Uncooled Thermal Infrared Detection Near the Fundamental Limit Using a Nanomechanical Resonator with a Broadband Absorber

TL;DR

This paper presents a nano-optomechanical silicon nitride resonator with a broadband platinum absorber achieving near-fundamental limit sensitivity for uncooled thermal infrared detection, characterized by fast response and high detectivity.

Contribution

The study introduces a broadband, impedance-matched absorber integrated with a nano-resonator, demonstrating near-ideal sensitivity and fast thermal response for uncooled IR detection.

Findings

Thermal time constant as low as 14 ms for 1 mm resonators

NEP of 27 pW/√Hz and D* of 3.8×10^9 cm√Hz/W for smallest resonators

Sensitivity within a factor of three of the theoretical maximum for ideal IR detectors

Abstract

This paper introduces a thermal infrared detector utilizing a nano-optomechanical silicon nitride (SiN) resonator, equipped with a free-space impedance-matched (FSIM) absorber composed of a platinum (Pt) thin film, offering a broadband spectral absorptance on average of 47%. To reduce photothermal back-action caused by intensity fluctuations of the readout laser, the FSIM absorber incorporates a circular clearance for the laser. The study provides a comprehensive characterization of the thermal time constant, power responsivity, and frequency stability of the resonators, with experimental results compared to analytical models and finite element method (FEM) simulations. The fastest thermal response is observed for the smallest 1 mm resonators, with a thermal time constant tau_th = 14 ms. The noise equivalent power (NEP) of the resonators is assessed, showing that the smallest 1 mm resonators exhibit the best sensitivity, with NEP = 27 pW/sqrt(Hz) and a respective specific detectivity of D* = 3.8e9 cm sqrt(Hz)/W. This is less than three times below the theoretical maximum for an ideal IR detector with 50% absorptance. This places our resonators among the most sensitive room-temperature IR detectors reported to date offering an extended spectral range from the near-IR to far-IR. This work underscores the potential of nano-optomechanical resonators for high-performance IR sensing applications.