PNNL Researchers Advance Silky Solution for Microelectronics

Silkworms spin the strong, flexible thread that is used to produce luxurious fabrics for ties, scarves, gowns and pajamas. With the help of researchers at the Department of Energy’s Pacific Northwest National Laboratory, the value of silk could be extended beyond textiles to include new applications in microelectronics and computing. 

While silicon is the conventional material of choice for computer memory chips, processors and transistors, silk offers promise for “designer” electronics. Its exceptional mechanical and optical properties, as well as biocompatibility and biodegradability, are particularly appealing for use in tiny health sensors that could be safely worn by or implanted in patients. 

Like wool, fur, feathers and other animal fibers, silk is a biological material, made of protein. The most prominent of the two main proteins in silk, silk fibroin, is the material with promising qualities. The challenge, however, is that silk fibroin has a disorderly molecular structure, which makes it difficult to control when trying to assemble electronic components—and, therefore, difficult to use.

Researchers at PNNL discovered a novel way to control the nanostructure of the silk protein, which is a key step toward designing and fabricating silk-based electronics. By taking advantage of the inherent way the silk molecules in a water-based solution interact with a solid substrate, they were able to produce a highly organized crystalline layer of silk on graphene, a material with high electrical conductivity and tunable electronic properties. 

Their technique involved working in precision laboratory conditions to coax along this “self-assembly” by painstakingly regulating the concentration of silk, which, in turn, limits how many layers will form. Laboratory experiments and theoretical analysis showed the uniform single layer of silk fibroin they produced not only had a stable structure but also retained the properties of natural silk.

Combining silk and graphene represents the first step in controlled silk layering for functional electronic components—advancing the possibility of using silk to build electronic structures such as transistors at microscopic proportions with many possible applications. 

Transistors are semiconductors that amplify or switch electronic signals. Typically made of silicon, transistors are ubiquitous in today’s electronics, from computers to cell phones, satellites, spacecraft and countless other products. In addition to making faster, smaller, more sensitive transistors, researchers are exploring how using a biological material rather than a mineral as the basis for these devices could yield environmental benefits for semiconductor nanomanufacturing. Unlike silicon-based electronics, those made from silk are biodegradable and developed in water-based, non-toxic processes. 

These same qualities, along with mechanical flexibility, bring new advantages to medical devices where biocompatible transistors could be used in tiny sensors, amplifying difficult-to-detect biochemical signals in the body as indicators of illness or disease. They also could be used to flip a switch in response to a signal, perhaps delivering an antibody or drug in response to certain conditions. 

Another possible application for silk-based electronics is memory transistors, also known as memristors. These devices are used in artificial neural networks, a type of machine learning that allows computers to process data in a way that mimics the human brain.

Building on their progress, the scientists plan to further exploit natural silk’s benefits while manipulating its proteins to enhance its performance and provide different electronic functions. They also plan to create purely synthetic silk from polymers that mimic silk molecules. 

As researchers strive to use silk—a sign of wealth for 5,000 years—in new and exciting ways, the adage “everything old is new again” comes to mind. This project is a good reminder of how scientific discovery may begin with unusual origins, including some dating back to ancient times. It also shows how patience, innovation and creativity can lead to novel solutions that can make the world a better place. 

Steven Ashby, director of Pacific Northwest National Laboratory, writes this column monthly. To read previous Director's Columns, please visit our Director's Column Archive.