Nonvolatile Memory Read Voltage Adjustment via On-Cell Counting
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Solution Overview
Problem
Nonvolatile memory devices, particularly flash memory systems, face data distortion issues due to varying threshold voltage distributions in charge trap flash memory cells, leading to uncorrectable errors that require additional storage and time for correction.
Innovation Solution
A nonvolatile memory system with a memory controller that performs an on-cell counting operation to adjust read voltages based on detected elapsed program time, using a look-up table to optimize read operations and reduce uncorrectable errors without separate storage for program time data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If control and monitoring of program time is implemented to compensate for threshold voltage distortion, then data accuracy is improved, but device complexity and storage requirements increase
Solution Approach 1:
The memory system performs self-diagnosis by counting on-cells during normal read operations to detect threshold voltage distortion. The memory controller automatically monitors program time effects and adjusts read voltages without requiring external intervention or separate monitoring systems, thereby improving data accuracy while avoiding additional device complexity
Solution Approach 2:
The read operation serves dual purposes: retrieving stored data and simultaneously counting on-cells to detect threshold voltage distortion. By making the read operation multi-functional, the system obtains program time monitoring capabilities without requiring separate dedicated monitoring hardware or operations
2Reliability
If separate storage area is allocated for program time monitoring, then data reliability is improved, but storage capacity is reduced
Solution Approach 1:
The system uses on-cell count data as an intermediary parameter to infer program time effects. Instead of storing actual program time values, the system counts on-cells during read operations, which serves as a proxy indicator for threshold voltage distortion. This intermediary approach provides reliable program time monitoring while consuming no additional storage capacity
Solution Approach 2:
The system changes the monitoring parameter from storing absolute program time values to counting on-cells during read operations. This parameter transformation converts a storage-intensive approach into a computation-efficient approach that derives program time information from existing read operation data, maintaining reliability without sacrificing storage capacity
3Measurement precision
If read operations are extended to include program time monitoring, then data accuracy is improved, but operation time increases
Solution Approach 1:
The on-cell counting function is merged with the existing read operation. The memory controller performs both data retrieval and program time monitoring in a single unified operation by counting on-cells while reading data, thereby improving read accuracy without requiring additional separate monitoring operations that would increase total operation time
Data Source
AI summary
A system comprises a nonvolatile memory device comprising a memory cell array comprising a plurality of memory blocks each comprising a plurality of cell strings, each of cell strings comprises the plurality of memory cells stacked in a direction perpendicular to a substrate, a ground selection transistor disposed between the memory cells and the substrate, and a string selection transistor disposed between the memory cells and a bitline, and configured to read stored data from the memory cells using a plurality of read voltages; and a memory controller configured to read the memory cells using a reference voltage to generate on-cell data, and adjust the read voltages of the nonvolatile memory device based on the generated on-cell data.