In a paper published in the journal Nature Communications, Zhenqiang "Jack" Ma, a University of Wisconsin-Madison professor of electrical and computer engineering, explains how he and his collaborators constructed a functional microwave amplifier circuit on a substrate of cellulose nanofibril paper, a wood product.
Microwave components, which are used in wireless communication, have proved difficult to produce in a flexible form and are typically constructed on integrated semiconductor chips or printed on circuit boards. But flexible versions, including thin-film transistors and other components Ma has been creating for more than a decade, could have widespread applications in wearable devices, drones and as part of large-area microwave arrays used in 5G wireless networks and advanced communication systems.
Previous attempts to produce flexible microwave amplifiers used rigid semiconductor-based integrated circuits that were thinned down and moved to flexible substrates, a cost-prohibitive approach.
In the new amplifier, Ma and his colleagues began with cellulose nanofibril paper as the substrate. In recent years, Ma has collaborated with researchers from the U.S. Department of Agriculture Forest Products Laboratory in Madison, and from the Wisconsin Institute for Discovery to assess the feasibility of using the material as a substrate for flexible electronic circuits. The paper is made by breaking wood fiber down into nanoscale fibrils, or tiny slender fibres, then recombining them to produce a strong, flexible, transparent and biodegradable film.
And, instead of layering the entire wood substrate with expensive gallium nitride, currently the highest performing microwave transistor material, the team used just a speck of the compound.