Multi-Layer Flash Memory Block Reclaim via Layer Segmentation
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Solution Overview
Problem
Flash memory devices face challenges in achieving a balance between performance, capacity, and cost, particularly in multi-level cell (MLC) configurations where endurance and performance degrade as the number of bits per cell increases.
Innovation Solution
A multi-layer memory system with a controller that manages data by relocating valid data from reclaim blocks to free up blocks, allowing for efficient data management across layers, and utilizing a storage address re-mapping algorithm to optimize memory usage and create additional free blocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-level cell (MLC) flash memory is used to increase storage capacity, then capacity increases, but endurance and performance degrade
Solution Approach 1:
The flash memory is divided into multiple layers (first layer and second layer), each with different bit-per-cell configurations. The controller segments data storage across these layers, allowing MLC layers to provide capacity while SLC layers provide high-endurance storage for critical data, thus resolving the contradiction between capacity and endurance.
Solution Approach 2:
Different layers are assigned different quality characteristics: the first layer uses SLC configuration for high reliability and performance, while the second layer uses MLC configuration for high capacity. This local differentiation allows each layer to optimize for its specific function, balancing overall system capacity and endurance.
2Quantity of substance
If multi-level cell (MLC) flash memory is used to increase storage capacity, then capacity increases, but cost decreases
Solution Approach 1:
The system segments storage into multiple layers with different MLC configurations (e.g., 2-bit/cell and 3-bit/cell). This allows the manufacturer to produce a single device with varied storage characteristics, effectively offering multiple product tiers from one manufacturing process, thereby reducing overall production costs while maintaining high capacity.
Solution Approach 2:
The invention changes the bit-per-cell parameter across different layers (2-bit in first layer, 3-bit in second layer), allowing the same physical structure to deliver different capacity-density ratios. This parameter variation enables cost optimization by matching storage density requirements with manufacturing efficiency.
3Productivity
If reclaim operations are performed in MLC flash memory, then free blocks are freed, but performance and endurance continue to degrade
Solution Approach 1:
Reclaim operations are segmented and performed separately in each layer. The controller identifies and reclaims free blocks in the first SLC layer and second MLC layer independently, allowing optimized reclaim strategies for each layer type, thereby maintaining endurance while improving free block availability.
Solution Approach 2:
The controller proactively identifies reclaim candidates and performs preliminary data relocation before blocks become completely full. By anticipating storage needs and performing reclaim operations in advance, the system maintains better endurance characteristics while ensuring sufficient free blocks are available.
Data Source
AI summary
A multi-later memory and method for operation is disclosed. The memory includes at least one flash memory die having multiple layers and a controller configured to execute block reclaim operations in a layer of the flash memory die until a net gain of at least one additional free block has been made in the layer. The method may include relocating data from reclaim blocks to relocation blocks within the same layer, or within a same partition in the same layer until a net gain of one free block has been achieved and an integer number of relocation blocks has been filled with relocated data. The method may also include moving data from reclaim blocks in a first layer into destination blocks in a second layer until a net gain of at least one free block has been achieved in the first layer.