Control Method And Controller Of 3D Nand Flash

What is this patent about?

’925 is related to the field of non-volatile memory, specifically 3D NAND flash memory. The background involves improving programming performance in these memories, which are used in various electronic devices. As memory density increases (MLC, TLC, QLC), the programming time becomes a critical factor, requiring efficient control of the number of programming voltage pulses.

The underlying idea behind ’925 is to optimize the programming process by adjusting the pulse widths of the programming voltage pulses applied to a memory cell. Instead of using uniform pulse widths, the invention proposes varying the pulse widths during the programming sequence, specifically making the last pulse wider than the preceding pulses.

The claims of ’925 focus on a method and a memory device that programs a memory cell by applying a sequence of pulses. This sequence includes a first pulse, middle pulses, and a last pulse. The key feature is that the last pulse has a wider pulse width than both the middle pulses and the first pulse. At least one of the middle pulses also has a pulse width wider than the first pulse.

In practice, this approach aims to reduce the overall programming time. By using a wider last pulse, the memory cell is given more time to reach the desired programmed state, potentially reducing the number of pulses needed. This is particularly relevant in 3D NAND flash, where programming time directly impacts read latency and overall system performance. The controller adjusts the waveforms to control the memory array.

This method differentiates itself from prior art by not using constant pulse widths for all programming pulses. Traditional methods increase the voltage of each pulse by a fixed amount (Vispp) while keeping the pulse width constant. ’925, however, introduces the concept of varying the pulse width , especially increasing the width of the final programming pulse, to achieve faster and more efficient programming. This allows for a narrower distribution of the threshold voltage Vt in the high state.