Selective Re-programming of Analog Memory Cells to Reduce Interference
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Solution Overview
Problem
Analog memory cells in memory devices face interference issues during data storage, leading to read errors and performance degradation due to cross-coupling from neighboring cells, which existing two-phase programming methods struggle to fully compensate for, especially when higher verification thresholds are required in the second phase, increasing the risk of over-programming and analog values drifting below zero.
Innovation Solution
The method involves defining a partial subset of non-erased programming states and selectively re-programming only those states in the second phase, using different verification thresholds to reduce interference effects and maintain a stable voltage range, while omitting re-programming for the lowest and highest states to minimize performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two-phase programming method is used to compensate for interference, then read errors are reduced, but over-programming risk increases and analog values may drift below zero
Solution Approach 1:
The patent applies different verification threshold strategies to different programming states. Intermediate states use higher verification thresholds in the second phase to compensate for interference, while the lowest and highest states use their originally programmed thresholds. This localized differentiation resolves the contradiction by applying interference compensation only where needed, avoiding over-programming of extreme states.
Solution Approach 2:
The patent segments the set of programming states into three groups: lowest state, intermediate states, and highest state. This segmentation allows the system to apply different verification threshold strategies to different segments, resolving the contradiction between interference compensation and over-programming prevention by treating each segment according to its specific characteristics.
2Stability of the object's composition
If higher verification thresholds are used in the second phase to compensate for interference, then data retention is improved, but the voltage range becomes unstable and may drift below zero
Solution Approach 1:
The patent applies higher verification thresholds selectively only to intermediate programming states in the second phase, while maintaining original thresholds for the lowest and highest states. This localized application stabilizes the voltage range by preventing excessive threshold adjustments that would cause drift below zero, while still improving data retention for the intermediate states that are most susceptible to interference.
3Reliability
If all non-erased programming states are re-programmed in the second phase, then interference compensation is maximized, but performance degradation increases
Solution Approach 1:
The patent segments the programming states and applies re-programming selectively only to intermediate states, excluding the lowest and highest states from second-phase re-programming. This segmentation resolves the contradiction by focusing interference compensation efforts where they are most needed (intermediate states) while avoiding the performance penalty of re-programming all states, thus improving productivity without sacrificing essential reliability.
Data Source
AI summary
A method for data storage includes defining, in a memory that includes multiple analog memory cells, an erased state, a set of non-erased programming states and a partial subset of the non-erased programming states. Data is initially stored in a first group of the analog memory cells by programming each of at least some of the memory cells in the first group from the erased state to a respective non-erased programming state selected from the set of non-erased programming states. After initially storing the data, a second group of the analog memory cells, which potentially cause interference to the first group, is programmed. After programming the second group, the first group is selectively re-programmed with the data by repeating programming of only the memory cells in the first group whose respective programming states belong to the partial subset.