Detection of volatile organic compounds using mid-infrared silicon nitride waveguide sensors

Mid-infrared (mid-IR) sensors consisting of silicon nitride (SiN) waveguides were designed and tested to detect volatile organic compounds (VOCs). SiN thin films, prepared by low-pressure chemical vapor deposition (LPCVD), have a broad mid-IR transparent region and a lower refractive index (n(SiN) = 2.0) than conventional materials such as Si (n(Si) = 3.4), which leads to a stronger evanescent wave and therefore higher sensitivity, as confirmed by a finite-difference eigenmode (FDE) calculation. Further, in-situ monitoring of three VOCs (acetone, ethanol, and isoprene) was experimentally demonstrated through characteristic absorption measurements at wavelengths lambda = 3.0-3.6 mu m. The SiN waveguide showed a five-fold sensitivity improvement over the Si waveguide due to its stronger evanescent field. To our knowledge, this is the first time SiN waveguides are used to perform on-chip mid-IR spectral measurements for VOC detection. Thus, the developed waveguide sensor has the potential to be used as a compact device module capable of monitoring multiple gaseous analytes for health, agricultural and environmental applications.

Automated summary

In this study, mid-infrared (mid-IR) sensors consisting of silicon nitride (SiN) waveguides were designed and tested for detecting volatile organic compounds (VOCs). The SiN waveguide showed a higher sensitivity compared to conventional materials, such as silicon, and allowed for on-chip monitoring of multiple VOCs. Therefore, the developed waveguide sensor has the potential to be used in various applications related to health, agriculture, and the environment.