbrunner and his team at the University of Tokyo. With the power problem solved, they could continue their work on the next electronic systems, those that could integrate with skin. “You cannot really wrap current flexible electronics around anything,” he says. “But if they were really thin, they could even go into the wrinkles of your skin.
The team set out knowing what they wanted: Inexpensive, super-thin, bendable circuits that can be fabricated over large areas. Using processes not-at-all revolutionary in the semiconductor industry (such as chemical vapor deposition and vacuum evaporation) Kaltenbrunner et al put integrated organic circuits onto ultrathin plastic films, also known as polymer foils.
After the researchers built their thin transistor, they then unified it with a tactile sensor that easily conforms to uneven surfaces, such as the roof of a person’s mouth. “If you imagine a person that cannot communicate with anything but their tongue, this would be a nice interface,” Kaltenbrunner says. “They could give yes or no answers by touching different spots of the sensor, and the device can conform so nicely that it wouldn’t be painful to wear.”
Kaltenbrunner continues: “I really like the idea of making thin-film plastic electronics that you can place on everything. We are getting really close to what I’ve seen in sci-fi movies, where you just touch a surface and it does something.”
Another use for a sensor of this type will be as artificial skin for the next electronic systems like robots, which will give them touch sensitivity. Other possibilities include organic solar cells, thin-film heaters, matrix-addressed tactile sensor foils for health care and monitoring, temperature and infrared sensors and displays.
By Gregory Baskin