NPGS  : Logarithmic Spirals

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This image shows a double logarithmic spiral where the marker at the bottom is 1 micron long. The lifted off metal is 45nm Au on 5nm Cr. This image shows just an initial test structure, while the final device will have each spiral written in a separate lithography step and will use the NPGS alignment feature for accurate registration of the overlap at the center. Note that in the pattern design, the "spirals" are defined as filled polygons where the polygon sides are short enough to effectively produce smooth curves. It is also important to note that NPGS does not fracture arbitrary filled polygons into trapezoids, as done in less sophisticated systems. Instead, NPGS sweeps the beam with a consistent point spacing while the length of each pass is constrained to fit into the arbitrary shape. This work was done by Dr. C. Berven while a postdoc with Dr. Martin Wybourne at Dartmouth College. (The image was acquired with the NPGS Digital Imaging feature on an otherwise analog SEM.)