Vertical NAND Word-Line Curing for Faster Voltage Recovery
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Solution Overview
Problem
As the generation of vertical NAND (VNAND) evolves, the increasing number of stacked word lines leads to higher voltage application requirements, resulting in longer time and power consumption for voltage setting and recovery, which negatively impacts performance due to the trade-off relationship with read/program/erase times.
Innovation Solution
A curing pulse is applied to non-selected word lines with a voltage level lower than the read voltage, managed by a pulse management circuit, to reduce residual voltage and prevent read disturbance, using a storage controller and non-volatile memories.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of stacked word lines is increased to improve storage efficiency, then storage capacity and die efficiency are improved, but the time and power required for voltage setting and recovery increase
Solution Approach 1:
The patent divides the word lines into selected word lines (actively accessed) and non-selected word lines (not accessed). Different voltage recovery strategies are applied to each segment: selected word lines use standard recovery procedures, while non-selected word lines use a simplified curing pulse approach. This segmentation allows the system to maintain high storage capacity with many word lines while reducing the overall voltage recovery time by focusing intensive recovery only where necessary.
Solution Approach 2:
The patent applies different voltage levels and recovery methods to different regions of the memory structure. Specifically, a curing pulse with voltage level lower than the read voltage is applied specifically to non-selected word lines, while selected word lines receive full voltage recovery treatment. This local differentiation optimizes the balance between storage capacity and recovery time by applying appropriate recovery intensity only where needed.
2Quantity of substance
If the number of stacked word lines is increased to improve storage efficiency, then storage capacity and die efficiency are improved, but power consumption for voltage management increases
Solution Approach 1:
The patent segments power management into two modes: full voltage recovery for selected word lines and reduced-voltage curing pulse for non-selected word lines. This segmentation significantly reduces total power consumption by avoiding unnecessary high-voltage application to word lines that do not require intensive recovery, while still maintaining storage capacity through efficient use of stacked word lines.
Solution Approach 2:
The patent applies localized power management by determining which word lines require full recovery based on access patterns. Non-selected word lines receive a curing pulse with lower voltage, reducing power consumption in those regions. This local quality approach ensures that power is consumed only where necessary for maintaining data integrity, enabling high storage capacity with reduced overall power usage.
3Reliability
If a high voltage is applied to non-selected word lines for complete recovery, then reliability is improved, but read disturbance occurs and performance decreases
Solution Approach 1:
The patent changes the voltage parameter for recovering non-selected word lines from the standard read voltage to a lower curing pulse voltage. This parameter change is sufficient to maintain data integrity and prevent read disturbance, as the curing pulse voltage is carefully selected to be low enough to avoid harmful effects while still achieving adequate recovery. This resolves the contradiction by finding an optimal voltage parameter that balances reliability with prevention of read disturbance.
4Reliability
If the voltage recovery time is extended to ensure complete recovery of all word lines, then reliability is improved, but the trade-off with read/program/erase time reduces performance
Solution Approach 1:
The patent segments the recovery process into two parallel tracks: selected word lines undergo complete recovery procedures to ensure reliability, while non-selected word lines receive a faster curing pulse treatment. This segmentation allows the system to maintain overall reliability by properly recovering accessed word lines while significantly reducing total recovery time through the expedited treatment of non-selected word lines, thereby improving operational speed without sacrificing data integrity.
Data Source
AI summary
A method of operating a storage device including a storage controller and non-volatile memories is described. The method includes detecting a trigger event for application of a curing pulse, determining a voltage level of the curing pulse, and applying a curing command which instructs generation of the curing pulse according to the determined voltage level. After a read operation on a target word line is completed, the target word line is expected not to be accessed for more than a predefined period of time. The trigger event corresponds to an event in which a block includes such as target word line. The curing pulse corresponds to a voltage pulse applied to at least one word line in a block or sub-block including the target word line on which the read operation has been performed. The voltage level of the curing pulse is less than a read voltage.