A Radial-Flux Permanent Magnet Micromotor With 3D Solenoid Iron-Core MEMS In-Chip Coils of High Aspect Ratio

Because of the difficulty in fabricating iron-core solenoid coils by micro electro-mechanical system (MEMS) processes, existing micromotors typically have an axial-flux structure with planar spiral coils or air-core solenoid coils. However, solenoid iron-core microcoils have a higher inductance and a lower magnetic resistivity than spiral coils and air-core solenoid coils. In this study, a radial-flux permanent magnet (PM) micromotor with 3D iron-core MEMS in-chip coils of high aspect ratio was designed and fabricated. The three-phase PM brushless direct current (BLDC) micromotor has four Nd-Fe-B magnet poles on a steel rotor and six solenoid Cu coils of high aspect ratio (coil height/line width = 14) in the silicon stator fabricated using MEMS processes. Iron cores were inserted into the coils, and a low-resistivity magnetic circuit was established. At 100 Hz, the inductance of a 15-turn coil was 13.2\mu \text{H} . The coils were embedded tightly in the silicon substrate, resulting in a good heat dissipation performance and thus a high current-carrying capacity. The hexagonal sheet-type micromotor weighed 2.25 g with a volume of 586.5 mm 3 before bearing packaging. The modeling results showed that at 10000 rpm, the torque was 676\mu \text{N}\cdot \text{m} and the power density was 314 W/kg. This micromotor incorporates a conventional large-scale BLDC motor structure and the proposed design will help improve the power density and efficiency of micromotors, thereby broadening their application prospects.