Yei Hwan Jung/Wisconsin Nano Engineering Device Laboratory

Computer chips made of wood promise greener electronics

U.S. and Chinese researchers have developed semiconductor chips that are nearly entirely made out of wood-derived material.
Aside from being biodegradable, the chips could be produced for only a fraction of the cost of conventional semiconductors, according to the group of 17 researchers, mostly from the University of Wisconsin-Madison with others from the U.S. Department of Agriculture.
The researchers used a cellulose material for the substrate of the chip, which is the part that supports the active semiconductor layer. Taken from cellulose, a naturally abundant substance used to make paper, cellulose nanofibril (CNF) is a flexible, transparent and sturdy material with suitable electrical properties.
That makes CNF better than alternative chip designs using natural materials such as paper and silk, they argue in a paper published in the journal Nature Communications
The researchers coated the CNF with epoxy to make its surface smooth and to prevent it from expanding as it heated. They also developed methods to fabricate gallium arsenide-based microwave devices, which are widely used in mobile devices such as phones and tablets, on the CNF substrate.
The CNF chip features “high-performance electronics that are comparable to existing state-of-the-art electronics,” they wrote.
Gallium arsenide is listed as a carcinogen by the California government, and is dangerous due to the presence of arsenic. It is expensive to chemically extract from discarded gadgets, so it is beneficial to limit the amount of it that electronic devices contain, for example by eliminating it from semiconductor substrates.
In a conventional chip, the support substrate is made of the same material as the active layer, but in the CNF chip, only the active layer is semiconductor material, Zhenqiang “Jack” Ma, a UW-Madison electrical and computer engineering professor who led the team, said via email.
“If commercializing the wooden chips, tremendous material cost will be saved,” Ma said. “We actually reduced the use of semiconductor material by 99.9 percent.”
The cost of the chips would depend on their applications, he said.
Fungi and moisture that exist in the wild are needed for the chips to begin to decompose, a controllable process that can take anywhere from days to months, Ma added.