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    Microelectromechanical Systems (MEMS) Thursday Sessions
       Session MM-ThM

Paper MM-ThM7
Thermal Characteristics of Microswitch Contacts

Thursday, November 1, 2001, 10:20 am, Room 130

Session: Characterization of MEMS Materials
Presenter: X. Yan, Northeastern University
Authors: X. Yan, Northeastern University
N.E. McGruer, Northeastern University
G.G. Adams, Northeastern University
S. Majumder, Analog Devices, Inc.
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Electrostatically actuated microswitches and relays developed at Northeastern University are approximately 100 x 100 µm in size and have been tested beyond 10@super 9@ cycles with a current of 2 mA per contact. For gold-gold contacts, the microswitches fail in a permanently closed mode in less than 10 cycles for currents exceeding 300 mA. At currents of approximately 1 A, the drain electrode melts, resulting in a permanently open switch. A number of authors have reported on various aspects of heat conduction through larger contacts. Hyman and Mehregany have discussed the contact physics of microcontacts, and modeled their thermal behavior.@footnote 1@ However, they do not consider the effect of the thin film traces leading up to the contacts in most MEMS switch designs. Finite element modeling and experiments have been used to study the thermal characteristics of microswitches. Because of the asymmetry in the contact geometry, the highest temperature is located in the thin film contact trace rather than at the contact interface. Contributions from convection and radiation are negligible, and conduction through the gas is marginally important. The hottest spot moves away from the contact as the contact radius increases, from 0.3 µm for a 100 nm contact radius to 2.7 µm for a 500 nm contact radius. Measurements show a sharp decrease in the contact resistance at a switch voltage of about 0.08 V and a current of 0.15 A, which may be due to softening of the contact surfaces and/or removal of surface contaminants. The result is in rough agreement with the onset of softening predicted by the model. The contact trace melts at a switch current of 1 A. The melted region is between 3.5 and 6 µm away from the center of the contact, slightly further than is predicted by the model. @FootnoteText@ @footnote 1@Daniel Hyman and Mehran Mehregany, Proc. of 44th IEEE Holm Conf. on Electrical Contacts (Arlington, VA, October 26-28, 1998, pp.133-140).