Noise in buried channel charge-coupled devices

In this paper we discuss the noise measured at the output of a buried channel charge-coupled device (BCCD) linear shift register. The measured noise arises from four sources; the electrical insertion of signal charge, the output amplifier, dark current, and bulk state trapping. In making these measurements the concept of correlated double sampling was used in an output circuit which had a noise level which was equivalent to less than 3O noise electrons. A critical component in this output was a low noise MOSFET which was achieved by use of the buried channel technology. A low noise input structure for electrical insertion of signal charge was used which introduced a signal which had a noise level which ranged from less than 10 e
^-
to as high as 60 e
^-
depending on the size of the signal charge. The dark current noise was found to be well characterized as a shot noise and levels on the order of 20 e
^-
were measured. The above low noise levels made possible direct measurement of the noise due to bulk state trapping, and depending on the signal size and clock rate noise levels were measured which ranged from less than 10 to over 100 noise electrons. One of the most important bulk traps was found to be due to gold impurities which had a density of ∼ 2 × 10
¹¹
cm
^-3
.