A group of electrical and computer engineers say they’re on track to create computer chips that are almost entirely biodegradable. But is this really plausible? According to the team, the answer is "yes."
In collaboration with the U.S. Department of Agriculture’s Forest Products Laboratory (FPL), engineers at the University of Wisconsin-Madison are developing a semiconductor chip consisting mostly of cellulose nanofibril (CNF), which is a flexible and biodegradable material derived from wood.
"The majority of material in a chip is support,” explained Zhenqiang “Jack” Ma, a UW-Madison electrical and computer engineering professor. “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."
Solving the thermal expansion issue
Ma teamed up with Zhiyong Cai, a project leader for an engineering composite science research group at FPL, who’s been working on sustainable nanomaterials for the past five years. “If you take a big tree and cut it down to the individual fiber, the most common product is paper,” Cai said. “The dimension of the fiber is in the micron stage. But what if we could break it down further to the nano scale? At that scale you can make this material, very strong and transparent CNF paper."
Some of the key issues with using wood involve thermal expansion and surface smoothness. But with the help of Shaoqin “Sarah” Gong, a UW-Madison professor of biomedical engineering, Cai’s team solved these problems. "You don't want it to expand or shrink too much,” Cai said. “Wood is a naturally hydroscopic material and could attract moisture from the air and expand. With an epoxy coating on the surface of the CNF, we solved both the surface smoothness and the moisture barrier."
The advantages of CNF
According to Gong, CNF boasts a number of advantages over traditional chip substrates. "The advantage of CNF over other polymers is that it's a bio-based material and most other polymers are petroleum-based polymers,” she said. “Bio-based materials are sustainable, bio-compatible and biodegradable. And compared to other polymers, CNF actually has a relatively low thermal expansion coefficient." The engineers say their biodegradable chip performs similar to existing ones. The difference is it doesn’t contain gallium arsenide, which can be quite toxic in mass quantities.
"I've made 1,500 gallium arsenide transistors in a 5-by-6 millimeter chip,” said Yei Hwan Jung, an electrical and computer engineering graduate student. “Typically for a microwave chip that size, there are only eight to 40 transistors. The rest of the area is just wasted," he says. "We take our design and put it on CNF using deterministic assembly techniques, then we can put it wherever we want and make a completely functional circuit with performance comparable to existing chips."
Mass production
Although it’s still in its early stages, Ma hopes his device will eventually be embraced by the industry. "Mass-producing current semiconductor chips is so cheap, and it may take time for the industry to adapt to our design," he says. "But flexible electronics are the future and we think we're going to be well ahead of the curve."
A detailed account of the group’s research was recently published in the journal Nature Communications. For more information, visit the University of Wisconsin-Madison’s website.
Do you think this device is plausible? Would issues such as mold and potential fires arise? Let us know what you think by commenting below.