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Polymer-based pull-in free electrostatic microactuators fabricated on wafer-level

: Lange, Nicolas; Wippermann, Frank; Beckert, Erik; Eberhardt, Ramona; Tünnermann, Andreas


Journal of Microelectromechanical Systems 24 (2015), Nr.4, S.949-957
ISSN: 1057-7157
ISSN: 1941-0158
Fraunhofer IOF ()

To further decrease feature sizes, the semiconductor industry heavily improved the photolithography. Photoresist layers are exposed through photomasks and structured accordingly. The underlying substrate is then selectively altered by adding or subtracting material. The unrivaled precision, resolution, and accuracy allow an unmatched level of miniaturization, and several thousand electrical components can be processed simultaneously. This technology was expanded to the fabrication of sensors and actuators, creating microelectromechanical systems. With silicon, the possibilities of further expanding this technology to new dimensions and applications are limited. Reasons are the stiffness, 2.5-D fabrication, and lack of optical transparency. To enable new applications, we present the successful translation of wafer-level fabrication to millimeter-scale actuators. This was achieved by changing the material to ultraviolet (UV)-curable polymers. Based on the electrostatic zipper actuator, avoiding the common pull-in-effect is essential for the successful realization of an acceptable microactuator. Therefore, the bottom electrodes are split and shaped to adjust the generated electrostatic forces, balancing the mechanical restoring forces. Besides the theoretical design, the fabrication technology based on classic photolithography is explained. Experimental results include voltage-dependent deflection measurements, achieving 110-μm deflection with 70 V driving voltage. The dynamic response measurements show resonance frequencies of 1.89 kHz.