Spectroscopic Chemical Sensing Based on Narrowband MEMS Resonant Infrared Detectors

This paper reports on the first experimental demonstration of transmission spectroscopy-based chemical sensing using narrowband uncooled microelectromechanical resonant infrared detectors. An aluminum nitride nano-plate resonator integrated with a spectrally-selective plasmonic absorber is used to measure the concentration of benzonitrile by targeting its characteristic absorption wavelength (~4.5um). The narrowband absorption property of the plasmonic resonant infrared detector (absorptance ~92% at 4.7um with a full width at half maximum ~800 nm) allows the use of a blackbody as infrared source to characterize the transmission of chemicals in the spectral bands of interest without the need of any lasers or filters. This provides having multiple such sensors occupying a small chip area to target different chemicals, resulting in overall improvement in sensor capabilities while enabling its miniaturization. Furthermore, thanks to the optimized thermal isolation of the device, a high resolution for thermal detection (noise equivalent power ~463pWIHz1/2) is achieved, which translates to a minimum detectable concentration of ~0.01% (Benzonitrile in Hexane).