Metasurface-Enabled Uncooled Silicon Germanium Oxide Infrared Microbolometers for Long-Wave Infrared Detection

Abstract

This paper investigated metasurface enabled uncooled silicon germanium oxide (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.425</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.512</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.063</sub> ) infrared (IR) microbolometers. The metasurface was used to engineer the IR absorption to achieve broadband or narrowband spectral response, eliminate the need for Fabry-Perot quarter wave resonant cavity typically used in conventional microbolometer under the pixel, and significantly improve the electrical performance of the temperature-sensing layer. This has facilitated the fabrication of the microbolometer with the supporting arms placed underneath the pixel without disrupting the Fabry-Perot cavity, and as a result, the supporting arms were fabricated with longer length without sacrificing the fill factor. The longer support arms reduced the thermal conductance between the microbolometer pixel and the underlying substrate and thus increased the voltage responsivity. The spectral responsivity and detectivity for the fabricated devices were measured in vacuum and demonstrated tunablility with narrow bands between 7 to 12 μm by changing the metasurface disk diameter and periodicity. The measured voltage responsivity, detectivity and thermal response time were > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> V/W and > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W and 2.01 ms to filtered blackbody infrared radiation between > 2 μm. The voltage noise power spectral density (PSD) of the fabricated devices were reduced by annealing the devices in vacuum.