Thermally Actuated Microswitches: Computation of Power Requirements for Alternate Heating Configurations

Steady state behavior of a thermally actuated RF MEMS switch in the open and closed positions is simulated using the governing thermal and structural equations. The switch is a bridge with a length of 250 microns, a width of 50 microns, and a thickness of 1 micron, in air with a pressure of 5 kPa. Simulations are performed for two different materials: silicon and silicon nitride. Three heating configurations are used: uniformly distributed heat, concentrated heat at the center of the top surface, and concentrated heat at the sides of the top surface. The steady state results show that the displacement at the center of the bridge is a linear function of the heat addition. This can be used to define a switch efficiency coefficient η*. In the uniformly distributed heat configuration, for a specific center displacement, a closed switch needs less heat at the top than an open switch. Adding concentrated heat at the center of the top surface yields a larger center displacement per unit heat addition than adding heat to the sides. When the heating is changed to a concentrated heat load at the center, the required heat is an order of magnitude less than heat added to the sides. Changing the contact length shows that variation in the length of the contact results in negligible changes in required heat to achieve a given displacement.