Magnetic/Fluid-Bearing Stage for Atomic-Scale Motion Control

This paper briefly describes the design, construction, controller implementation, and performance of a magnetically-suspended six-degree-of-freedom precision motion control stage. The suspended platen (3 kg mass) is floated in oil to support its weight and to provide mechanical damping and high-frequency coupling. Twelve electromagnets and six capacitance probes operate through the resulting oil film to exert control forces and to measure the position of the stage, respectively. Our hybrid approach of magnetic and fluid bearings allows the stage to achieve performance not possible with either approach alone. The magnetic/fluid-bearing stage is designed to ultimately achieve 1 angstrom (.004 /lin) resolution in a 100 /lm cube of accessible travel. The stage has applications in areas such as scanned probe microscopy, fine motion control for X-ray and optical photolithography, diamond tool machining, and probing and analysis of integrated circuit structures. At the present time, the stage is operational, with travel of 100 /lm and noise under one nanometer peak-to-peak. vVe have used the stage to provide scanning motions for scanned tunnelling microscopy and have imaged nanometer-scale features with good performance.