Asymmetrical Polysilicon Electrothermal Microactuators for Achieving Large In-Plane Mechanical Forces and Deflections
- PDF / 2,250,367 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 25 Downloads / 194 Views
Asymmetrical Polysilicon Electrothermal Microactuators for Achieving Large In-Plane Mechanical Forces and Deflections Edward S. Kolesar, Peter B. Allen, Noah C. Boydston, Jeffery T. Howard, Simon Y. Ko, Matthew D. Ruff, Josh M. Wilken and Richard J. Wilks Texas Christian University, Department of Engineering, Fort Worth, TX 76129 ABSTRACT This research focuses on the design and experimental characterization of two types of asymmetrical MEMS electrothermal microactuators. Both MEMS polysilicon electrothermal microactuator designs use resistive (Joule) heating to generate thermal expansion and movement. Deflection and force measurements as a function of applied electrical power are presented. INTRODUCTION Numerous electrically-driven microactuators have been investigated for positioning individual elements in microelectromechanical systems (MEMS). The most common modes of actuation are electrostatic, magnetostatic, piezoelectric and thermal expansion [1]. Unfortunately, the forces produced by electrostatic and magnetostatic actuators tend to be small, and to achieve large displacements, it is necessary to either apply a large voltage or operate the devices in a resonant mode. On the other hand, piezoelectric and thermal expansion actuators can be configured to produce large forces and large displacements. Unfortunately, piezoelectric materials are not routinely supported in the fabrication processes offered by commercial MEMS foundries. As a result, these limitations have focused attention on thermally-actuated devices for generating the large forces and displacements frequently required to position and assemble complex MEMS [2]. This research focuses on improving the design and performance of the MEMS electrothermal microactuator [3]. As depicted in Figure 1, a conventional MEMS polysilicon electrothermal microactuator uses resistive (Joule) heating to generate thermal expansion and movement [3]. When current is passed through the actuator, the larger current density in the narrower “hot” arm causes it to heat and expand in length more than the “cold” arm. Since both arms are joined at their free (released) ends, the difference in length of the two arms causes the microactuator tip to move in an arc-like pattern about the flexure element incorporated at the anchor end of the “cold” arm. Removing the current from the device allows it to return to its equilibrium state. The design of the flexure used in electrothermal microactuators is an important functional element [4]. Ideally, the flexure element should be as narrow as possible. Narrower flexures allow more of the force generated by the thermal expansion of the “hot” arm to cause movement at the tip of the microactuator. In the conventional electrothermal microactuator depicted in Figure 1, electrical current passes through the flexure. If the flexure were to be narrower than the “hot” arm, the temperature of the flexure element would be greater than the “hot” arm, and it could be destroyed by excessive heat. Additionally, the flexure element needs to be sufficient
Data Loading...
