The Belgian semiconductor research center IMEC has developed a way to put integrated circuits into flexible and stretchable materials without impairing the microchip’s functionality. The technique could lead to more sophisticated biomedical implants or electronics embedded in clothing.

Flexible electronics usually consist of circuits made up of individual components embedded in an elastic material and connected together by stretchable interconnects. This approach can create basic circuits capable of, for example, simple sensing functions.

Jan Vanfleteren, an electrical engineer at the Interuniversity Micro Electronics Centre at the University of Ghent, in Belgium, has developed a new approach. It involves “thinning” an off-the-shelf microchip from 725 micrometers down to just 30 micrometers using a conventional grinding process. Vanfleteren says the process does not impair the performance of the microchip.

The chips are processed while still on the wafer from which they are cut, embedded within a thin substrate, and then connected to other components embedded within the plastic via a stretchable copper interconnect.

Vanfleteren presented a prototype flexible microcontroller at the Electronics and System Integration Technology Conference in Amsterdam last month. It can be stretched beyond 50 percent of its length (20 percent is sufficient for a biomedical device), and can be flexed 10,000 to 100,000 times before breaking. It is even machine washable, Vanfleteren notes, making it suitable for clothing.

Making the chip so thin makes it bendable, says Vanfleteren, but the material is still too brittle be stretched—it’s the S-shaped copper interconnects that allow the entire embedded device to be stretched and deformed.

Vanfleteren says flexible medical implants containing these circuits could, for example, monitor and respond to physiological changes rather than having to send data to an external computing unit, he says.

Other researchers, including John Rogers at the University of Illinois, Urbana-Champaign, are developing flexible electronics. Rogers’ technology has been spun out into a Cambridge, Massachusetts-based company called MC10. But existing approaches involve connecting individual components rather than using a premade chip.

Rogers says using off-the-shelf computer chips should make it easier to build more sophisticated devices. “A key advantage is that these strategies enable commercial, off-the-shelf components to be configured into flexible, stretchable formats,” he says.

Stéphanie Lacour, head of the Laboratory for Soft Bioelectronic Interfaces at the Ecole Polytechnique Fédérale de Lausanne, in Switzerland, says the IMEC approach will make it easier to mass-produce flexible electronics because it’s compatible with conventional fabrication methods. “What’s interesting about this approach is that they have managed to use conventional materials and electronics,” she says.