Flash Memory Pre-Programming Narrowing Threshold Voltage Distribution
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Solution Overview
Problem
Flash memory devices with Multi-Level Cells (MLCs) face high failure rates and increased program times due to wide threshold voltage distributions during erase and program operations, leading to inefficient data storage and processing.
Innovation Solution
Implementing a method that reduces the voltage range of threshold voltages in MLCs through pre-programming, selectively programming cells with slow speeds, and adjusting step voltages in the Incremental Step Pulse Programming (ISPP) method to narrow the distribution and improve erase and program efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MLCs are erased using conventional methods, then the erase operation can be completed, but the threshold voltage distribution becomes wide causing high failure rates and increased program times
Solution Approach 1:
The patent applies pre-programming to a subset of MLCs before the erase operation. This preliminary action shifts the threshold voltage distribution of selected MLCs to a lower voltage range, ensuring that after erase, all MLCs (including previously pre-programmed ones) have threshold voltages within an acceptable range. This prevents over-erasure and reduces the width of threshold voltage distribution, thereby improving both reliability and manufacturing precision.
Solution Approach 2:
The patent selectively pre-programs only certain MLCs (a subset of the total MLCs) rather than all MLCs uniformly. This local quality approach allows different groups of MLCs to have different initial threshold voltage states before erasure, optimizing the overall threshold voltage distribution after erase operation while reducing failure rates.
2Productivity
If conventional erase and program operations are performed on MLCs, then data can be stored, but the overall program time increases due to wide threshold voltage distributions
Solution Approach 1:
By pre-programming selected MLCs before the erase operation, the patent ensures that these MLCs start with threshold voltages in a lower range. After erasure, this preliminary action helps maintain tighter threshold voltage distribution, reducing the number of iterative program cycles needed and thereby shortening the overall program time while improving productivity.
3Reliability
If the voltage range of threshold voltages is not reduced, then all MLCs can be uniformly processed, but failure occurrences increase and program efficiency decreases
Solution Approach 1:
The patent implements local quality by selectively applying pre-programming to specific MLCs based on their initial threshold voltage characteristics. This selective processing creates optimized local threshold voltage distributions that improve both reliability (by preventing over-erasure failures) and productivity (by reducing subsequent program time), rather than uniformly processing all MLCs.
Data Source
AI summary
Erase and program methods of a flash memory device including MLCs for increasing the program speed are described. In the erase method, MLCs are pre-programmed so that a voltage range in which threshold voltages of MLCs are distributed can be reduced. Therefore, a fail occurrence ratio can be reduced when erasing MLCs, the threshold voltage distribution of MLCs can be improved and an overall program time can be shortened in a subsequent program operation.