Optimization of the Geometry of the MEMS Electrothermal Actuator to Maximize In-Plane Tip Deflection
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Optimization of the Geometry of the MEMS Electrothermal Actuator to Maximize InPlane Tip Deflection Edward S. Kolesar, Thiri Htun, Brandon Least, Jeffrey Tippey, and John Michalik Department of Engineering, Texas Christian University, TCU Mail Stop 298640, Tucker Technology Center, 2840 Bowie Street West, Fort Worth, TX, 76129 ABSTRACT Several microactuator technologies have been investigated for positioning individual elements in large-scale microelectromechanical systems (MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion represent the most common modes of microactuator operation. This investigation optimized the geometry of the asymmetrical electrothermal actuator to maximize its in-plane deflection characteristics. The MEMS polysilicon surface micromachined electrothermal actuator uses resistive (Joule) heating to generate differential thermal expansion and movement. In this investigation, a 3-D model of the electrothermal actuator was designed, and its geometry was optimized using the thermo-mechanical finiteelement analysis (FEA) capabilities of the ANSYS computer program. The electrothermal actuator's geometry was systematically varied to establish optimum values of several critical geometrical ratios that maximize tip deflection. The value of the ratio of the length of the flexure component relative to the length of the hot arm was discovered to be the most sensitive geometrical parameter ratio that maximizes tip deflection. INTRODUCTION The single-hot arm electrothermal actuator depicted in Figure 1 is a widely used positioning component in MEMS devices. This actuator is popular because it is capable generating the large tip forces and deflections required to position various MEMS components compared to electrostatic and piezoelectric devices. Polysilicon electrothermal actuators can operate in the conventional IC current/voltage regime, and their fabrication process is compatible with that of semiconductor devices. The magnitude of the actuator’s tip force and deflection is the primary performance metric associated with its design and application. Many studies have focused on the analysis of the dimensions of the different components of the electrothermal actuator to maximize tip deflection, and numerous researchers have proposed different models. Figure 1. Single-hot arm polysilicon electrothermal actuator. Guckel et al [1] proposed the original flexure-based electrothermal actuator in 1992. Huang et al [2] were first to develop an analytical model to predict the response of the Guckel electrothermal actuator. Hickey et al [3] then proposed a model that included the effect of thermal conduction through the device’s narrow air gap to the substrate. Mankame et al [4] presented a model that accounted for all the modes of heat transfer, and it included the temperature dependence of the thermophysical properties. Pan et al [5] presented a modified
version of the Guckel actuator that permitted different adjacent arm lengths, but they had to have the same cross sections. Lee
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