The quantitative effects of interface states on the performance of charge-coupled devices

The several effects of interface states in limiting the performance of surface channel charge-coupled devices (CCD's) are described and evaluated. The limitations on transfer efficiency may be minimized by using a background charge in the device at all times. Experimental measurements of transfer inefficiency on three-phase devices and a two-phase device are presented and correlated with the predicted values, although measurements of the density and capture cross sections of interface states after device fabrication are required for accurate quantitative predictions of transfer inefficiencies. It is concluded that trapping effects are a limitation on the transfer efficiencies obtainable in surface channel charge-coupled devices, particularly, for example, at frequencies less than 1 MHz for devices having 10-µm-long transfer electrodes, but are not a direct limitation on the high-frequency performance. The effect of interface states in adding transfer noise onto the charge packets is also described, and is shown to be small, although in some devices it may reduce the signal-to-noise ratios that might otherwise be possible.