Estimation of the mechanical stiffness constant of MEMS-based parallel-plate micro-actuators
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TECHNICAL PAPER
Estimation of the mechanical stiffness constant of MEMS-based parallel-plate micro-actuators Deginet Admassu1
•
Tejumade Durowade1 • Silviu Velicu2 • Sivalingam Sivananthan1 • Wei Gao2
Received: 18 August 2020 / Accepted: 30 August 2020 Ó Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The fabrication and testing of a parallel plate MEMS electrostatic micro-actuator is reported. The device consists of stationary bulk silicon and movable membrane chips with three spring-like x-beam configurations fabricated from a silicon on insulator (SOI) wafer. A SU-8 photoresist layer was deposited on the stationary chip to act as a spacer since its thickness determines the electrostatic force that can be applied. This in turn has an effect on the displacement of the micro-actuator. We investigated the effects of the applied voltage on the displacement of movable x-beam membranes for different arm designs with similar surface areas. We achieved maximum stable displacements of 8.75 lm and 9.89 lm for spacer thicknesses of 28 lm and 33 lm at 95 VDC and 128 VDC, respectively, for a serpentine arm design. Beyond these voltages, we found the displacement of the micro-actuator tended to be non-uniform and unstable. We also estimated the mechanical stiffness constants of our x-beam designs from the snap-in conditions. Our estimates for various spacer thicknesses were within 5% of one another.
1 Introduction The fabrication of MEMS-based devices meant for integration with fully-developed sensing systems is a steadily advancing field. It is now possible to fabricate resonators, sensors, actuators and cantilever beams that exhibit reproducible characteristics on the micro-scale (Tachi et al. 1987). However, the integration of these devices with fully-developed systems, such as infrared detectors, is a challenge that still limits their use in high speed applications. In the case of a MEMS micro-actuator, non-idealities & Deginet Admassu [email protected] Tejumade Durowade [email protected] Silviu Velicu [email protected] Sivalingam Sivananthan [email protected] Wei Gao [email protected] 1
Microphysics Laboratory, Physics, University of Illinois at Chicago, 845 W Taylor Street, Chicago 60607, USA
2
EPIR Technologies Inc, 590 Territorial Dr Ste H, Bolingbrook 60440, USA
such as non-parallelity, oscillations and non-ideal anchors make integration with infrared devices difficult. Knowledge of the mechanical stiffness constant is important since it has an impact on the electromechanical characteristics of the device (Balakrisnan et al. 2012). In this paper, we report the electrostatic actuation of a parallel plate MEMS micro-actuator. We confirmed that the thickness of the spacer that separates the movable membrane and stationary bulk chips alters the electrostatic force, which in turn affects the displacement of the movable membrane; we use this information to estimate the sensitivity and mechanical stiffness. Unlike other mechanical hardness tests that require the d
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