Drift-aiding fringing fields in charge-coupled devices

Transverse electric fields at the Si-SiO/SUB 2/ interface (fringing fields) can aid transfer of charge from one potential well to another in charge- coupled devices (CCD). The magnitudes of these drift-aiding fringing fields are evaluated by an approximate analysis and also by computer. The analytical approach assumes zero space charge in the silicon and agrees with the computer solutions in that limit. When the depletion width becomes less than the gate width the fringing field is reduced considerably. Transit times associated with these fringing fields are evaluated. Trapping of charge in interface states rather than transfer of free charge is expected to be the fundamental limitation on speed and transfer efficiency in appropriately designed CCDs.