A micro corona motor

A micro corona motor was fabricated and tested. Intense electric fields at sharp stator electrodes ionize air molecules, and ionized charges are transferred onto the rotor surface. Coulomb repulsion between rotor and electrodes rotates and levitates the rotor. Important design parameters, such as electrode spacing, air gap, and electrode-tilt angle, were studied using an electrostatic field simulator. For good performance, the stator's electrodes should be axially thick and have sharp tips. Therefore, X-ray lithography was adopted for precise, high aspect ratio characteristics. To avoid the fabrication difficulty of a membrane X-ray mask, a built-on X-ray mask technique was employed with negative-toned SU-8 photoresist. Speed and torque of a fabricated micro motor were measured. High rotating speed (>104 rpm) was obtained with several hundred DC volts applied. Using the spin-down method, the torque was estimated in the order of 10 nN m. For over 20 million cycles, the motor showed good stability with no additional control action.