Nonvolatile Memory Controller Read Disturb Mitigation
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Solution Overview
Problem
Data storage devices face challenges in efficiently performing read operations on memory blocks, particularly in distinguishing between open and closed blocks to adjust pass bias, which can lead to data corruption due to read disturb effects.
Innovation Solution
A data storage device with a controller that determines whether a target memory block is open or closed, adjusting the pass bias for unselected memory cells during read operations based on an adjustment index calculated from the number of erased word lines or memory regions, thereby minimizing the read disturb effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a standard pass bias is applied to all memory blocks during read operations, then the read operation can be performed uniformly, but data corruption occurs due to read disturb effects on open blocks
Solution Approach 1:
The controller performs preliminary determination of whether a target memory block is an open block before executing the read operation. Based on this preliminary classification, the controller pre-adjusts the pass bias voltage level, thereby preventing read disturb effects before they occur and ensuring data reliability without requiring complex real-time adjustments during the read operation
Solution Approach 2:
The pass bias voltage is made dynamic rather than static. The controller adjusts the pass bias level according to the determined status of the memory block (open or closed), applying a first pass bias level for open blocks and a second pass bias level for closed blocks. This dynamic adjustment resolves the contradiction by adapting the read operation to the specific block state, preventing data corruption while maintaining operational simplicity
2Reliability
If the pass bias is adjusted for every read operation based on block status, then data corruption is prevented, but the operation time and processing overhead increase
Solution Approach 1:
The controller determines the open/closed status of the memory block in advance before the read operation commences. This preliminary determination allows the system to pre-select the appropriate pass bias level, avoiding time-consuming adjustments during the actual read process and minimizing additional operation time while ensuring data integrity
Solution Approach 2:
The pass bias voltage parameter is changed based on the memory block status. By adjusting this single critical parameter (pass bias level) according to whether the block is open or closed, the system achieves reliable read operations without requiring complex procedural changes or multiple operation cycles, thereby limiting time overhead to a simple parameter selection
Data Source
AI summary
A data storage device includes a nonvolatile memory device including a nonvolatile memory device including a plurality of memory blocks each having a plurality of memory cells and a controller suitable for determining whether a target memory block for a read operation among the memory blocks is an open block, adjusting a pass bias to be applied to unselected memory cells during the read operation for the target memory block, according to a result of the determination, and controlling the nonvolatile memory device to perform the read operation using the adjusted pass bias.