https://www.sciencedaily.com/releases/2021/12/211222153005.htm

As electronic devices get smaller and smaller, and the desire to have bendable, wearable, and on-skin electronics increases, conventional methods of constructing these devices have become impractical. One of the biggest problems is how to connect and integrate multiple devices or pieces of a device that each reside on separate ultra-thin polymer films. Conventional methods that use layers of adhesive to stick electrodes together reduce flexibility and require temperature and pressure that are damaging to super-thin electronics. Conventional methods of direct metal-to-metal bonding are available, but require perfectly smooth and clean surfaces that are not typical in these types of electronics.

A team of researchers led by Takao Someya at RIKEN CEMS/CPR has developed a new method to secure these connections that does not use adhesive, high temperature, or high pressure, and does not require totally smooth or clean surfaces. In fact, the process takes less than a minute at room temperature, followed by about a 12-hour wait. The new technique, called water-vapor plasma-assisted bonding, creates stable bonds between gold electrodes that are printed into ultra-thin -- 2 thousandths of a millimeter! -- polymer sheets using a thermal evaporator.