The mechanical modeling process begins with a statement of the desired mechanical and electrical/microwave specifications of the device. Typical mechanical specifications include actuation voltage, mechanical resonance frequency, and contact forces; while typical electrical specifications include scattering parameters (insertion loss, return loss, and isolation), switching time, and power dissipation?induced temperature rise. Before detailed numerical simulation begins, approximate reducedorder analytical models are used to arrive at an approximate baseline device structure from which numerical simulations can depart. The numerical simulation process begins with a layout of the device structure (i.e., its geometry, dimensions, and constituent materials). This description is combined with information on the fabrication process in order to emulate the effect of the process steps on the structure and to produce the 3-D solid model reflecting the process peculiarities. The solid model, thus obtained, is then meshed in preparation for the electromechanical finiteelement simulation.
At this point the numerical model becomes a laboratory in itself, as number runs are undertaken to explore the dependence of intended performance measures, in the context of the design space, and to arrive at the specific device design that meets the mechanical specifications. The design space typically includes geometry (i.e., structure length, width, and thickness), the dimensions of certain air gaps, the actuation area, and the effect of process-induced phenomena such as residual stress and stress gradients on performance. Further details on the mechanical design are beyond the scope of this book.