Boundary Word Line Data Retention via Soft Programming
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Solution Overview
Problem
Existing storage devices face limitations in data retention for boundary word lines in open blocks due to strong electric fields, leading to higher fail bit counts and reduced performance, especially in zone mapping and higher-density memory cell systems, which restrict the duration blocks can be kept open and increase read operations, causing read disturb and fail bit count errors.
Innovation Solution
Implementing soft and soft-fine programming operations to reduce bit failures and fail bit counts in boundary word lines by programming them with the same data as source blocks, using pre-verify and soft-fine programming to maintain threshold voltages and prevent over-programming, thereby enhancing data retention and reducing write amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If blocks are kept open for extended periods in zone mapping systems, then data capacity and cost efficiency are improved, but boundary word lines become vulnerable to errors due to strong electric fields
Solution Approach 1:
The system performs preliminary actions by periodically closing blocks that have been open for extended periods, even before data retention failures occur. This preventive closing and subsequent reopening maintains the integrity of boundary word lines while allowing blocks to remain open long enough to achieve the capacity and cost benefits of zone mapping.
Solution Approach 2:
The system applies preliminary anti-action by implementing monitoring mechanisms that detect early signs of boundary word line vulnerability and trigger corrective actions (closing the block) before actual data retention failures occur. This counteracts the harmful electric field effects before they can cause permanent damage.
2Reliability
If the time duration for keeping blocks open is limited to maintain data retention, then boundary word line reliability is improved, but zone mapping efficiency and capacity utilization are reduced
Solution Approach 1:
The system implements dynamic block management where blocks are not statically kept open or closed, but are dynamically transitioned between states based on monitored conditions. Blocks remain open as long as retention criteria are met, and are only closed when monitoring indicates approaching failure thresholds, optimizing both reliability and efficiency.
Solution Approach 2:
The system uses feedback mechanisms to continuously monitor block status and adjust block management decisions accordingly. By monitoring parameters such as program/erase cycle counts and time duration, the system receives feedback on boundary word line health and adjusts block opening/closing decisions to maintain optimal balance between reliability and productivity.
3Productivity
If more read operations are performed per memory cell in higher-density systems, then data capacity is increased, but read disturb errors and fail bit counts increase
Solution Approach 1:
The system performs preliminary actions by proactively closing blocks before read disturb errors accumulate to problematic levels. By monitoring the number of read operations and closing blocks preventively, the system eliminates read disturb issues before they cause data corruption, maintaining high capacity utilization while preventing error accumulation.
Data Source
AI summary
Storage devices are capable of utilizing failed bit count (FBC) reduction devices to reduce FBCs for word lines in blocks. An FBC reduction device may include a FBC count component, a threshold component, a pre-verify component, and a soft program component. The FBC count component may access the FBC for the word line, where the block has unprogrammed word lines in an unprogrammed region separated from programmed word lines of a programmed region by the word line. The threshold component may determine whether the FBC of the word line exceeds a predetermined threshold. When the FBC exceeds the threshold, the pre-verify component may perform pre-verify operations on the programmed region. The soft program component may program the word line with first data equal to second data programmed in a second block. In response to disabling pre-verify operations, the program component may program the unprogrammed word lines in the unprogrammed region.