Low‐temperature characteristics of buried channel charge‐coupled devices

Abstract

AbstractThis paper aims at the improvement of the characteristics of the buried‐channel charge‐coupled device (BCCD), which is used in such low‐temperature operation as the infrared image sensor. The measurement and analysis are performed for the transfer loss of BCCD below 100°K. The transfer loss in this temperature region is dominated by the carrier freeze‐out to the impurity level composing the n‐well of the buried‐channel. The loss in this temperature region depends on the period and the fall‐time of the driving clock. The dependence of the loss on the driving condition can be accounted for by the model in which two time‐constants exist for the emission from the trap. The reason for the different emission time‐constants from a trap depending on time is that the fringing field in the channel depends on time. When a large fringing field exists, the effective barrier of the trap is lowered by the Poole‐Frenkel effect, thereby decreasing the emission time‐constant. To reduce the transfer loss in this temperature region, there are several methods, such as utilization of impurity with shallow donor level in the n‐well of the buried‐channel, reduction of the impurity concentration, and increase of the fringing field.