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

Abstract

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 (nSiN = 2.0) than conventional materials such as Si (nSi = 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 λ = 3.0–3.6 μm. 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.

Environmental Monitoring: A Comprehensive Review on Optical Waveguide and Fiber-Based Sensors

“…To investigate VOCs, silicon nitride (SiN) waveguide-based mid-IR sensors were developed and tested [ 132 ]. With a lower refractive index than common materials such as Si, SiN thin films made using low-pressure chemical vapor deposition (LPCVD) have a wider mid-IR transparent zone, which results in a stronger evanescent wave and increased sensitivity.…”

“… ( a ) Sensor device with PDMS chamber and SiN waveguides. Waveguides for the input and output had a 5 mm offset [ 132 ], ( b ) SEM image of the waveguide and inset shows the side wall [ 132 ], ( c ) near-field pattern of the fundamental mode [ 132 ]. …”

Environmental Monitoring: Emphasis on Optical Waveguide and Fiber-Based Sensors: A Review

“…To investigate VOCs, silicon nitride (SiN) waveguide-based mid-IR sensors were developed and tested [132]. With a lower refractive index than common materials like Si, SiN thin films made using low-pressure chemical vapor deposition (LPCVD) have a wider mid-IR transparent zone, which results in a stronger evanescent wave and increased sensitivity.…”

“…This shows that the input light was tightly contained within the SiN waveguide and that the offset design effectively reduced the background light in the substrate layer. (c) Near-field pattern of the fundamental mode [132].…”

Spatio-temporal photolysis rate profiles of UV254 irradiated toluene

“…Most VOCs are hazardous and harmful to the human’s health and are considered environmental pollutants as they cause some environmental problems; e.g. a photo-chemical smog 1 , 9 , 10 . Different treatments are followed in order to minimize the emissions of VOCs into the ambient air.…”