Design Rules for Capillary Force-Induced Clustering and Recovery of Monolithic Microbridges on Microapertured Polymer Membrane.

ABSTRACT

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