Used in products ranging from brake lights to billboards, LEDs are ideal components for backlighting and displays in electronic devices because they are lightweight, thin, energy-efficient, and visible in different types of lighting. Micro LEDs, which can be as small as 2 micrometers and bundled to be any size, provide higher resolution than other LEDs. Their size makes them a good fit for small devices such as smartwatches but they can be bundled to work in flat-screen TVs and other larger displays. LEDs of all sizes, however, are brittle and typically can only be used on flat surfaces.
Researchers have developed a method to create micro LEDs that can be folded, twisted, cut, and stuck to different surfaces. The research helps pave the way for the next generation of flexible, wearable technology. The detachable LED can be transferred onto clothing or even rubber and can survive even if it is wrinkled. It also can be cut to use half of the LED.
The flexible LED was created through a technique called remote epitaxy, which involves growing a thin layer of LED crystals on the surface of a sapphire crystal wafer, or substrate. Typically, the LED would remain on the wafer. To make it detachable, researchers added a nonstick layer to the substrate, which acts similarly to the way parchment paper protects a baking sheet and allows for the easy removal of cookies, for instance. The added layer, made of a one-atom-thick sheet of carbon called graphene, prevents the new layer of LED crystals from sticking to the wafer.
The graphene does not form chemical bonds with the LED material, so it adds a layer that allows the LEDs to be peeled from the wafer and stuck to any surface. Laboratory tests of LEDs were conducted by adhering them to curved surfaces as well as to materials that were subsequently twisted, bent, and crumpled. Bending and cutting do not affect the quality or electronic properties of the LED.
The bendy LEDs have a variety of possible uses including flexible lighting, clothing, and wearable biomedical devices. From a manufacturing perspective, the fabrication technique offers another advantage: Because the LED can be removed without breaking the underlying wafer substrate, the wafer can be used repeatedly. The researchers also are applying the fabrication technique to other types of materials.