Utilizing nand strings in dummy blocks for faster bit line precharge

Abstract

In NAND Flash memory, bit line precharge/discharge times can be a main component in determining program, erase and read performance. In a conventional arrangement bit line levels are set by the sense amps and bit lines are discharged to a source line level is through the sense amplifier path. Under this arrangement, precharge/discharge times are dominated by the far-side (relative to the sense amps) based on the bit lines' RC constant. Reduction of bit line precharge/discharge times, therefore, improves NAND Flash performance and subsequently the overall system performance. To addresses this, an additional path is introduced between bit lines to the common source level through the use of dummy NAND strings. In an exemplary 3D-NAND (BiCS) based embodiment, the dummy NAND strings are taken from dummy blocks, where the dummy blocks can be placed throughout the array to evenly distribute the discharging current.