Design Rules\nfor Capillary Force-Induced Clustering\nand Recovery of Monolithic Microbridges on Microapertured Polymer\nMembrane

Microbridge structures have been widely used in microelectromechanical\nsystems. When the devices with microbridges operate in diverse environments,\nincluding wet conditions, structural failures such as crumples, clustering,\nand collapse of micro/nanostructures occur due to the capillary force\nof liquid in this environment. It is necessary to establish comprehensive\ndesign criteria to address this. Herein, we investigate the structural\nstability of microbridges on microsized apertures in wet conditions.\nThe multiscale structure is fabricated with microbridge width, spacing\nof 10 μm, and height of 6 μm while varying the supporting\nmicro aperture size. The behavior of the microbridges is observed\nthrough an optical microscope during water dispensing on the bridges\nand evaporation. It is found that the microbridges remain stable on\napertures of 100 μm in diameter, while clustering occurs on\nlarger-sized apertures (300, 500 μm). Interestingly, in contrast\nto the 500 μm-sized aperture, the clustered microbridges on\nthe 300 μm-sized aperture gradually recover to their original\nconfiguration after completely evaporating water. A simple theoretical\nmodel for capillary force-induced clustering and recovery is proposed\nto elucidate this phenomenon, which agrees with the experimental results.\nThe microbridges constructed following the design rule can ensure\nrobust and stable operation even in wet conditions. These findings\ncontribute to advancing micro/nanoscale engineering and offer insights\nfor developing innovative microdevices.