Creep and Fatigue Failure in Single- and Double Hot Arm MEMS Thermal Actuators

Abstract

Determination of the failure mechanisms of mechanical devices is the key to the design of reliable products. This paper reports an investigation on creep and fatigue failure of microelectromechanical (MEMS) thermal actuators. Finite element modeling is used to predict thermomechanical behavior of actuators under low to moderate voltage differences. The modeling results are compared with experimental results to evaluate the models. Two probable failure modes associated with thermal actuators, that is, fatigue and creep, are investigated, and it is found that creep is the dominant failure mechanism. The creep behaviors of several U-shape and double hot arm thermal MEMS actuators are examined, and their deformation-time curves are obtained numerically and experimentally. The curves follow a typical three-stage creep curve usually observed in metals. The creep life cycles of the devices are compared on the basis of their stress and temperature distributions. This study shows that actuators with the maximum temperature occurring at the location where the high stress is induced have shorter life spans than those experiencing the high stress away from the maximum temperature location. It is concluded that the double hot arm actuators with equal length have longer creep life than the U-shape (single hot arm) actuators.

Mechanical and tribological characterization of a thermally actuated MEMS cantilever

“…This type of actuation has the advantage of producing relatively large force and displacement compared to electrostatic actuation (Zhu et al 2006;Geisberger et al 2003). Moreover thermal actuators are usually simpler, more reliable and easier to fabricate using surface micromachining processes (Paryab et al 2009). However, these force performances cost a very large input of energy and are performed at very low operating frequency due to the time response to reach thermal equilibrium (Rebeiz 2003;Yang et al 2008).…”