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SU-8 Electrothermal Actuators: Optimization of Fabrication and Excitation for Long-Term Use

Microtechnology and Electromechanical Systems Laboratory, Institute of Electromechanical Design, Technische Universität Darmstadt, Merckstr. 25, 64283 Darmstadt, Germany
Laboratory of Experimental Solid and Micro Mechanics, Faculty of Automotive Engineering, Westsächsische Hochschule Zwickau, Dr.-Friedrichs-Ring 2A, 08056 Zwickau, Germany
Author to whom correspondence should be addressed.
Micromachines 2014, 5(4), 1310-1322;
Received: 2 October 2014 / Revised: 14 November 2014 / Accepted: 21 November 2014 / Published: 2 December 2014
(This article belongs to the Special Issue Microactuators)
PDF [4684 KB, uploaded 2 December 2014]


In this paper we examine the suitability of SU-8 2000 as a construction material for electrothermal actuators and the actuator stability for long-term operation. The fabrication of SU-8 was optimized for mechanical and thermal stability. Samples with different softbake duration, exposure dose and postbake temperature were evaluated using Fourier-Transform IR-spectroscopy and dynamic-mechanical analysis. The exposure dose and postbake temperature proved to have a strong influence on the cross-linking and the glass transition temperature. A final hardbake levels the effects of the process history. A high degree of crosslinking, a low drop of the dynamic modulus over temperature (30%) up to the glass transition temperature 100–140 °C were achieved for SU-8 with an exposure dose of 1500 mJ/cm², a postbake temperature of 95 °C and hardbake of 240 °C. Electrothermal actuators proved to be stable until the end of the experiment after 2400 duty cycles. Actuator deflections up to 55 μm were measured (actuator length: 4 mm) for input powers up to 160 mW and a maximum operating temperature of 120 °C. Higher temperatures led to permanent deformations and failure. An offset drift of up to 20% occurs during actuation, but converges after a burn-in phase of about two hours. View Full-Text
Keywords: electrothermal actuator; SU-8; long-term stability; pseudo-bimorph; glass transition temperature electrothermal actuator; SU-8; long-term stability; pseudo-bimorph; glass transition temperature

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Winterstein, T.; Staab, M.; Nakic, C.; Feige, H.-J.; Vogel, J.; Schlaak, H.F. SU-8 Electrothermal Actuators: Optimization of Fabrication and Excitation for Long-Term Use. Micromachines 2014, 5, 1310-1322.

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