Radiation Effects in N-Buried Channel CCDS Fabricated with a Hardened Process

In this paper, we present ionizing radiation data on 4-phase n-buried channel 128 bit CCDs with a polysilicon overlapping polysilicon gate structure which were fabricated with a radiation hardened process. These CCDs can be operated well up to 1.2×106 rads (Si) without changing any biasing conditions. The threshold voltage shifts are ≤-1.8V for the buried polysilicon gate test MOSFETs, and ≤-0.4V for the surface polysilicon gate test MOSFETs. The charge transfer efficiency is better than 0.9998 after 1.2×106 rads with 20% fat zero. The average dark current increases to 107 nA/cm2 for OV gate bias and to 65 nA/cm2 for OV gate bias. Further optimization of the CCD hardness is suggested here by optimum choice of surface gates or buried gates for the input and the output structures.