In a surface-channel C.C.D., electric fields have been computed with the help of a finite-difference method. The normal field, higher than the critical value, can create impact ionization under the gates but not in the gaps. Nevertheless this field is not crucial for the C.C.D. operation as a shift register. The longitudinal field, defined as the sum of two components, is higher than the critical field but at the very beginning of the transfer. All those results have been found again for a theoretical device with 1.5 µm gate length. Nevertheless this heating of the carriers is found to be the major limitation to the maximum transfer frequency.
展开▼
