In-plane tip deflection and force achieved with asymmetrical polysilicon electrothermal microactuators

Several microactuator technologies have recently been investigated for posi tioning individual elements in large-scale microelectromechanical systems ( MEMS). Electrostatic, magnetostatic, piezoelectric and thermal expansion ar e the most common modes of microactuator operation. This research focuses o n the design and experimental characterization of two types of asymmetrical MEMS electrothermal microactuators. The motivation is to present a unified description of the behavior of the electrothermal microactuator so that it can be adapted to a variety of MEMS applications. Both MEMS polysilicon el ectrothermal microactuator design variants use resistive (Joule) heating to generate thermal expansion and movement. In a conventional electrothermal microactuator, the 'hot' arm is positioned parallel to a 'cold' arm, but be cause the 'hot' arm is narrower than the 'cold' arm, the electrical resista nce of the 'hot' arm is higher. When an electric current passes through the microactuator (through the series connected electrical resistance of the ' hot' and 'cold' arms), the 'hot' arm is heated to a higher temperature than the 'cold' arm. This temperature increase causes the 'hot' arm to expand a long its length, thus forcing the tip of the device to rotate about a mecha nical flexure element. The new thermal actuator design eliminates the paras itic electrical resistance of the 'cold' arm by incorporating an additional 'hot' arm. The second 'hot' arm results in an improvement in electrical ef ficiency by providing an active return current path. Additionally, the 'col d' arm can have a narrower flexure than the flexure in a conventional singl e-'hot' arm device because it does not have to pass an electric current. Th e narrower flexure element manifests improved mechanical efficiency. Deflec tion and force measurements of both actuators as a function of applied elec trical power have been presented in this work. (C) 2000 Elsevier Science B. V. All rights reserved.