Travel range extension of a MEMS electrostatic microactuator

Electrostatic comb microactuators have had a fundamental limitation in that the allowable travel range is limited to one-third of the total gap between comb fingers. Travel beyond this allowable range results in "pull-in" instability, independent of mechanical design parameters such as stiffness and mass. This brief focuses on the development of an active control system that stabilizes the actuator and allows travel almost over the entire available gap between comb fingers. The challenges to be addressed include the nonlinear dynamics of the actuator and system parameters that vary with each fabricated device. A nonlinear model inversion technique is used to address the nonlinear dynamics of the system. An adaptive controller is developed to provide improved position tracking in the presence of fabrication imperfections. The developed control system is then implemented on a special microelectromechanical systems (MEMS) electrostatic microactuator fabricated using deep reactive ion etching (DRIE) on silicon-on- insulator (SOI) wafers. The use of DRIE allows the fabrication of a high aspect ratio device that can produce large electrostatic forces with low actuation voltages. Experimental results presented in the brief show that the resulting system is capable of traveling 4.0 μm over a 4.5 μm full range without "pull in." Good tracking performance is obtained over a wide frequency band. Potential applications of the actuator are in the manipulation of subcellular structures within biological cells, microassembly of hybrid MEMS devices, and manipulation of large molecules such as DNA or proteins.