NAND Flash Sensing Node Voltage Restoration
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Solution Overview
Problem
In NAND flash memory, the recovery of sensing nodes is time-consuming, affecting reading speed and accuracy, especially during continuous reading operations, where the latch reset must be performed efficiently to maintain voltage levels and prevent offsetting of bit-line clamp voltages, which can impact sensing accuracy.
Innovation Solution
A method involving pre-charging, discharging, and recharging the sensing node using a voltage-supply node, with specific transistor control to maintain the selected bit line in a floating state until unselected bit lines finish discharging, ensuring accurate voltage restoration and minimizing noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the latch is reset after pre-charging the bit line and before discharging the NAND string, then the reading speed can be increased, but the sensing node voltage restoration time increases, affecting sensing accuracy
Solution Approach 1:
The sensing node is pre-charged to the clamp voltage level before the latch reset operation begins. This preliminary charging action ensures that when the sensing node needs to be restored after the latch reset, it can quickly return to the correct voltage level without causing offsetting of the bit line clamp voltage, thereby maintaining both high reading speed and accurate sensing.
2Measurement precision
If the selected bit line is blocked from the voltage-supply node during unselected bit line discharge, then the clamp voltage offset is prevented, but the sensing node may be affected by unexpected noise in floating state
Solution Approach 1:
The sensing node serves as an intermediary element that is connected to both the selected bit line and the voltage-supply node through controlled transistors. By using the sensing node as a mediator and carefully controlling its connection state, the patent prevents noise interference while maintaining voltage stability during the bit line discharge operation.
3Measurement precision
If the sensing node is restored to original voltage after latch reset, then the voltage can be accurately restored, but the recovery time increases the reading time
Solution Approach 1:
The sensing node voltage restoration is performed continuously and in parallel with other reading operations rather than as a separate sequential step. The node is maintained at the correct voltage level throughout the reading process, eliminating idle waiting time and ensuring that voltage restoration does not increase the overall reading time while maintaining accurate voltage levels.
Data Source
AI summary
A semiconductor device capable of performing high-speed read or high-reliability read is provided. A reading method of a NAND flash memory includes: pre-charging a sensing node through a voltage-supply node; discharging the sensing node to the voltage-supply node for a prescribed operation; recharging the sensing node by the voltage-supply node after the prescribed operation; and discharging a NAND string and sensing a memory cell.