Influence of material stiffness and geometrical variations on the electro-thermally driven microactuator performance

Abstract

In order to make robust design of microdevices, it is important to implement a model considering uncertainty analysis. The high cost of experimentation and product development has led to an emphasis on simulated based design to achieve the success in the first-pass design and reliability. In this paper, finite element model is developed to investigate the effects of geometrical and material stiffness variations on an electro-thermally driven microactuator performance as an example. These microactuators are generally composed of two suspended beam (arm) joined at the free end. This device generates deflection through asymmetric heating of the hot and cold polysilicon arms with variable length or cross-section. These microactuators based on the force and deflection characteristic of elastic members are particularly sensitive to uncertainty in material properties. Polysilicon as a microdevice material shows a wide variation rang for Young's modulus from batch to batch fabrication process. Also, the microfabrication process that are utilized for microdevice production can yield sometimes shapes that are not geometrically perfect, either due to the microfabrication process limitations itself or because of phenomena that take place during or after microfabrication. These geometrical errors can decrease the net cross section and will affect both modeling and experimental results. The effect of fillet radius at the juncture of this flexible microactuator and contact pads is investigated in this model. The residual stresses due to the fabrication process are taken into account too. The analysis is performed at multiple input voltages to estimate uncertainty bands around the deflection curve of the microactuator. Simulation results are compared with experimental results in literature. The results demonstrate how each of these factors affects the microactuator performance and justifies the deviation of previous nominal results from experimental results.

Effect of dimensional and material property uncertainties on thermal flexure microactuator response using probabilistic methods

“…In microfabrication process, as a consequence of photolithography exposure, etch undercut, both widths and the lengths of parts can be p offset = 0.1 ± 0.08 lm (Fig. 2) less than specified value with standard deviation of 0.04 lm for 95% confidence (Shamshirsaz et al 2009;Tanner et al 2003;Gupta 2000). In this paper, the variation in beam widths and lengths of microactuator and gap between hot and cold arms are assumed similar to data reported by Wittwer (Wittwer 2005):…”

“…This device generates deflection through asymmetric heating of the hot and cold polysilicon arms with variable length or cross-section. However, many efforts have been carried out to explore the characterization and behavior of electro-thermally driven microactuators (Shamshirsaz et al 2009;Huang and Lee 1999a, b;Atre 2006;Pan and Hsu 1997), but few works have been carried out to consider the influence of material and geometrical uncertainties on electrothermal microactuator performance. Simulation-based design under uncertainty for compliant microelectromechanical systems has been studied by Wittwer using response surface metamodeling (RSM) (Wittwer 2005).…”

“…Simulation-based design under uncertainty for compliant microelectromechanical systems has been studied by Wittwer using response surface metamodeling (RSM) (Wittwer 2005). Also, influence of material stiffness and geometrical variations on the electro-thermally driven microactuator performance using finite element model has been studied by Shamshirsaz et al (2009).…”

“…The thermal microactuators based on the force and deflection characteristic of elastic members are particularly sensitive to dimensional and material property uncertainties (Wittwer 2005;Shamshirsaz et al 2009). Due to the high cost and slow turn-around during the prototyping stage of these microactuator designs, it is important to take uncertainties into account in order to increase first-pass success and shorten the product cycle (Wittwer 2005).…”

Dynamic modelling for thermal micro-actuators using thermal networks

“…FEM analysis is principally used to demonstrate the feasibility of the design and to simulate the behaviour; for example, the relationship between the applied voltage and the displacement [1,37,43,44], or the effects of geometrical and material stiffness variations on the performance [45].…”