Design and implementation of high fill factor structures on low-cost uncooled infrared sensors

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2015
Ertürk, Ozan
This thesis presents the design and implementation steps of high fill factor structures for existing SOI diode low-cost microbolometer FPAs. Advancements in uncooled infrared detectors enable high performance military grade uncooled microbolometers as well as ultra-low-cost infrared imagers for civilian applications. The trend in uncooled microbolometers to reduce the pixel pitch has become increasingly significant to lower the cost of detector and system integration due to optics, and increase spatial resolution with range. However, reducing pixel size reduces the temperature sensitive area, not to mention the need for larger space to design longer thermal isolation legs. Therefore, many uncooled infrared imaging arrays employ additional structures that increase the fill factor. A second level of sacrificial layer is used to form the high fill factor structure (referred as umbrella) to form an optical cavity in order to maximize the absorption. This study demonstrates the design of umbrella layer in mechanical, thermal, and optical domain by providing simulations and examples from the literature. Challenges and optimization steps of realizing the umbrella structure are also conveyed. Successful implementation of umbrella structures onto SOI diode pixels with pixel sizes of 50 μm and 70 μm is demonstrated. The fill factor of the low-cost detector pixels with 50 μm pitch is increased from 46 % to 92 % while the fill factor of the pixels with 70 μm pitch is increased from 36 % to 94 %. The umbrella integrated FPAs are tested under vacuum conditions to obtain responsivity data and evaluate the contribution to the signal generated by addition of umbrella structures. It is concluded that the addition of umbrella structures improve the responsivity of FPAs with 50 μm pitch pixels by 30 % while the responsivity of FPAs with 70 μm pitch pixels is improved by 40 %.

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Citation Formats
O. Ertürk, “Design and implementation of high fill factor structures on low-cost uncooled infrared sensors,” M.S. - Master of Science, Middle East Technical University, 2015.