Radiation Damage E ects in CCD Sensors for Tracking Applications in High Energy Physics Ph.D. Thesis

This thesis presents systematic studies on the radiation damage e ects in 2and 3-phase Charge Coupled Devices (CCD). CCDs are one of the primary options for tracking devices at the vertex detector of a future Linear Collider due to their high precision and twodimensional resolution. The radiation backgrounds near the interaction point impose considerable challenge to the tolerance of the CCD sensors to radiation damage e ects. To estimate the e ects from the expected radiation background, surface and bulk damage have been extensively studied in electronand neutron-irradiated CCDs from two di erent manufacturers, Hamamatsu Photonics and Marconi Applied Technologies. Special attention was paid to the application of CCD in radiation environment at near-room temperatures. Multi Pinned Phase (MPP) mode CCDs, which o er more than an order of magnitude lower dark current than conventional devices were studied. The at band voltage shifts, caused by ionizing radiation have been found to be considerable, especially in devices irradiated under bias. In Hamamatsu devices additional dark signal, induced by the clocking was observed and found to be a major device problem. That current is explained by impact ionization from holes, emitted from radiation-induced defects at the Si-SiO2 interface. Dark current spikes (\hot pixels"), some of which generate current in the form of Random Telegraph Signals (RTS) were found in neutron irradiated devices. It was shown, that although potentially dangerous, RTS are unlikely to be a limiting factor to the device application at suÆciently fast readout even at room temperatures. Charge transfer losses, or Charge Transfer IneÆciency (CTI) in CCDs, caused by radiation-induced bulk defects was one of the major issues under study. Charge losses in 2and 3-phase CCDs, which are nowadays the most widely used devices, were studied both theoretically and experimentally. The in uence of the clock timing and pattern, temperature, dark current, signal density and pixel occupancy on the CTI was investigated in order to nd the optimal operating conditions for reduced charge losses. The clock