Vertical, capacitive microelectromechanical switches produced via direct writing of copper wires

Three-dimensional (3D) direct writing based on the meniscus-confined electrodeposition of copper metal wires was used in this study to develop vertical capacitive microelectromechanical switches. Vertical microelectromechanical switches reduce the form factor and increase the area density of such devices in integrated circuits. We studied the electromechanical characteristics of such vertical switches by exploring the dependence of switching voltage on various device structures, particularly with regard to the length, wire diameter, and the distance between the two wires. A simple model was found to match the experimental measurements made in this study. We found that the electrodeposited copper microwires exhibit a good elastic modulus close to that of bulk copper. By optimizing the 3D structure of the electrodes, a volatile electromechanical switch with a sub-5 V switching voltage was demonstrated in a vertical microscale switch with a gap distance as small as 100 nm created with a pair of copper wires with diameters of ~1 μm and heights of 25 μm. This study establishes an innovative approach to construct microelectromechanical systems with arbitrary 3D microwire structures for various applications, including the demonstrated volatile and nonvolatile microswitches.