Flexing of scratch drive actuator plates: modelling and experimentation

The scratch drive actuator (SDA) is a key element in microelectromechanical-system (MEMS) technology. This type of actuator can be designed to travel over very long distances with precise step sizes. The MEMS designer requires models of the SDA to incorporate these devices into their microsystem applications. Models are developed for the SDA in its working state, building on previous work reported in the literature. A suspended SDA plate actuated by electrostatic forces has been analysed. A mathematical model has been established based on electrostatic coupled mechanical theory. Two SDA modes have been analysed namely the noncontact mode and the contact mode. The noncontact mode allows the designer to establish the threshold voltage after which the actuator plate snaps down. For the contact mode, the relationship between applied voltage and contact length is first obtained. Subsequently, the geometrical model of a bent plate is used to determine the relationship between contact distance and step size. These two results are then combined to obtain the value of actuator step size against applied voltage. A coupled-field electromechanical simulation of the microactuators has been performed using the commercially available software tool, IntelliSuite. On the experimental front, a Veeco NT1000 surface profiling tool has been used to measure the bending of the SDA plate. The results obtained from modelling, simulation and experimentation are compared.