A multi-asperity model of the contact resistance in a MEMS microswitch has been developed. This model includes the effects of elastic and plastic deformation, adhesion, and scale-dependent constrictive resistance. The number of asperities in contact is small enough that a discrete, rather than a continuous, distribution of asperity heights is used. Due to the combined effects of plasticity and adhesion, the surface profile changes with repeated load and unload cycles. Furthermore, adhesion produces significant hysteresis in the contact resistance vs. contact force characteristics. Measurements of the contact resistance as a function of actuation voltage show good qualitative agreement with the model.

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