On the buckling behavior of micromachined beams

Thin film materials are normally under residual stresses as a result of fabrication processes. Unlike microelectronics devices, a micromechanical structure is no longer constrained by its underlying silicon substrate after anisotropic etch undercutting; therefore, residual stresses may result in the bending and buckling of a micromechanical structure. The buckling behavior has been exploited to measure the residual stresses of thin films. This characteristic can also be applied to fabricate out-of-plane three-dimensional micromechanical structures if their deflections are controllable. The buckling of a microbridge is difficult to predict since it is strongly dominated by its fabrication processes and boundary conditions. Currently the information regarding the buckling of micromachined structures is still not complete. The application of the buckling behavior is therefore limited. In this research, the effects of boundary conditions and gradient residual stresses on the buckling behavior of microbridges were studied using analytical and experimental approaches. The variations of the buckling amplitude orientations with the thickness and length of the microbridges were obtained; therefore, the buckling behavior can be predicted and then exploited to fabricate useful micromechanical structures. The potential application of this research lies in preventing the leakage of the microvalves.