The next time you upgrade your smartphone, imagine tossing your old iphone into the woods like an apple core. As e-waste piles up around the world, engineers are looking at creative ways to minimize or eliminate the hazardous components that make up popular electronic devices. Researchers from the University of Wisconsin-Madison have now developed microwave thin-film transistors derived from wood that could lead to biodegradable computer chips in the future.
The team of biomedical and electrical engineers demonstrated the feasibility of replacing the silicon wafers of computer chips with cellulose nanofibril (CNF), a transparent, flexible, and sustainable material made from trees. The natural material has several advantages over the petroleum-based substrates that are typically used in today’s electronic devices. Switching to a biodegradable material would be much better for the environment, but that’s not the only reason researchers are excited about CNF chips. It turns out that CNF has a relatively low thermal expansion coefficient and is an excellent candidate for flexible electronics.
Although silicon is still the active material in the new transistor, the bulk of the chip is made of cellulose. Researcher Zhenqiang “Jack” Ma said, “The majority of material in a chip is support—we only use less than a couple of micrometers for everything else. Now the chips are so safe you can put them in the forest and fungus will degrade it. They become as safe as fertilizer.” To create the compostable devices, researchers glued silicon nanomembranes thinner than a human hair onto the wood-based substrate. Then, they had to solve two essential challenges with using a natural material in electronics: surface smoothness and thermal expansion. By applying an epoxy coating to the surface of the CNF, they ensured that the transistor would stay smooth and would not expand or shrink when exposed to heat or moisture.
In a paper published May 26, 2015, in the journal Nature Communications, the researchers showed that their environmentally-friendly transistors performed as well as existing devices. This work could be the foundation of sustainable flexible electronics in the future. Next, the University of Wisconsin-Madison team is working on a more complicated circuit system based on the biodegradable transistors.