Radiation Tolerance of Fully-Depleted P-Channel CCDs Designed for the SNAP Satellite

TL;DR

This study demonstrates that fully-depleted p-channel CCDs developed for the SNAP satellite exhibit high radiation tolerance, maintaining performance after proton and electron irradiation, with minimal degradation over a six-year space mission.

Contribution

The paper presents the radiation tolerance performance of fully-depleted p-channel CCDs, showing significant improvements over conventional n-channel CCDs for space applications.

Findings

CCDs maintain charge transfer efficiency after irradiation

Dark current increases by 20 e/pixel/hr over six years without annealing

Parallel CTE degrades by 3e-6, serial CTE by 1e-6 after radiation exposure

Abstract

Thick, fully depleted p-channel charge-coupled devices (CCDs) have been developed at the Lawrence Berkeley National Laboratory (LBNL). These CCDs have several advantages over conventional thin, n-channel CCDs, including enhanced quantum efficiency and reduced fringing at near-infrared wavelengths and improved radiation tolerance. Here we report results from the irradiation of CCDs with 12.5 and 55 MeV protons at the LBNL 88-Inch Cyclotron and with 0.1-1 MeV electrons at the LBNL Co60 source. These studies indicate that the LBNL CCDs perform well after irradiation, even in the parameters in which significant degradation is observed in other CCDs: charge transfer efficiency, dark current, and isolated hot pixels. Modeling the radiation exposure over a six-year mission lifetime with no annealing, we expect an increase in dark current of 20 e/pixel/hr, and a degradation of charge transfer efficiency in the parallel direction of 3e-6 and 1e-6 in the serial direction. The dark current is observed to improve with an annealing cycle, while the parallel CTE is relatively unaffected and the serial CTE is somewhat degraded. As expected, the radiation tolerance of the p-channel LBNL CCDs is significantly improved over the conventional n-channel CCDs that are currently employed in space-based telescopes such as the Hubble Space Telescope.