Capacitor over Bitline (COB) DRAM Cell and its Contributions to High Density DRAMs

The capacitor over bitline (COB) cell has significantly contributed to the increase of DRAM density. A simple idea of making capacitors over bitlines changed the memory cell structure and fabrication steps, and enabled the cell to maintain sufficient storage capacitance in ever decreasing memory cell. The COB cell has been proved to be the most suitable DRAM cell structure for this decade. In this presentation, I would like to review the COB cell development and its contributions to the high density DRAMs. Outlook on future cell structures based on the COB cell will also be discussed.