Recently, Micro Electro Mechanical Systems (MEMS) components featured micro structures are extensively integrated into the applications of sensing and actuating, such as accelerometers, gyroscopes, or micro scanning mirrors.
FIG. 1A is a cross-sectional view of conventional comb-drive actuator 100. The comb-drive actuator 100 includes a supporting base 102 and an oscillating element 104. The supporting base 102 comprises a substrate 106, an insulation layer 108 and a device layer 110. Both the oscillating element 104 and the device layer 110 are co-planar, and the oscillating element 104 is suspended over a cavity. Due to co-planar arrangement of the comb finger electrodes, the torque generated by the comb-drive actuator 100 is insufficient to maintain the oscillating element 104 at a specific rotational angle. In addition, a constant biasing force may be required to activate the rotational motion of the oscillating element 104, which leads to a more complicated design for the comb-drive actuators 100.
FIG. 1B is a cross-sectional view of another conventional comb-drive actuator 100. The comb-drive actuator 100 includes a supporting base 102 and an oscillating element 104. The supporting base 102 comprises a substrate 106, an insulation layer 108 and a device layer 110. The oscillating element 104 is suspended over a cavity formed by device layer 110. It is necessary to partially remove the insulation layer 108 and the device layer 110 under the oscillating element 104 by isotropic etching step for forming the comb electrode structure. However, during the isotropic etching step, lateral undercut will be formed in the device layer 110 such that the dimension of the comb electrode structure cannot be controlled precisely. To certain extent the oscillating element 104 is asymmetrically positioned in relation to the supporting base 102 and the comb-drive actuator 100 thus cannot be normally operated.
FIG. 1C is another cross-sectional view of a conventional comb-drive actuator 100. The actuator 100 includes a supporting base 102 and an oscillating element 104. The supporting base 102 further includes a substrate 106, an insulation layer 108 and a device layer 110. The height “h1” of the device layer 110 is arranged to be less than the height “h2” of the oscillating element 104. The overlapping area between the oscillating element 104 and the device layer 110 is smaller than the comb-drive actuator as depicted in FIG. 1A. Therefore, extra input power is required for the actuator as depicted in FIG. 1C to maintain the same electrostatic driving force as the actuator as depicted in FIG. 1A. In addition, due to process variation, it is difficult to maintain a constant height difference between h1 and h2 on wafer batch process. Consequently, there is a need to develop a novel comb-drive actuator and manufacturing method thereof to solve the aforementioned problems.