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Theoretical calculations are made of low frequency transfer inefficiency for the conductively connected charge-coupled device (C4D). Two mechanisms for transfer inefficiency arise in the C4D which are not found in correctly operated charge-coupled devices (CCD's) but are found in bucket brigade devices. These are 1) barrier length modulation and 2) diffusion over the barrier. Theoretical analyses are made for both of these mechanisms, and both are found to be significant (~0.05 percent/transfer for a 5 μm barrier) and independent of frequency. The transfer inefficiency increases sharply as feature size is reduced but decreases as oxide thickness is reduced. The fabrication and testing of C4D's with barrier lengths in the range 1.75 μm to 5 μm are described, and the measured transfer inefficiencies compare well with theoretical predictions.