MOTOR AND TURBO-MOLECULAR PUMP

PROBLEM TO BE SOLVED: To obtain a high vacuum from the atmospheric pressure, by securing the clearance of a ceramic gas bearing to the heat in a high frequency rotation condition, even when the clearance of the ceramic gas bearing is set narrow by the reason of the high frequency rotation condition or the like, in a motor using a ceramic gas bearing. SOLUTION: In the rotary body 25 of a motor 10, its outer peripheral part is formed of an inner tube 28, and a dynamic pressure groove is formed on the outer peripheral surface of the inner tube. An outer tube 29 is provided at the outer peripheral side of the rotary body 25. An air bearing 30 (a ceramic dynamic pressure gas bearing) to support the load of the rotary body in the radial direction is composed of an inner tube and an outer tube. In a motor used to a turbo-molecular pump, the clearance is set at 3 to 6 μm, for example, by its exhaust gas speed, the using rotation frequency, and the like. The ceramic material of the inner tube is a silicon carbide, while the ceramic material of the outer tube consists of an alumina, and the thermal expansion coefficient is made smaller in the ceramic material of the inner tube, than in the ceramic material of the outer tube.