Experimental observation of signal degradation in recirculating charge-coupled devices

A circular charge-coupled device structure has been devised. Entrance and exit gates allow a signal to be admitted, recirculated a given number of times, and then examined. In this way a small device permits simulation of very long shift registers (whose length depends on the number of recirculations) without passing the signal through input and output diffusions. Maximum length is limited by transfer efficiency effects and thermal generation, and is greater at low temperature. In a surface mode device clocked at 100 Khz, delays of 8000 transfers (4000 “bits”) have been observed at 77°K. An oscilloscope motion picture demonstrating degradation of an actual circulating signal will be shown. Dependence of observed transfer efficiency on temperature and clock frequency will be discussed.