Flash Memory Modulation Coding for Threshold Stability
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Solution Overview
Problem
In multi-bit flash memory devices, the reliability of data storage is compromised due to threshold voltage shifts caused by factors like lateral charge spreading, programming disturbance, and dielectric layer defects, leading to increased error rates during read operations.
Innovation Solution
A data processing method that encodes data into modulation codes, specifically run length limited codes, to prevent adjacent memory cells from being programmed into states with significant threshold voltage differences, thereby mitigating the effects of lateral charge spreading and other disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-bit memory cells are used to increase storage capacity, then integration density is improved, but threshold voltage stability deteriorates due to lateral charge spreading and programming disturbance
Solution Approach 1:
The patent applies preliminary action by encoding data before programming to prevent problematic threshold voltage combinations. The modulation coding is performed in advance on the data to be written, ensuring that adjacent memory cells will not be programmed into states with large threshold voltage differences, thereby preventing lateral charge spreading issues before they occur.
Solution Approach 2:
The patent changes the parameter representation by using modulation coding to transform the data bits into a format that constrains threshold voltage transitions. Specifically, it limits the number of adjacent memory cells with large threshold voltage differences, effectively changing how data is represented in terms of threshold voltage states to improve stability.
2Adaptability or versatility
If data is programmed into adjacent memory cells with different states, then data storage flexibility is improved, but error probability increases due to read disturbance and threshold voltage shifts
Solution Approach 1:
The patent performs preliminary modulation coding on the data before programming, which proactively prevents the formation of problematic patterns where adjacent memory cells would have large threshold voltage differences. This preliminary encoding step ensures that even though data storage remains flexible, the problematic configurations that lead to read disturbance and errors are avoided from the outset.
3Duration of action of stationary object
If floating gates store electric charges to maintain data, then nonvolatile storage is achieved, but charge leakage through dielectric defects causes threshold voltage drift
Solution Approach 1:
The patent applies preliminary modulation coding to prevent data patterns that would create large threshold voltage differences between adjacent cells. By doing so before programming, it reduces the stress on dielectric layers and minimizes charge leakage pathways, thereby maintaining data retention while improving threshold voltage stability over time.
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
This approach reduces the probability of error occurrence by maintaining stable threshold voltages across memory cells, enhancing data retention and reliability in multi-bit flash memory devices.
Implementation Method 1
issues such as lateral charge spreading become important
Implementation Method 2
Electric charges (or electrons) stored in floating gates may be leaked through various failure mechanisms such as thermion emission
Implementation Method 3
Electric charges (or electrons) stored in floating gates may be leaked through various failure mechanisms such as thermion emission, electronic charge spreading
Data Source
AI summary
Provided is a data processing method in a semiconductor memory device. The data processing method arranges data, which is to be programmed in a row and column of a nonvolatile memory device, in a row or column direction. The data processing method encodes the programmed data into a modulation code in the row or column direction such that adjacent pairs of memory cells of the nonvolatile memory device are prevented from being programmed into first and second states.