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Proceedings Paper

Degradation evaluation of microelectromechanical thermal actuators
Author(s): J. K. Luo; Y. Q. Fu; Q. A. Huang; J. A. Williams; W. I. Milne
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Paper Abstract

Metal based thermal microactuators normally have lower operation temperatures than those of Si-based ones; hence they have great potential for applications. However, metal-based thermal actuators easily suffer from degradation such as plastic deformation. In this study, planar thermal actuators were made by a single mask process using electroplated nickel as the active material, and their thermal degradation has been studied. Electrical tests show that the Ni-based thermal actuators deliver a maximum displacement of ~20 m at an average temperature of ~420 °C, much lower than that of Si-based microactuators. However, the displacement strongly depends on the frequency and peak voltage of the pulse applied. Back bending was clearly observed at a maximum temperature as low as 240 °C. Both forward and backward displacements increase with increasing the temperature up to ~450 °C, and then decreases with power. Scanning electron microscopy observation clearly showed that Ni structure deforms and reflows at power above 50mW. The compressive stress is believed to be responsible for Ni piling-up (creep), while the tensile stress upon removing the pulse current is responsible for necking at the hottest section of the device. Energy dispersive X-ray diffraction analysis revealed severe oxidation of the Ni-structure induced by Joule-heating of the current.

Paper Details

Date Published: 18 February 2008
PDF: 10 pages
Proc. SPIE 6884, Reliability, Packaging, Testing, and Characterization of MEMS/MOEMS VII, 688405 (18 February 2008); doi: 10.1117/12.760918
Show Author Affiliations
J. K. Luo, Univ. of Bolton (United Kingdom)
Y. Q. Fu, Univ. of Cambridge (United Kingdom)
Q. A. Huang, Southeast Univ. (China)
J. A. Williams, Univ. of Cambridge (United Kingdom)
W. I. Milne, Univ. of Cambridge (United Kingdom)

Published in SPIE Proceedings Vol. 6884:
Reliability, Packaging, Testing, and Characterization of MEMS/MOEMS VII
Allyson L. Hartzell; Rajeshuni Ramesham, Editor(s)

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