On the buckling behavior of micromachined beams

Thin film materials are normally under residual stresses as a result of fab rication processes. Unlike microelectronics devices, a micromechanical stru cture is no longer constrained by its underlying silicon substrate after an isotropic 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 ch aracteristic can also be applied to fabricate out-of-plane three-dimensiona l micromechanical structures if their deflections are controllable. The buc kling of a microbridge is difficult to predict since it is strongly dominat ed by its fabrication processes and boundary conditions. Currently the info rmation regarding the buckling of micromachined structures is still not com plete. The application of the buckling behavior is therefore limited. In th is research, the effects of boundary conditions and gradient residual stres ses on the buckling behavior of microbridges were studied using analytical and experimental approaches. The variations of the buckling amplitude orien tations with the thickness and length of the microbridges were obtained; th erefore, the buckling behavior can be predicted and then exploited to fabri cate useful micromechanical structures. The potential application of this r esearch lies in preventing the leakage of the microvalves.