The new technique allows any object to sense its environment or be controlled through the application of a high-tech sticker, and also eliminates several manufacturing steps and the associated costs.
Our connected world
Billions of objects ranging from smartphones and watches to buildings, machine parts, and medical devices have become wireless sensors of their environments, expanding a network called the “Internet of Things.”
As society moves toward connecting all objects to the internet—even furniture and office supplies—the technology that enables these objects to communicate and sense each other will need to scale up. The new fabrication method for making electronic circuit stickers may be a step in that direction.
Eventually, these stickers could also facilitate wireless communication. The researchers demonstrate capabilities with various objects in a paper in the Proceedings of the National Academy of Sciences.
“We could customize a sensor, stick it onto a drone, and send the drone to dangerous areas to detect gas leaks, for example,” says Chi Hwan Lee, assistant professor of biomedical engineering and mechanical engineering at Purdue University.
The power of peeling
Most of today’s electronic circuits are individually built on their own silicon “wafer,” a flat and rigid substrate. The silicon wafer can then withstand the high temperatures and chemical etching used to remove the circuits from the wafer.
High temperatures and etching damage the silicon wafer, however, forcing the manufacturing process to accommodate an entirely new wafer each time.
Lee’s new fabrication technique, called “transfer printing,” cuts down manufacturing costs by using a single wafer to build a nearly infinite number of thin films holding electronic circuits. Instead of high temperatures and chemicals, the film can peel off at room temperature with the energy-saving help of simply water.
“It’s like the red paint on San Francisco’s Golden Gate Bridge—paint peels because the environment is very wet,” Lee says. “So in our case, submerging the wafer and completed circuit in water significantly reduces the mechanical peeling stress and is environmentally friendly.”
A ductile metal layer, such as nickel, inserted between the electronic film and the silicon wafer, makes the peeling possible in water.
Cut and paste
Researchers can then trim these thin-film electronics and paste them onto any surface, granting that object electronic features.
Putting one of the stickers on a flower pot, for example, made that flower pot capable of sensing temperature changes that could affect the plant’s growth.
Lee’s lab also demonstrated that the components of electronic integrated circuits work just as well before and after they were made into a thin film peeled from a silicon wafer. The researchers used one film to turn on and off an LED light display.
“We’ve optimized this process so that we can delaminate electronic films from wafers in a defect-free manner,” Lee says.