A multispectral hybrid HgCdTe FPA/dewar assembly for remote sensing in the Atmospheric Infrared Sounder (AIRS) instrument

Abstract

AIRS is a key instrument in NASA's Earth Observing System (EOS) Program. Passive IR remote sensing is performed using a high resolution grating spectrometer design with a wide spectral coverage focal plane assembly (FPA). The hybrid HgCdTe focal plane consists of twelve modules, ten photovoltaic (PV) and two photoconductive (PC), providing spectral response from 3.7 to 15.4 micrometers. The PV modules use silicon readout integrated circuits (ROICs) joined to the detector arrays as either direct or indirect hybrids. The PC modules are optically chopped and led out to warm electronics. Operating at 58 K, the sensitivity requirements approach BLIP in the critical 4.2 and 15.0 micrometer bands. The optical footprint coupled with the support and interface components of the focal plane make it a very large assembly, 53 mm multiplied by 66 mm. Dispersed energy from the grating is presented to the modules through 17 narrowband filters mounted 0.2 mm above the focal plane in a single, removable precision assembly. With PV and PC devices on the same focal plane operating simultaneously, shielding and lead routing as well as ROIC design have been optimized to minimize any interactions between them. Multilayer carriers have been designed to lead out the closely spaced PC arrays and the entire focal plane itself. Multilayer shielded flex cables are used to interconnect the focal plane to a very unique dewar. The tightly spaced optical pattern, along with more than 50 components in the focal plane, make this a highly complex assembly. The vacuum dewar, while providing approximately 600 leadouts, is directly coupled to the cold spectrometer and operates at 155 K while cooling the focal plane to 58 K via a sapphire rod interfaced to a pulse tube cooler. This paper discusses the key features of the FPA/dewar assembly, modeling/analyses done in support of the design, and results of design validation activities to date.