A 99% biodegradable computer chip

May 29, 2015

A cellulose nanofibril (CNF) computer chip shown on a leaf (credit: Yei Hwan Jung, Wisconsin Nano Engineering Device Laboratory)

University of Wisconsin-Madison and U.S. Department of Agriculture Forest Products Laboratory (FPL) researchers have jointly developed a wood chip in an effort to alleviate the environmental burden* of electronic devices.

Well, actually, a wood-substrate-based semiconductor chip. They replaced the silicon substrate portion in a conventional chip with environment-friendly cellulose nanofibril (CNF). CNF is a flexible, biodegradable material made from wood, as the researchers note in an open-access paper published May 26 in the journal Nature Communications.

“[More than 99%] of the material in a chip is support,” said Zhiyong Cai, project leader of an engineering composite science research group at FPL. With the new substrate, the chips are “so safe you can put them in the forest and fungus will degrade it. They become as safe as fertilizer.”

The new material is especially important for microwave chips (such as those used in mobile phones) made with gallium arsenide, which is especially difficult to fabricate on foreign substrates. That’s because of the small feature sizes and high temperature processes required for high performance.

Cai’s group addressed two key barriers to using wood-derived materials in an electronics setting: surface roughness and thermal expansion. “You don’t want it to expand or shrink too much. Wood is a natural hydroscopic [water-absorbing] material and could attract moisture from the air and expand,” Cai says. “With an epoxy coating on the surface of the CNF, we solved both [problems].”

* In 2007, it was estimated that over 426,000 cell phones (most of them were still functional) and 112,000 computers were discarded every day in the US, totalling 3.2 million tons of electronic waste generated per year, the researcher note in the paper.

Abstract of High-performance green flexible electronics based on biodegradable cellulose nanofibril paper

Today’s consumer electronics, such as cell phones, tablets and other portable electronic devices, are typically made of non-renewable, non-biodegradable, and sometimes potentially toxic (for example, gallium arsenide) materials. These consumer electronics are frequently upgraded or discarded, leading to serious environmental contamination. Thus, electronic systems consisting of renewable and biodegradable materials and minimal amount of potentially toxic materials are desirable. Here we report high-performance flexible microwave and digital electronics that consume the smallest amount of potentially toxic materials on biobased, biodegradable and flexible cellulose nanofibril papers. Furthermore, we demonstrate gallium arsenide microwave devices, the consumer wireless workhorse, in a transferrable thin-film form. Successful fabrication of key electrical components on the flexible cellulose nanofibril paper with comparable performance to their rigid counterparts and clear demonstration of fungal biodegradation of the cellulose-nanofibril-based electronics suggest that it is feasible to fabricate high-performance flexible electronics using ecofriendly materials.