Lateral polysilicon microrelays with a mercury microdrop contact

The authors present two designs for electrostatically actuated polysilicon relays with a stationary mercury microdrop contact: a large displacement cantilever design; and a comb-drive design, both fabricated using the multiuser microelectromechanical systems process of MCNC, Research Triangle Park, NC, USA. Microscale mercury relays combine the high density and batch fabrication of a microscale device with the quality and reliability of a mercury contact. Contact resistances of the devices were found to be ~1 kΩ in air with no attempt made to reduce the oxidation of the polysilicon and mercury surfaces. The devices can switch currents over 10 mA. Switching results are presented. The cantilever device is based on a curved electrode design, providing both relatively large force and large displacement of the tip, which contacts the mercury for switching. Nonlinear modeling of the beam movement is also provided. The comb-drive device has the usual double-folded beam design, but has a mercury drop near its center. Fabrication of 10-μm diameter mercury drops as the last step of the processing sequence is also discussed