3D Memory Edge Word Line Read Disturb Mitigation
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Solution Overview
Problem
Three-dimensional (3D) stacked memory devices face challenges with hot electron injection (HEI) type of read disturb, particularly on edge word lines, due to large voltage gradients during sensing operations, which can lead to electron injection into adjacent memory cells, altering their threshold voltage and causing data integrity issues.
Innovation Solution
The solution involves controlling the voltages of select gates and word lines to minimize read disturb by ramping down select gate voltages before word line voltages, particularly for edge word lines, and ensuring capacitive coupling is reduced by elevating the selected word line voltage before ramping down to match adjacent unselected word lines, thereby reducing channel gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sensing operations are performed on 3D stacked memory devices, then read operations can be executed, but hot electron injection occurs into adjacent memory cells altering threshold voltage
Solution Approach 1:
The patent applies preliminary action by elevating the selected word line voltage to match unselected word line voltages before ramping down. This pre-conditioning of the voltage state prevents the formation of large voltage gradients that would otherwise cause hot electron injection during the sensing operation's voltage transition phase.
Solution Approach 2:
The patent changes the voltage parameter sequence by first elevating the selected word line voltage to match unselected word line voltages, then ramping down both simultaneously. This parameter change eliminates the harmful voltage gradient that causes hot electron injection while maintaining proper sensing functionality.
2Productivity
If word line voltages are ramped down during sensing operations, then sensing can be completed, but large voltage gradients form causing electron injection
Solution Approach 1:
Before ramping down the word line voltages, the selected word line voltage is first elevated to match the unselected word line voltages. This preliminary equalization ensures that when the ramp-down occurs, no large voltage gradients are created, preventing hot electron injection while still allowing the sensing operation to complete.
Solution Approach 2:
The patent maintains continuous voltage control during the sensing operation by first elevating then simultaneously ramping down both selected and unselected word line voltages. This continuous coordinated control ensures the useful sensing action completes without interruption while preventing the harmful voltage gradient formation.
3Device complexity
If select gate voltages are not ramped down before word line voltages, then sensing operation is simplified, but channel gradients increase causing read disturb
Solution Approach 1:
The patent applies preliminary action by ramping down the select gate voltages before the word line voltages. This sequential preliminary action reduces the channel gradients that would otherwise form during the sensing operation, minimizing read disturb effects while adding only moderate complexity to the voltage control sequence.
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 HEI read disturb, minimizing the alteration of threshold voltages in unselected memory cells and maintaining data integrity by controlling voltage transitions during sensing operations.
Implementation Method 1
ensuring capacitive coupling is reduced by elevating the selected word line voltage before ramping down to match adjacent unselected word lines
Implementation Method 2
hot electron injection (HEI) type of read disturb, particularly on edge word lines, due to large voltage gradients during sensing operations, which can lead to electron injection into adjacent memory cells
Data Source
AI summary
Read disturb due to hot electron injection is reduced in a 3D memory device by controlling the magnitude and timing of word line and select gate ramp down voltages at the end of a sensing operation. In an example read operation, a predefined subset of word lines includes source-side and drain-side word lines. For the predefined subset of word lines, word line voltages are ramped down before the voltages of the select gates are ramped down. Subsequently, for a remaining subset of word lines, word line voltages are ramped down, but no later than the ramping down of the voltages of the select gates. The timing of the ramp down of the selected word line depends on whether it is among the predefined subset or the remaining subset. The predefined subset can include a number of adjacent or non-adjacent word lines.