Holographic microscope for measuring displacements of vibrating microbeams using time-average holography

摘要

An optical microscope, utilizing the principles of time-average hologram interferometry, is described for MicroElectroMechanical Systems (MEMS) applications. MEMS are devices fabricated via techniques such as micro photolithography to create miniature actuators and sensors. Many of these sensors find their way into applications which rely on, or depend upon, the dynamic behavior of the sensor. Typical dimensions of current MEMS devices are measured in microns, and the current trend is to further decrease the size of MEMS devices to submicron dimensions. However, the smaller MEMS become, the more challenging it is to measure with accuracy the dynamic characteristics of these devices. In this paper, the theory and construction of an electro-optic holographic microscope (EOHM) for the purpose of studying the dynamic behavior of MEMS devices are described. Additionally, by performing measurements within an EOHM image, object displacements are determined as illustrated by representative examples. With the EOHM, MEMS devices with surface sizes ranging from approximately 35×400 microns down to 5×18 microns have been studied while undergoing resonant vibrations at frequencies as high as 2 MHz.