Abstract
The application of plasmonics to thermal emitters is generally assisted by absorptive losses in the metal because Kirchhoff’s law prescribes that only good absorbers make good thermal emitters. Based on a designed plasmonic crystal and exploiting a slow-wave lattice resonance and spontaneous thermal plasmon emission, we engineer a tungsten-based thermal emitter, fabricated in an industrial CMOS process, and demonstrate its markedly improved practical use in a prototype non-dispersive infrared (NDIR) gas-sensing device. We show that the emission intensity of the thermal emitter at the CO2 absorption wavelength is enhanced almost 4-fold compared to a standard non-plasmonic emitter, which enables a proportionate increase in the signal-to-noise ratio of the CO2 gas sensor.
Highlights
The application of plasmonics to thermal emitters is generally assisted by absorptive losses in the metal because Kirchhoff’s law prescribes that only good absorbers make good thermal emitters
non-dispersive infrared (NDIR) spectroscopy provides excellent stability, selectivity and sensitivity[20] and is the preferred gas sensing method widely used in e.g. air quality monitoring, medicine and the manufacturing industry
Since, fundamentally, thermal emission from a structure is proportional to its emissivity, namely
Summary
Design and fabrication of the nanoplasmonic crystal IR thermal emitter. The nanoplasmonic crystal IR emitter consists of a multi-ring resistive tungsten heating element (600 μ m diameter) embedded within a silicon dioxide membrane (850 μ m diameter), passivated with silicon nitride. The membrane was formed by a Deep Reactive Ion Etching (DRIE) of the silicon handling substrate, with the buried silicon dioxide layer acting as effective etch stop. We used the Finite-Element Method (FEM), employing periodic boundary conditions in the plane of the device, for the calculation of the absorption at λ = 4.26 μ m (Fig. 2a) and the absorption spectra. Emission from the structure is collected over a broad range of angles and directed through the gas cell that is alternately filled with varying concentrations of CO2 and purged again with dry air (see Fig. 1a).
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