A Doped Surface Two-Phase CCD

The successful operation of an n-channel two-phase charge-coupled device has been achieved. The asymmetry in the surface potential profile necessary to force the charge to move unidirectionally was obtained by ion implanting a nonuniform doping distribution in the Si substrate under each gate. An eight-stage shift register with a length per stage of 80 µm was made, and was operated as both a digital and an analog device. There are two ways to clock the device. Either both clock lines are driven with square waves, out of phase by one half of a period, or one clock is held at a fixed DC potential while the other is driven with a square wave. Using the latter method, the charge transfer efficiency was better than 99.9 percent per transfer over the clock frequency range of 103Hz to 6.5 × 106Hz.