Flash Memory Multi-Step Erase with Metadata Tracking
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Solution Overview
Problem
Flash memory devices, particularly vertical NAND (VNAND) using charge trapped flash (CTF) cells, experience prolonged erase times, which negatively impact system performance.
Innovation Solution
Implementing a multi-step erase process for flash memory blocks, where a controller manages and stores metadata to track the completion of each erase step, allowing for efficient management and reduction of erase time through firmware operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-step erase operation is used for flash memory blocks, then the erase operation is simple and fast, but the reliability of complete erasure is insufficient
Solution Approach 1:
The erase operation is divided into multiple sequential steps (first erase step and second erase step) rather than a single operation. Each step targets specific charge states within the memory cells, ensuring complete erasure through incremental removal of trapped charges. This segmentation improves reliability while managing complexity through structured progression.
Solution Approach 2:
The first erase step performs a preliminary erasure operation to remove the majority of trapped charges before the second erase step completes the process. This preliminary action reduces the workload for the final step and ensures progressive erasure, improving overall reliability without requiring a single complex high-power pulse.
2Reliability
If multiple erase steps are implemented, then erasure reliability is improved, but erase time increases
Solution Approach 1:
By segmenting the erase operation into multiple steps, each step can be optimized for specific charge removal requirements. The first step handles bulk charge removal while the second step addresses residual charges, allowing parallel optimization of speed and reliability without the need for a single prolonged high-power erase pulse.
3Productivity
If metadata tracking is implemented for erase steps, then erase management efficiency is improved, but device complexity increases
Solution Approach 1:
Metadata is stored to track the erase step completion status of each memory block, providing feedback to the controller. This feedback mechanism enables the controller to manage erase operations more efficiently by knowing which blocks require which steps, optimizing productivity through informed control decisions.
Solution Approach 2:
The metadata tracking system allows the erase operation to be self-managed by providing the controller with automatic status information about which blocks have completed which steps. This self-service approach improves management efficiency without requiring complex external monitoring or manual tracking mechanisms.
Data Source
AI summary
A memory system, including a flash memory including multiple memory blocks, and a controller configured to erase each of the memory blocks using multiple steps. The controller stores, for each of the memory blocks, metadata indicating which of the multiple steps have been completed, and erases each of the memory blocks based on the stored metadata.