Uncooled two-microbolometer stack for long wavelength infrared detection

Abstract

We have investigated an uncooled infrared (IR) detector utilizing a dual level architecture. This was achieved by combining two-microbolometer stack in the vertical direction to achieve high IR absorption over two distinct spectral windows across the long wavelength infrared region (LWIR). In addition, we have studied amorphous silicon germanium oxide (Si_xGe_yO_1-x-y) as an IR sensitive material, and metasurface to control IR absorption/reflection in interaction with standard Fabry-Perot cavity. The bottom microbolometer uses a metasurface to selectively absorbs a portion of the spectrum and reflects radiation outside this window range. At the same time, the top microbolometer uses a conventional Fabry-Perot resonant cavity to absorb a different portion of the spectrum and transmit any unabsorbed radiation outside this window. This device can be used to measure the absolute temperature of an object by comparing the relative signals in the two spectral bands. The spectral responsivity and detectivity, and thermal response time were > 10⁵ V/W, > 10⁸ cm Hz^1/2/W, and 1.13 ms to filtered blackbody infrared radiation between (2-16) µm. The microbolometer voltage noise power spectral density was reduced by annealing the microbolometers in vacuum at 300 °C.