Storage Controller String Programming Order for Program Disturb Mitigation
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Solution Overview
Problem
Program disturb errors occur in memory cells when other cells in the same wordline are programmed, leading to unmasked errors when switching from higher bits per cell to lower bits per cell, particularly affecting important metadata and increasing bit error rates.
Innovation Solution
A storage system with a controller that changes the programming order of strings within each wordline, ensuring the last string programmed varies, allowing for timely error correction and reducing the likelihood of stripe failures by highlighting program disturbs earlier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If strings in a wordline are programmed in a fixed order, then programming process is simple and efficient, but program disturb errors occur in memory cells when other cells in the same wordline are programmed
Solution Approach 1:
The patent applies dynamics by changing the programming order of strings dynamically across different wordlines. Instead of a fixed programming sequence, the system varies which string is programmed last in each wordline, making the programming process adaptive rather than static. This dynamic approach prevents program disturb errors while maintaining programming efficiency.
Solution Approach 2:
The patent changes the parameter of programming sequence by varying the last programmed string position across different wordlines. This parameter change transforms the fixed programming order into a variable one, where the sequence is adjusted based on wordline characteristics, thereby eliminating program disturb errors without significantly impacting programming speed.
2Quantity of substance
If higher bits per cell are used to increase storage capacity, then storage density improves, but unmasked errors occur when switching to lower bits per cell particularly affecting metadata
Solution Approach 1:
The patent applies preliminary action by detecting and correcting program disturb errors during the higher bits per cell usage phase, before switching to lower bits per cell. By proactively identifying and addressing errors while they are still masked, the system prevents error escalation when metadata becomes vulnerable during mode switching, thereby protecting data integrity.
Solution Approach 2:
The patent implements feedback by continuously monitoring for program disturb errors during programming operations and using this information to adjust error correction strategies. The system provides feedback loops that detect errors early and trigger corrective actions, ensuring that metadata and other critical data remain protected during bit-per-cell mode transitions.
Data Source
AI summary
A storage system has a memory that is organized in wordlines. Each wordline has a number of strings. A controller in the storage system changes, in each of the wordlines, which of the strings is a last string programmed. Doing so can unmask a program disturb error when triple-level cells in the memory are used as pseudo-multi-level cells. By unmasking the program disturb error, the controller can detect and correct the error.