Scientists at the RIKEN research institute in Japan have developed a new method of connecting gold electrodes within flexible electronics. The technology, which does not require adhesives or high temperatures that can damage sensitive electronic components, enables extremely thin and flexible electronics and could lead to new types of medical wearables. The team’s method is based on exposing tiny gold electrodes to a water vapor plasma before they are connected to one another. The plasma creates hydroxyl groups that help bond the gold surfaces together, and the process can take place at room temperature.
Conformity test on a curved surface (radius: 0.5 mm). Ultra-thin foils that are glued with (above) steam plasma-assisted bonding or (below) standard adhesive.
Wearables offer tremendous opportunities for medical care as continuous health monitoring enables doctors to keep track of the condition of their patients over time to identify adverse events before they lead to long-term complications. However, many monitoring modalities require skin contact, and this often means that the electrical components in a portable device must be flexible and thin, but also tough enough to withstand repetitive movement.
One issue is connecting tiny electrodes within the flexible thin films that form the basis of many wearables. Conventional processes, which typically require adhesives or high temperatures, can damage sensitive electronic components or impair the flexibility of the wearable.
To remedy this, these researchers used a gentler technique, though they came across it by accident. Their method is to attach gold electrodes to an ultra-thin polymer sheet and then expose them to water vapor plasma for 40 seconds. The researchers then press the polymer films together so that the electrodes touch where they are supposed to connect. After 12 hours, the electrodes are glued and the flexible film can be used as desired.
“This is the first demonstration of ultra-thin, flexible gold electronics made without glue,” said Kenjiro Fukuda, a researcher involved in the study. “With this new direct-bond technology, we were able to produce an integrated system from flexible organic solar cells and organic LEDs.”
(A) Evaporated gold surfaces on 2 µm thick parylene substrates were exposed to water vapor plasma. (B) Bonding of steam plasma treated gold was accomplished by overlapping the two substrates and storing them in ambient air for a few seconds to several hours with no pressure or heat applied.
So far, Japanese researchers have made thin films containing a variety of electrical components, including LEDs, and twisted and crumpled them around a rod flawlessly by wringing them out.
“We expect this new approach to become a flexible, next-generation wiring and assembly technology for wearable electronics that can be attached to clothing and skin,” said Fukuda. “The next step is to develop this technology for use with cheaper metals like copper or aluminum.”
Check out one of the films in the video below.
Study of scientific advances: Direct gold bonding for flexible integrated electronics
Flashbacks: Washable and flexible batteries for portable medical devices; Flexible transistors for body worn and implantable medical devices; Printing custom flexible electronics directly on skin, bandages, medical devices; Hydrogels with flexible electronics open up new medical possibilities
Over: RIKEN
