William C. Hart

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Check valves are used frequently within the field of microfluidic MEMS, particularly in micropump applications. Check valves serve to limit the flow of a fluid to one direction through a channel. This project was an attempt to manufacture an efficient check microvalve using polysilicon as the valve cover material. Previous work on a microvalve at RIT has been unsuccessful, as the final KOH etch has attacked the polysilicon, thus removing the valves from the openings in the silicon. It was determined that pinholes in the LPCVD nitride were allowing KOH to penetrate the etch mask and attack the substrate surface and the polysilicon. In this attempt, black wax was used as a protective coating over the LPCVD nitride on the cover side of the substrate. A crucial part of this project was the testing of the produced microvalves. In this project, nine valve designs were patterned; with each valve differing in arm length and flap overlap across the substrate opening. Of these, one valve functioned correctly after processing. The remaining valves either failed to release during the final oxide etch or were etched through during KOH etching. Testing consisted of forward and reverse flow rate measurements using compressed gaseous nitrogen.

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