Study On Out-of Plane Motion In MEMS Using Phase-stepping Microscopic Interferometry And Stroboscopic Imaging Technique

MEMS dynamic testing technique is an important part of MEMS testing technology.It can result many key data, such as dynamic characteristics, material characteristicsand mechanical parameters, by measuring the three-dimensional motion of MEMS.But it must be resolved to record the motion moment of MEMS and analyze theout-of plane motion of MEMS surface. After we have learned a lot of knowledges, the paper set up a MEMS out-of planemotion measuring system based on stroboscopic imaging technique andphase-stepping microscopic interferometry and promoted a new algorithm nameddouble-direction phase unwrapping. In experiments, the new system had a success tomeasure the out-of plane motion of micro-resonator. The major works in paper arefollowing:1. Setting up a MEMS out-of plane motion measuring system. The paper has a general explain for the principle of phase-stepping microscopic interferometry, analyzes its technique details including the optical layout of interference microscope, phase-shifting interferometry, and phase unwrapping technique, and discusses various methods or algorithms in each part, especially the main factors which lead to measuring errors largely. During setting up the system, I selected LED light source by comparing capability, improved LED driving circuit, modified high voltage amplifier circuit, and made each part work together.2. Advancing a new double-direction phase unwrapping algorithm which unwraps phases along both spatial and temporal directions based on stroboscopic imaging technique. The paper finds a good phase-stepping algorithm that is immune to linear and nonlinear phase shift error, non-sinusoidal characteric of fringe intensity signal, and nonlinear response of CCD camera. After the characteristics of MEMS out-of plane measuring is discussed, a simple and practical phase unwrapping algorithm is promoted in paper. And I programmed a data processing software using MATLAB software which integrated phase wrapped, phase unwrapping, phase-height conversion and basic plane leveling functions.3. Setting up the synchronized control system of stroboscopic imaging based on virtual instrumentation technique. This section includes hardware building, waveform edition of driving signal and control signals, and the design of synchronized control strategy. For time relay in work has a strong influence onsystem natural function, calibrating time relay and its countermeasure are carried out and depicted in paper.4. Testing the new system. First, there was static out-of plane height measurement experiment using NIST-traceable triangle step-height standard which had 44nm height to ensure system's measuring precision. It was indicated by results that the repeatability precision of system was 0.52nm.Then measuring the out-of plane motion of micro-resonator was performed. Stroboscopic imaging synchronized control system recorded successfully interferograms of micro-resonator motion moment. And the data processing software restored its out-of plane motion tracks perfectly. The system also carried out frequency-scanning measurement to micro-resonator's out-of plane motion.