Optimization of pull-in voltage and contact force for MEMS series switch using Taguchi method

Cantilever based metal-to-metal contact type MEMS series switch has many applications namely in RFMEMS, Power MEMS etc. A typical MEMS switch consists of a cantilever as actuating element to make the contact between the two metal terminals of the switch. In electrostatic type switches the cantilever is pulled down by applying a pull-in voltage to the control electrode that is located below the middle portion of the cantilever while only the tip portion of the cantilever makes contact between the two terminals. Detailed analysis of bending of the cantilever for different pull-in voltages reveals some interesting facts. At low pull-in voltage the cantilever tip barely touches the two terminals, thus resulting in very less contact area. To increase contact area a very high pull-in voltage is applied. However it lifts the tip from the free end due to concave curving of the cantilever in the middle region of the cantilever where the electrode is located. It again results in less contact area. Furthermore, the high pull-in voltage produces large stress at the base of the cantilever close to the anchor. Therefore, an optimum, pull-in voltage must exist at which the concave curving is eliminated and contact area is maximum. In this paper authors report the procedure for finding a optimum voltage that can give maximum contact force across the two terminals. Taguchi method which is well suited to solve such optimization problem is used in the present work. The switch parameters, like cantilever length, cantilever width, electrode position, thickness of the metal of two terminals, are taken as 'control factors' with 4 levels each and simulation is performed for various combinations of the control factors as these appear in the rows of the L16 orthogonal array. The paper reports the optimum design of the MEMS switch.