Microstructure Deflection Research Articles

Fatigue fracture mechanics in gold-based MEMS notched specimens: experimental and numerical study

The characterization of fatigue fracture mechanics in gold-MEMS notched specimens is presented in this work. A test microstructure with a central notched specimen is specifically designed and built to perform on-chip fatigue test. The central specimen undergoes cyclic loading due to the application of alternating voltage. The variation in the microstructure deflection is measured using an optical profilometer and is attributed to the crack growth in the gold material, causing the variation in the specimen stiffness. The occurrence of pull-in condition is used as a fracture detector, then the fracture of the specimen can be recognized without performing scanning electron microscope inspections during the fatigue test. Crack propagation in the test specimen is simulated through a coupled-field electromechanical fracture finite element model and the resulting crack path is compared to the experimental measurments performed with scanning electron microscope analyses. Finally, Paris’ law is applied and the number of cycles to failure is computed by exploiting the results of the fracture model and experimental measurements. Both experimental and numerical results demonstrate that the notch acts as a stress and strain raiser, fostering crack nucleation, and that the linear elastic fracture mechanics theory is still valid to describe crack propagation in micro-size samples.

Deflection Measurement and Determination of Young’s Modulus of Micro-cantilever Using Phase-shift Shadow Moiré Method

The deflection of micro-structures have been previously measured using optical interferometry methods. In this study, the classical phase-shift shadow moire method (PSSM) was applied to measure the deflection of a silicon micro-cantilever and to determine the Young’s modulus of the cantilever material. The modulus value was determined from the profile based on deflection equation. A normal white light source and a grating of 40 line pairs per mm were used to generate the moire fringes. Since the use of white light and high-resolution grating produces low contrast moire fringes, the fringe visibility was enhanced by applying contrast enhancement and filtering techniques. The Young’s modulus of the silicon cantilever material was estimated to be 165.9 GPa with an uncertainty of ±11.3 GPa (6.8%). The experimental results show that the PSSM method can be successfully applied for characterizing micro-cantilevers. Comparison of the deflection profile from the proposed method and a commercial 3-D optical profiler showed that the measurement range and sensitivity of PSSM are not affected by the poor contrast images.

Mechanical behavior of a novel resonant microstructure for magnetic applications considering the squeeze-film damping

The mechanical behavior of a novel resonant microstructure for magnetic applications through analytical and finite element (FE) models is presented. The squeeze-film damping is included with the development of a theoretical model which considers the parallel and transversal beams of the resonant structure. The response of the microstructure is obtained considering various magnetic fields orientations, and AC excitation currents with different magnitudes and frequencies. The microstructure has thin beam elements of polysilicon, 1.5 μm thickness by 20 μm width. It is suspended by air-gap of 2.5 μm and operates in the first torsional mode taking advantage of the Lorentz force principle. The analytical and FE results indicate a linear behavior of the microstructure deflection with a low consumption of AC current (574 μA) caused for 2 V AC voltage. Optimum response obtained using the mathematical analysis was 530 nm/Tesla with the magnetic field parallel to the microstructure (θ = 90° and α = 0°). These results show good agreement with the FE models.

Estimation of bending stress of microcantilever. Investigation of measuring principle using macro-model.

A measurement system constructed with a micro fizeau interferometer and the spatial fringe analysis method is proposed to measure precisely a deflection of micro structures. The results of the deflection are given as the boundary condition of the FEM. A stress in the element is analyzed by the FEM. To confirm the validity of the principle, the experiment is performed with a macro model. The measuring optical system for the macro model is constructed with a projection moire system. Without any contacts, the stress map in the element can be estimated by this method. Comparing the results from this method and strain gauges, it confirms that the accuracy of the estimation of the stress is less than 5 MPa in the macro model. On basis of results in the macro model, a stress in a micro cantilever can be estimated.