Development of nanocavity sealing process for MEMS optical interferometric biosensor

This paper reports a MEMS-based Fabry-Perot interferometric biosensor that utilizes an optical transmittance change via Fabry-Perot interference to enhance the conversion efficiency from the mechanical displacement to electrical readout. The novel signal transducing technique was performed in three steps, namely, mechanical deflection, transmittance change, and photocurrent change. The newly proposed flat sensor structure with a trench refill provides reliability, robustness, and high yield. The polychloro-para-xylylene thin film was released by XeF₂ using a polysilicon sacrificial layer. The etching holes were sealed to prevent any liquid contamination into the Fabry-Perot cavity. A 30-μm-thick photosensitive dry film resist was laminated on the substrate. The sensing area was opened by standard photolithography, exposing UV light using a manual aligner. The interference peak position indicated that the freestanding parylene-C film kept hollow construction without stiction. During the liquid supplying to the sensor, no liquid leakage was observed because output current shows constant. In conclusion, the nanocavity sealing process was successfully demonstrated.