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Materials

Electronic “Skin” Emits Light When Pressed

Researchers unveil one of the most complex electronic systems ever built on plastic.

Flexible electronic devices could enable new types of applications in a wide range of contexts, from medicine to general purpose computing.

A sheet of thin plastic that emits light with an intensity that precisely reflects the amount of pressure applied to its surface hints at a new breed of flexible computer interface. Its creators say future iterations of the interface could be used for robotics, car dashboards, mobile displays, or even “interactive wallpaper.”

pressure sensitive LED
Pressure pixels: A fully fabricated piece of “electronic skin.” Each pixel emits light in response to applied pressure.

Described today in Nature Materials, the new light-emitting “electronic skin,” as its inventors call it, is an extension of previous work from the lab of Ali Javey, a professor of electrical engineering and computer science at the University of California, Berkeley. Javey’s group has developed processes that draw heavily on traditional silicon manufacturing techniques to uniformly and reliably integrate various organic and inorganic components on top of plastic.

In recent years, there have been an increasing number of efforts to make electronic devices on surfaces less rigid than the silicon wafers used in traditional manufacturing. Flexible, bendable electronics would open the door to a multitude of new applications, from medical sensors that wrap around organs to foldable displays. Certain plastics can serve as substrates for electronic systems, but reliably fabricating complicated circuits on plastic has been a challenge.

The team previously demonstrated a network of high-resolution pressure sensors made of nanowires arrayed on a relatively large area of plastic, which produced an electronic readout of pressure applied to the surface. The aim of the new work, says Javey, was to make a pressure sensor array that could directly interact with humans.

Javey and colleagues set out to make the electronic skin respond optically. The researchers combined a conductive, pressure-sensitive rubber material, organic light emitting diodes (OLEDs), and thin-film transistors made of semiconductor-enriched carbon nanotubes to build an array of pressure sensing, light-emitting pixels. Whereas a system with this kind of function is relatively simple to fabricate on a silicon surface, “for plastics, this is one of the more complex systems that has ever been demonstrated,” says Javey.

The diversity of materials and components that the researchers combined to make the light-emitting pressure-sensor array is impressive, says John Rogers, a professor of materials science at the University of Illinois at Urbana-Champaign. Rogers, whose group has produced its own impressive flexible electronic sensors (see “Electronic Sensors Printed Directly on the Skin), says the result illustrates how research in nanomaterials is transitioning from the fundamental study of components and simple devices to the development of “sophisticated, macroscale demonstrator devices, with unique function.”

Javey says tools and schemes used to build conventional liquid crystal displays could also be used to manufacture his group’s electronic skin, which could in principle contain other types of sensors and be engineered to respond in other ways. His group is also pursuing methods for printing electronics directly onto plastic. These are at an early stage of development, but could eventually provide a pathway to efficiently producing very large interactive sensor arrays, says Javey.

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