Duke University Engineers Develop World's First Recyclable Printed Transistor

If you're anything like most people in the West, you upgrade to a new smartphone every two years. Your computers, TVs, and other devices likely don't last much longer. We live in a world full of devices designed for planned obsolescence and most of those devices end up as garbage, because they aren't easy to recycle. Some components of electronic devices are recyclable, but harvesting them is difficult. Other components can't be recycled at all. In an effort to increase the sustainability of device manufacturing, Duke University engineers developed the world's first recyclable printed transistor.

A transistor is the most basic building block of all digital computing. Transistors act like tiny switches and enable Boolean logic, which is the basis of every operation a computer performs. CPUs, GPUs, and many other components contain millions of transistors. The Apple A14 Bionic SoC (System On a Chip), used in the iPhone 12, contains a whopping 11.8 billiontransistors. Unfortunately, most transistors have silicon insulators and are impossible to recycle. That means that we have an ever-growing pile of electronic components that are obsolete but that can't be reused or harvested for resources.

That's why this development is so important, because these transistors are recyclable. The engineers constructed their transistors by printing special inks onto paper substrates. One ink, made from carbon nanotubes, acts as the semiconductor material. A second ink, made from graphene, acts as the conductor material. The final ink, which is the key development here, is the insulator. That ink is made from nano cellulose, which is processed from natural plant fiber. An inkjet printer sprays those inks on the paper substrate in the correct pattern to form a functional transistor.

When it comes time to recycle one of these transistors, the paper substrate goes through a series of chemical baths and a centrifuge ride to separate out the carbon nanotubes and graphene. Those are reusable. All that gets left behind is the paper substrate and the nano cellulose, both of which are biodegradable. While these transistors are still far too large and expensive to be practical, this research is incredibly important for paving the way for devices that are truly sustainable.