Article

Radiation-induced charge collection in infrared detector arrays

Space Telescope Science Institute, Baltimore, Maryland, United States
IEEE Transactions on Nuclear Science (Impact Factor: 1.46). 01/2003; DOI: 10.1109/TNS.2002.805382
Source: IEEE Xplore

ABSTRACT A modeling approach is described for predicting charge collection in space-based infrared detector arrays due to ionizing particle radiation. The modeling uses a combination of analytical and Monte Carlo techniques to capture the essential features of energetic ion-induced charge collection to detector pixels in a two-dimensional array. The model addresses several aspects that are necessary for high-fidelity simulation of complex focal plane array structures including multiple layers, subregions within layers, variation of linear energy transfer with range, secondary electron scattering, free-field diffusion, and field-assisted diffusion. Example results are given and predictions are compared to experimental data.

Full-text

Available from: Bernard Rauscher, Jun 02, 2014
0 Followers
 · 
106 Views
  • Source
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We hypothesize that the "snowballs" observed in HgCdTe infrared detectors are caused by natural radioactivity in the devices themselves. As characterized by Hilbert (2009) in the WFC3 flight IR array (FPA165), "snowballs" are transient events that instantaneously saturate a few pixels and deposit a few hundred thousand electrons over a ~5-pixel (~100-um) diameter region. In 2008, prior to flight of detector FPA165, Hilbert (2009) detected 21 snowballs during thermal vaccum test three (TV3) and inferred a rate of ~1100 ± 200 snowballs per year per cm2 of the HgCdTe detector. Alpha particles emitted from either (or both) naturally radioactive thorium and/or uranium, at ~1 ppm concentrations within the device, can explain the observed characteristics of the "snowballs." If thorium is present, up to four distinctly observable snowballs should appear at the same location on the pixel array over the course of many years. While the indium in the bump bonds is almost entirely the radioactive isotope In-115, and 12% of the cadmium is naturally radioactive Cd-113, both of those emit only betas, which are too penetrating and not energetic enough to match the observed characteristics of "snowballs." Also, the Cd-113 emission rate is much less than that of the observed snowballs.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The operability requirements of NASA's 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: omicr 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: omicr A dead/low-DQE pixel: a pixel deviating by >30% from the DQE mean value omicr 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.
    Proceedings of SPIE - The International Society for Optical Engineering 10/2004; DOI:10.1117/12.553079 · 0.20 Impact Factor