Flash Memory Controller Predicting Writes for Reclaim
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Solution Overview
Problem
Flash memory devices face challenges with high integration due to capacitive coupling between memory cells, leading to uncorrectable error correction codes (UECC) during read operations, and inefficient reclaim operations that can degrade storage device performance.
Innovation Solution
A storage device utilizing a nonvolatile memory with a 3D structure and a machine learning-based controller that predicts write operations to determine the type of reclaim command, either block reclaim or partial reclaim, based on the predicted number of writes, to optimize storage efficiency and prevent UECC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a conventional conductive floating gate structure is used in flash memory, then programming speed and data storage capacity are improved, but capacitive coupling between memory cells causes physical limitations on high integration
Solution Approach 1:
The patent changes the fundamental parameter of the charge storage structure from conductive floating gate to insulating charge trap layer. This parameter change enables higher integration by eliminating capacitive coupling issues while maintaining programming functionality through tunneling electrons into the insulating charge trap layer.
Solution Approach 2:
The patent employs composite material structures including insulating charge trap layers (such as Si3N4, Al2O3, HfAlO, or HfSiO) combined with tunnel oxide layers. This composite approach enables reliable charge storage at higher integration densities by using the insulating properties of the charge trap layer to prevent capacitive coupling.
2Device complexity
If charge trap flash memory uses an insulating film as charge storage layer, then integration is improved, but electrons and holes rearrange/recombine after program or erase operations, changing threshold voltages and causing uncorrectable errors
Solution Approach 1:
The patent applies preliminary action by performing reclaim operations before UECC occurs. The controller predicts when reclaim is needed and proactively relocates data from blocks with high write counts to blocks with lower write counts, preventing threshold voltage changes from causing uncorrectable errors before they happen.
Solution Approach 2:
The patent implements feedback mechanisms where the controller monitors write counts of memory blocks and uses this information to determine when reclaim operations are necessary. This feedback loop allows dynamic adjustment of data relocation strategies to maintain threshold voltage stability and prevent UECC.
3Reliability
If reclaim operations are performed frequently to prevent UECC, then data reliability is improved, but storage device performance degrades due to increased write amplification
Solution Approach 1:
The patent applies partial action by performing reclaim operations only when necessary, not continuously. The controller determines the appropriate timing for reclaim based on predicted write counts and block characteristics, executing partial reclaim operations that relocate only the necessary data, thereby preventing UECC while minimizing performance impact.
Solution Approach 2:
The patent uses preliminary action through predictive reclaim operations. The controller predicts future write counts and performs reclaim operations in advance before UECC occurs, rather than reacting after errors happen. This proactive approach optimizes the timing of reclaim operations to balance reliability and performance.
Data Source
AI summary
A storage device is provided. The storage device includes a nonvolatile memory device including a first block and a second block, and a controller including processing circuitry configured to, predict a number of writes to be performed on the nonvolatile memory device using a machine learning model, determine a type of reclaim command based on the predicted number of writes, the reclaim command for reclaiming data of the first block to the second block, and issue the reclaim command.