Study on Ultrahigh Vacuum Compatible Ultrasonic Motor

Abstract

As requirements for processing and observing nanometer order sized structure are increasing, significance of electron beam systems such as SEM, TEM and EB machine tools is rising. To make the best use of these systems, they should be incorporated with devices that can position their work pieces or specimens very precisely. In addition to this precision, high or ultrahigh vacuum compatibility and nonmagnetism are required of those positioners that are installed in the specimen chamber of such electron beam systems. To realize such devices, the authors are developing an ultrasonic motor that can operate keeping ultrahigh vacuum condition of the chamber in which it is installed. In this paper, friction material at stator-rotor interface is discussed. Several plastics and ceramics were tested as candidates of rotor surface in preliminary experiments, and stainless steel SUS304 and zirconia ceramic were selected as materials of stator and rotor surface. After 48 hours bakeout treatment at 200°C, gas pressure in a vacuum chamber on which the motor is installed decreased to 2.0×10-8Pa. When the motor operation was initiated, the gas pressure rose up to higher 10-7Pa and gradually decreased and reached an ultrahigh vacuum range of 8×10-8Pa after 3hours of operation.