High frequency, stretchable circuits could yield new era of wearable electronics

Researchers at the University of Wisconsin—Madison - led by Zhenqiang "Jack" Ma, the Lynn H. Matthias Professor in Engineering and Vilas Distinguished Achievement Professor in electrical and computer engineering, have created what the researchers believe to be the world's fastest stretchable, wearable integrated circuits, an advance that could be a key driver for the Internet of Things and a play an important role in the growing connected, high-speed wireless world.

According to the researchers the advance is a platform for manufacturers seeking to expand the capabilities and applications of wearable electronics — including those with biomedical applications — particularly as they strive to develop devices that take advantage of a new generation of wireless broadband technologies referred to as 5G.

The say what makes the new, stretchable integrated circuits powerful is their unique structure, inspired by twisted-pair telephone cables. Essentially, they contain two ultra-tiny intertwining power transmission lines in repeating S-curves.

This serpentine shape — formed in two layers with segmented metal blocks, like a 3-D puzzle — gives the transmission lines the ability to stretch without affecting their performance. It also helps shield the lines from outside interference and, at the same time, confine the electromagnetic waves flowing through them, almost completely eliminating current loss.

Further, unlike other stretchable transmission lines, whose widths can approach 640 micrometers (or .64 millimeters), the researchers' new stretchable integrated circuits are just 25 micrometers (or .025 millimeters) thick. At these dimensions they are tiny enough to be highly effective in epidermal electronic systems, among many other applications.

The advance could allow health care staff to monitor patients remotely and wirelessly. In an intensive care unit, epidermal electronic systems (electronics that adhere to the skin like temporary tattoos) could allow health care staff to monitor patients remotely and wirelessly, increasing patient comfort by decreasing the customary tangle of cables and wires.

Currently, the researchers' stretchable integrated circuits can operate at radio frequency levels up to 40 GHz. In mobile communications, the wide microwave radio frequencies of 5G networks will accommodate a growing number of cellphone users and notable increases in data speeds and coverage areas. With wavelength sizes between a mm and a meter, microwave radio frequencies are electromagnetic waves that use frequencies in the .3GHz to 300GHz range - these falls directly in the 5G range.

Jack Ma’s group has been developing 'transistor active devices' for the past decade. This latest advance marries the researchers' expertise in both high-frequency and flexible electronics.

The work was supported by the Air Force Office of Scientific Research.

Zhenqiang 'Jack' Ma, the Lynn H. Matthias Professor in Engineering and Vilas Distinguished Achievement Professor in electrical and computer engineering at UW–Madison, said, "We’ve found a way to integrate high-frequency active transistors into a useful circuit that can be wireless. " Jack added "This is a platform. This opens the door to lots of new capabilities."