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.
With wavelength sizes between a millimeter and a meter, microwave radio frequencies are electromagnetic waves that use frequencies in the .3 gigahertz to 300 gigahertz range. That falls directly in the 5G range.
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.
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.
Fabricated in interlocking segments like a 3-D puzzle, the new integrated circuits could be used in wearable electronics that adhere to the skin like temporary tattoos. Because the circuits increase wireless speed, these systems could allow health care staff to monitor patients remotely, without the use of cables and cords.
CREDIT Image courtesy of Yei Hwan Jung and Juhwan Lee/University of Wisconsin-Madison
What makes the new, stretchable integrated circuits so powerful is their unique structure, inspired by twisted-pair telephone cables. They contain, essentially, 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. Currently, the researchers' stretchable integrated circuits can operate at radio frequency levels up to 40 gigahertz.
And, 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. That's tiny enough to be highly effective in epidermal electronic systems, among many other applications.
Ma's group has been developing what are known as transistor active devices for the past decade. This latest advance marries the researchers' expertise in both high-frequency and flexible electronics.
"We've found a way to integrate high-frequency active transistors into a useful circuit that can be wireless," says Ma, whose work was supported by the Air Force Office of Scientific Research. "This is a platform. This opens the door to lots of new capabilities."
Advanced Functional Materials - High-Speed, Flexible Electronics by Use of Si Nanomembranes
Traditionally, flexible electronics have addressed low or moderate operating frequency applications because the materials for flexible electronics, such as polymer and noncrystalline inorganic semiconductors, have poor electrical properties. Fast flexible electronics that operate at radiofrequencies (RFs) regime, particularly at microwave frequencies, could lead to myriad novel RF applications that conventional rigid solid-state electronics cannot easily fulfill. Single-crystalline semiconductor nanomembranes that can be released from various source wafers not only show very good flexibility and durability but also exhibit outstanding electrical properties that are equivalent to those of their bulk counterparts. These thin and flexible single-crystalline materials can furthermore be placed, via transfer-printing techniques, onto nearly any substrates, thus creating the opportunity to realize RF flexible electronics. In this chapter, we present various RF active devices made of semiconductor nanomembranes on plastic substrates such as flexible transistors and switches.
SOURCE - University of Wisconsin-Madison, Advanced Functional Materials