MEMS Lamellar Based Interferometer for the Detection of Toxic Chemicals

In order to satisfy the DOD and commercial needs for the detection and identification of chemical warfare agents, toxic industrial chemicals or biological compounds, we propose a compact, low-cost sensor based on the integration of HgCdTe photodiode detection technology with micro-opto-electromechanical systems (MOEMS) technology, which matches HgCdTe’s sensitivity with an inexpensive microscale MOEMS lamellar grating interferometer (LGI) device. The sensor is operated in stand-off mode and has longer lifetimes than those obtained in conventional solid state sensors based on chemo-sensitive layers. We will fabricate LGI devices operated in short and mid IR wavelength ranges using a modified Silicon-On-Insulator (SOI) process. Prior work has used SOI processing but the deep reactive ion etch (DRIE) used to pattern the thick silicon layer has led to significant roughness on the optical surfaces leading to performance limitations associated with the resulting variability in the optical path length difference. We will use an oxidation and strip process to minimize residual roughness left on the optical surfaces after the DRIE etch step. We have used this processing successfully to remove related sidewall roughness on silicon waveguides and we estimate a final roughness of 0.5 nm in the gratings, suitable for short and mid-IR operation of the fabricated LGIs.