Unprecedented advancement in technology and electronics, in recent years, has left buyers with far too many options to choose from, especially in the case of portable devices. Most of these gadgets are made from non-biodegradable and non-recyclable materials, and often contain toxic substances, like gallium arsenide (GaAs). To tackle the prevailing environmental problem, a team of researchers has come up with an innovative solution in the form of semiconductor chips built almost entirely using wood.
Today, the consumer race rat to own the current most sought-after gadget is one of the primary causes behind the growing e-waste problem. As many as 142,000 computers and nearly 426,000 cell phones are discarded every day in the U.S. alone. Of these, many are still in perfect working condition. In addition to the increasing volume of trash, the toxicity of electronic scraps is gradually becoming a major environmental concern. As part of a collaboration between Madison-based U.S. Department of Agriculture Forest Products Laboratory (FPL) and the University of Wisconsin-Madison, the team, led by Zhenqiang “Jack” Ma, a professor of electrical and computer engineering, has devised a technique for building biodegradable microwave chips using nano-sized wood fibers. Ma said:
The majority of material in a chip is support. 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.
The research was published, in May, in the Nature Communications journal. In an attempt to do away with the non-biodegradable GaAs, silicon and petroleum-based substrates present in most electronic devices, the scientists fashioned sustainable, “green” chips, out of a special type of paper called cellulose nanofibril (CNF). Unlike regular paper, which usually contains 10-micrometer-thick wood fibers, the CNF substrate is made up of significantly smaller fibers. Speaking about the breakthrough, Ma added:
If you chop down the wood into nanosize fibers, you find that the fibers are single crystals. If you put this material together to make a substrate, it becomes very strong—stronger than the paper we use. It also becomes transparent and has low RF energy loss.
To construct the CNF-based microchips, the researchers selected a number of gadgets containing GaAs and silicon substrates. Following that, they removed the circuits from the original contraptions and transfer-printed them onto the specially-designed nanofibril substrates. By doing so, the team managed to create several eletronic devices, featuring the green “paper” chips, like GaInP/GaAs heterojunction bipolar transistors, RF inductors, Schottky diodes and others. According to the scientists,the efficiency of these flexible, eco-friendly devices is almost at par with the existing technology. Shaoqin “Sarah” Gong , a biomedical engineering professor at UW-Madison and a member of the research team, said:
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. And, compared to other polymers, CNF actually has a relatively low thermal expansion coefficient.
Two of the main drawbacks, when using wood-based materials in electronics, are the lack of proper surface smoothness and uniform thermal expansion. Additionally, wood is known for being hygroscopic, and therefore, attracts moisture from the atmosphere quite easily. This in turn causes it to expand further. By incorporating a layer of epoxy coating, the team made the CNF substrate smooth as well as impervious to moisture. According to the researchers, technology could be used as an alternative to non-biodegradable silicon and GaAs-based electronic devices. Furthermore, the nanofibril chips could be used in photovoltaic cells, and also in displays. Ma said:
Mass-producing current semiconductor chips is so cheap, and it may take time for the industry to adapt to our design. But flexible electronics are the future, and we think we’re going to be well ahead of the curve.