Rigorous Electromagnetic Analysis of Uncooled Microbolometer

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.