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M. Piller, N. Luhmann, M.-H. Chien, S. Schmid:
"Nanoelectromechanical infrared detector";
Proceedings of SPIE, Vol. 11088 (2019), S. 11088021 - 11088027.

The sensitive detection of infrared (IR) radiation is a essential task in today´s modern world. The sensitivity of the state-of-the-art uncooled thermal infrared detectors is still several orders of magnitude above the fundamental photon noise limit. Thermal detectors based on temperature sensitive micro- and nanomechanical resonators are a promising approach to obtain improved thermal IR detectors. Here, we present an uncooled infrared detector based on a 1 mm×1 mm large nanoelectromechanical drum resonator made of 50 nm thick low-stress silicon nitride (SiN). The detector features a titanium nitride absorber with an absorptivity of ∼30% over the entire mid-IR range. The detector drum is driven at its resonance frequency by means of a phase-locked loop. Absorbed IR radiation results in an observable detuning of the drum´s oscillation frequency. We measured an Allan deviation of σA = 5.5 × 10−7 at room temperature at a noise bandwidth of 25 Hz. With a responsivity of R = 343 W−1 this results in a sensitivity defined as noise equivalent power (NEP) of NEP = 320 pW/rtHz for an IR beam at a wavelength of 9.5 µm. For this measurement, the IR beam focus spot diameter was equal to the drum size. The drum´s responsivity improves by a factor of ten for a focal spot size smaller than ∼ 100 μm. For smaller spots the responsivity remains constant. Based on this analysis we predict a sensitivity of ∼ 30 pW/rtHz for an IR spot size smaller than 100 μm. The detector can be improved further by e.g. optimizing the tensile pre-stress to a lower value or by improving the absorptivity.

http://dx.doi.org/10.1117/12.2528416