Device architecture for metasurface integrated uncooled SixGeyO1-x-y infrared microbolometers

This paper reports the design, fabrication, characterization, and noise reduction of metasurface based uncooled infrared microbolometers with focus on device architecture. Two designs are investigated. In the first design, the devices are fabricated with the legs positioned underneath the microbolometer pixel. This is facilitated by the use of the metasurface which removes the need for a Fabry-Perot 1/4 cavity. Placing the legs underneath the pixel permits longer legs without sacrificing fill factor and raises the thermal resistance between the microbolometer and the substrate. The metasurface potentially allows spectrally dependent IR absorption. The second design extends this architecture to include a second microbolometer suspended above the first microbolometer to form a single pixel. Metasurfaces on each microbolometer can be designed to capture a portion of the spectrum with the combined structure maximizing the total absorptance across the Long Wave Infrared (LWIR) band. The TCR and resistivity are measured on the fabricated devices with and without the addition of the metasurface for both designs. The metasurface produces a slight increase in the TCR 5% to 12% and a dramatic reduction in the resistivity (>5×) which leads to a two order of magnitude reduction in the microbolometer noise voltage Power Spectral Density (PSD) after annealing in vacuum. The measured single cavity microbolometer has a voltage responsivity of 4.1×10⁴ V/W and detectivity of 3.57×10⁸ cm·Hz^1/2/W.