Stanford Researchers Develop Flexible, Biodegradable Semiconductor

bio semiconductor

Engineers have gotten quite good at designing ever more powerful and advanced electronics, but we’re not so good at properly disposing of them when they’re out of date. The United Nations Environment Program estimates almost 50 million tons of electronic waste will end up in landfills this year, a 20 percent increase over last year. With that troubling statistic in mind, Stanford engineer Zhenan Bao and her team set out to design a new type of semiconductor that could simply biodegrade when it’s no longer needed.

The key to this new semiconductor is a polymer that degrades into harmless organic molecules. It won’t just fall apart while you’re using it, though. The material only decomposes when exposed to a weak acid, for example vinegar (dilute acetic acid). Before that, it’s a flexible sheet that can bend and stretch to fit almost any given structure. This required the use of other specialized components, though. It wouldn’t be any good if the semiconductor was flexible but the rest of the board wasn’t.

The biodegradable polymer was the most challenging bit of the project — it’s not easy from a chemistry perspective to develop a polymer that is both conductive and can decompose safely. Past materials designed by Bao’s team have been flexible, but biodegradable and flexible was a tough nut to crack. The solution was to use a special type of chemical linkages between polymer subunits called reversible imine bonds. The application of a weak acid causes these bonds to break and the polymer to decompose.

biodegrading

In addition to the biodegradable polymer, the proof-of-concept circuit built in the lab made use of experimental electrical components and substrate materials. Electrical components are often made from gold, but this board used iron. That’s a more environmentally friendly metal to release when the polymer breaks down. The substrate is composed primarily of cellulose, a naturally occurring polymer that gives plants structure; just like it does here for the biodegradable semiconductor. These cellulose fibers were modified to be transparent and break down more easily.

The team sees this design as a potential replacement for the rigid boards used in wearables and in scientific field work. Bao envisions flexible patches that contain embedded processing and sensors that could simply be disposed of after a few days. For scientists, micro-computers based on this technology could be spread around an area to conduct environmental research without worrying about collecting them again later. It’s still a long way from being a commercial product, so for the time being you’ll have to keep recycling your old electronics.

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