Researchers at the University of Illinois at Urbana-Champaign say they have developed a way to manufacture large-sized flexible displays that can be conformed to curved surfaces, while also providing a useable level of transparency. The paper, which appears in this month’s issue of Science, describes the development of "methods for creating microscale inorganic light-emitting diodes (ILEDs) and for assembling and interconnecting them into unusual display and lighting systems." The paper, titled Printed Assemblies of Inorganic Light-Emitting Diodes for Deformable and Semitransparent Displays, summarizes the research efforts of the twelve-author team at the University of Illinois.

The large display screens are said to combine the scale and durability of light-emitting diodes ordinarily used to make flat, lighted billboards, with the flexibility of screens made using organic materials. While current technology using inorganic materials produces large individual LED lights that need to be placed using robotic manufacturing techniques, screens made using organic materials can be sprayed or painted onto a film surface, but they are not as bright or durable. The research team solved these problems by building their ILEDs on a thin layer of film that is chemically etched. The approach affixes tiny plastic tabs on the corners to hold the ILEDs in place during the chemical bath.

According to the paper, conventional LED fabrication and placement processes typically require wafer sawing, serial pick-and-place, wire bonding, and packaging on a device-by-device basis, followed by incorporation into displays by robotic assembly into tiles, and finally device interconnection using large quantities of bulk wiring. In contrast, OLEDs are typically manufactured using planar batch processing, and this type of manufacture can greatly expand application opportunities. Examples include not only ILED displays for desktop monitors, home theater systems, and instrumentation gauging, but also flexible or stretchable forms.

The new process involves four key components:

1. Epitaxial semiconductor multilayers designed for lateral demarcation and release from a source wafer to yield isolated arrays of ILEDs. These arrays remains tethered to the wafer by polymeric "breakaway" anchor structures.
2. Printing techniques for manipulating the resulting ILEDs in schemes that enable formation of large-scale arrays on foreign substrates and in arbitrary spatial layouts.
3. Planar processing methods for establishing electrical interconnects to the devices, in direct or matrix addressable configurations.
4. Integration strategies capable of yielding ILED displays in flexible or stretchable formats and with conventional, semitransparent, or bidirectional emission characteristics.

The project was initially funded in part by Ford Motor Co., which was looking for a way to make brake lights that can follow the surface contour of a car. The National Science Foundation and the U.S. Department of Energy also funded the project. The techniques developed in the project should enable manufacturers to build better and cheaper displays that overcome the disadvantages of OLEDs — high prices and manufacturing obstacles — but retain the devices’ advantages of physical flexibility and display response.