COMB-DRIVE ACTUATORS FOR LARGE DISPLACEMENTS

The design, fabrication and experimental results of lateral-comb-drive actuators for large displacements at low driving voltages is presente d. A comparison of several suspension designs is given, and the latera l large deflection behaviour of clamped-clamped beams and a folded fle xure design is modelled. An expression for the axial spring constant o f folded flexure designs including bending effects from lateral displa cements, which reduce the axial stiffness, is also derived. The maximu m deflection that can be obtained by comb-drive actuators is bounded b y electromechanical side instability. Expressions for the side-instabi lity voltage and the resulting displacement at side instability are gi ven. The electromechanical behaviour around the resonance frequency is described by an equivalent electric circuit. Devices are fabricated b y polysilicon surface micromachining techniques using a one-mask fabri cation process. Static and dynamic properties are determined experimen tally and are compared with theory. Static properties are determined b y displacement-to-voltage, capacitance-to-voltage and pull-in voltage measurements. Using a one-port approach, dynamic properties are extrac ted from measured admittance plots. Typical actuator characteristics a re deflections of about 30 mu m at driving voltages around 20 V, a res onance frequency around 1.6 kHz and a quality factor of approximately 3.