Roger Foltz

The Wide-Field Camera 3 detectors

The Wide-field Camera 3 (WFC3) is a fourth-generation instrument planned for installation in Hubble Space Telescope (HST). Designed as a panchromatic camera, WFC3s UVIS and IR channels will complement the other instruments onboard HST and enhance the observatorys scientific performance. UVIS images are obtained via two 4096×2051 pixel e2v CCDs while the IR images are taken with a 1024×1024 pixel HgCdTe focal plane array from Teledyne Imaging Sensors. Based upon characterization tests performed at NASA/GSFC, the final flight detectors have been chosen and installed in the instrument. This paper summarizes the performance characteristics of the WFC3 flight detectors based upon component and instrument-level testing in ambient and thermal vacuum environments.

Performance of the QWIP focal plane arrays for NASA's Landsat Data Continuity Mission

The focal plane assembly for the Thermal Infrared Sensor (TIRS) instrument on NASAs Landsat Data Continuity Mission (LDCM) consists of three 512 x 640 GaAs Quantum Well Infrared Photodetector (QWIP) arrays. The three arrays are precisely mounted and aligned on a silicon carrier substrate to provide a continuous viewing swath of 1850 pixels in two spectral bands defined by filters placed in close proximity to the detector surfaces. The QWIP arrays are hybridized to Indigo ISC9803 readout integrated circuits (ROICs). QWIP arrays were evaluated from four laboratories; QmagiQ, (Nashua, NH), Army Research Laboratory, (Adelphi, MD), NASA/ Goddard Space Flight Center, (Greenbelt, MD) and Thales, (Palaiseau, France). All were found to be suitable. The final discriminating parameter was the spectral uniformity of individual pixels relative to each other. The performance of the QWIP arrays and the fully assembled, NASA flight-qualified, focal plane assembly will be reviewed. An overview of the focal plane assembly including the construction and test requirements of the focal plane will also be described.

The 55 Fe X-Ray Energy Response of Mercury Cadmium Telluride Near-Infrared Detector Arrays

A technique involving 55 Fe X-rays provides a straightforward method to measure the response of a detector. The detectors response can lead directly to a calculation of the conversion gain (eADU � 1 ), as well as aid detector design and performance studies. We calibrate the 55 Fe X-ray energy response and pair production energy of HgCdTe using 8 HST WFC3 1.7 μm flight grade detectors. The results show that each Kα X-ray generates 2273 � 137 electrons, which corresponds to a pair-production energy of 2:61 � 0:16 eV. The uncertainties are dominated by our knowledge of the conversion gain. In future studies, we plan to eliminate this uncertainty by directly mea- suring conversion gain at very low light levels.

Mechanisms and Temperature Dependence of Single Event Latchup Observed in a CMOS Readout Integrated Circuit From 16–300 K

Heavy ion-induced single event latchup (SEL) is characterized in a commercially available CMOS readout integrated circuit operating at cryogenic temperatures. SEL observed at 24 K and below is believed to be possible when free carriers produced by an ion strike initiate an exponential increase in the free carrier density via shallow-level impact ionization (SLII). This results in a large current increase that proceeds to a sustained latched state, even though the classic condition for parasitic bipolar gain product is not met since it is much less than unity. The LET threshold for SEL is significantly lower at 20 K as compared to 300 K although the saturated cross section is 2-3 times higher at 300 K. The temperature dependence of the SEL cross section is characterized from 16-300 K. SEL behavior attributed to the classical cross-coupled parasitic bipolar model is observed from ~135-300 K, and the reduction in the SEL cross section is remarkably modest as the temperature is lowered from room temperature to ~200 K. Temperature dependent electrical latchup characterization of a 130 nm pnpn test structure also indicates a change in the latchup behavior at ~50 K consistent with the SLII mechanism.

Wide Field Camera 3 CCD Quantum Efficiency Hysteresis: Characterization and Mitigation

In ground testing of the Hubble Space Telescope Wide Field Camera 3 (HST/WFC3), the CCDs of its UV/visible channel exhibited an unanticipated quantum efficiency hysteresis (QEH) behavior. The QEH first manifested itself as an occasionally observed contrast in response across the format of the CCDs, with an amplitude of typically 0.1-0.2% or less at the nominal -83°C operating temperature, but with contrasts of up to 3-5% observed at warmer temperatures. The behavior has been replicated in the laboratory using flight spare detectors and has been found to be related to an initial response deficiency of ~5% amplitude when the CCDs are cooled with no illumination. A visible light flat-field (540nm) with a several times full-well signal level is found to pin the detector response at both optical (600nm) and near-UV (230nm) wavelengths, suppressing the QEH behavior. We have characterized the timescale for the detectors to become unpinned (days for significant response loss at -83°C and have developed a protocol to stabilize the response in flight by flashing the WFC3 CCDs with the instruments internal calibration system.

Radiation induced luminescence of the CdZnTe substrate in HgCdTe detectors for WFC3

Proton induced luminescence in the HgCdTe detectors for the Wide Field Camera 3 instrument has been investigated. A radiation experiment has been conducted to localize the source of the luminescence. Conclusive evidence is shown that the luminescence originates in the CdZnTe substrate and propagates toward HgCdTe photodiodes as ~800 nm radiation. Luminescence is proportional to the proton energy deposited in the substrate. Subsequent testing of detectors with the substrate removed confirmed that substrate removal completely eliminates proton induced luminescence.

Reciprocity failure in 1.7 µm cut-off HgCdTe detectors

The Detector Characterization Laboratory at NASA/GSFC has investigated the reciprocity failure characteristics of 1.7μm cut-off HgCdTe devices provided by Teledyne Imaging Sensors to the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) project. The reciprocity failure follows a power law behavior over the range of fluxes tested (0.1-104 photons/second). The slope of the power law varies among detectors, ranging from ~0.3-1%/dex at 1.0μm, which is much smaller than the ~6%/dex effect observed with the HST NICMOS 2.5μm cut-off detectors. In addition, the reciprocity failure exhibits no wavelength dependence, although only a restricted range of wavelengths (0.85-1.0μm) has been explored to date. Despite its relatively small magnitude, reciprocity failure is nevertheless an important effect in the calibration of WFC3 data, as well as in other applications in which there is a large difference in flux between the photometric standards and the scientific sources of interest.

Characterization of the Detector Subsystem for the Near Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope

We present interim results from the characterization 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 NASAs Goddard Space Flight Center will perform the Detector Subsystem characterization tests. In this paper, we update the initial test results obtained with engineering grade components.

NIMBUS: the Near-infrared Multi-Band Ultraprecise Spectroimager for SOFIA

We present a new and innovative near-infrared multi-band ultraprecise spectroimager (NIMBUS) for SOFIA. This design is capable of characterizing a large sample of extrasolar planet atmospheres by measuring elemental and molecular abundances during primary transit and occultation. This wide-field spectroimager would also provide new insights into Trans-Neptunian Objects (TNO), Solar System occultations, brown dwarf atmospheres, carbon chemistry in globular clusters, chemical gradients in nearby galaxies, and galaxy photometric redshifts. NIMBUS would be the premier ultraprecise spectroimager by taking advantage of the SOFIA observatory and state of the art infrared technologies. This optical design splits the beam into eight separate spectral bandpasses, centered around key molecular bands from 1 to 4μm. Each spectral channel has a wide field of view for simultaneous observations of a reference star that can decorrelate time-variable atmospheric and optical assembly effects, allowing the instrument to achieve ultraprecise calibration for imaging and photometry for a wide variety of astrophysical sources. NIMBUS produces the same data products as a low-resolution integral field spectrograph over a large spectral bandpass, but this design obviates many of the problems that preclude high-precision measurements with traditional slit and integral field spectrographs. This instrument concept is currently not funded for development.

Performance overview of the Euclid infrared focal plane detector subsystems

In support of the European space agency (ESA) Euclid mission, NASA is responsible for the evaluation of the H2RG mercury cadmium telluride (MCT) detectors and electronics assemblies fabricated by Teledyne imaging systems. The detector evaluation is performed in the detector characterization laboratory (DCL) at the NASA Goddard space flight center (GSFC) in close collaboration with engineers and scientists from the jet propulsion laboratory (JPL) and the Euclid project. The Euclid near infrared spectrometer and imaging photometer (NISP) will perform large area optical and spectroscopic sky surveys in the 0.9-2.02 μm infrared (IR) region. The NISP instrument will contain sixteen detector arrays each coupled to a Teledyne SIDECAR application specific integrated circuit (ASIC). The focal plane will operate at 100K and the SIDECAR ASIC will be in close proximity operating at a slightly higher temperature of 137K. This paper will describe the test configuration, performance tests and results of the latest engineering run, also known as pilot run 3 (PR3), consisting of four H2RG detectors operating simultaneously. Performance data will be presented on; noise, spectral quantum efficiency, dark current, persistence, pixel yield, pixel to pixel uniformity, linearity, inter pixel crosstalk, full well and dynamic range, power dissipation, thermal response and unit cell input sensitivity.