If a centuries-old material can undergo an extreme makeover, this is it: wood, a staple in keeping humans warm and sheltered for ages, could soon be found in your smartphone.
Research at the Forest Products Laboratory (FPL) is taking a thrilling turn with the advent of nanocellulose, and Zhiyong Cai, a research materials engineer at FPL, and his partners at the University of Wisconsin-Madison are situated at the forefront of possibility, developing a semiconductor chip made almost entirely of wood.
The research team, led by UW-Madison electrical and computer engineering professor Zhenqiang “Jack” Ma, described the new device in a recently published paper in the journal Nature Communications. The paper demonstrates the feasibility of replacing the substrate, or support layer, of a computer chip, with cellulose nanofibril (CNF), a flexible, biodegradable material made from wood.
“The majority of material in a chip is support. We only use less than a couple of micrometers for everything else,” Ma says. “Now the (new) chips are so safe you can put them in the forest and fungus will degrade it. They become as safe as fertilizer.”
Cai, who has been developing sustainable nanomaterials since 2009, explains that the most common product from broken-down wood is paper, and the dimension of those fibers 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,” says Cai.
Working withShaoqin “Sarah” Gong, a UW-Madison professor of biomedical engineering, Cai’s group addressed two key barriers to using wood-derived materials in an electronics setting: surface smoothness and thermal expansion.
“You don’t want it to expand or shrink too much. Wood is a natural hydroscopic 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 the surface smoothness and the moisture barrier.”
Gong and her students also have been studying bio-based polymers for more than a decade. CNF offers many benefits over current chip substrates, she says.
“The advantage of CNF over other polymers is that it’s a bio-based material and most other polymers are petroleum-based polymers. Bio-based materials are sustainable, bio-compatible and biodegradable,” Gong says. “Compared to other polymers, CNF actually has a relatively low thermal expansion coefficient.”
The group’s work also demonstrates a more environmentally friendly process that mirrors the performance of existing chips. The majority of today’s wireless devices use gallium arsenide-based microwave chips due to their superior high-frequency operation and power handling capabilities. However, gallium arsenide can be environmentally toxic, particularly in the massive quantities of discarded wireless electronics.
Yei Hwan Jung, a graduate student in electrical and computer engineering and a co-author of the paper, says the new process greatly reduces the use of such expensive and potentially toxic material.
The environmental benefits don’t stop there. The Forest Service sees promise in nanocellulose as a means for promoting forest restoration activities. Severely overcrowded forests are at risk for catastrophic wildfires, insect infestation, and disease. The high cost of thinning these forests to a healthy state could be greatly reduced if the material removed can be converted to a high-value material like nanocellulose, which is applicable in countless industries.
The incorporation of these materials will have a positive impact on the environment, and Ma says the flexibility of the technology can lead to widespread adoption of these electronic chips.
“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.”
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