Nonvolatile Memory Read-Voltage Tracking for Error Reduction
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Solution Overview
Problem
Existing memory systems face challenges in maintaining optimal read voltages due to variations in threshold voltage distributions of memory cell transistors, leading to increased error rates and reduced operating efficiency.
Innovation Solution
A memory system with a memory controller that performs a patrol process to determine and adjust read voltages using shift amount information, executing tracking processes to optimize read operations and reduce error bits through shift read processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed read voltages are used in memory systems, then device complexity is reduced and operation is simplified, but threshold voltage variations cause increased error rates and reduced reliability
Solution Approach 1:
The system performs a patrol process before actual read operations to pre-determine optimal read voltages based on threshold voltage distributions. This preliminary voltage determination stores shift amount information that compensates for threshold variations during subsequent read operations, improving reliability without adding complexity to the main read path
Solution Approach 2:
The memory system performs self-diagnosis and self-adjustment by monitoring its own threshold voltage distributions and automatically determining appropriate voltage shifts. The patrol process and tracking process enable the system to self-correct for threshold variations without external intervention, maintaining high read accuracy while keeping the control mechanism relatively simple
2Reliability
If dynamic voltage adjustment is performed to compensate for threshold voltage variations, then data read accuracy is improved, but operating time increases due to patrol and tracking processes
Solution Approach 1:
The patrol process is executed periodically or under specific conditions (such as when errors are detected) rather than continuously before every read operation. This periodic execution maintains error correction capability while minimizing the time penalty by performing voltage adjustments only when necessary
Solution Approach 2:
Voltage adjustment parameters are determined in advance through the patrol process and stored for reuse. Once optimal voltages are found during the patrol process, they are applied to multiple subsequent read operations without repeating the full tracking process, reducing the time penalty to a single initial measurement period
3Manufacturing precision
If shift read processes are executed to optimize read voltages, then manufacturing precision requirements are relaxed, but device complexity and operation complexity increase
Solution Approach 1:
The system introduces shift amount information as an intermediary parameter that compensates for threshold voltage variations. Instead of directly controlling threshold voltages (which would require precise manufacturing), the system uses voltage shifts as a mediator to achieve accurate reads, relaxing manufacturing precision requirements while automating the compensation process
Solution Approach 2:
The tracking process uses feedback from read results to automatically adjust voltage shifts. By monitoring read accuracy and threshold voltage distributions, the system feeds back information to determine optimal shift amounts, eliminating the need for manual calibration while achieving high read accuracy despite manufacturing variations
Data Source
AI summary
A memory system includes a nonvolatile memory and a memory controller. The memory controller is configured to: execute a first tracking process to determine a value of a first voltage in a patrol process that is carried out independently of a request from a host, execute a first data read process to read first data from the nonvolatile memory in response to receiving a read request from the host, cause the nonvolatile memory to execute a second tracking process using the first voltage when error correction of the first data fails, receive a value of a second voltage from the nonvolatile memory as a result of the second tracking process, and execute a second data read process using the second voltage to read second data from the nonvolatile memory.