Elizabeth J. Polidan

Comparisons of the proton-induced dark current and charge transfer efficiency responses of n- and p-channel CCDs

The proton-induced charge transfer efficiency (CTE) behavior for the Lawrence Berkeley National Laboratory (LBNL) p-channel CCD [being developed for the Supernovae Acceleration Probe (SNAP)] is compared with the Hubble Space Telescope’s (HST) Wide Field Camera 3 (WFC3) n-channel CCDs CTE using 55Fe x-rays, first pixel edge response (FPR), and extended pixel edge response (EPER) techniques. The pre- and post-proton radiation performance parameters of p-channel CCDs designed by LBNL and fabricated at Dalsa Semiconductor, Inc. are compared with n-channel CCDs from E2V, Inc. LBNL p-channel CCDs both with and without notched parallel registers are compared with the E2V CCD43 [a notched, multi-phase pinned (MPP) device] and the E2V CCD44 (an un-notched, non-MPP device), using the same readout timing and measured over the same range of temperatures. The CTE performance of the p-channel CCD is about an order of magnitude better than similar n-channel CCDs for the conditions measured here after a 63 MeV proton fluence of 2.5 x 109 cm-2, which is equivalent to 2.5 years in the HST orbit behind shielding comparable to about 2.5 cm Al. Our measurements are compared with previous CTE measurements at 12 MeV by Bebek et al. The ~ 10 x CTE improvements relative to n-channel CCDs is seen at -83°C, a temperature which is optimized for n-channel CCD performance. Advantages from p-channel CCDs should be greater at other temperatures. Dark current measurements and hot pixel issues are also discussed.

A comparison of charge transfer efficiency measurement techniques on proton damaged n-channel CCDs for the Hubble Space Telescope Wide-Field Camera 3

We examine proton-damaged charge-coupled devices (CCDs) and compare the charge transfer efficiency (CTE) degradation using extended pixel edge response, first pixel response, and /sup 55/Fe X-ray measurements. CTEs measured on Marconi and Fairchild imaging sensors CCDs degrade similarly at all signal levels, though some of the Fairchild CCDs had a supplementary buried channel.

Hot pixel annealing behavior in CCDs irradiated at -84/spl deg/C

A Hubble space telescope wide field camera 3 e2v CCD was irradiated while operating at -84/spl deg/C and the dark current studied as a function of temperature while the charge coupled device was warmed to a sequence of temperatures up to a maximum of +30/spl deg/C. The device was then cooled back down to -84/spl deg/ and remeasured. Hot pixel populations were tracked during the warm up and cool down. Hot pixel annealing began below -40/spl deg/C and the anneal process was largely completed by the time the detector reached +20/spl deg/C. There was no apparent sharp annealing temperature. Although a large fraction of the hot pixels fell below the threshold to be counted as a hot pixel, they nevertheless sustained a higher leakage rate than the remaining population. The mechanism for hot pixel annealing is not presently understood. Room temperature irradiations do not adequately characterize the hot pixel distributions for cooled applications.

Hot pixel behavior in WFC3 CCD detectors irradiated under operational conditions

A Hubble Space Telescope Wide Field Camera 3 (WFC3) CCD detector was tested for radiation effects while operating at -83°C. The detector has a format of 2048 x 2048 pixels with a 15 μm square pixel size, a supplemental buried channel, an MPP implant, and is back side illuminated. Detector response was tested for total radiation fluences ranging from 1x103 to 2.5x109 of 63.3 MeV protons/cm2 and for a range of beam intensities. Radiation damage was investigated and the annealing of damage was tested by warming up to +30°C. The introduction rate of hot pixels and their statistics, hot pixel annealing as a function of temperature and time, and radiation changes to the mean value of dark current were investigated. Results are compared with the experiences of other HST instruments.

A study of hot pixel annealing in the Hubble Space Telescope Wide Field Camera 3 CCDs

A Hubble Space Telescope Wide Field Camera 3 (WFC3) CCD detector was tested for radiation effects while operating at -83C. The goal of the experiment was to evaluate the introduction and annealing rates of hot pixels and to assess the dynamics of that process. The device was irradiated while cold and warmed to +30°C for a 4 hour soak, then cooled back down to -83°C. Hot pixel populations were tracked during warm up and cool down. The results showed that the hot pixels begin to anneal around -40°C and the anneal process was largely completed before the detector reached +30°C. It was also found that, although a large fraction of the hot pixels dropped below the threshold, they remained warmer than the remaining population.

Transient radiation effects in ultra-low noise HgCdTe IR detector arrays for space-based astronomy

We present measurements of proton-induced single event transients in ultra-low noise HgCdTe IR detector arrays being developed for space-based astronomy and compare to modeling results.

Radiation effects in WFC3 IR detectors

A Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) flight-like IR detector was tested for radiation hardness by exposing it to high energy protons while operating at the nominal flight temperature of 150 K. The detector is a 1.7 μm cutoff HgCdTe detector with a CdZnTe substrate. The device is hybridized to a silicon multiplexer. The detector response was tested for gradually increasing fluence from less than 1x103 to a total of 5x109 63 MeV protons/cm2. Dark current changes were evaluated after each step. An increase in dark current and new hot pixels were observed after large steps of irradiation. The increased dark current was observed to partially anneal at 190K and fully anneal at room temperature. Radiation effects, hot pixel distribution, and results of annealing at different temperatures are presented here.

The infrared detectors for the wide field camera 3 on HST

We present the performance of the IR detectors developed for the WFC3 project. These are HgCdTe 1Kx1K devices with cutoff wavelength at 1.7 μm and 150K operating temperature. The two selected flight parts, FPA#64 (prime) and FPA#59 (spare) show quantum efficiency higher than 80% at λ=1.6 μm and greater than 40% at λ>1.1μm, readout noise of ~25 e- rms with double correlated sampling, and mean dark current of ~0.04 e/s/pix at 150K. We also report the results obtained at NASA GSFC/DCL on these and other similar devices in what concerns the QE long-term stability, intra-pixel response, and dark current variation following illumination or reset.

Radiation-induced transient effects in HgCdTe IR focal plane arrays

The operability requirements of NASAs James Webb Space Telescope (JWST) impose specific challenges on radiation effects mitigation and analysis. For example, the NIRSpec Instrument has the following requirements: •The percentage of pixels defined as operable for target acquisition shall not be less than 97% (TBR) (goal 99%) of the total number of pixels... An inoperable pixel is: ο A dead pixel: a pixel with no radiometric response o A noisy pixel: a pixel with a total noise greater than 21 e-, per Fowler 8 exposure •The percentage of pixels defined as operable for science observations shall not be less than 92% (TBR) (goal 98%) of the total number of pixels... An inoperable pixel is: ο A dead/low-DQE pixel: a pixel deviating by >30% from the DQE mean value ο A noisy pixel: a pixel with a total noise greater than 12 e- (goal 9e-). With these performance requirements and operation in space, the radiation environment from galactic cosmic rays (GCR), energetic solar particles, and activation of spacecraft materials can contribute significantly to the number of inoperable pixels. The two most important issues to date are radiation-induced transient effects and hot pixels. This paper focuses on the methods used to assess the impact of ionizing radiation induced transients on the HgCdTe SCA selected by JWST. Hot pixel effects in these detectors has been previously presented. Both effects are currently under investigation.

Selection of the infrared detectors for Wide Field Camera 3 on the Hubble Space Telescope

Wide Field Camera 3 is a fourth generation instrument for the Hubble Space Telescope (HST), to be installed during the next HST Servicing Mission 4. For its infrared channel Rockwell Scientific Company has developed a new type of HgCdTe 1Kx1K detector, called WFC3-1R, with cutoff wavelength at 1.7μm and 150K operating temperature. The WFC3-IR detectors are based on HgCdTe MBE grown on a CdZnTe substrate and use a new type of multiplexer, the Hawaii-1R MUX. Two flight detectors, a prime and a spare, have been recently selected on the basis of the measures performed at NASA Goddard Research Center - Detector Characterization Laboratory. These parts show quantum efficiency higher than 80% at λ=1.6μm and greater than 40% at λ>1.1μm, readout noise of ~25 e- rms with double correlated sampling, and mean dark current of ~0.04 e/s/pix at 150K. We show that the IR channel of WFC3, equipped with one of these flight detectors, beats the instrument requirements in all configurations and promises to have a discovery efficiency significantly higher than NICMOS. In particular, a two-band wide-area, deep survey made with WFC3 exceeds the discovery efficiency of NICMOS before and after the installation of NCS by a factor of 15 and 10, respectively.