Dubbed "e-skin," the work of the UC Berkeley researchers was described Sunday in the online publication of the journal Nature Materials. The team is the first to use crystalline silicon in developing pressure-sensitive artificial skin. The work is important because it addresses a major problem in robotics, which is the ability for a machine to distinguish between picking up a heavy piece of metal and a delicate flower.
"Humans generally know how to hold a fragile egg without breaking it," Ali Javey, associate professor in electrical engineering and head of the UC Berkeley research team, said in a statement. "If we ever wanted a robot that could unload the dishes, for instance, we'd want to make sure it doesn't break the wine glasses in the process. But we'd also want the robot to be able to grip a stock pot without dropping it."
In addition, the development of touch-sensitive artificial skin could be used in creating prosthetics. However, major advancements would be needed in integrating e-skin with the human nervous system before such artificial limbs could be built.
The innovation developed by Javey and his team was in developing a technique for depositing semiconductor nanowires made of the crystalline silicon onto a flexible sheet of polyimide film. In the past, organic materials were used because they're more flexible than inorganic materials. However, the latter uses far less electricity, making them more useful in artificial skin.
The researchers got around the flexibility problem by rolling the nanowires on to the polyimide film using a roller that acted much like a lint roller in reverse. Rather than pickup fiber, the roller deposited transistors made up of hundreds of the hair-like nanowires into an area roughly 2.75 inches square. The transistors were then integrated with a pressure-sensitive rubber on top to provide the sensing functionality.
The e-skin required less than 5 volts of power to operate. It also remained functional after undergoing more than 2,000 "bending cycles," the researchers said. The technology also was shown to be capable of detecting pressure ranges found in daily activities, such as typing on a keyboard or holding an object.
The technique used in creating the artificial skin could in theory be used to create far larger sheets of e-skin, researchers said. The project was supported in part by the National Science Foundation and the Defense Advanced Research Projects Agency, or DARPA.