Uncooled thermal infrared detection near the fundamental limit using a silicon nitride nanomechanical resonator with a broadband absorber

Abstract

Thermal infrared detection plays a critical role in applications like environmental monitoring and biomedical sensing. While many infrared detectors operate at room temperature with broadband spectral detection, their sensitivity is limited by noise from sources such as electronic readout and photothermal back-action. This paper introduces a thermal infrared detector using a nano-optomechanical silicon nitride resonator with a free-space impedance-matched platinum thin-film absorber, achieving an average broadband absorptance of 47%. To reduce photothermal back-action, the absorber incorporates a circular clearance for the laser. The thermal time constant is τth = 14 ms for the smallest 1 mm resonators, which also exhibit the best sensitivity with a noise equivalent power of 27 pWHz⁻¹/² and a specific detectivity of 3.8×10⁹cm√HzW⁻¹. Experimental results are compared to analytical models and finite element method simulations. These results place our resonators among the most sensitive room-temperature infrared detectors reported to date.