Fabrication and performance of silicon-embedded permanent-magnet microgenerators

This paper focuses on the design, fabrication, and characterization of silicon-packaged permanent-magnet (PM) microgenerators. The use of silicon packaging favors fine control on shape and dimensions in batch fabrication and provides a path toward high rotational speeds (∼ 1 Mr/min), a requirement for ultimate compactness of microgenerators. The successful silicon packaging of these microgenerators consisted of three essential elements: 1) a winding scheme allowing both nonplanar fabrication and through-wafer interconnects; 2) laminations built into the silicon for enhanced electrical performance; and 3) a balancing scheme for the heavy PM rotor to ensure its maximum performance. The devices were fabricated using bonded silicon wafers, integrated magnetics, and an electroplated metal. The mechanical strength of the 12-mm-diameter silicon-packaged PM rotors was evaluated at high rotational speeds using an external spindle drive. Speeds up to 200000 r/min were achieved prior to a mechanical rotor failure. The generators were electrically characterized, and an output power in excess of 1 W across a resistive load of 0.32 Ω was measured at a maximum speed. A 225% power increase was also experimentally determined due to the addition of a laminated stator back iron.