Paper MN+NS-TuA4
Meso Scale MEMS Motion Transformer and Amplifier Electrostatically Actuated by Parallel Plate Electrodes

Tuesday, November 11, 2014, 3:20 pm, Room 301

Meso scale microelectromechanical structures found on the upper scale of microelectromechanical systems (MEMS) can potentially replace conventional mechanical devices produced by common for the macro-engineering approaches such as machining and assembly of individual parts. When realized as a compliant mechanism containing a single flexible member rather than multiple parts attached by joints they provide smooth frictionless motion without backlash and exhibit improved reliability and robustness. Batch fabrication using micromachining processes established in MEMS allows improved yield and significantly lower cost. However, actuation of these devices remains challenging. Electrostatic actuation, which is the most widely used in smaller MEMS devices, is viewed to be less suitable for the actuation at the meso scale due to unfavorable scaling laws, namely quadratic reduction of the actuating force with the distance between the electrodes. For this reason, most of the meso scale micro devices are actuated by thermal transducers, distinguished by slow response and high power consumption or by piezoelectric or magnetic motors, which cannot be integrated within the device and require post-fabrication assembly.

In this work we report on the design, fabrication and characterization of an electrostatically actuated meso scale microelectromechanical motion transformer and amplifier. The actuator corporate a transducer with multiple parallel plate electrodes and is realized as a compliant mechanism relying on flexible pseudo hinges. The 5000 µm × 4000 µm device converts linear motion of the transducer into mechanically amplified angular motion of a rotating lever. By combining a highly efficient small-gap parallel plate electrode and a motion amplification the device is designed to provide a lever tip displacement of 60µm, an initial blocking force of 0.001N at zero displacements and a blocking force of 0.012N in the maximal displacement configuration when the parallel plate actuator is in its closed position. The devices were fabricated using DRIE from a SOI wafer with (111) front surface orientation and a 150µm thick device layer. The devices were operated in ambient air conditions and the functionality of the device was demonstrated experimentally. The voltage-displacement dependence and resonant curves were built using image processing procedure implemented in Matlab. Excellent agreement between the results provided by the Finite Elements models and the experimental data was observed. The results of the work demonstrate an ability to achieve both large displacements and high blocking forces in an electrostatically actuated meso scale compliant mechanism.