Radiation damage effects in charge coupled devices
The effects of Sr90 beta radiation and Co60 gamma radiation on the operation of EEV buried channel charge coupled devices (CCDs) have been studied. This work was instigated by the need to qualify CCDs for the SLD vertex detector. However, the work is also relevant to other small signal, low noise applications. The results of the batch qualification are presented and the data base of ionising radiation effects on EEV CCDs has been extended to include the effects of irradiation whilst clocking at 180K. Particular attention has been aimed at investigating the charge transfer degradation due to low levels of bulk defects. The measured energy level, capture cross section and introduction rate of the main radiation induced defect agrees well with published results for the Si-E centre. Annealing studies are also presented. A model for the charge transfer degradation is proposed. This includes the effects of temperature, readout rate, signal density and irradiation type and energy. Observations are also presented on the effect of irradiation on the noise characteristics of the single stage output circuit. For low noise applications the output is run in buried channel mode. In this mode the increase in noise is dominated by the change in the operating point of the output MOSFET.