Shape optimization of MEMS switches for miniaturization

Ahmed, Imran
This thesis presents miniature optimized cantilever beam MEMS contact switches for low pull-in voltage, low switching time and relatively high contact force for stable switch operation. Beam based MEMS switches are promising replacements of CMOS based p-i-n diodes and field effect transistor (FET) diode switches due to structural and operation advantages over these solid state switches. High isolation, zero power consumption and very low manufacturing cost are promising advantages compared to solid state switches. In this thesis, optimized miniature shape of gold made MEMS cantilever beam contact switches for low pull-in voltage, small switching time and high contact force have been presented. Low pull-in voltage ensures low power consumption, small switching time facilitates faster operation and high contact force ensures stable operation of switch. Four cantilever beams with thickness 1.6 µm, 1.4 µm, 1.2 µm and 1 µm have been critically analyzed. 11 configurations for each beam based on different length and width have been modeled. A rectangular hole has been introduced at the anchor point of the beam in order to reduce the stiffness of beam which in turn reduces pull-in voltage. Results show that hole at anchor point significantly reduces stiffness of the beam, and hence pull-in voltage also decreases. It has been also found in this study that, small dimension switch gives high pull-in voltage, small switching time and high contact force whereas large dimension switch gives low pull-in voltage, moderate switching time and low contact force. The configuration with dimension 22 µm × 22 µm has been found as miniature optimized shape of switch with thickness 1.6 µm. This configuration gives pull-in voltage of 35.62 V, contact force of 17.87 µN and switching time of 0.74 µs. In case of switch with thickness 1.4 µm, configuration with dimension 18 µm × 18 µm has been found as miniature optimized shape. It gives pull-in voltage of 42.81 V, switching time of 0.59 µs, contact force of 15.60 µN. In case of switches with thickness 1.2 µm and 1 µm, no configuration provides satisfactory results for MEMS application. Any of one criterion from pull-in voltage, switching time and contact force does not satisfy the desired requirement for stable switch operation.