CTI distribution within a damaged CCD pixel having a notch structure

Abstract

Radiation hardness is one of the most important aspect of a charge coupled device (CCD) working in the space environment. A notch structure is employed so that a charge packet is confined in a notch region within a pixel. We report here the effect of the ’notch structure’ inside the CCD that is designed to be radiation hard. Using a proton beam, we confirmed that the notch structure improved the charge transfer inefficiency (CTI) by a factor of 3. We applied a mesh technique in the proton beam experiment on a CCD. The CCD employed has 1024×1024 pixels with a notch structure. The mesh technique enables us to confine the proton beam of about 600 keV to a circular region of 2 μm diameter within a 24μm pixel. The total proton fluence is 2 × 10 9 protons/cm 2 before the mesh that corresponds to 100 protons for each hole. Some pixels are damaged in the notch region while others in the out-of-notch region. After the proton irradiation, we measured the CTI for each pixel using X-rays from 55 Fe. We found that the CTI of pixels damaged in the notch region is larger by a factor of 3 than that of pixels damaged in the out-of-notch region. We experimentally showed how the notch structure improved the CTI of the CCD.