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Millipixel image correlation for sub nm measurement of MEMS motion

A 1D digital image correlation algorithm capable of measuring the motion of microelectromechanical systems (MEMS) devices with sub nm resolution is presented. Successive micro photographic images are recorded, then subsets of the images are column averaged and the resulting 1D profiles are cross correlated. Factors that limit the correlation resolution are examined and methods for achieving millipixel level repeatability are discussed. Key to high resolution correlation of MEMS motion were low image noise and high sum of square of subset intensity gradients (SSSIG), a measure of image contrast. Using this correlation algorithm, the motion of MEMS thermal actuators was measured. Sub nm resolution was achieved using a wide range of image subsets, with measured standard deviations as low as 0.10 nm (0.6 millipixels).