Microscale Liquid-Metal Switches—A Review

Microelectromechanical systems (MEMS) have constituted an active R&D area over the last two to three decades, with one of the earliest application topics being microswitches. Typical designs involve actuation of microscale flexural elements (e.g., beams and membranes) to make a short or an opening in the transmission (signal) line. However, the problem of reliability of these switches persisted due to the presence of a solid-solid contact. Inspired by the regular mercury switches that use liquid-solid contact to solve the problems, several researchers have been exploring the use of liquid metal (LM) in developing microscale switches. Over time, the following two different approaches have evolved: LM-wetted microswitches and LM-actuated microswitches. In this paper, we summarize the progress of both approaches over the last decade by reporting a series of LM microswitches, each with the mechanism, fabrication, and performance. In addition, the properties of various LMs and LM alloys and the issues of fabrication and packaging involving LM are presented to help understand the reported developments as well as to assist in designing future LM microswitches.