Date of Award

Winter 12-2023

Author's School

McKelvey School of Engineering

Author's Department

Mechanical Engineering & Materials Science

Degree Name

Master of Science (MS)

Degree Type



Ultrasonic microdroplet generators are useful devices with broad applications ranging from aerosolized drug delivery to three-dimensional (3D) printing-based additive manufacturing. One such technology comprises a microfabricated array of nozzles with droplet production driven by a piezoelectric transducer. The present study focuses on refining a critical fabrication step, anisotropic wet etching of pyramidal nozzles using a basic potassium hydroxide (KOH) solution. Given the integral role of nozzle geometry in device operation, high-precision techniques including Reactive Ion Etching (RIE), Deep Reactive Ion Etching (DRIE), and KOH wet etching were employed. A tapering geometry is preferred for acoustic wave focusing and efficient droplet generation, and KOH etching naturally yields pyramids due to preferential removal of the (100) plane versus the (111) plane of single-crystal silicon. Though wet etching is less precise than dry etching, it is difficult to form these 3D shapes using dry etching alone. Thus, this work focused on realizing the highest possible level of control over KOH etching. Challenges were encountered in using a conventional etching setup to achieve uniform etching and good surface smoothness, which are crucial to definition of the pyramidal tip geometry. These aspects are also important for use of KOH etching to define microstructures in a range of microfluidic systems. Here, we introduce an ultrasonic-assisted etching method to enhance the KOH etching process, addressing issues like non-uniform etching rates and surface roughness. This research not only provides insight into the microfabrication of ultrasonic microdroplet generators but also contributes to further improvements in microfluidic device manufacturing.


English (en)


John Mark Meacham

Committee Members

Patricia Weisensee Xianglin Li