Fabrication of Buried Microchannels with Almost Circular Cross-Section Using HNA Wet Etching

In this paper, a novel fabrication process for the realization of large, suspended microfluidic channels is presented. The method is based on Buried Channel Technology and uses a mixture of HF, HNO₃, and water etchant, which has high selectivity between the silicon substrate and the silicon-rich silicon nitride mask material. Metal electrodes for actuation and read-out are integrated into the fabrication process. The microfluidic channels are released from the silicon substrate to allow the vibrational movement needed for the application. The resulting microfluidic channels have a near-circular cross-section, with a diameter up to 300 μm and a channel wall thickness of 1.5 μm. The structure of a micro-Coriolis mass-flow and density sensor is fabricated with this process as an example of a possible application.