Fabrication of Conical Microstructure Array for Stable Droplet Generation Over Wide Flow Rate Range

Droplet generators with the ability to resist flow fluctuations are of importance for microfluidic chip analysis systems. However, obtaining stably desired-size droplets is still a bugbear since even slight fluctuations can cause polydisperse droplets. In this study, a high-performance droplet generator is achieved with a functional conical array housed in the junction of the channels. The conical microstructures are fabricated through the selective etching of the scratched silicon nitride/silicon (Si₃N₄/Si) substrate in potassium hydroxide (KOH) etchant, where the combination of lateral and normal material removal contributes to the structure formation. It is found that the key role of the conical microstructures is to regulate the flow rate of the continuous phase, which allows droplet generation to turn to the necking phase and enables droplets to shed more easily. It is also noted that the droplet generator with such a conical array can produce monodisperse droplets in wide-range flow, providing new insights for high-quality device design.