On-Chip Data Copying Between NAND Flash and ReRAM
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Solution Overview
Problem
Non-volatile data storage devices face challenges with data retention and endurance due to the use of single-level cell (SLC) memory, which is costly and has limited endurance, and volatile memory that loses data upon power loss.
Innovation Solution
Implementing an on-chip resistive random access memory (ReRAM) that supports on-chip copying of data between NAND flash memory and ReRAM, allowing data to be stored in ReRAM during write operations and copied to NAND flash memory, ensuring data retention even in case of power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SLC memory is used to store data that can persist in the case of power loss, then data retention is improved, but cost increases and endurance is limited
Solution Approach 1:
The memory system is segmented into two distinct memory types: volatile NAND flash memory for primary data storage and non-volatile ReRAM for backup storage. This segmentation allows each memory type to be optimized for its specific function, with NAND flash providing high-capacity storage and ReRAM providing persistent data retention, thereby resolving the contradiction between data retention and cost by avoiding the need for expensive SLC memory throughout the system.
Solution Approach 2:
ReRAM acts as an intermediary between volatile NAND flash memory and persistent storage requirements. The ReRAM serves as a buffer that temporarily holds data in a non-volatile state, mediating between the speed of NAND flash and the data retention requirements, thus reducing the need for expensive SLC memory while maintaining data persistence.
2Reliability
If SLC memory is used to store data that can persist in the case of power loss, then data retention is improved, but endurance is limited
Solution Approach 1:
The system segments the storage function between NAND flash memory (for high-endurance primary storage) and ReRAM (for persistent data retention). This segmentation allows NAND flash to handle frequent write operations due to its superior endurance, while ReRAM provides the necessary data persistence, thereby resolving the contradiction between data retention and endurance.
Solution Approach 2:
ReRAM serves as an intermediary layer that protects the endurance of NAND flash memory. By using ReRAM for data retention and only copying data to NAND flash when necessary, the system reduces wear on the NAND flash memory, thereby extending its operational lifespan while maintaining data persistence capabilities.
3Reliability
If data is stored in ReRAM and copied to NAND flash memory, then data retention is improved, but write operation time increases
Solution Approach 1:
Data is first written to ReRAM in a preliminary action, taking advantage of its non-volatile nature to ensure data retention. The subsequent copying to NAND flash memory is then performed asynchronously or in the background, allowing the initial write operation to complete quickly while data persistence is already ensured in ReRAM, thereby reducing the critical path write time.
Solution Approach 2:
The system maintains continuity of useful action by implementing asynchronous data copying from ReRAM to NAND flash memory. This allows the primary write operation to complete immediately in ReRAM, ensuring data retention, while the copying process continues in the background without blocking subsequent operations, thereby minimizing the impact on write operation time.
Data Source
AI summary
A data storage device includes a memory die, where the memory die includes a NAND flash memory and a resistive random access memory (ReRAM). The memory die also includes an interface coupled to the ReRAM and the NAND flash memory. The interface is configured to support on-chip copying of data between the NAND flash memory and the ReRAM.