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Materials

Sticking it to the internet of things

Futuristic “smart” decals rely on conventional semiconductor materials and processing, but also 3-D printing

by Matt Davenport
October 17, 2016

Credit: Adv. Mater. Technol.
The flexible circuit sitting at the center of the 3-D printed butterfly sticker relies on some of the same technology that made the less shapely, but more conventional circuit board shown.

The technology of tomorrow will be powered by what’s on hand today if the smart stickers developed by researchers at King Abdullah University of Science & Technology are any indicator.

The researchers combined established semiconductor processing techniques with inkjet and three-dimensional printing to create inexpensive digital decals bearing sensors and data storage electronics (Adv. Mater. Technol. 2016, DOI: 10.1002/admt.201600175). Any object bearing one of these stickers could become an instant, ad hoc environmental monitor or data collector.

For instance, a pressure-sensitive sticker stuck to a mattress could help restless sleepers document their tossing and turning, explains Muhammad M. Hussain, who led the team that developed the smart decals. But the possibilities are vast for the stickers in the emerging frontier known as the internet of things, he adds.

The internet of things refers to the growing collection of everyday items elevated to “smart” status with circuitry to collect and transmit data, including dolls, flower pots, air-handling systems, and more.

But creating simple stickers to fit into this futuristic vision required using well-established protocols from the silicon semiconductor industry. The team first used standard cleanroom techniques—including photolithography, metal sputtering, and atomic layer deposition—to create data storage circuits from zinc oxide, aluminum oxide, and silicon. Similar techniques yielded separate aluminum-based electronics to act as sensors for humidity or pressure. Making all these circuits microscopically thin ensured they would be flexible, but also fragile.

To address this frailty, the team turned to a less mature technology. A commercial 3-D printer created flexible and custom-shaped polylactic acid enclosures to protect a sticker’s electronics. The researchers also “printed” additional wires to complete electrical connections with an inkjet printer and a conductive silver ink.

Still, it’s the team’s incorporation of standard semiconductor materials and processes that Zhenqiang (Jack) Ma finds most noteworthy. Ma leads Wisconsin Nano Engineering Device Laboratory at the University of Wisconsin, Madison, and was not involved in the study. By using standard semiconductor materials and processes to create their smart stickers, Hussain and his team have developed “decal electronics that can be easily spread into practical applications,” Ma says.

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