| Stiction, a term commonly used in Micro Electro Mechanical Systems (MEMS) to refer to adhesion, is a major failure mode in MEMS. Undesirable stiction, resulting from contact between surfaces, can compromise MEMS reliability. To improve reliability, a solid knowledge of forces that cause stiction is required. The main objective of this thesis is to develop a theoretical model that can explain sticky forces between rough micro surfaces.;Finally, stiction in MEMS is modeled by combining the above models. The results from the numerical simulations of the model in dry and wet environments are compared with the data from experimental measurements of stiction by other groups. The model exhibits good agreement with the experimental data.;As the first step, a new multiple point asperity model, called n-point asperity model, is developed for modeling contact geometry. Various parameters of interest such as distribution of asperity heights and curvatures are formulated using the new model. A special case of the model is considered for a Gaussian distribution and exponential autocorrelation function (ACF). The results are compared with measurements from simulated and sampled profiles with a remarkable agreement. In the next step, using the n-point asperity model, a new model is developed for the elastic/plastic deformed area and contact load. The new model demonstrates a very good agreement with the available numerical models. Van der Waals (vdW) force is a source of stiction in MEMS. In this thesis, this force is formulated using two different methods: one is based on the n-point asperity model, and the other is based on summing up the vdW forces using the one-dimensional distribution of heights. Comparing the two methods, a very good agreement is obtained, which in turn validates the n-point asperity model, and verifies the reliability of each individual models. Capillary force is another source of stiction in MEMS. In this thesis, the n-point asperity model is used for modeling this force. The case of Gaussian distribution and exponential ACF is considered as a special case, and the capillary force is found to be proportional to the reciprocal of the rms roughness. |
