Exploitation of the coffee-ring effect to realize mechanically enhanced inkjet-printed microelectromechanical relays with U-bar-shaped cantilevers

We report a mechanically enhanced inkjet-printed microelectromechanical (MEM) relay with a U-bar-shaped cantilever by exploiting the coffee-ring effect. The printed cantilever shape, especially the effective thickness caused by the elevated walls, can be controlled during the drying process by outward convective flow of silver nanoparticles. This enhances mechanical stiffness to efficiently produce a strongly suspended cantilever that is immune to collapse- and curling-related failures. This approach to enhancing cantilever stiffness is unique to printing-based processes using metal-nanoparticle inks and is not feasible for conventional photolithography processes. The resulting printed MEM relays show a pull-in voltage of only 6.6V and an on/off ratio of 10⁸ with extremely low on-state resistance (∼14.3 Ω) and off-state leakage that is comparable to those of conventional silicon-based MEM relays.