Deformation measurement of a micro-rf capacitive switch membrane using laser interferometry

We have developed a measurement method to evaluate deformation of a metallic membrane (thickness 2 μm) in a micro-radio-frequency switch. The method is based on a modified Michelson interferometer incorporated with optoelectronic devices including a He-Ne laser, conventional optics, a CCD sensor, and a photodiode. To detect the deformation of the membrane in the rf switch, a He-Ne laser probe 10 µm in diameter is directed onto the specimen. The laser beam reflected off the membrane is combined with a reference beam. The combined laser beams are regulated to follow a common path. The resulting circular interference fringe pattern is simultaneously recorded by a CCD sensor and a photodiode. The deformation of the membrane is determined from the order of the resulting fringe pattern. As demonstrated by the experimental results, the proposed method is capable of measuring deformation of the rf switch at submicron levels.