Non-Volatile Memory Read Operations With Adjacent Word Line Compensation
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Solution Overview
Problem
In non-volatile memory systems, floating gate to floating gate coupling causes shifts in apparent charge storage, leading to erroneous read operations, especially in multi-state devices with narrower threshold voltage ranges, due to increased coupling between adjacent memory cells as they shrink in size.
Innovation Solution
Compensations are applied during read operations by reading the adjacent word line first and storing data in data latches, then using these compensations to adjust read reference voltages for the selected word line based on the states of adjacent memory cells, minimizing chip space and improving data accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cells are shrunk in size to increase storage density, then storage capacity is improved, but floating gate coupling between adjacent cells increases causing read errors
Solution Approach 1:
The patent reads the adjacent word line before reading the selected word line, storing the adjacent data in data latches in advance. This preliminary action allows the system to prepare compensation values before the actual read operation, enabling correction of coupling effects that would otherwise cause read errors in densely packed memory cells
Solution Approach 2:
The patent uses data from the adjacent word line read operation to generate compensation values that are fed back into the read reference voltage generation for the selected word line. This feedback mechanism dynamically adjusts the read reference based on the actual state of adjacent cells, correcting for coupling effects and maintaining read accuracy despite increased cell density
2Reliability
If compensations are applied by reading adjacent word line and storing data in data latches, then read accuracy is improved, but chip space is consumed
Solution Approach 1:
The patent makes the existing data latches serve dual purposes: storing data from the selected word line and temporarily storing data from the adjacent word line for compensation purposes. By overwriting latch contents with adjacent word line data during the compensation phase, the system avoids needing dedicated compensation storage elements, thus saving chip space while maintaining read accuracy
Solution Approach 2:
The patent temporarily uses data latches to store adjacent word line data for compensation calculations, then discards this temporary data after compensation is applied. The latches are recovered and reused for storing the actual read data from the selected word line, maximizing resource utilization and minimizing chip space requirements
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 compensates for floating gate coupling, reducing errors in read operations by efficiently managing data latches and adjusting read voltages, thereby maintaining data integrity in non-volatile memory systems.
Implementation Method 1
floating gate to floating gate coupling causes shifts in apparent charge storage
Data Source
AI summary
Shifts in the apparent charge stored by a charge storage region such as a floating gate in a non-volatile memory cell can occur because of electrical field coupling based on charge stored by adjacent cells. To account for the shift, compensations are applied when reading. When reading a selected word line, the adjacent word line is read first and the data stored in a set of data latches for each bit line. One latch for each bit line stores an indication that the data is from the adjacent word line. The selected word line is then read with compensations based on the different states of the cells on the adjacent word line. Each sense module uses the data from the adjacent word line to select the results of sensing with the appropriate compensation for its bit line. The data from the adjacent word line is overwritten with data from the selected word line at the appropriate time and the indication updated to reflect that the latches store data from the selected word line. The efficient use of the data latches eliminates the need for separate latches to store data from the adjacent word line.