The Far-Out World of Nanofibril for Biodegradable Microchips

Jun 6th, 2015 8:39am by Kimberley Mok

Electronic waste is a growing problem worldwide. Could biodegradable microchips and electronics be the solution?

Many consumer gadgets — from smartphones to laptops — are designed with planned obsolescence in mind. It shortens the replacement cycle, and when combined with slick marketing techniques, places consumers on a constant hamster wheel, hankering after the latest gadgets which will be outdated in a few months time — a seemingly endless cycle that also conveniently increases profits for manufacturers.

But the toll on the environment is even more severe: according to the Electronics TakeBack Coalition, 50 million tons of electronic waste is globally generated each year, contaminating soils and water with toxins and heavy metals. The e-waste recycling industry is still far from efficient, and it’s projected that it will get worse before it will get better. E-waste from industrialized countries is also being illegally dumped in developing nations, where electronics recycling often exists in an informal and unregulated capacity.

Cellulose Nanofibril to the Rescue

It’s a disaster that unfolds out of sight, out of mind — but is unfolding nonetheless. With the aim of slowing this environmental and public health train wreck, scientists from University of Wisconsin, in collaboration with the US Department of Agriculture Forest Products Laboratory, are developing a semiconductor material based out of wood. Yes, wood — or more precisely, nano-scaled cellulose. Instead of using petro-chemically based materials that do not biodegrade, the researchers looked at the feasibility of using bio-based, biodegradable and flexible cellulose nanofibril papers to create microchips that could someday fertilize soil. Electrical engineering professor Zhenqiang Ma, who led the study that was published in “Nature” last week, explains that there is an inefficient use of non-biodegradable materials in current microchips:

In a typical semiconductor electronic chip, the active region comprises the top thin layer and is only a small portion of the chip, whereas the bottom substrate that holds the chip consists of more than 99 percent of the semiconductor materials. In microwave chips for wireless functions, besides the waste of the bottom substrate, only a tiny fraction of the lateral chip area is used for the required active transistors/diodes with the rest being used only for carrying other non-active components.

A more environmentally friendly microchip would be made out of cellulose nanofibril (CNF), a nano-scaled material consisting of cellulose fibers. At this scale, this abundantly available organic polymer is very strong, flexible, and transparent, exhibiting properties that are even “pseudo-plastic.” However, cellulose is susceptible to moisture and expansion, but this problem would be solved with an extra coating, says study co-author Zhiyong Cai: “With an epoxy coating on the surface of the CNF, we solved both the surface smoothness and the moisture barrier.”

The paper describes how these biodegradable microchips would be made: “Fully formed electronic devices can be fabricated on a sacrificial material in a dense array format, where each micro-scale device can be released and transfer printed onto any type of substrate, including biodegradable flexible substrates.”

Fast and “as Safe as Fertilizer”

Researchers have been looking into alternatives to conventional semiconductor materials for several years now, but CNF is particularly promising, compared to synthetic polymers and silk, which are vulnerable to water and solvents. In addition, organic electronics made out of CNF perform much better than other substitutes, says Ma: “There have been other organic electronics but nothing that matches the operating speed that this chip [is capable of].” Moreover, CNF can be broken down by fungi, and is bio-compatible, meaning that it can function in intimate contact with living tissue, meaning that CNF materials could also have applications in the medical industry.

But first and foremost, the implementation of CNF as a semiconductor material will reduce the use of carcinogenic gallium arsenide (GaAs) in electronics. “It is impossible to find an alternative to gallium arsenide,” says PhD student Yei Hwan Jung, one of the authors of the paper. “But we have made the [CNF] semiconductors so thin that the amount used meets the EPA standard required for drinking water.”

Despite the obvious advantages of a biodegradable microchip, it will take manufacturers some time to incorporate new, sustainable materials like CNF. But a future where electronic waste is eliminated would be worth it, asserts Ma: “Now the [CNF] chips are so safe you can put them in the forest and fungus will degrade it. They will become as safe as fertilizer.”