Soft-Decision Read Method for Nonvolatile Memory Cells
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Solution Overview
Problem
Non-volatile memory devices face challenges in efficiently reading and writing data due to the need for multiple verification voltages and increased read/program time as the number of data bits stored in memory cells grows, leading to reduced read margins and increased response times.
Innovation Solution
A soft-decision read method is implemented in non-volatile memory devices, where bit lines connected to selected memory cells are pre-charged and voltages are maintained constant, allowing for continuous sensing operations without varying the read voltage applied to the word line, enabling detection of memory cells with different threshold voltages using a single read voltage and reducing the need for multiple verification operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple verification voltages are used to read memory cells with different threshold voltages, then reading accuracy is improved, but read time and device complexity increase
Solution Approach 1:
The patent changes the parameter of word line voltage from multiple discrete verification voltages to a single read voltage level. By using a single read voltage and maintaining constant bit line voltages during continuous sensing, the system achieves reading accuracy without requiring multiple voltage verification steps, thus reducing read time while maintaining measurement precision.
Solution Approach 2:
The patent implements continuous sensing operations where the sensing process continues without interruption once initiated. By maintaining constant voltages on bit lines and word lines throughout the sensing period and using soft decision reading algorithms, the system performs useful sensing action continuously rather than in discrete verification steps, thereby reducing total read time while maintaining accuracy.
2Measurement precision
If multiple verification voltages are applied to detect memory cell states, then detection accuracy improves, but device complexity and operation complexity increase
Solution Approach 1:
The patent simplifies the voltage parameter control by using a single read voltage instead of multiple verification voltages. The control logic maintains constant voltages on bit lines and word lines throughout the sensing operation, significantly reducing the complexity of voltage control and timing coordination while still achieving accurate detection through continuous sensing and soft decision algorithms.
Solution Approach 2:
The single read voltage serves multiple functions: it acts as both the sensing voltage and the verification voltage. The constant voltage levels on bit lines and word lines serve both as signal carriers and as stable reference conditions for continuous sensing. This multi-functionality reduces the need for separate control mechanisms for different voltage levels, thereby reducing device and operation complexity.
3Quantity of substance
If the number of data bits stored in memory cells increases, then storage density improves, but read margins decrease and response time increases
Solution Approach 1:
The continuous sensing operation allows the system to maintain stable voltage conditions throughout the entire sensing period, which is crucial for maintaining read margins. By continuously monitoring the sensing node voltage without interruption and using soft decision reading algorithms, the system can accurately distinguish between different threshold voltage states even as storage density increases, thereby maintaining reliability while improving storage capacity.
Data Source
AI summary
A soft-decision read method of a nonvolatile memory device includes receiving a soft-decision read command, applying a read voltage to a selected word line, pre-charging bit lines respectively connected to selected memory cells of the selected word line, continuously sensing states of the selected memory cells. The pre-charged voltages of the bit lines and the read voltage supplied to the selected word line are not varied during the sensing states of the selected memory cells.