Electrostatic beam actuator for switching applications fabricated by Ni-microelectroplating and thermal postprocessing

Abstract

As displacement and electrode gap coincide in parallel plate electrode configurations, electrostatic actuators struggle with elevated actuation voltages for reasonable displacements or restoring forces in MEMS. A curved-cantilever-beam-type actuator overcoming this dependence was presented by several workgroups for microvalves, microrelays or micro-mirrors. Stress gradients achieved during fabrication result in out-of-plane curvature of the beam electrode. The tip deflection can be scaled by the beam length, while the minimum electrode gap is kept small aiming at actuation voltages common to microelectronics. This actuator appeals to switching applications requiring low-power drive, high deflections and short cycle times. Our approach employs microelectroplating of nickel and thermal postprocessing instead of multi-layer stacks achieved from semiconductor-based fabrication technologies. As stress gradients needed for the beam curvature distribute on wafer level and may alter during packaging or even in operation, advanced methods for controlling the actuator’s bending geometry are needed. A bending predefinition can be obtained during electroplating. The final beam curvature is achieved by tempering on wafer level for stabilisation and succeeding fine-tuning with local LASER-treatment near the suspension. Advanced actuator prototypes for microvalves or microrelays will be presented. Also, the suitability of the actuator for rf-switches will be indicated.