Fabrication of polymer cantilevers for force-controlled atomic force microscope

We developed the fabrication process of all-plastic cantilever for force controlled atomic force microscope. The force controlled atomic force microscope can prevent damage during the scanning of the soft sample. However it has a drawback in its stability. To stabilize the system the cantilever is required to have small Q factor. The negative photo resist for MEMS (SU-8) has ideal properties, micromachinability and small Q factor, for this purpose. Here we demonstrate the cantilever consists of tip, lever and base with same polyimide. The mold of the probing tip is the pyramidal pit pattern on silicon wafer formed by direct leaser writing and anisotropic etching of silicon. Other elements of the cantilever are formed by contact lithography. The photo mask is also fabricated by direct laser writing. By arranging the dimensions of the cantilever, we can control its spring constant and resonant frequency. For the spring constant of 0.1N/m and the first resonant frequency of 2kHz, the typical dimensions of the cantilever is 1030 x 300 x 7 μm3. The fabrication error in cantilever geometry was 1.5%. The estimated resonant frequency has a good agreement with the designed value.

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