This paper introduces a method of broadband absorption enhancement that can be integrated with the conventional suspended microbolometer process with no significant additional cost. The premise of this study is that electric field can be enhanced throughout the structural layer of the microbolometer, resulting in an increase in the absorption of the infrared radiation in the long wave infrared window. A concentric double C-shaped plasmonic geometry is simulated using the FDTD method, and this geometry is fabricated on suspended pixel arrays. Simulation results and FTIR measurements are in good agreement indicating a broadband absorption enhancement in the 8 μm - 12 μm range for LWIR applications. The enhancement is attained using metallic geometries embedded in the structural layer of the suspended microbridge, where the metallic-dielectric interface increases the average absorption of a 35 μm pixel from 67.6% to 80.1%. © 2013 SPIE

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This paper presents a detailed analysis examining the absorption performance of a metal-dielectric slab with subwavelength size periodic perforations exploiting quarter-wave impedance matching (QWIM) technique within long wave infrared (LWIR) regime (8-12µm). Integration of perforations to a simple stack with various period sizes and perforated area ratios are examined through theory, simulation, and measurements that are in great agreement. Advantages of perforated absorbers for thermal detectors are discussed in maximizing optical absorption and reducing thermal-mass point of view. Introducing perforation in umbrella type absorbers is mainly employed for reducing the thermal-mass while maintaining the high absorption performance. Within the scope, it is experimentally shown that a perforation ratio (width/period) of 50% with square holes for the umbrella layer is possible without degrading the maximum LWIR absorption performance of 96% when the sheet resistance of Rs=400Ω/□ is employed for the absorbing metal layer, which is close to free space impedance of 377Ω/□. Nevertheless, this ratio can be increased up to 77% by depositing a thicker absorber metal with smaller sheet resistance, such as Rs=100Ω/□ while still maintaining an average absorption performance of 93%, which are all predicted numerically by simulations and physically explained through effective medium approach (EMA).

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