Dual-gate bucket-brigade devices

The low charge-transfer efficiency of the basic bucket-brigade circuit and the speed limitation of the tetrode approach have so far prevented bucket-brigade devices (BBD's), in spite of their greater fabrication simplicity, from competing with charge-coupled devices, excepting for audio applications. A novel charge-transfer device is presented and experimentally evaluated. The "dual-gate BBD" is a two-step-transfer device (a CCD transfer followed by a BBD transfer), showing operational performances comparable to surface-channel CCD's and, at the same time, enjoying the fabrication simplicity proper to bucket-brigade circuits. The concept is implemented using conventional p-channel aluminum-gate technology combined with an additional shadowed-gap float-off process. The characteristic features and the performance capabilities of the device are discussed.