Radiation-hard, charge-coupled devices for the extreme ultraviolet variability experiment

The Extreme-Ultraviolet Variability Experiment (EVE) is a component of NASA's Solar Dynamics Observatory (SDO) satellite, aimed at measuring the solar extreme ultraviolet (EUV) irradiance with high spectral resolution, temporal cadence, accuracy, and precision. The required high EUV quantum efficiency (QE), coupled with the radiation dose to be experienced by the detectors during the five year mission (~1 Mrad), posed a serious challenge to the charge-coupled device (CCD) detectors. MIT Lincoln Laboratory developed the 2048 × 1024 pixel CCDs and integrated them into the detector system. The devices were back-side thinned and then back surface passivated using a thin, heavily boron-doped silicon layer grown by molecular beam epitaxy (MBE) at less than 450°C. Radiation-hardness testing was performed using the Brookhaven National Laboratory's National Synchrotron Light Source (BNL/NSLS). The MBE-passivated devices were compared against devices with back surfaces passivated with a silver charge chemisorption process and an ion-implant/furnace anneal process. The MBE devices provided both the highest QE at the required (-100°C) operating temperatures, and superior radiation hardness, exceeding the goals for the project. Several flight-ready devices were delivered with the detector system for integration with the satellite.