Rigorous Electromagnetic Analysis of Uncooled Microbolometer

Abstract

Abstract : The specific goal of this project was to develop a rigorous three dimensional electromagnetic model of an uncooled microbolometer array. The optical absorption of the thin-film thermal infrared detector was calculated as a function of wavelength, pixel size, incident angle and area fill factor using the finite-difference-time-domain (FDTD) method. The results indicate that smaller pixels absorb a significantly higher percentage of incident energy than larger pixels with the same fill factor. A polynomial approximation to the FDTD results was derived for use in system models. This model can then be used to analyze the coupling efficiency of the bolometer array as a function of various structural and source variations. These include varying the pixel pitch, fill factor and incident field wavelength and incident angle. Most Significant Findings: (1) The optical coupling efficiency of microbolometers varies as a complex function of the pixel pitch and fill factor. (2) Due to small pixel diffraction effects the coupling efficiency actually improves as the pixel size is reduced (3) There is an optimal combination of pixel pitch and fill factor that will maximize the coupling efficiency, and (4) The optical coupling is not sensitive to small variations in incident angle (< 45 degrees).