AVS 47th International Symposium
    MEMS Friday Sessions
       Session MM+VT-FrM

Paper MM+VT-FrM10
Thermal Characteristics of Microswitch Contacts

Friday, October 6, 2000, 11:20 am, Room 309

Session: MEMS Actuators, Pumps, Power Devices, and Tribology
Presenter: X. Yan, Northeastern University
Authors: X. Yan, Northeastern University
N.E. McGruer, Northeastern University
S. Majumder, Analog Devices
G.G. Adams, Northeastern University
Correspondent: Click to Email
Electrostatically actuated microswitches and relays have been developed at Northeastern University.@footnote 1@,@footnote 2@ Devices are approximately 100 @micron@ x 100 @micron@ in area and operate with an actuation voltage of 50-60 V, corresponding to a contact force of 100-150 microNewtons. The contact resistance varies less than 0.5 @ohms@ over 10@super 7@ cycles, with 4-10 mA current cold-switched. Switches have also been tested up to 10@super 9@ cycles with less than 0.5 @ohms@ variation in contact resistance, and with 330 mA of current for up to 18 cycles. The contacting bodies are a "drain" electrode approximately 0.2 @micron@ thick, and a pair of cylindrical bumps 1 µm in radius protruding from a 6 µm thick cantilever. The actual contact area is much smaller and consists of one or more small asperities. In this paper we study the microswitch contact properties at high currents. Finite element electrical and thermal models have been developed using ANSYS, and the modeled current handling limits are compared with experiments. Modeling shows that for a range of switch designs with thin-film drains, the highest temperature is located within the drain rather than at the contact interface, and this location moves further away from the contact interface as the drain thickness decreases or the length of the drain trace increases. Experiments confirm these trends, and show that switches fail catastrophically due to evaporation of the drain trace metal. SEM analysis of contact surfaces at various current densities is also presented. SEM analysis shows that even at the highest currents at which the trace metal evaporates, the contact surfaces typically show relatively little damage, mainly material transfer from one contact surface to the other. @FootnoteText@ @footnote 1@ S. Majumder, N. E. McGruer, "Study of Contacts in an Electrostatically Actuated Microswitch", Proceedings of 44th IEEE Holm Conference on Eletrical Contacts, pp 127-132 (1998) @footnote 2@ P.M. Zavracky, S. Majumder, and N.E. McGruer, "Micromechanical Switches Fabricated Using Nickel Surface Micromachining," J. Microelectromechanical Systems, Vol. 6, pp 3 (1997)