Write-Once Memory Encoding for Flash Endurance
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Solution Overview
Problem
Memory devices, such as NAND flash memory, face challenges in extending their lifespan due to increased bit-error rates (BER) resulting from repeated program/erase cycles, which lead to reduced endurance and increased total number of erases between programming operations.
Innovation Solution
The implementation of Write-Once Memory (WOM) encoded data within memory sub-systems, which allows for multiple programming operations without performing an erase operation between them, thereby reducing the total number of erases and extending the memory device's lifespan.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If repeated program/erase cycles are performed to increase storage capacity utilization, then more data can be stored and retrieved, but the bit-error rate increases and endurance decreases
Solution Approach 1:
The memory system segments data storage into multiple pages within a block. By allowing multiple programming operations on different pages without intermediate erases, the system increases storage utilization while maintaining reliability. The block is divided into pages that can be independently programmed, enabling efficient use of storage capacity without subjecting the entire block to repeated erase cycles.
Solution Approach 2:
The system performs a preliminary erase operation on the entire block before initiating multiple programming operations on individual pages. This preliminary action resets the block to a known state, allowing subsequent pages to be programmed without requiring intermediate erases. The counter mechanism tracks programming operations to determine when the next erase should occur, optimizing the balance between storage utilization and reliability.
2Reliability
If erase operations are performed frequently to maintain data integrity, then bit-error rate is reduced, but the total number of bits written (TBW) decreases and lifespan is reduced
Solution Approach 1:
The system enables continuous programming operations across multiple pages within a block without interrupting for intermediate erases. The counter tracks the number of programming operations and only triggers an erase when the threshold is reached, allowing the memory device to maintain data integrity through controlled erasing while maximizing the total number of bits written over its lifespan.
Solution Approach 2:
A counter mechanism provides feedback on the number of programming operations performed on each block. This feedback controls when erase operations should be performed, ensuring that erases occur only when necessary to maintain data integrity. The system monitors and regulates erase frequency based on actual usage patterns, preventing premature erases that would reduce device lifespan.
3Duration of action of stationary object
If the number of erases between programming operations is increased to extend lifespan, then device longevity improves, but storage capacity utilization and productivity decrease
Solution Approach 1:
By segmenting the block into multiple programmable pages, the system allows intensive use of storage capacity through multiple programming operations on different pages before a single erase is required. This segmentation enables high storage utilization while limiting the total number of erases per block, thereby extending device longevity.
Solution Approach 2:
The system changes the parameter of erase frequency by introducing a counter that tracks programming operations. Instead of erasing after each program operation or after a fixed time period, the system adjusts erase timing based on the number of programming operations performed, optimizing the balance between storage utilization and device lifespan.
Data Source
AI summary
A method includes receiving first data, determining a number of programming operations performed on a plurality of flash memory cells subsequent to a most recent erase operation performed on the plurality of flash memory cells, encoding the first data to provide a first write-once memory (WOM) encoded data, and storing the first WOM encoded data, based at least in part on the determined number of programming operations, within a number of the plurality of flash memory cells.