The technology, which could enable many uses of emerging 5G and 6G wireless networks, is based on large-area electronics, a way of fabricating electronic circuits on thin, flexible materials. The researchers described its development in a paper published Oct. 7 in Nature Electronics.
The approach overcomes limitations of conventional silicon semiconductors, which can operate at the high radio frequencies needed for 5G applications, but can only be made up to a few centimeters wide, and are difficult to assemble into the large arrays required for enhanced communication with low-power devices.
“To achieve these large dimensions, people have tried discrete integration of hundreds of little microchips. But that’s not practical — it’s not low-cost, it’s not reliable, it’s not scalable on a wireless systems level,” said senior study author Naveen Verma, a professor of electrical and computer engineering and director of Princeton’s Keller Center for Innovation in Engineering Education.
“What you want is a technology that can natively scale to these big dimensions. Well, we have a technology like that — it’s the one that we use for our displays” such as computer monitors and liquid-crystal display (LCD) televisions, said Verma. These use thin-film transistor technology, which Verma and colleagues adapted for use in wireless signaling.
The researchers used zinc-oxide thin-film transistors to create a 1-foot-long (30-centimeter) row of three antennas, in a setup known as a phased array. Phased antenna arrays can transmit narrow-beam signals that can be digitally programmed to achieve desired frequencies and directions. Each antenna in the array emits a signal with a specified time delay from its neighbors, and the constructive and destructive interference between these signals add up to a focused electromagnetic beam — akin to the interference between ripples created by water droplets in a pond.
A single antenna broadcasts a fixed signal in all directions, “but a phased array can electrically scan the beam to different directions, so you can do point-to-point wireless communication,” said lead study author Can Wu, a postdoctoral researcher at Stanford University who completed a Ph.D. in electrical and computer engineering at Princeton earlier this year.