Ionizing radiation hardening of a CCD technology

A three-level polysilicon, buried channel charge coupled device (CCD) technology has been tested for Co⁶⁰ ionizing radiation damage up to a total dose of 90 krad(Si). For this purpose CCD image sensors have been irradiated together with their associated test structures. These include different types of MOSFETs, natural transistors, buried channel transistors, field transistors, and diodes. The devices have been fully characterized during irradiation and afterwards, as a function of time. The standard technology has been assessed, leading to the implementation of process and design modifications. The modified technology has been further tested according to the same procedure and significant improvement in the sensors´ behavior under irradiation and during annealing has been observed. The radiation hardness of the CCDs has been correlated with the results of the test structures, allowing a better understanding of the degradation phenomena and of the countermeasures needed for a radiation-hardened technology