3D NAND Flash Memory ISPP Step Adjustment
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Solution Overview
Problem
In 3D NAND flash memory, aggressive scaling leads to reliability concerns and over-programming issues during programming operations, which can result in data loss and reduced memory cell performance.
Innovation Solution
A programming method using incremental step pulse programming (ISPP) is employed, where voltage steps are applied to the word line to increase the threshold voltage of memory cells. The method involves determining the quantity of memory cells with threshold voltages between first and second verification voltages, calculating a step adjustment value, and adjusting the initial step value to mitigate over-programming.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If voltage steps are applied to increase threshold voltage toward programming state, then programming speed is improved, but over-programming occurs causing reliability deterioration
Solution Approach 1:
The patent implements a feedback mechanism by sensing the threshold voltage distribution of memory cells during programming and using this information to dynamically adjust the ISPP step value. The controller determines the quantity of memory cells with threshold voltages between verification voltages and adjusts subsequent programming steps based on this feedback, preventing over-programming while maintaining programming speed.
Solution Approach 2:
The patent makes the programming step value dynamic rather than fixed. The ISPP step value is adjusted based on the sensed threshold voltage distribution and the quantity of memory cells in specific voltage ranges. This dynamic adjustment allows the programming process to adapt to the actual state of memory cells, optimizing both speed and reliability.
2Ease of operation
If fixed step value is used in ISPP, then programming operation is simple, but over-programming cannot be mitigated
Solution Approach 1:
The programming system performs self-adjustment by automatically sensing its own state (threshold voltage distribution) and modifying its behavior accordingly. The controller determines the quantity of memory cells in specific voltage ranges and uses this information to self-correct the programming step value, eliminating the need for external intervention or complex control mechanisms.
3Measurement precision
If verification voltage range is expanded to detect more memory cells, then programming precision is improved, but programming time increases
Solution Approach 1:
The patent segments the threshold voltage range into specific regions defined by verification voltages (e.g., between Vva1 and Vva2, or between Vvb1 and Vvb2). By focusing sensing efforts on these specific segments rather than the entire voltage range, the system achieves precise measurement of memory cells that need adjustment while minimizing unnecessary sensing operations.
Data Source
AI summary
A method includes performing a programming operation on the memory cell using incremental step pulse programming. The programming operation includes applying one or more first voltage steps to the word line using a first step value to increase a threshold voltage of the memory cell toward a programming state. The programming operation also includes determining a quantity of memory cells that have a threshold voltage between first and second verification voltages. The second verification voltage is less than the first verification voltage and outside of a range of threshold voltages corresponding to the programming state. The programming operation also includes determining a step adjustment value based on the determining of the quantity. The programming operation also includes adjusting the first step value using the step adjustment value.