Nonvolatile Memory Read Voltage Adjustment for Error Correction
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Solution Overview
Problem
As memory cell sizes decrease in nonvolatile semiconductor memory devices, read errors become more frequent due to disturbances between memory cells, reducing operation reliability.
Innovation Solution
A method involving multiple read voltages applied to a selected word line in a nonvolatile memory device, with logical operations and error correction to generate read data, improving reliability by adjusting the read voltage based on count values and flags.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If memory cell size is decreased to increase integration, then productivity and storage capacity are improved, but read error rate increases due to disturbance between memory cells
Solution Approach 1:
The patent applies preliminary actions by performing multiple read operations at different voltages before final data output. The first read voltage generates initial sensing data, the second read voltage generates additional sensing data, and these are combined through logical operations to produce determination data. This preliminary processing at multiple voltage levels prepares corrected data before the final read operation, preventing read errors caused by cell disturbance in high-density memory configurations.
Solution Approach 2:
The patent implements feedback mechanisms by using sensing flags obtained during read operations to determine whether error correction is needed. The count value generated from determination data provides feedback on the number of bits requiring correction, which then adjusts the shift voltage applied in subsequent read operations. This feedback loop continuously optimizes read voltage based on actual memory state, improving reliability in high-density configurations where disturbance effects vary.
2Reliability
If multiple read voltages and error correction operations are applied, then read operation reliability is improved, but device complexity and operation time increase
Solution Approach 1:
The patent segments the read operation into distinct functional parts: a first read operation at a first voltage to generate initial sensing data and flags, a second read operation at a second voltage to generate additional sensing data, and a final read operation at a shifted voltage based on determination data. Each segment performs a specific function (initial reading, error detection, correction), and the results are combined through logical operations. This segmentation allows complex error correction to be achieved through manageable, modular steps rather than a single complex operation.
3Reliability
If multiple read voltages and error correction operations are applied, then read operation reliability is improved, but operation time increases
Solution Approach 1:
The patent applies partial action by performing error correction only when necessary, as determined by the sensing flags and count value. The shift voltage is adjusted based on the actual number of bits requiring correction, rather than always applying maximum correction. This allows the system to achieve sufficient error correction for high reliability while avoiding unnecessary operations that would increase read time, thus balancing reliability improvement with time efficiency.
Data Source
AI summary
A method of reading a nonvolatile memory device including a plurality of pages coupled to a plurality of word lines and a plurality of bit lines, each of the plurality of pages including a data region storing a data and a flag region storing a flag, includes applying a first read voltage to a selected word line to generate first sensing data and a first sensing flag; applying a second read voltage to the selected word line to generate second sensing data and a second sensing flag, generating determination data by performing a logical operation on the first and second sensing data; determining a shift voltage based on the determination data and the read flag; and applying a third read voltage, based on the shift voltage, to the selected word line to generate a read data.