Radiation damage in charge coupled devices
This thesis is concerned with the effects of radiation damage in CCDs used for space applications. The manufacturing process and operational principles of CCDs are presented in Chapter 2. The space radiation environment, the two radiation damage mechanisms relevant to CCDs, and the effects of radiation on the operational characteristics of CCDs are described in Chapter 3. Chapter 4 presents a study to assess the suitability of novel low light level L3Vision CCD technology to applications in space. Two L3Vision CCDs were subjected to proton irradiations representative of doses expected to be received by spacecraft in low Earth orbit. Post-irradiation the devices were found to operate as expected, the effects of radiation on the operational characteristics of the devices being comparable to previous studies. The effect of low energy protons on CCDs is the subject of Chapter 5. The study was initiated in response to the finding that soft protons could be focused by the mirror modules of the XMM-Newton spacecraft onto the EPIC CCD detectors. Two EPIC devices were irradiated with protons of a few keV to find that soft protons cause more damage than that expected by the Non-Ionising Energy Loss damage relationship, as they deposit most of their energy within the CCD. The observed change in CTI of the EPIC devices on XMM-Newton is however comparable to the pre-launch prediction, and the component attributable to low energy protons is small, <20 %. Chapter 6 presents a study of a specific radiation induced phenomenon, ‘Random Telegraph Signals’. Development of analysis software and the irradiation of two CCDs are discussed before a detailed characterisation of the generated RTS pixels is presented. The study shows that the mechanism behind RTS involves a bi-stable defect linked with the E-centre, in combination with the high field regions of a CCD pixel.