There is an ever-growing pile of discarded electronic devices that either don’t work anymore or have been cast away in favor of a newer model. Part of the problem is that electronic devices are difficult to recycle. While scraps of copper, aluminum, and steel can be recycled, the silicon chips at the heart of the devices cannot.
Engineers now have developed a completely recyclable, fully functional transistor made out of three carbon-based inks that can be easily printed onto paper or other flexible, environmentally friendly surfaces. Carbon nanotubes and graphene inks are used for the semiconductors and conductors, respectively. While these materials are not new to the world of printed electronics, the path to recyclability was opened with the development of a wood-derived insulating dielectric ink called nanocellulose.
The team developed a method for suspending crystals of nanocellulose that were extracted from wood fibers that — with the sprinkling of a little table salt — yield an ink that performs admirably as an insulator in printed transistors. Using the three inks in an aerosol jet printer at room temperature, the team showed that the all-carbon transistors perform well enough for use in a wide variety of applications, even six months after the initial printing.
By submerging the devices in a series of baths, gently vibrating them with sound waves, and centrifuging the resulting solution, the carbon nanotubes and graphene are sequentially recovered with an average yield of nearly 100%. Both materials can then be reused in the same printing process while losing very little of their performance viability. And because the nanocellulose is made from wood, it can simply be recycled along with the paper it was printed on.
Compared to a resistor or capacitor, a transistor is a relatively complex computer component used in devices such as power control or logic circuits and various sensors. The technology could be used in a large building needing thousands of simple environmental sensors to monitor its energy use or customized biosensing patches for tracking medical conditions.