Nanoelectromechanical Infrared Detector

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 mmx1 mm large nanoelectromechanical drum resonator made of 50 nm thick low-stress silicon nitride (SiN). The detector features a thin film absorber with an absorptivity of similar to 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 sigma(A) = 5.5 x 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 mu m. 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 similar to 100 mu m. For smaller spots the responsivity remains constant. Based on this analysis we predict a sensitivity of similar to 30 pW/rtHz for an IR spot size smaller than 100 mu m. The detector can be improved further by e.g. optimizing the tensile pre-stress to a lower value or by improving the absorptivity.