No abstract

No abstract

No abstract

Atmospheric remote-sensing have been one of the primary drivers toward longer wavelength infrared sensors beyond the 8 to 12 um atmospheric window typically used for terrestrial imaging systems. This paper presents the recent performance improvement attained with very long wavelength infrared (VLWIR) focal plane arrays, by the stringent control of the small bandgap HgCdTe material quality. Array operability is further enhanced by design using a 2:1 super-pixel detector format scheme with programmable bad element de-select and our new detector input offset optimization circuitry within each unit cell. Focal plane arrays with peak quantum efficiencies in excess of 80 percent, and cutoff wavelengths out to 15 µm have NEI operabilities around 95 percent for mid 10 14 ph/s-cm 2 fluxes operating near 50 K. Average NEI of 3.5 x 10 10 ph/s-cm 2 was demonstrated for a 14 µm cutoff wavelength focal plane array, consisting of over 55,000 elements, operating with an effective sample time of 87.5 ms. IntroductionRecent strides in very long wavelength infrared (VLWIR) HgCdTe focal planes have reinvigorated their use in VLWIR atmospheric remote sensing applications. These VLWIR focal plane arrays, comprised of HgCdTe photovoltaic diodes, have demonstrated unprecedented operability for large area arrays with detector cutoffs beyond 14 µm. Significant improvement in array yield have occurred over the last 10 years due to all aspects of the array fabrication, including larger and more uniform substrates with tighter process controls, and better understanding of defects which have led to successful mitigation strategies [1-3]. The readouts for these arrays have also improved and several features have been added specifically to address yield issues to achieve producible high operability performance above 95 percent [4]. The two main features are SuperPixels, where each pixel is sub-divided into several sub-elements that can be individually deselected if found defective, and through input bias optimization on a pixel by pixel basis to remove CMOS threshold variations across the chip. This latter feature allows the reverse bias of each detector to be optimized. The data also clearly shows the operability benefit of using smaller pixel higher density FPAs to cover the same focal plane area, demonstrating that the majority of the defects are randomly distributed defects that are much smaller than a pixel.In this paper we discuss the VLWIR detector technology at BAE Systems in section 2, followed by the excellent photodiode array performance presented in section 3. The operability performance of two staring VLWIR FPA systems using these detector arrays are discussed in section 4. The first FPA is a 256 x 256 array on 40 µm pitch specifically designed for low background applications with a frame rate of 100 Hz and a charge capacity of 11 million electrons. Each pixel is divided into a 2 x 2 array of sub-elements for SuperPixel de-selection. The baseline operation of this device uses the best 3 of every 4 sub-elements per pixel for optimal...

AIRS is a key facility instrument on the first post meridian (PM) platform as part of NASA's Earth Observing System (EOS) program. The Atmospheric Infrared Sounder measurement technique is based on passive JR remote sensing using a high spectral resolution grating spectrometer. The structure of the infrared focal plane for the AIRS instrument has been defined and is presented in this paper.The optical footprint of 8. 1 mm by 36.3 mm along with the necessary support and interface components leads to a ftcal plane assembly of 53 mm by 66 mm. the largest ever built at LIRIS. With 4208 diodes and 274 photoconductois in the same frcal plane to achieve the wide spectral coverage from 3.7 to 15.4 tim, a modular approach is required. Ten PV modules utilize silicon Readout Integrated Circuits (ROICs)joined to the detector arrays as either direct or indirect hybrids while two PC modules coyer the I 3.7 to 1 5.4 mm range, optically chopped and led out to uncooled preamplifiers. The simultaneous operation of PV and PC devices in the same focal plane has required unique approaches to shielding, ROTC output design and lead routing.High Dfs of 7El4 and 3E1 1 cm-Hzl/2/W are needed to meet the sensitivity requirements of the 4.2 and 15.0 .tm regions respectively. The 35 .tm by 800 jim PC detectors on a 50 im pitch have necessitated modifications to standard delineation techniques. while the MW performance is nearly D BLIP for PV devices. Dispersed energy is presented to the modules through 1 7 narrow band filters packaged into a single precision assembly mounted within 0. 1 8 -0.25 mm of the focal plane surface. The more thaii 50 componelits comprising the focal plane in conjunction with the tightly spaced optical pattern preseited by the grating add a high degree of complexity to the assembly process. This paper focuses on the architectural constraints derived from performance, interface and reliability requirements. Key aspects of these requirements are presented and their impact on the partitioning of the I 2 modules is discussed. The rationale for the spectral range assigned to each module is reviewed relative to PV and PC performance capabilities, ROIC design guidelines and physical constraints due to manufacturahility and assembly. Results of structural and thermal analyses for the various module configurations and assembled focal plane to determine compliance with the stringent stability and positional requirements are presented. Specific features of the module carrier/interface boards and the multilayered focal plane carrier/interface board are included as well as a review of the overall assembly sequence of the focal plane as influenced by repairability and reliability considerations.The comprehensive redundance strategy applied to the design of the FPA/dewar assembly will be reviewed, and the approach for operation/survival in the radiation environment is discussed. Key features of the ROIC. PV and PC array designs will he presented, along with results of analyses performed. This work is being funded by NASA Goddard Spa...