The Infrared Array Camera (IRAC) is one of three focal plane instruments in 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. Two nearly adjacent 5.2×5.2 arcmin fields of view in the focal plane are viewed by the four channels in pairs (3.6 and 5.8 µm; 4.5 and 8 µm). All four detector arrays in the camera are 256×256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. IRAC is a powerful survey instrument because of its high sensitivity, large field of view, and four-color imaging. This paper summarizes the in-flight scientific, technical, and operational performance of IRAC.
Measurements of the mechanical quality factor Q in a single crystal of silicon vs. temperature have been made. A value of 2x lO 9 has been measured at T=3.5K.We have been studying large dielectric and semiconductor single crystals as possible gravitational wave detectors. 1 These detectors are frequently cylinders instrumented to detect vibrations of the first longitudinal mode. One of the important desirable properties is a high mechanical quality factor Q. With an ideal transducer the sensitivity to gravitational waves is proportional to Q. The inverse quality factor Q-1 is a direct measure of the dominant mechanism of the attenuation of first sound. Measurements of Q are frequently the best way to gather information concerning the various internal loss mechanisms of a substance. In the region of very high Q (low loss) this sometimes is the only easy method. We report here on measurements on a large single crystal of silicon whose Q values exceed 10 9.The crystal was manufactured by Monsanto by the zero-dislocation Czochralski process in the form of a cylinder (diameter 10.6 cm, length 22.9 cm, mass 4.9 kg), with the [111] axis parallel to the cylinder axis. The ends were polished by the University of Rochester Institute of Optics personnel to better than one wavelength of light. The barrel of the crystal, somewhat wavy from the crystal growing process, was left in this state so that its edge deviates from straightness by -1 mm. The crystal is a p-type
Space astronomy requires large-area cryogenic infrared focal plane arrays ͑FPAs͒ with high quantum efficiency, extremely low dark current, low power dissipation, and background limited noise performance. To meet these requirements, especially at temperatures of 5-15 K, Santa Barbara Research Center designed and fabricated a new multiplexer, CRC-744. The FPAs made by bonding InSb detector arrays to CRC-744 multiplexers were evaluated at the University of Rochester. The best array achieved the read noise of 5 e Ϫ with 12 s integration and 7 e Ϫ with 200 s integration with Fowler-64 sampling at 15 K, the average dark current of Ͻ0.2 e Ϫ /s at both 15 and 29 K, and the average quantum efficiency of 87% at both 15 and 29 K. The 10%-90% rise time was 4 s driving a 600 pF external load. The power dissipation was 0.3-0.4 mW when running flat-out ͑100% duty cycle͒. The full well capacity was 10 5 e Ϫ ͑230 mV͒ with 400 mV of applied bias. The above test results demonstrate that the FPAs meet background-limited space experiment requirements. The CRC-744 multiplexer works well down to at least 5 K ͑the lowest temperature of our tests͒.
1K × 1K Si:As Impurity Band Conduction (IBC) arrays have been developed by RVS for the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI). MIRI provides imaging, coronagraphy, and low and medium resolution spectroscopy over the 5 -28 µm band. The IBC devices are also suitable for other low-background applications. The Si:As IBC detectors have a pixel dimension of 25 µm and respond to infrared radiation between 5 and 28 µm, covering an important Mid-IR region beyond the 1 -5 µm range covered by the JWST NIRCam and NIRSpec instruments. Due to high terrestrial backgrounds at the longer Mid-IR wavelengths, it is very difficult to conduct ground-based observations at these wavelengths. Hence, the MIRI instrument on JWST can provide science not obtainable from the ground. We describe results of the development of a new 1024 × 1024 Si:As IBC array that responds with high quantum efficiency over the wavelength range 5 to 28 µm. The previous generation's largest, most sensitive infrared (IR) detectors at these wavelengths were the 256 × 256 / 30 µm pitch Si:As IBC devices built by Raytheon for the SIRTF/IRAC instrument 1 . Detector performance results will be discussed, including relative spectral response, Responsive Quantum Efficiency (RQE) vs. detector bias, and dark current versus temperature. In addition, Sensor Chip Assembly (SCA) data will be presented from the first Engineering SCAs. The detector ROIC utilizes a PMOS Source Follower per Detector (SFD) input circuit with a well capacity of about 2 × 10 5 electrons. The read noise of the "bare" MUX is less than 12 e-rms with Fowler-8 sampling at an operating temperature of 7 K. A companion paper by Craig McMurtry (University of Rochester) will discuss the details of SB305 MUX noise measurements 2 . Other features of the IBC array include 4 video outputs and a separate reference output with a frame rate of 0.36 Hz (2.75 sec frame time). Power dissipation is about 0.5 mW at a 0.36 Hz frame rate. Reset modes include both global reset and reset by row (ripple mode). Reference pixels are built-in to the output data stream. The 1K × 1K IBC is packaged in a robust modular package that consists of a multilayer motherboard, SiC pedestal, and cable assembly with 51-pin MDM connector. All materials of construction were chosen to match the thermal expansion coefficient of Silicon to provide excellent module thermal cycle reliability for cycling between room temperature and 7 K.
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