Abstract
Micro torsion actuator is widely used in micro torsion reflecting mirror to be one of the important applications of MOEMS (Micro-Optical-Electro-Mechanical system). For fabrication benefits and improving yield ratio, the upper electrodes of torsion actuator are often used as reflecting mirror, too. However, the structure of actuator would be deformed by induced thermal residual stress due to mismatch of thermal expansion coefficients between the upper electrode and structure layer after devices being cooled down to room temperature from hundreds degree process of depositing electrodes layer. And the performance of mirror would be affected by deformation. Therefore, effect of electrodes size and position on deformation is investigated in this work. The FEM software ANSYS is used as analyzing tool. It is found the smaller electrode area would induce less deformation. And the electrodes positioning more close to the torsion axis of actuator would have larger deformation initially. When the upper electrode is more near to the free end, it will have smaller deformation. Effect of dividing the whole electrode into several smaller sub-electrodes on deformation is also discussed. The results show the deformation becomes smaller as the number of divided sub-electrodes increasing. However, as the number is larger than five, the deformation will reach a limit value, that is, the deformation has no significant difference as the number increasing.
