Word Line Refresh Read Control for Stable NAND Read Setup
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Solution Overview
Problem
Non-volatile memory devices face challenges in maintaining performance and reliability due to variations in threshold voltage (Vth) of memory cells caused by the coupled-up state of word lines during read operations, leading to shifts in Vth that affect data states.
Innovation Solution
Implementing a control mechanism to apply a refresh read voltage to selected word lines at predetermined intervals and adjust read setup time based on the occurrence of refresh read operations, maintaining memory cells in a second read condition and ramping up word lines during read operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If word lines are coupled up to residual voltage level during read operations, then read speed is improved, but threshold voltage shifts occur affecting data state reliability
Solution Approach 1:
The patent applies periodic refresh read operations at predetermined intervals to maintain word lines in the second read condition (coupled up state). This periodic action prevents threshold voltage shifts by regularly resetting the voltage state, allowing fast reads to continue without compromising data state reliability over time.
Solution Approach 2:
The patent changes the voltage parameter of word lines dynamically - maintaining them at residual voltage level (second read condition) during active read operations for speed, then periodically refreshing them to prevent threshold voltage shifts. This parameter change strategy resolves the contradiction between speed and reliability.
2Reliability
If read setup time is extended to discharge channel fully, then read reliability is improved, but read speed decreases
Solution Approach 1:
The patent performs preliminary channel discharge during the read setup time period. By discharging the channel before the actual read operation begins, the system ensures reliable reading conditions are established in advance, allowing the main read operation to proceed quickly without extended setup time compromising speed.
3Stability of the object's composition
If refresh read operations are performed frequently, then threshold voltage stability is improved, but device complexity increases
Solution Approach 1:
The patent implements a control mechanism that monitors the state of word lines and channels, using feedback to determine when refresh read operations are needed. This feedback-based approach maintains threshold voltage stability by performing refresh operations based on actual system state rather than fixed scheduling, reducing unnecessary operations and simplifying the overall control 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 stabilizes the threshold voltage of memory cells, reducing read disturb issues and maintaining consistent data states across varying read conditions, thereby enhancing memory device performance and reliability.
Implementation Method 1
a second read condition in which the word line voltage of the plurality of word lines is coupled up to a residual voltage level
Implementation Method 2
a read setup time in which the plurality of word lines are ramped up and the channel is discharged
Data Source
AI summary
A memory apparatus and method of operation are provided. The apparatus includes memory cells connected to word lines and disposed in memory holes each comprising a channel. The memory cells retain a threshold voltage and are operable in one of a first read condition in which a word line voltage of the word lines is discharged and a second read condition in which the word line voltage of the word lines is coupled up to a residual voltage level. A control means is configured to apply a predetermined refresh read voltage to the word lines at predetermined intervals of time during a refresh read operation to maintain the memory cells in the second read condition. The control means also adjusts a read setup time in which the word lines are ramped up and the channel is discharged during a read operation based on occurrences of the refresh read operation.