The James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) incorporates two 5 μm cutoff
(λco =5 μm) 2048×2048 pixel Teledyne HgCdTe HAWAII-2RG sensor chip assemblies. These detector arrays,
and the two Teledyne SIDECAR application specific integrated circuits that control them, are operated in space
at Τ ~ 37 K. This article focuses on the measured performance of the first flight-candidate, and near-flight
candidate, detector arrays. These are the first flight-packaged detector arrays that meet NIRSpec's challenging
6 e- rms total noise requirement. The current version of this paper has had a correction made to it at the request of the author. Please see the linked Errata for further details.
The Wide-field Infrared Survey Explorer is a NASA Midex mission launching in late 2009 that will survey the entire
sky at 3.3, 4.7, 12, and 23 microns (PI: Ned Wright, UCLA). Its primary scientific goals are to find the nearest stars
(actually most likely to be brown dwarfs) and the most luminous galaxies in the universe. WISE uses three dichroic
beamsplitters to take simultaneous images in all four bands using four 1024×1024 detector arrays. The 3.3 and 4.7
micron channels use HgCdTe arrays, and the 12 and 23 micron bands employ Si:As arrays. In order to make a
1024×1024 Si:As array, a new multiplexer had to be designed and produced. The HgCdTe arrays were developed by
Teledyne Imaging Systems, and the Si:As array were made by DRS.
All four flight arrays have been delivered to the WISE payload contractor, Space Dynamics Laboratory. We present
initial ground-based characterization results for the WISE arrays, including measurements of read noise, dark current,
flat field and latent image performance, etc. These characterization data will be useful in producing the final WISE data
product, an all-sky image atlas and source catalog.
The HAWAII-2RG based focal plane arrays represent one the most advanced imaging sensor technologies for near-infrared
and visible astronomy. Since its introduction a few years ago, the HAWAII-2RG has been selected for a large
number of space and ground-based instruments, including the James Webb Space Telescope. In addition, the SIDECAR
ASIC, a fully integrated FPA controller system-on-a-chip, has been matured and is now being implemented in many of
the next generation instruments. As a result of the SIDECAR ASIC, the detector system becomes a fully digital unit that
is superior to the conventional discrete focal plane electronics with respect to power consumption, mass, volume and
noise immunity. This paper includes an introductory description of the HAWAII-2RG and the SIDECAR ASIC, and
presents the latest test results. It also discusses the latest generation of astronomy FPAs: the HAWAII-4RG. This new
multiplexer contains all of the HAWAII-2RG features, but provides 4 times as many pixels at a pixel pitch of 10μm.
Preliminary HAWAII-4RG test data is presented.
We present early results from the performance test development for the Detector Subsystem of the Near-Infrared
Spectrograph (NIRSpec). NIRSpec will be the primary near-infrared spectrograph on the James Webb Space Telescope
(JWST). The Detector Subsystem consists of a Focal Plane Assembly containing two Teledyne HAWAII-2RG arrays,
two Teledyne SIDECAR cryogenic application specific integrated circuits, and a warm Focal Plane Electronics box. The
Detector Characterization Laboratory at NASA's Goddard Space Flight Center will perform the Detector Subsystem
characterization tests. In this paper, we summarize the initial test results obtained with engineering grade components.
KEYWORDS: James Webb Space Telescope, Sensors, Spectrographs, Staring arrays, Near infrared, Space telescopes, Silicon, Infrared sensors, Infrared telescopes, Cameras
The Near Infrared Spectrograph (NIRSpec) will be the James Webb Space Telescope's (JWST's) primary near-infrared spectrograph. NIRSpec is a multi-object spectrograph with fixed-slit and integral field modes. EADS/Astrium is building NIRSpec for the European Space Agency (ESA), with NASA is providing the detector subsystem and programmable multi-aperture mask. In this paper, we summarize recent progress on the detector subsystem including tests demonstrating that JWST's Rockwell HAWAII-2RG sensor chip assemblies have achieved Technology Readiness Level 6 (TRL-6). Achieving TRL-6 is an important milestone because TRL-6 is required for flight.
Advancements in space and ground-based astronomy focal plane array (FPA) technology at Rockwell Scientific
Company (RSC) are presented. The review covers the broad base of astronomy work at RSC for both present and
next generation FPAs, and details recent achievements in detector, readout, and packaging technologies. RSC
astronomy FPA progress includes: RSC FPA delivery for NASA's successful Deep Impact mission, progress on
RSC's programs supplying H-2RG FPAs for James Webb Space Telescope (JWST) instruments JWST NIRCam,
NIRSpec and FGS; selection of RSC's SIDECAR Application Specific Integrated Circuit (ASIC) for use on JWST
instruments NIRCam, NIRSpec and FGS and the development of the JWST SIDECAR space flight package; first
silicon on the 16 million pixel HAWAII-4RG (4Kx4K); optimization of NIR FPAs for space telescope missions;
construction of multiple 16 million pixel 2x2 mosaic FPAs using the HAWAII-2RG readouts, and the development
of the Microlensing Planet Finder (MPF) very large, 150 million pixel FPA.
KEYWORDS: James Webb Space Telescope, Sensors, Analog electronics, Cadmium sulfide, Connectors, Electronics, Clocks, Electrons, Staring arrays, Control systems
The SIDECAR ASIC is a fully integrated FPA controller system-on-a-chip. Compared to conventional control electronics, it requires significantly less power, less space and less weight. The SIDECAR ASIC, which can operate at ambient and cryogenic temperatures, is currently being space-qualified for integration in the science instruments of the James Webb Space Telescope (JWST). This paper gives an overview of the SIDECAR architecture and its supporting drive electronics. It describes the JWST flight configuration including the custom packaging approach. Test results obtained as part of the space qualification effort are presented. CDS noise of the ASIC itself amounts to less than 25 μV for full 2K x 2K data frames. The noise reduces to less than 6 μV for up-the-ramp-sampling with 88 frames. Based on the existing qualification results and a number of additional tests in the next few months, NASA Technology Readiness Level 6 (TRL6) will be demonstrated by August 2006.
Burst noise (also known as popcorn noise and random telegraph signal/noise) is a phenomenon that is understood to be a result of defects in the vicinity of a p-n junction. It is characterized by rapid level shifts in both positive and negative directions and can have varying magnitudes. This noise has been seen in both HAWAII-1RG and HAWAII-2RG multiplexers and is under investigation. We have done extensive burst noise testing on a HAWAII-1RG multiplexer, where we have determined a significant percentage of pixels exhibit the phenomenon. In addition, the prevalence of small magnitude transitions make sensitivity of detection the main limiting factor. Since this is a noise source for the HAWAII-1RG multiplexer, its elimination would make the HAWAII-1RG and the HAWAII-2RG even lower noise multiplexers.
Traditionally, focal plane arrays require extensive external focal plane electronics (FPE) to provide clocks and biases as well as to digitize the analog output signals. The FPE has to be well-designed and is typically large, heavy and powerhungry. Most importantly, the FPE has to be placed some distance away from the FPA, which complicates maintaining low noise performance throughout the complete system. To offer an alternative to the discrete electronics, Rockwell Scientific has developed a new approach known as the SIDECAR application-specific integrated circuit (ASIC). This single chip provides all the functionality necessary to operate an infrared array with the convenience of a pure digital interface to the outside world. This paper will present performance data on the latest generation of the SIDECAR ASIC operating the JWST H2RG detector arrays at cryogenic temperature. The test results demonstrate that an ASIC based FPA system will meet or exceed all performance requirements for the JWST mission. The SIDECAR ASIC has been selected by NASA to become the FPA drive electronics for all shortwave infrared instruments on JWST.
Future infrared space missions will undoubtedly employ passively cooled focal plane arrays (T ~ 30K), as well as passively cooled telescopes. Most long-wave detector arrays (e.g. Si:As IBC) require cooling to temperatures of ~ 6-8K. We have been working with Rockwell Scientific Company to produce <= 10 micron cutoff HgCdTe detector arrays that, at temperatures of ~30K, exhibit sufficiently low dark current and sufficiently high detective quantum efficiency, as well as high uniformity in these parameters, to be interesting for astronomy. Our goal is to achieve dark current below the target
value of ~ 30 e-/s/pixel with at least 60mV of actual reverse bias across the diodes at T ~ 30K. To this end, Rockwell Scientific Company has delivered three 10 micron cutoff HgCdTe low dark current detector arrays with small capacitance diodes for characterization in Rochester. The most recent presentation showed the remarkable preliminary performance of the first of these devices. We present further results on the first device along with results on the subsequent two deliveries.
The Near-Infrared Spectrograph (NIRSpec) is the James Webb Space Telescope’s primary near-infrared spectrograph. NASA is providing the NIRSpec detector subsystem, which consists of the focal plane array, focal plane electronics, cable harnesses, and software. The focal plane array comprises two closely-butted λco ~ 5 μm Rockwell HAWAII-2RG sensor chip assemblies. After briefly describing the NIRSpec instrument, we summarize some of the driving requirements for the detector subsystem, discuss the baseline architecture (and alternatives), and presents some recent detector test results including a description of a newly identified noise component that we have found in some archival JWST test data. We dub this new noise component, which appears to be similar to classical two-state popcorn noise in many aspects, “popcorn mesa noise.” We close with the current status of the detector subsystem development effort.
The NIRCam instrument will fly ten of Rockwell Scientific’s infrared molecular beam epitaxy HgCdTe 2048x2048 element detector arrays, each the largest available with current technology, for a total of 40 Megapixels. The instrument will have two varieties of MBE HgCdTe, a SWIR detector with λco = 2.5 μm, for the shortwave channel of NIRCam (0.6-2.3 μm); and a MWIR detector with λco = 5.3 μm, for the longwave channel of NIRCam (2.4-5.0 μm). Demonstrated mean detector dark currents less than 0.01 electrons per second per pixel at operating temperatures below 42 K for the MWIR and below 80 K for the SWIR, combined with quantum efficiency in excess of 80 percent and read noise below 6 electrons rms, make these detector arrays by far the most sensitive SWIR and MWIR devices in the world today. The unique advantages of molecular beam epitaxy as well as FPA data on noise, dark current, quantum efficiency, and other performance metrics will be discussed. In addition, the focal plane assembly package designs will be presented and discussed.
This paper discusses the latest technologies for space and ground-based astronomy being pursued by Rockwell Scientific. The discussion covers the latest demonstrated performance of large format NIR (~1.7um cutoff) detectors mated to the HAWAII-2RG readout integrated circuit, our proven readout for large-format arrays for astronomy. Developmental work is presented on the HAWAII-4RG family (consisting of 4k x 4k, 4k x 8k, and 8k x 8k formats), RSC’s newest additions planned to the HAWAII series of astronomy readout integrated circuits. We also present the status of our multifunctional command-and-control ASIC for FPAs, which was first reported at the August 2002 SPIE.
The ambitious science goals of the James Webb Space Telescope (JWST) have driven spectacular advances in λco ~ 5um detector technology over the past five years. This paper reviews both the UH/RSC team’s Phase A development and evaluation of 2Kx2K arrays exceeding the detector requirements for JWST’s near infrared instruments and also the hardware integration of these into a 4Kx4K (16Mpxl) close packed mosaic focal plane array housed in an Ultra Low Background test facility. Both individual first generation 2Kx2K SCA’s and 4Kx4K mosaic focal planes have been extensively characterized in the laboratory and, since September 2003, a NIR camera utilizing the 4Kx4K mosaic focal plane has been in use for nearly 100 nights at the UH 2.2 m telescope on Mauna Kea. Typical test results for the first generation 2Kx2K arrays and their integration into 4Kx4K mosaic focal planes are reported. Demonstration of the design concepts and both array and mosaic focal plane performance in actual hardware, as described here, has provided the foundation for design iterations leading to later generations of 2Kx2K arrays and 4Kx4K mosaic focal planes. Four major technology developments leading to first generation hardware demonstrations of both 2Kx2K SCA’s and a 4Kx4K mosaic FPA are reviewed. These are: 1) improvement in test equipment and procedures to characterize the detectors against JWST requirements and goals, primarily at 37K but with the capability to test from 30K to 100K; 2) optimization of λc ~ 5 um MBE HgCdTe material on a CZT substrate for low dark current (goal of 0.003 e-/sec at 37K) with high quantum efficiency, low cross-talk and greatly reduced image persistence; 3) development of the 2Kx2K HAWAII-2RG multiplexer designed specifically to take full advantage of these detector characteristics for a wide range of astronomical applications (and fully compatible with an ASIC controller developed under the JWST Instrument Technology Development initiative) and 4) development of molybdenum SCA carriers allowing modules to be close-butted on three sides and easily installed onto a molybdenum plate to form a 4Kx4K mosaic focal plane. We describe both the improvements in the KSPEC test facility and in test procedures for individual 2Kx2K arrays and the Ultra Low Background (ULB) test facility developed specifically to evaluate 4Kx4K mosaic focal plane assemblies required for the NIRCam instrument. The laboratory test configuration of the ULB facility utilizes multiple shields and internal light sources to achieve background fluxes <1 photon/hour per pixel for λc ~ 5um while providing temperature stability <1mK over periods of weeks. An alternate configuration utilizes fore optics to allow the mosaic FPA module of the ULB facility to be mounted at the Cassegrain focus of the UH 2.2 meter telescope, providing an image scale of 0.25”/pixel over a 17’x17’ field. A cold PK 50 lens cuts off around 1.7 um, limiting the background at wavelengths below 1.65 um (where the array can be used with normal filters and where narrow band filters reduce the background to levels comparable to NIRCam on JWST). Observations at the telescope, which provide the best way of verifying certain JWST requirements and allow direct astronomical characterization of the detectors, are reported.
Future infrared space missions will undoubtedly employ passively cooled focal plane arrays (T ~ 30K), as well as passively cooled telescopes. Most long-wave detector arrays (e.g. Si:As IBC) require cooling to temperatures of ~ 6-8K. We have been working with Rockwell Scientific Company to produce ≥ 10 μm cutoff HgCdTe detector arrays that, at temperatures of ~ 30K, exhibit sufficiently low dark current and sufficiently high detective quantum efficiency, as well as high uniformity in these parameters, to be interesting for astronomy. Our goal is to achieve dark current below the target value of ~30 e-/s/pixel with at least 60mV of actual reverse bias across the diodes at T ~ 30K. To this end, Rockwell Scientific Company has delivered the first array in a new order, for characterization in Rochester. Recent array deliveries of 10μm cutoff HgCdTe bonded to a Hawaii-1RG multiplexer utilize the smallest capacitance diode type. We present preliminary results on this latest 10 μm cutoff HgCdTe low dark current detector array.
Large two-dimensional imaging arrays, spanning infrared focal plane arrays through visible CCDs, usually require extensive support electronics. We present an application specific integrated circuit (ASIC) that combines, on a single chip, all necessary functions to operate CMOS-based focal plane arrays and provide digital data from 12 to 16 bits. The interface to the external world is completely digital, thus eliminating the complexity of dealing with sensitive analog voltages. The ASIC's first application is for use with the HAWAII-2RG (a 2048 x 2048 multiplexer specifically optimized for the Next Generation Space Telescope). Due to its flexibility, it can control other FPAs and SCAs not requiring clocks or biases higher than 3.3 V. The low-power, system-on-chip controller comprises a 16-bit microcontroller, program and data memory, clock generator, bias generator, 36 programmable gain amplifiers (0 to 27 dB), thirty-six 12-bit 10 MHz A/D converters, thirty-six 16-bit 500 kHz A/D converters, glue logic and programmable I/O pads. When configured for NGST, we estimate ≤ 8.4 mW continuous power for the 2k x 2k FPA and ASIC. The programmable ASIC, dubbed SIDECAR, for System for Image Digitization, Enhancement, Control And Retrieval, is likely an optimum "back-end" solution for other high-performance instruments.
Future infrared space missions will undoubtedly employ passively cooled focal planes (T ~ 30K), as well as passively cooled telescopes. Most long-wave detector arrays (e.g. Si:As IBC) require cooling to temperatures of ~ 6-8K. We have been working with Rockwell to produce 10μm cutoff HgCdTe detector arrays that, at temperatures of ~ 30K, exhibit sufficiently low dark current and sufficiently high detective quantum efficiency to be interesting for astronomy. In pursuit of these goals, Rockwell Scientific Company has delivered twelve 256 x 256 arrays (several of them engineering arrays), with cutoff wavelengths at 30K between 7.4 and 11μm for characterization at Rochester. Seven of these arrays utilize advanced structure diodes with differing capacitances arranged in rows (banded arrays), and the materials properties of the HgCdTe also vary significantly from array to array. Of ultimate interest to astronomy is the fraction of pixels with dark current below the target value of ~ 100e-/s with 10-60mV of actual reverse bias across the diodes at T ~ 30K. These arrays were developed for the purpose of selecting diode architecture: we use this fraction as one criterion for selection. We have determined from these experiments the optimal diode architecture for future array development. Measurement of the dark current as a function of reverse bias and temperature allows us to ascertain the extent to which trap-to-band tunneling dominates the dark current at this temperature. We present the results for one representative array, UR008.
The HAWAII-2RG is a major upgrade of our prior 2048 x 2048 CMOS readout for astronomy (HAWAII-2) to support the requirements of the Next Generation Space Telescope and enable breakthrough capability for ground-based astronomy. By migrating to 0.25μm CMOS, for the first time guide mode readout is simultaneously supported in combination with various programmable science modes on a frame-by-frame basis. Consequently, the readout simultaneously supports programmable guide mode window and full-field science using the rest of the 4.2 million pixels at read noise <5 e-. Also for the first time with any imaging sensor, low and high background astronomy is supported using from 1 to 32 low-noise outputs via low-speed and high-speed signal paths. The latter supports throughput rate of up 320 MHz for real time imaging at >60 Hz. As with the HAWAII-2, the readout can be mated to our infrared and visible detector arrays including low dark current MBE HgCdTe at cutoff wavelengths from 1.5μm to 14μm, 2.5μm PACE HgCdTe, and silicon p-i-n detectors with superior quantum efficiency to backside-illuminated CCDs.
CMOS-based imaging system-on-chip (i-SoC) technology is successfully producing large monolithic and hybrid FPAs that are superior in many respects to competing CCD-based imaging sensors. The hybrid approach produces visible 2048 by 2048 FPAs with <6 e- read noise and quantum efficiency above 80% from 400 nm to 920 nm; 4096 by 4096 mosaics are now being developed. The monolithic approach produces visible 12-bit imaging system-on-chips such as a 1936 by 1088 with higher quantum efficiency than mainstream CCDs, <25 e- read noise, <0.02% fixed pattern noise, automatic identification and replacement of defective pixels, black-level clamping, total power dissipation of only 180 mW, and various programmable features. Several successors having ≥12 Mpixels are in development. In both cases low-light-level performance is boosted by coupling the sensors to image intensifiers.
The past 2 to 3 years has been a period of explosive growth in technology development for imaging sensors at Rockwell Scientific Co. (RSC). The state of the art has been advanced significantly, resulting in a number of unique advanced imaging sensor products. A few key examples are: 2048 x 2048 sensor chip assemblies (SCA) for ground and space-based applications, 4096 x 4096 mosaic close-butted mosaic FPA assemblies, a very high performance 10 x 1024 hybridized linear SCA for optical network monitoring and other applications, the revolutionary CMOS ProCam-HD imaging system-on-a-chip for high definition television (HDTV), and RSC's near-infrared emission microscope camera for VLSI defect detection/analysis. This paper provides selected updates of these products and thereby provides an overview of the ongoing highly fertile period of technology and product development at Rockwell Scientific. A view into future directions for advanced imaging sensors is also provided.
The goal of achieving background-limited performance in SIRTF's cryogenic telescope environment places stringent demands on focal plane sensitivity. SIRTF's prime imaging instrument, the InfraRed Array Camera (IRAC), employs 256 X 256 Si:As Impurity-Band Conduction (IBC) arrays for its two longest wavelength channels at 5.8 micrometers and 8.0 micrometers . Background-limited performance is achieved at very low levels of zodiacal background radiation with cryo-optimized readout and detector technology from Raytheon. Presented here are performance measurements of IRAC flight candidate IBC arrays. Operating at a temperature of 6 K, these devices meet all IRAC sensitivity requirements, with dark currents well below the 10 e-/s specification, Fowler-sampled noise levels of 16 e-, and excellent photometric stability.
SIRTF requires detector arrays with extremely high sensitivity, limited only by the background irradiance. Especially critical is the near infrared spectral region around 3 micrometers , where the detector current due to the zodiacal background is a minimum. IRAC has two near infrared detector channels centered at 3.6 and 4.5 micrometers . We have developed InSb arrays for these channels that operate with dark currents of < 0.2 e/s and multiply-sampled noise of approximately 7 e at 200 s exposure. With these specifications the zodiacal background limited requirements has been easily met. In addition, the detector quantum efficiency of the InSb devices exceeds 90% over the IRAC wavelength range, they are radiation hard, and they exhibit excellent photometric accuracy and stability. Residual images have been minimized. The Raytheon 256 X 256 InSb arrays incorporate a specially developed (for SIRTF) multiplexer and high-grade InSb material.
This paper will review the state-of-the-art IR detectors at the Raytheon IR Center of Excellence for both grou8nd-based and space-based astronomy applications. Performance data will be presented on 0.5 to 5.0 micron Indium Antimonide (InSb) arrays and 0.9 to 5.0 micron Mercury Cadmium Telluride arrays. In addition, performance data on 2 to 28 micron Arsenic-doped Silicon impurity band conductor arrays will be presented. These very high performance detector array offer another important window into the universe for ground- and space-based astronomical work. Data will include performance data on InSb and Si:As IBC arrays for the IR array camera instrument on NASA's Space IR Telescope Facility and the IRC instrument on the ISAS ASTRO-F IR Imaging Survey (IRIS) mission. Data obtained with the HgCdTe arrays developed for the Visible and IR Thermal Imaging Spectrometer H and M instruments for the ESA ROSETTA mission will also be presented. Readouts for both ground-based and space-based astronomy applications will be highlighted, including the first prototype multiplexer and 4 K X 4 K Focal Plane Array for the next generation space telescope.
This paper is a review of current astronomy projects at Raytheon/SBRC in the near-IR band. Another paper in this same session (3354-11) covers astronomy projects in longer wavelengths. For ground-based astronomy, InSb arrays with formats of 256 X 256, 512 X 512, and 1024 X 1024 have been developed and tested. For space-based astronomy, four projects are discussed with array formats ranging from 256 X 256 to 2K X 2K. The space projects support instruments on the SIRTF, IRIS, NGST, and Rosetta missions. Representative data are presented from 1024 X 1024 and 256 X 256 arrays obtained by test facilities at NOAO and the University of Rochester.
Raytheon/SBRC has demonstrated high quality Si:As IBC IR FPAs for both ground-based and space-based Mid-IR astronomy applications. These arrays offer in-band quantum efficiencies of approximately 50 percent over a wavelength range from 6 micrometers to 26 micrometers and usable responses from 2 micrometers to 28 micrometers . For high background, ground-based applications the readout input circuit is a direct injection (DI) FET, while for low background, space-based applications a source follower per detector (SFD) is used. The SFD offers extremely low noise and power dissipation, and is implemented in a very small unit cell. The DI input circuit offers much larger bucket capacity and better linearity compared with the SFD, and is implemented in a 50 micrometers unit cell. SBRC's Si:As IBC detector process results in very low dark current sand our Raytheon/MED readout process is optimized for very low redout noise at low temperature operation. SBRC is committed to achieving still better performance to serve the future needs of the IR astronomy community.
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.
Higher resolution and wider IR spectral coverage is needed to improved infrared sounding instruments. The Atmospheric Infrared Sounder (AIRS), chosen by NASA to fly on the Earth Observing System, addresses these needs with advanced PV HgCdTe detector arrays designed to cover the spectral range from 3.7 micrometers to 13.6 micrometers with an average resolution of (lambda) /(Delta) (lambda) equals 1200. High performance detectors and advanced readout integrated circuit electronics make it possible to meet mission requirements. For convenience, the AIRS focal plane has been partitioned into four MWIR modules spanning the spectral range from 3.7 micrometers to 8.22 micrometers , and six LWIR modules for wavelengths above 8.8 micrometers . This paper focuses on the AIRS readout device and recent developments in p-on-n heterojunction detector technology at Loral. The detector arrays, operating at 60 K, readily satisfies the requirements of the AIRS instrument. Detector arrays with 4.7 micrometers cutoff wavelength at 60 K and 20 mV reverse bias have RdAs typically greater than 1010 (Omega) (DOT) cm2, with dark signals less than 0.6 fA and detector capacitances less than 0.6 pf for a 50 micrometers by 10 micrometers detector. AR coated MW arrays exhibit quantum efficiencies of greater than 80 percent. Reverse breakdowns are more than -150 mV. Module data for 15.1 micrometers detectors with anti-reflection coating exhibit quantum efficiencies greater than 70 percent and dark currents less than 8 nanoamps at 20 mV reverse bias. Also, excellent module linearity meeting the AIRS stringent requirements is achieved. Of course, measurements of MW detectors require extremely high gain transimpedance amplifiers. The AIRS MWIR readout structures prove to be exceptional in their ability to characterize these high impedance detectors. The charge sensitive input amplifiers on these readout devices utilize an equivalent input integration capacitor of less than 10 fFd to achieve ultrahigh transimpedance gain, and reset noise is suppressed with on focal plane correlated double sampling. LWIR readouts use ultralow noise buffered direct injection preamplifiers. The readouts have a robust architectures with differential input and outputs to minimize EMI and built in redundancy for survivability. Description of the readout device is presented, as well as linearity measurements of both the readout and complete modules.
AIRS is a key facility instrument on the first post meridian platform as part of NASA'a Earth Observing System (EOS) program. The Atmospheric Infrared Sounder measurement technique is based on passive IR 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 focal plane assembly of 53 mm by 66 mm, the largest ever built at LIRIS. With 4208 diodes and 274 photoconductors in the same focal plane to achieve the wide spectral coverage from 3.7 to 15.4 micrometers , 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 cover the 13.7 to 15.4 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, ROIC output design and lead routing. High D*'s of 7E14 and 3E11 cm- Hz1/2/W are needed to meet the sensitivity requirements of the 4.2 and 15.0 micrometers regions respectively. The 35 micrometers by 800 micrometers PC detectors on a 50 micrometers 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 17 narrow band filters packaged into a single precision assembly mounted within 0.18-0.25 mm of the focal plane surface. The more than 50 components comprising the focal plane in conjunction with the tightly spaced optical pattern presented 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 12 modules is discussed. The rationale for the spectral range assigned to each module is reviewed relative to PV and PC performance capabilites. ROIC design guidelines and physical contraints due to manufacturability 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 presneted. 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 be presented along with results of analyses performed.
Cryogenic space telescopes such as the Space Infrared Telescope Facility (SIRTF) require large-area focal plane arrays (FPAs) with high sensitivity. Such applications set requirements for the readout arrays to simultaneously provide low noise and low power dissipation at very low temperatures. The Hughes Technology Center (HTC) has developed a low-noise 256 X 256-pixel hybrid FPA composed of a PMOS readout array hybridized to an arsenic- doped silicon (Si:As) impurity-band conduction (IBC) detector which is designed to operate below 10 K. The readout unit cell employs a switched source-follower-per-detector (SFD) design where in signals are multiplexed onto four outputs. The detector was processed using high-purity, multilayered epitaxial processing. The readout was processed using the p-channel subset of HTC's CryoCMOS process.
We are investigating trapping/recombination centers in near-infrared (1 - 5 micrometers ) InSb imaging arrays via experimentation and theoretical modeling. The presence of impurities, lattice defects and/or surface states can compromise the operational qualities of an imaging array by introducing latent images, signal rate/quantum efficiency loss at low signal levels, and by increasing noise and dark current. Identification of these trapping centers should enable a reduction in their number density by appropriate changes in the material processing and fabrication steps. We have performed experiments and analyses on both gate-controlled arrays (SiOx surface passivation) and recently received gateless arrays (Si3N4 surface passivation). All of the gated arrays showed latent images at temperatures 6 - 26 K for signal fluxes as low as 1500 e-/s/pixel, while neither of the two gateless arrays examined has shown latent images in the same temperature range; no latent image was detected (to a level of < 50 e-) in a 5 second integration after exposure to a 2 X 106 e-/sec/pixel signal flux. We interpret this as evidence for surface state charge trapping in the region of the gate oxide, which is largely eliminated by the new passivation. The physics of surface states is investigated theoretically in order to gain an understanding of the surface contribution to the observed behavior, and a model is presented to explain the experimental results.
SIRTF, and other infrared space astronomy projects, require detector arrays with extremely high sensitivity. It is a goal of SIRTF to achieve background limited performance at all wavelengths. Especially critical is the spectral region around 3 micrometers , where the detector current due to the zodiacal background radiation is a minimum. For background limited operation, at a spectral resolution of 100, the dark current must be less than 0.1 e-/s/pixel. The detector noise must be less than the noise given by fluctuations in the number of zodiacal background photons (< 9 e-/pixel). Other detector array goals include: high quantum efficiency (> 90%), radiation hardness, minimal image latency, and excellent photometric accuracy and stability. Many of the performance goals have been met with Santa Barbara Research Center's 256 X 256 InSb arrays.
The newest 256 X 256 InSb arrays (CRC-590 and CRC-463 multiplexers) from Santa Barbara Research Center have reached a milestone in low noise performance. Using the Fowler-sampling technique to acquire data, we have achieved 10 - 13 e- multiply sample read-out (MSR) noise with the new arrays. With this remarkably low noise performance, background limited performance occurs at relatively small signal levels, viz. a few percent of full-well depth. The signal-to-noise capability of infrared detectors operating in both read noise and background limited performance is an important parameter for evaluating the efficacy of various data sampling methods. We conclude that both line-fitting and Fowler- sampling are the best sampling methods covering the whole performance regime, providing large improvement in the read-noise dominated regime and approaching CDS capability in the photon-noise dominated regime.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.