摘要
During wet etching of sacrificial layer in surface micromachining fabrication, a microstructure may be pinned on the substrate due to the capillary force of liquid. This paper investigates the adhesion criterion between a center-anchored circular plate and its underlying substrate caused by strong capillary forces. Using catastrophe theory, a non-dimensional elastocapillary number N <sub>EC</sub> , in terms of structure sizes and material properties, is derived. Theoretically, when N <sub>EC</sub> > 1 the center-anchored circular plate will restore to its desired position from substrate, while N <sub>EC</sub> > 1, it will be attached to substrate. The proposed devices have been successfully fabricated through surface micromachining to examine the proposed N <sub>EC</sub> and the results show the feasibility of using N <sub>EC</sub> to determine the adhesion criterion. From experimental data, the ratio of inner and outer radii of plates r <sub>i</sub> /r <sub>o</sub> , ranging from 0.4 to 0.7, can be used as the first approach of the adhesion criteria. By observing the experimental results, a novel adhesion criterion N <sub>AD</sub> , in terms of material properties, plate thickness, gap, r <sub>i</sub> /r <sub>o</sub> , and residual stress, is therefore defined and used to estimate the adhesion effect. The experimental results showed that only 8.87% error occurs if N <sub>AD</sub> is employed.