Two-Axis Electromagnetic Scanner Using an Asymmetric Frame on a One-Axis Lateral Magnetic Field

Abstract

Conventional electromagnetic microelectromechanical system scanners require a biaxial (two-axis) external magnetic field to obtain a biaxial torque, which increases the number of bulky external permanent magnets and the packaging size caused by 45 • -orientated placement of permanent magnets. Thus, this study developed a two-axis resonant electromagnetic scanner with an asymmetric gimbal frame that generates two-axis torque via a one-axis lateral external magnetic field. As external permanent magnets can be placed parallel to the device die, the proposed method reduced the packaging size. Two driving forces were generated by two independent electromagnetic actuators placed on both sides of the asymmetric gimbal frame, which converted the unidirectional forces into two-axis torque. As the two driving actuators were independent of the connecting beams, gimbal frame, and mirror and were connected to the thick outer Si handle frame, the temperature increase of torsion beams and the asymmetric gimbal frame, which affects the resonant performance, were reduced. Additionally, as the current paths were not multiturn coil shapes, the paths can be formed with a via-less single metal layer. Also, the drive circuit can be simplified since drive signals for two-axis rotation can be applied to individual actuators. We demonstrated biaxial scanning using the proposed structure with a 4-mm mirror. The optical scanning angle was 4.84 • for the 1.308 kHz X-axis scan and 16.1 • for the 2.568 kHz Y-axis scan when a current of 300 mA was applied independently to the X-and Y-axes driving actuators. We obtained the large displacement at the resonant frequency using the asymmetric gimbal frame under a lateral magnetic field.[