MECHANICAL DESIGN ISSUES IN LATERALLY-DRIVEN MICROSTRUCTURES

The mechanical issues influencing the design and performance of laterally-driven resonant-structure micromechanical systems are identified and quantified. Two forms of resonant-structure suspensions are presented and the performance of each is calculated and compared. One represents tension-generating flexure, while the second, a 'crab-leg' flexure, utilizes motion-generated bending of the suspension. This second device is an unusual case of lateral motion (parallel to the substrate) with suspension elements subjected to lateral bending. The limit of linear motion (magnitude of motion subject to a constant flexural spring rate) is determined and a stress analysis is performed. An optimal design theory for each flexure is developed in which the objective is to obtain the greatest deflection per unit of allowable material stress. Preliminary results indicate that the inclusion of special design details can generate a two-to-one decrease in stress for a given level of displacement. In accordance with this optimal design theory, a prototype 'crab-leg' flexure is fabricated with a stress-to-displacement ratio calculated to be as low as 65 MPa/μm. © 1990.