Multi-Pass Programming for NAND Flash Memory Cells
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Solution Overview
Problem
NAND flash memory technologies face challenges such as widening of threshold voltage distributions and increased program disturb as process geometries shrink, affecting the accuracy and reliability of data storage in semiconductor memory devices.
Innovation Solution
A multi-pass programming technique, specifically a four-pass or multi-pass programming method, is employed to program non-volatile memory cells, including an LM programming pass, a Foggy programming pass, a First Fine programming pass, and a Second Fine programming pass, to minimize the Yupin effect and stabilize threshold voltage distributions, ensuring accurate data storage and retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If process geometries are shrunk to increase storage density, then storage capacity is improved, but threshold voltage distribution widens and program disturb increases
Solution Approach 1:
The programming operation is divided into multiple sequential passes (e.g., first pass, second pass, third pass) with each pass applying progressively lower program voltages. This segmentation allows the memory cells to be programmed in stages, with each pass addressing specific portions of the threshold voltage distribution, thereby reducing the widening effect caused by scaling while maintaining high storage density.
Solution Approach 2:
Before performing the final programming operation, preliminary programming passes are executed to pre-condition the memory cells. These preliminary passes establish initial threshold voltage levels that prevent excessive widening during subsequent operations, thereby maintaining reliable threshold voltage distributions even as process geometries are shrunk to increase storage capacity.
2Productivity
If program voltage is increased to improve programming speed, then programming efficiency is improved, but Yupin effect increases causing reading disturbances
Solution Approach 1:
The high-voltage programming operation is segmented into multiple passes with decreasing voltage levels. The first pass uses a higher voltage to establish initial programming, while subsequent passes use progressively lower voltages to refine the threshold voltage levels. This segmentation maintains programming speed by distributing the work across multiple operations rather than requiring a single high-voltage pass, thereby reducing the Yupin effect and associated reading disturbances.
Solution Approach 2:
The programming process employs periodic action through multiple alternating passes of programming and verification. Each programming pass is followed by a verification pass to detect and correct any Yupin effect-induced errors. This periodic cycle of programming and verification ensures that reading disturbances are minimized while maintaining efficient overall programming throughput.
3Measurement precision
If multi-pass programming is used to reduce Yupin effect, then reading accuracy is improved, but programming time increases
Solution Approach 1:
The multi-pass programming scheme applies partial action by performing programming operations only on the portions of the threshold voltage distribution that require adjustment in each pass. Rather than repeatedly programming all cells at full voltage, each subsequent pass targets only the necessary refinements, thereby reducing the total programming time while maintaining high reading accuracy through the cumulative effect of the passes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The multi-pass programming technique effectively reduces the Yupin effect, stabilizes threshold voltage distributions, and ensures accurate data storage and retrieval by minimizing changes in the electric field environment during programming and reading, thereby enhancing the reliability and efficiency of semiconductor memory devices.
Implementation Method 1
a memory cell can include a floating gate that is positioned above and insulated from a channel region in a semiconductor substrate... The threshold voltage (Vth) of the transistor thus formed is controlled by the amount of charge that is retained on the floating gate
Implementation Method 2
The multi-pass programming technique... to minimize the Yupin effect and stabilize threshold voltage distributions... by minimizing changes in the electric field environment during programming and reading
Data Source
AI summary
A method is provided for programming non-volatile memory cells. The non-volatile memory cells are accessible by a plurality of word lines. The method includes using a four-pass programming technique to program a block of the non-volatile memory cells.