Water vapor plasma bonds gold electrodes for flexible electronics

SOPHIA CHEN: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics in materials research. My name is Sophia Chen.   

Picture a sensor, sewn onto a glove, for measuring blood oxygen. Or a circuit woven onto a sleeve that measures your muscle activity. These are all potential applications for the budding new technology of flexible electronics. Flexible electronics consist of electronic circuits that sit on a thin substrate, usually plastic, on the order of a few microns thick. 

But one key challenge is connecting one flexible component to another, according to Kenjiro Fukuda, a physicist at RIKEN in Japan. In regular electronics, you might use solder, or some other type of adhesive to attach components—but that increases the device’s thickness, making it more rigid. 

KENJIRO FUKUDA: The thick adhesive layer is not good to make fully flexible systems. 

SOPHIA CHEN: Fukuda’s team has developed a new method to connect flexible electronics while keeping the devices thin. They demonstrated the method on two gold electrodes. 

To make the two pieces of gold bond, they treated the gold with water vapor plasma, as Masahito Takakuwa, a mechanical engineering graduate student at Waseda University explained. Water vapor plasma is a phase of old-fashioned H2O that consists of charged particles, such as hydroxyl, oxygen, and hydrogen radicals.  

Takakuwa overlapped two gold electrodes, treated them with the water vapor plasma, and then left them in ambient air.  

MASAHITO TAKAKUWA: After the twelve hours the two films were bonded. 

SOPHIA CHEN: They call their method water vapor plasma assisted bonding. Using x-ray photoelectron spectroscopy, they determined that hydroxyl radicals from the water vapor plasma deposit on the gold electrodes. They say these hydroxyl radicals enable the gold electrodes to bond. 

MASAHITO TAKAKUWA: If we use the argon or oxygen gas, instead of the water vapor gas, the bonding phenomenon does not happen. 

SOPHIA CHEN: They used this technique to electrically connect the gold electrodes of an organic photovoltaic to an organic LED. They demonstrated the connection by making the LED light up. In addition, they showed that they could connect the LED to the photovoltaic without adding significant thickness. 

MASAHITO TAKAKUWA: It maintained pretty good flexibility. 

SOPHIA CHEN: They should be able to apply this technique to adhere other types of electrodes. 

MASAHITO TAKAKUWA: I want to try to bond using the copper or silver instead of the gold. 

SOPHIA CHEN: They’re particularly excited that the new technique will allow them to more easily connect flexible electronic components.  

KENJIRO FUKUDA: This can enable complicated integrated devices.

SOPHIA CHEN: This work was published in a recent issue of the Science Advances. My name is Sophia Chen from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.