A dual-styli micro-machined system for precise determination of the thickness of free-standing thin films

Free-standing thin membranes have now been widely applied in various research and industrial fields. As one of the key parameters of thin membranes, the membrane thickness is demanded to be precisely determined. A traceable membrane thickness measurement system is presented in this paper. It utilizes a pair of micro-machined nano-force transducers to actively detect both surfaces of a free-standing micro-machined membrane. Thanks to the high force sensitivity (down to a few Nanonewton) and a relatively large movement range (up to 10 μm) of the MEMS transducers in use, the proposed thickness measurement micro-system is capable of measuring membranes with small open aperture and membrane thicknesses down to sub-100 nm. In addition, the in-plane movement of the MEMS-transducers is measured in real-time by a single-frequency laser interferometer with nanometric resolution, which is traceable to the SI unit. Numerical analysis of the tip-membrane mechanical contact at nano-scale has been undertaken, which guides the selection of appropriate stylus radius used for experiments. Design and construction of the miniature thickness measurement system are detailed in this paper, including the first measurement results, which prove the feasibility of the proposed measurement system.