A semiconductor chip composed of wood

"Most of the material included in a chip is the substrate. We only use a few micrometers for its other components," explains the lead researcher. "Now, the chips are so environmentally safe that you can leave them in the forest and let the fungi break them down

Electronic components included in mobile devices - which are often composed of non-renewable, non-biodegradable and potentially toxic materials - are thrown into the trash at an alarming rate as part of the consumer's pursuit of the most advanced electronic device. Such deposits of electronic waste are a danger in many areas of the world.

As part of the effort to lighten the environmental load of electronic devices, a team of researchers from the University of Wisconsin-Madison managed to develop a surprising solution: a semiconductor chip composed almost entirely of wood. The research findings were recently published in the prestigious scientific journal Nature Communications. The article demonstrates how the usual substrate, or base layer, of a computer chip can be easily replaced with cellulose nanofibers (Wikipedia) - a flexible, biodegradable material obtained from wood.

"Most of the material included in a chip is the substrate. We only use a few micrometers for its other components," explains the lead researcher. "Now, the chips are so environmentally safe that you can leave them in the forest and let the fungi break them down. They become as safe as fertilizers." If you take a large tree and break it down into its individual fibers, the most common product is paper. The dimension of the fiber is at the micron level," explains the researcher. "But what would happen if we broke it down even further to the nanometer level? At that level, you can turn this product into a transparent and very strong paper composed of cellulose fibers."

The researchers faced two main barriers when it came to using wood-based materials in electronic devices: the smoothness of the surface and thermal expansion. “You don't want the material to expand or contract too much. "Wood is a hygroscopic natural material capable of absorbing moisture from the air and expanding," explains the researcher. "By using an epoxy coating on the surface of the cellulose nanofibers, we solved both problems together."

"The great advantage of cellulose nanofibers compared to other polymers lies in the fact that it is a biological material, while the other polymers are polymers based on petroleum and its products. "Biomaterials are sustainable, biocompatible materials that break down biologically," the researcher notes. "Also, compared to other polymers, cellulose nanofibers actually have a relatively low coefficient of thermal expansion."

The researchers also demonstrated a more environmentally friendly process for manufacturing these chips. Most wireless devices today include gallium-arsenide chips due to their improved high-frequency operation and electronic performance. At the same time, the material gallium-arsenide may be toxic to the environment, especially following the disposal of considerable quantities of wireless electronic devices. The researchers succeeded in developing a new process that sharply reduces the use of this expensive and toxic substance. "I was able to place 1500 gallium-arsenide transistors on a chip with an area of ​​5 x 6 millimeters. For a chip of this size, usually only 40-8 transistors are placed. The rest of the area is simply unnecessary," he notes. "We took our design and applied it to cellulose nanofibers using an efficient assembly method, so we are able to place them wherever we want and create a fully active electrical circuit with performance on par with existing chips."

While the ability of these materials to biodegrade will have a positive impact on the environment, the researcher points out that the flexibility of the technology will lead to widespread adoption of these electronic chips. "The current mass production of semiconductor chips is very cheap, so it may be a long time before the industry starts using our design," says the researcher. "However, flexible electronics are the future, and we believe we are very close to getting there."

The news about the study on the website of the University of Wisconsin in Medicine