Metasurface based uncooled Sixgeyo1-x-y microbolometer for infrared detection
Authors:   , Abdullah Amjed 
Published: September 2022

[EMBARGOED UNTIL 6/1/2023] In this research, we have investigated metasurface integrated uncooled SixGeyO1-x-y microbolometers. Two device architecture were fabricated and characterized. The first design presents the implementation of metasurface integrated uncooled infrared (IR) silicon germanium oxide (Si-Ge-O) microbolometers for Long Wavelength Infrared (LWIR) detection. Metasurface materials were proposed in this design to increase the absorption of the microbolometer and to provide wavelength selectively based on the geometry of the metasurface material. The inclusion of the metasurface permits engineering the IR absorptance with respect to wavelength. Absorption by the metasurface eliminates the need for a 1/4-wave resonant cavity under the microbolometer. In addition, the metasurface can significantly improve the electrical performance of the temperature-sensing layer. Experimental results show an increase in the Temperature Coefficient of Resistance (TCR) and a decrease in the resistivity of the amorphous Si-Ge-O films. These parameters scale with the periodicity and area fraction of the metasurface. The voltage noise power spectral density was reduced by annealing the devices in vacuum and in forming gases. The results demonstrated that annealing in vacuum lowered the noise much more than that of annealing in forming gases. The lowest measured noise in vacuum annealing for the metasurface integrated microbolometer was 1.2x10-16 V2/Hz at the corner frequency, where Johnson noise meet 1/f-noise. This frequency was lowered to 10 Hz (from 87 Hz) after 4 hours annealing. In addition, the corresponding Hooge's parameters [gamma], [beta] and Kf for the device were 1.02, 2.01, 2.637x10-14, respectively. The measured responsivity and detectivity approached 104 V/W and 108 cm Hz1/2/W to filtered blackbody infrared radiation. The microbolometer PSD noise was studied in detail and reduced using vacuum annealing and forming gases annealing and the results showed significant reduction of the noise level and the corner frequency compared to the noise without annealing. In addition, the spectral responsivity and detectivity were measured in vacuum as a function of IR wavelength over the range from 4 [mu]m to 14 [mu]m. In the second microbolometer architecture, A new uncooled microbolometer is presented that utilizes an amorphous silicon germanium oxide (SixGeyO1-x-y) infrared (IR) sensitive material, a dual level architecture with dual-air cavity fabricated on top of each other, and a metasurface to control IR absorption/reflection in interaction with standard Fabry-Perot cavity. The design combines two-microbolometer stack in a single pixel to achieve high IR absorption over two distinct spectral windows across the long wavelength infrared region (LWIR) without using a filter wheel. The bottom microbolometer uses a metasurface to selectively absorbs a portion of the spectrum, and reflects radiation outside this window range, while 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 [greater than] 105 V/W, [greater than] 108 cm Hz1/2/W, and 1.13 ms to filtered blackbody infrared radiation between 2-16 [mu]m. The microbolometer voltage noise power spectral density was reduced by annealing the microbolometers in vacuum at 300 oC.