Wl Under-Driving Scheme With Decremental Step Voltage And Incremental Step Time For High-Capacity Nand Flash Memory

In this work, we compared the WL driving schemes in 512 Gb planar NAND with 32 KB page size. In the conventional WL driving scheme, the rising time of the selected WL voltage is very large because of the large coupling capacitance between the selected and unselected WLs. The WL under-driving scheme (WLUDS) reduces the effect of coupling capacitance by using the 2-phase control of unselected WL voltage. However, when WLUDS is used, the relationship between the rising time and overshoot of the selected WL voltage should be considered in order to achieve the small rising time Therefore, we proposes a novel implementation method for WLUDS that controls the under-driving voltage and under-driving timing by using the decremental step voltage and incremental step time (DSVIST) to enhance the rising time considering the overshoot constraint. The HSPICE simulation using the 0.25-mu m PTM model with the parasitic RC in 32 KB page size shows that the rising time in the proposed WLUDS with DSVIST is improved to 988 mu s compared to 1206 mu s in the conventional WL driving scheme.