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Electronics that vanish without a trace

Resorb circuits US researchers have developed a new kind of electronic device that dissolves in fluids.

A vanishing electronic may not be desirable in smartphones or tablets, but it could improve environmental sensors and bio-compatible medical implants that need to function in wet, hot or cold places typically unfriendly to electronics.

Instead of making electronics extra resilient to last forever, the team of scientists designed computer parts that disappear after their function is complete.

"Usually the device operates in a diagnostic or therapeutic mode as a wound is healing or as a broken bone is mending," says Professor John Rogers of the University of Illinois, co-author of the paper appearing today in the journal Science.

"It became obvious that maybe one way to deal with the problem of long-term biocompatibility is just to avoid it entirely - just make the device resorb, disappear and dissolve in the body after its useful lifetime is already served," he says.

Rogers calls the technology "transient electronics."

The researchers started with silk-coated silicon to make thin nanomembranes, which they used as semiconductors; magnesium for electrodes and interconnects, and magnesium oxide for gates and interlayer dielectrics. Each element used amounted to less than the recommended daily allowance.

Being naturally occurring elements helped the electronics do their vanishing act, but their ultra-thinness played a big role as well. Normally it takes silicon a long time to dissolve - hundreds of years for a silicon wafer. But the nano-membranes used in this project were thin enough to disappear in days or weeks.

A coating, made of dissolved and recrystallised silk, kept the membrane from dissolving too fast. In fact, the thickness of the silk coating can be controlled, making it possible to tune the transient device's lifespan for a specific application.

Other applications

"Once you start thinking about devices that dissolve and disappear in the body, the next place your mind turns to is the environment," says Rogers.

Environmental monitors could be used in a variety of ways, for example after a chemical spill or to collect weather data or air quality measurements. Sensors could even be built into computer devices to track electronic waste.

"If you think of applications like environmental monitors, it's hard to find the manpower to go out and get data," says Professor Yonggang Huang, a civil and mechanical engineer at Northwestern University.

"This way, you can read the device, monitor the environment for three months, six months or one year and then the device dissolves by itself. It doesn't have any long-term adverse effect of the environment."

Among the transient electronic devices or components the teams created were transistors, diodes, wireless power coils, temperature and strain sensors and most impressively, a 64-pixel digital camera.

"It's fully transient. Everything fully dissolves in water or biofluids," says Rogers. "It consists of an array of silicon based photo detectors and silicon diodes. It's in a layout that allows us to do matrix-based addressing, which is behind the scheme that you would ultimately need to employ for a high-resolution imager."

As of now, it remains a tiny system that bears no resemblance to what we commonly think of as a camera.

But for now, Rogers and his team are focused on more tangible goals, such as finding manufactures to balance and tackle the engineering challenges that such a delicate process requires.

The researchers are poised to make their case that, despite their impermanence, transient electronics may be here to stay.