The great potential of wearable technologies has been, however, held back by a technical restraint: they have never really felt "wearable" to their users. Though they were supposed to feel like a second skin of the wearer, it has been technically impossible to devise "wearable" devices that are comfortable to bend and stretch and also keep good data recording capabilities on soft and curved skin. Wearable smart devices gather a person's bio measurements by connecting electrodes to the surface of the skin.
Schematic illustrations (left) and scanning-electron microscopic images (right) of various 3D structures of printed stretchable metal composites. 3D interconnection can overlap Scale bars are 100 μm.
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Inside the device are 3D-shaped electrode wirings (i.e. interconnects) that transmit electrical signals. To date, not only can the wirings only be formed on a hard surface, but also the components of such interconnects delicate and hardly-stretchable metals such as gold, copper, and aluminum.
In a paper published in the journal Nano Letters, the joint research team led by Prof. Jang-Ung Park at the Center for Nanomedicine within the Institute for Basic Science (IBS) in Daejeon, South Korea, and Prof. Chang Young Lee at the Ulsan National Institute of Science and Technology (UNIST) in Ulsan, South Korea reported fully-transformable electrode materials that also feature a high electric conductivity.
Notably, this novel composite is super-thin, 5 micrometers in diameter, which is half of the width of conventional wire bonding. By enabling ever-slimmer 3D interconnects, this study can help to revolutionize the physical appearance of smart gadgets, in addition to reinforcing their technical functions.
The research team used liquid metals (LM) as the main substrate since LMs are highly stretchable and have relatively high conductivities similar to solid metals. To improve the mechanical stability of the metal liquid, carbon nanotubes (CNT) were dispersed uniformly.
"To have a uniform and homogeneous dispersion of CNTs in liquid metal, we selected platinum (Pt), for having a strong affinity to both CNT and LM, as the mixer and it worked," said Young-Geun Park, the first author of the study.
This study also demonstrated a new interconnection technology that can form a highly conductive 3D structure at room temperature: For having a high conductivity, the new system does not require any heating or compressing process. Also the soft and stretchable nature of the new electrode makes it easy to come through the nozzle in a fine diameter. The research team used a nozzle for the direct printing of various 3D patterning structure. Park explains, "Forming high-conductivity 3D interconnections at room temperature is an essential technology that enables the use of various flexible electronic materials.
COMPAMED-tradefair.com; Source: Institute for Basic Science