Engineers create wood-based electronics circuits

July 2, 2015

By: CNBC

It’s hoped that the development could someday help reduce the environmental impact from America’s growing volume of discarded electronics. The flexible and transparent circuit also can be used in wearables and “smart” textiles.

Consumers in the United States threw away 2.37 million tons of electronics in 2009, the most recent year for which data are available, and the country only recycled about 25 percent of that total, according to EPA estimates. About 152 million mobile phones were thrown away in that year alone. And that was in 2009.

“Many more gadgets may be discarded daily, considering the larger quantities and more varieties being produced in the recent years,” the engineers wrote Tuesday in the journal Applied Physics Letters. “This will not only lead to a large amount of consumption of our limited natural resources, but also generate a large amount of waste that could pollute our environment.”

Part of the problem with e-waste stems from types of materials used. For instance, the silicon or gallium arsenide-based chips that make up much of the guts of electronics contain materials that do not decompose well and can leach chemicals into soil and water supplies.

“If you open up a mobile phone, you have a battery and you have chips,” said Zhenqiang Ma, one of the authors on the study. “The hardest things to recycle are the chips themselves.”

Another route to reducing e-waste, and to conserving potentially precious ingredients, may lie in developing biodegradable alternatives.

Silicon chips, for example, use much more silicon than they actually need, the researchers say. A standard 12-inch silicon wafer is about 775 micrometers thick, but only a tiny fraction of that thickness—one micrometer—is actually used by circuits. The rest of the wafer just provides physical support for the circuits—which is really a waste of silicon, Ma said.

Ma and his colleagues at the University of Wisconsin and the USDA Forest Products Laboratory used a substrate made out of wood pulp, called “cellulose nanofibrillated fiber,” and combined it with only the thinnest layer of silicon needed for the transistors that do the work on chips.

Cellulose nanofibrils have been around and used in other applications, but Ma and his team have demonstrated that the material can work at the frequencies that would make it useful for use in wireless devices.

The scientists say their material performed as well as conventional chip materials in their tests, and can biodegrade naturally over the course of several weeks with the help of fungi that are common in nature. The amount of silicon used is so minimal that it’s far below the limits set by the Environmental Protection Agency, Ma told CNBC.

By: CNBC

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