20 May 2011 Improvements of a digital 25 μm pixel-pitch uncooled amorphous silicon TEC-less VGA IRFPA with massively parallel Sigma-Delta-ADC readout
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Abstract
This paper presents the improvements of an advanced digital VGA-IRFPA developed by Fraunhofer-IMS. The uncooled IRFPA is designed for thermal imaging applications in the LWIR (8 .. 14 μm) range with a full-frame frequency of 30 Hz and a high sensitivity with NETD < 100 mK @ f/1. The microbolometer with a pixel-pitch of 25 μm consists of amorphous silicon as the sensing layer. The structure of the microbolometer has been optimized for a better performance compared to the 1st generation IRFPA1. The thermal isolation has been doubled by increasing the length and by decreasing the width of the legs. To increase the fill-factor the contact areas have been reduced. The microbolometers are read out by a novel readout architecture which utilizes massively parallel on-chip Sigma-Delta-ADCs. This results in a direct digital conversion of the resistance change of the microbolometer induced by incident infrared radiation. Two different solutions for the vacuum package have been developed. To reduce production costs a chip-scale-package is used. This vacuum package consists of an IR-transparent window with antireflection coating and a soldering frame which is fixed by a wafer-to-chip process directly on top of the read substrate. An alternative solution based on the use of a standard ceramic package is utilized as a vacuum package. This packaging solution is used for high performance applications. The IRFPAs are completely fabricated at Fraunhofer-IMS on 8" CMOS wafers with an additional surface micromachining process.
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Dirk Weiler, Marco Ruß, Daniel Würfel, Renee Lerch, Pin Yang, Jochen Bauer, Jennifer Heß, Piotr Kropelnicki, Holger Vogt, "Improvements of a digital 25 μm pixel-pitch uncooled amorphous silicon TEC-less VGA IRFPA with massively parallel Sigma-Delta-ADC readout", Proc. SPIE 8012, Infrared Technology and Applications XXXVII, 80121F (20 May 2011); doi: 10.1117/12.883791; https://doi.org/10.1117/12.883791
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