The Infrared Array Camera (IRAC) on Spitzer Space Telescope includes four Raytheon Vision Systems focal plane arrays, two with InSb detectors, and two with Si:As detectors. A brief comparison of pre- flight laboratory results vs. in-flight performance is given, including quantum efficiency and noise, as well as a discussion of irregular effects, such as residual image performance, "first frame effect", "banding", "column pull-down" and multiplexer bleed. Anomalies not encountered in pre-flight testing, as well as post-flight laboratory tests on these anomalies at the University of Rochester and at NASA Ames using sister parts to the flight arrays, are emphasized.
The Infrared Array Camera (IRAC) is one of three focal plane instruments on board the Spitzer Space Telescope. IRAC is a four-channel camera that obtains simultaneous broad-band images at 3.6, 4.5, 5.8, and 8.0 μm in two nearly adjacent fields of view. We summarize here the in-flight scientific, technical, and operational performance of IRAC.
As the logical extension of the 20-year mission of the Hubble Space Telescope, NASA plans to launch the James Webb Space Telescope (JWST, formerly NGST) near the end of this decade. As Hubble's scientific and technological successor, equipped with a 6-meter-class deployable mirror, JWST will allow observations of the very early universe
and initial formation of galaxies at levels not achievable today. JWST's unprecedented sensitivity cannot be utilized without a new class of IR focal plane arrays whose performance matches that of the telescope. In particular, JWST focal planes must be able to withstand the ionizing-particle radiation environment expected for its Lagrange-point (L2) orbit and ten-year mission lifetime goal. To help determine their suitability for JWST, NASA is evaluating prototype
megapixel-class readouts and hybrid detector arrays under proton bombardment to simulate the anticipated JWST lifetime radiation dose. This report describes the results of early tests on devices from two manufacturers using photovoltaic (HgCdTe or InSb) candidate near-infrared detector structures. Results to date have shown encouraging
performance, along with some areas of continuing concern.
The Orion program developed a 2048x2048 infrared focal plane using InSb PV diodes for detectors. Several of these focal planes have been produced. However, the yield of the original readout multiplexer was not up to expectations owing to unanticipated shorts in the fabrication process. Since these shorts occurred at the metal 1-metal 2 crossover points and there are over 9 million such crossovers, the design had to be modified to work around these problems. Thus the Orion II readout was developed. The work is being done at the Raytheon Vision Systems (RVS) division (most recently Raytheon Infrared Operations, but better known as SBRC) by many of the same people who created the Orion I and ALADDIN focal planes. The design is very similar to the Orion I design with the addition of circuitry to work around the effect of the metal 1-metal 2 shorts. In this paper we will discuss the unique design features of this device as well as present test data taken from the new devices.
Si:As Impurity Band Conduction (IBC) detectors offer many significant advantages over other conventional photon detectors utilized for the infrared. SiAs offer excellent spectral response out to 28 μm with dark current in the 0.01e/second range at 7K over a wide bias range with no tunneling limitations. In addition, because of the perfect thermal match between the Si:As IBC detector and the readout IC (ROIC), hybrids formed by mating Si:As IBCs and ROICs are mechanically stable and have no hybrid reliability problems. Since Si:As IBC detectore are fabricated on readily available Si substrates, large formats are realizable. Si:As IBC detectors have been under development since the mid 80's at Raytheon Vision Systems (RVS). Under the NSAS SIRTF program, a 256 x 256 Si:As array was developed and successfully integrated into the SIRTF IRAC instrument. This same array is also utilized in the ASTRO-F IRC instrument. Both missions will be launched shortly and provide a significant improvement in our ability to measure the spectral signatures of solar type stars and galaxies at high redshifts under very low background conditions in space. Under the NASA Origins program, in collaboration with NASA Ames Research Center (ARC), RVS developed a high performance 1024 x 1024 Si:As IBC array. This array was tested at Ames Research Center. This paper will review the progress of Si:As IBC development at RVS, present test data from ARC, and discuss the more recent developments in Si:As IBC detectors for the JWST MIRI instrument and future missions such as SPICA, TPF, FIRST and DARWIN.
Orion is a program to develop a 2048x2048 infrared focal plane using InSb PV detectors. It is the natural follow-on to the successful Aladdin 1024x1024 program, which was the largest IR focal plane of the 90's. Although the pixels are somewhat smaller than Aladdin, the overall focal plane is over 50mm in size and for the present is the largest IR focal plane of the 21<sup>st</sup> century. The work is being done by Raytheon Infrared Operations (RIO but better known as SBRC) by many of the same people who created the Aladdin focal plane. The design is very similar to the successful Aladdin design with the addition of reference pixels to lower noise and drift effects in long integrations. So far we have made five focal plane modules with hybridized InSb detectors. In this paper we will discuss the unique design features of this device as well as present test data taken from these devices.
A mid-infrared(5-30 micron) instrument aboard a cryogenic space telescope can have an enormous impact in resolving key questions in astronomy and cosmology. A space platform's greatly reduced thermal backgrounds (compared to airborne or ground-based platforms), allow for more sensitive observations of dusty young galaxies at high redshifts, star formation of solar-type stars in the local universe, and formation and evolution of planetary disks and systems. The previous generation's largest, most sensitive infrared detectors at these wavelengths are 256 x 256 pixel Si:As impurity band conduction devices built by Raytheon Infrared Operations for the SIRTF/IRAC instrument. Raytheon has successfully enhanced these devices, increasing the pixel count by a factor of 16 while matching or exceeding SIRTF/IRAC device performance. NASA-Ames Research Center in collaboration with Raytheon has tested the first high performance large format (1024 x 1024) Si:As IBC arrays for low background applications, such as for the mid-IR instrument on NGST and future IR Explorer missions. These hybrid devices consist of radiation-hard SIRTF/IRAC-type Si:As IBC material mated to a readout multiplexer that has been specially processed for operation at low cryogenic temperatures (below 10 K), yielding high device sensitivity over a wavelength range of 5-28 microns. In this paper, we present laboratory test results from these benchmark devices. Continued development in this technology is essential for conducting large-area surveys of the local and early universe through observation and for complementing future missions such as NGST, TPF, and FIRST.
The Astrobiology Explorer (ABE) is a MIDEX mission concept, currently under Concept Phase A study at NASA's Ames Research Center in collaboration with Ball Aerospace & Technologies, Corp., and managed by NASA's Jet Propulsion Laboratory. ABE will conduct infrared spectroscopic observations to address important problems in astrobiology, astrochemistry, and astrophysics. The core observational program would make fundamental scientific progress in understanding the distribution, identity, and evolution of ices and organic matter in dense molecular clouds, young forming stellar systems, stellar outflows, the general diffuse ISM, HII regions, Solar System bodies, and external galaxies. The ABE instrument concept includes a 0.6 m aperture Ritchey-Chretien telescope and three moderate resolution (R = 2000-3000) spectrometers together covering the 2.5-20 micron spectral region. Large format (1024 x 1024 pixel) IR detector arrays will allow each spectrometer to cover an entire octave of spectral range per exposure without any moving parts. The telescope will be cooled below 50 K by a cryogenic dewar shielded by a sunshade. The detectors will be cooled to ~7.5 K by a solid hydrogen cryostat. The optimum orbital configuration for achieving the scientific objectives of the ABE mission is a low background, 1 AU Earth driftaway orbit requiring a Delta II launch vehicle. This configuration provides a low thermal background and allows adequate communications bandwidth and good access to the entire sky over the ~1.5 year mission lifetime.
The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12x5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detector arrays in the camera are 256x256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functional and calibration tests completed at Ball Aerospace during the integration with the cryogenic telescope assembly, and provide updated estimates of the in-flight sensitivity and performance of IRAC in SIRTF.
Airborne and space telescope astronomical observations in the 5-25 micron wavelength region are critical for understanding the physical conditions, composition, chemistry, and excitation of many environments in the interstellar medium, external galaxies, solar system objects, extra-solar systems, and stars. The scientific impact is particularly unique in the 5-8 micron and 14-25 micron regions which are inaccessible or poorly observed from ground-based observatories. Large format mid-infrared detectors sensitive over these wavelengths and operable under moderate backgrounds (~10<sup>6</sup> photons/s/pixel at R=2000, at 10 microns) are essential for efficient large-area survey imaging and for taking moderate resolution spectra over a large spectral range. Both SOFIA and passively cooled Explorer observatories could benefit from this technology. Current first-light SOFIA instruments use small-format mid-infrared focal plane arrays of sizes 256 × 256 pixels. With the collaboration of Raytheon Infrared Operations, NASA-Ames Research Center has developed and tested the first 1024 × 1024 mid-infrared device suitable for operating under moderate backgrounds: a combination of the ALADDIN III readout multiplexer, cryo-processed for 6 K operation, with Si:As IBC detector material designed for high QE. This device has exhibited low dark current, moderate noise levels, and > 200,000 electron linear well size at 6 K operation. We conclude with suggestions for future device development for optimal performance under moderate background, SOFIA- and low Earth orbit observing conditions.
The Astrobiology Explorer (ABE) is a MIDEX mission concept under study at NASA's Ames Research Center in collaboration with Ball Aerospace & Technologies, Corp. ABE will conduct IR spectroscopic observations to address important problems in astrobiology, astrochemistry, and astrophysics. The core observational program would make fundamental scientific progress in understanding the distribution, identity, and evolution of ices and organic matter in dense molecular clouds, young forming stellar systems, stellar outflows, the general diffuse ISM, HII regions, Solar System bodies, and external galaxies. The ABE instrument concept includes a 0.6 m aperture Cassegrain telescope and two moderate resolution (R equals 2000-3000) spectrographs covering the 2.5-16 micron spectral region. Large format (1024x1024 pixel or larger) IR detector arrays and bandpass filters will allow each spectrograph to cover an entire octave of spectral range or more per exposure without any moving parts. The telescope will be cooled below 50 K by a cryogenic dewar shielded by a sunshade. The detectors will be cooled to ~8K. The optimum orbital configuration for achieving the scientific objectives of the ABE mission is a low background, 1 AU Earth driftaway orbit requiring a Delta II launch vehicle. This configuration provides a low thermal background and allows adequate communications bandwidth and good access to the entire sky over the ~1-2 year mission lifetime.
The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12 X 5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detectors arrays in the camera are 256 X 256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functionality and calibration tests completed at Goddard Space Flight Center, and provide estimates of the in-flight sensitivity and performance of IRAC in SIRTF.
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.
A brief overview of the Next Generation Space Telescope science instrument module is given, development plans for engineering design, enabling technologies, and science instruments are discussed. Up-coming schedule milestones of community interest are also presented.
This paper summarizes the findings of the Next Generation Space Telescope (NGST) Detector Requirements Review Panel. This panel was comprised of NGST Integrated Science Instrument Module study representatives, detector specialists, and members of the NGST project science team. It has produced a report that recommends detector performance levels, and has provided rationale for deriving these levels from basic, anticipated NGST science goals and programs. Key parameters such as detector array format, quantum efficiency, and noise are discussed and prioritized.
In this paper we describe a potential new Explorer-class space mission, the AstroBiology Explorer (ABE), consisting of a relatively modest dedicated space observatory having a 50 cm aperture primary mirror which is passively cooled to T < 65 K, resides in a low-background orbit (heliocenter orbit at 1 AU, Earth drift-away), and is equipped with a suite of three moderate resolution spectrographs equipped with first-order cross-dispersers and large format (1024 X 1024 pixel) near- and mid-IR detector arrays cooled by a modest amount of cryogen.
We describe the instrument package concept that we have investigated as part of the Goddard Space Flight Center study for NGST. It is composed of highly integrated, high performance cameras and spectrometers covering the spectral region from 0.6 to 30 microns and with a large field of view.the suite has been configured to reduce cost and complexity with no sacrifice in scientific merit. A common optical bench minimizes interfaces, a guiding system integrated in the science module makes use of the science cameras with minimal penalty to science, and all near IR instruments are built around the same detector module.
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.
The Space IR Telescope Facility (SIRTF) contains three focal plane instruments, one of which is the IR Array Camera (IRAC). IRAC is a four-channel camera that provides simultaneous 5.12 X 5.12 arcmin images at 3.6, 4.5, 5.8 and 8 microns. The pixel size is 1.2 arcsec in all bands. Two adjacent fields of view in the SIRTF focal plane are viewed by the four channels in pairs. All four detector arrays in the camera are 256 by 256 pixels in size, with the two short wavelength channels using InSb and the two longer wavelength channels using Si:As IBS detectors. The IRAC sensitivities at 3.6, 4.5, 5.8, and 8.0 microns are 6, 7, 36, and 54 microJanskys, respectively. Two of the most important scientific objectives of IRAC will be to carry out surveys to study galaxy formation and evolution during the early stage of the Universe, and to search for brown dwarfs and superplanets.
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.
Four 58 X 62-element Si:As impurity-band-conduction (IBC) detector arrays produced by the Hughes Technology Center were tested to evaluate their usefulness for space- and ground- based astronomical observations. PMOS circuitry was used in the multiplexers to improve low-temperature noise performance. Laboratory tests at background levels simulating those expected on space-based observing platforms were combined with ground-based telescope IR observations. The devices have shown read noise levels below 120 rms e-, dark currents below 10 e-/s, and detective quantum efficiencies of 20%.
The planned set of future NASA space astrophysics missions has been continually undergoing evaluation and analysis, to identify major technology needs and to suggest development programs capable of providing this necessary technology. At a recent workshop, a panel of users and technologists worked to assess the state-of-the-art of relevant approaches in the area of direct infrared (IR) detectors. The set of candidate mission concepts was grouped into the categories of low-background and moderate-background systems; development strategies were outlined for each. For low-background systems, detectors with the ultimate in sensitivity are required, and minimum read noise and dark current are critically important. For moderate- background systems, characteristics such as higher detector operating temperature, large charge storage capacity, and large (or very large) formats are important. Novel photon counting schemes could greatly enhance the capability of future systems. Since readouts often determine overall performance of IR focal plane systems, continued development was needed. Future development programs need to be well coupled to the expertise within the astronomical community.
The performance of a multielement Ge:Ga linear array under low-background conditions is investigated. On-focal plane switching is accomplished by MOSFET switches and the integrated charge is made available through MOSFET source followers. The tests were conducted at 106 microns and the radiation on the detectors was confined to a spectral window 1.25 microns wide using a stack of cold filters. At 4.2 K, the responsivity was measured to be nominally 584 A/W, and the NEP was 1.0 x 10 exp -16 W/sq rt Hz. A detailed description of the test setup and the procedure is presented.