Surface-Plasmon-Resonance Based Narrow-Bandwidth Infrared Carbon Monoxide Detection System

A narrow-bandwidth non-dispersive infrared (NDIR) carbon monoxide (CO) detection system is demonstrated in this work. Based on surface-plasmon-resonance devices, the newly developed CO detection system can be implemented without expensive optical filters. In this CO detection system, the narrow-bandwidth infrared thermal emitter (NBITE) has a Au $/$ SiO ₂ $/$ Au tri-layer structure with hexagonal-hole pattern on the top gold layer. The pattern is a waveguide structure to generate narrow-bandwidth radiation by thermal energy. The waveguide structure is designed to match the absorption wavelength ( $4.6 \mu \text{m}$ ) of the carbon monoxide $\text{C}\equiv \text{O}$ bond. To optimize NBITE, different SiO ₂ thicknesses and heating temperatures were experimentally investigated. The full width at half maximum (FWHM) of the fabricated NBITE is $0.05 \mu \text{m}$ . On the other hand, the narrow-bandwidth infrared photodetector (NBIPD) has a Au $/$ amorphous-Si:H $/$ Au tri-layers structure with gold grating pattern on the top layer. The grating pattern is designed to absorb the $4.6 \mu \text{m}$ infrared wavelength emitted from NBITE. The amorphous-Si:H layer absorbs the infrared energy and changes its resistance. Therefore, the slope of NBIPD current versus time can be used to discriminate CO concentration. To experimentally evaluate the developed CO emitter $/$ detector, a prototype system for CO detection was also designed and implemented. Based on this system, CO can be detected down to 50 ppm, which is the permissible exposure limit suggested by Occupational Safety and Health Administration (OSHA).