High speed rotation of small rotors is needed more and more in many industrial applications. Classical examples are compact devices like scanners, gyroscopes, centrifuge units and so on. The key to achieve high rotating speeds is to have contactless bearings. Active magnetic bearings (AMBs) allow the levitation of a body by magnetic forces with no mechanical contact; therefore AMBs offer a very good solution for rotating machines of which speed is limited by friction and wear. A conventional AMB is basically composed of electromagnetic coils, an automatic controller and position sensors. This thesis investigates the rotating speed limitations and suggests solutions to increase the rotating speed. Three micro-motors, consisting of a one or three axis AMB with an induction motor, are proposed in order to levitate and spin sub-millimetric spherical rotors (down to 0.5 [mm] diameter). Small spherical rotors with diameter down to 0.5 [mm] have been levitated and spun. For the three axis AMB micro-motor, the maximum reported rotating speed for the 1 [mm] rotor is 186'000 [rpm] at atmospheric pressure and 2'880'000 [rpm] at 0.05 [mbar]. This last result is the second fastest rotating speed ever reached.