Memory Controller Read Voltage Adjustment for Lateral Charge Migration
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Solution Overview
Problem
Existing memory systems, particularly charge trap type NAND flash memories, face challenges in reducing bit errors caused by lateral migration of electric charges, which affect threshold voltage and are not adequately addressed by existing methods that focus on cell-to-cell interference.
Innovation Solution
A memory system and method that determines read voltages based on the threshold voltages of adjacent cells, using a classification and determination unit to generate read voltages that account for the changes in threshold voltage due to lateral migration, thereby reducing bit errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a distance between memory cells decreases due to process shrink, then storage capacity increases, but threshold voltage is influenced by cell-to-cell interference and lateral migration of electric charges
Solution Approach 1:
The patent applies parameter changes by adjusting read voltages based on the threshold voltage states of adjacent memory cells. The memory controller dynamically modifies read voltage parameters to compensate for CCI and lateral migration effects, allowing reliable reading despite reduced cell spacing that increases interference.
Solution Approach 2:
The patent implements feedback mechanisms where the memory controller monitors adjacent cell states and uses this information to determine appropriate read voltages. This feedback loop enables the system to adapt to changing threshold voltage conditions caused by lateral migration and CCI, maintaining reading accuracy despite increased cell density.
2Ease of operation
If existing read methods are used without considering adjacent cell threshold voltages, then reading process is simple, but bit errors occur due to lateral migration of electric charges
Solution Approach 1:
The patent applies preliminary action by determining read voltages in advance based on adjacent cell states before performing the actual read operation. The memory controller pre-calculates appropriate read voltages considering potential CCI and lateral migration effects, ensuring accurate reading without requiring complex real-time adjustments during the read process.
3Device complexity
If read voltage is determined without considering adjacent cell influence, then determination process is simple, but threshold voltage changes over time due to lateral migration cause reading errors
Solution Approach 1:
The patent dynamically changes read voltage parameters based on the threshold voltage states of adjacent cells. By adjusting these parameters in response to detected adjacent cell conditions, the system maintains measurement precision without requiring overly complex determination processes.
Solution Approach 2:
The memory controller performs multiple functions using the same basic mechanism: it determines read voltages for normal reading operations and simultaneously compensates for CCI and lateral migration effects. This multi-functional approach improves read voltage accuracy without proportionally increasing device complexity.
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 effectively reduces bit errors by determining optimal read voltages that account for the changes in threshold voltage over time, improving data reliability in memory systems.
Implementation Method 1
a phenomenon (referred to as lateral migration of electric charges) may occur in which electric charges stored in the memory cell move to an adjacent cell, according to a difference between threshold voltages of adjacent cells
Data Source
AI summary
According to one embodiment, a memory system includes a nonvolatile memory and a memory controller. The nonvolatile memory includes a first word line including a plurality of first cells and a second word line adjacent to the first word line and including a plurality of second cells. The memory controller determines a read voltage to be used with respect to the plurality of the first cells, according to a plurality of adjacent voltages representing respective threshold voltages of the plurality of the second cells. The memory controller reads data from the first word line using a plurality of determined read voltages.