Nonvolatile Memory Read Method Using Flag Cell Sensing
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Solution Overview
Problem
Existing nonvolatile memory devices face challenges in accurately reading data from multi-level memory cells (MLCs) due to charge loss in flag cells, leading to increased read errors.
Innovation Solution
A method is introduced that performs multiple sensing operations on flag cells using different read voltages to determine the number of bits programmed in MLCs and detect charge loss, allowing for selective re-reading of data based on these results to reduce errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single read operation is performed on MLCs, then reading speed is improved, but data read accuracy deteriorates due to charge loss in flag cells
Solution Approach 1:
The patent performs a first sensing operation on the flag cell before the read operation to determine the number of bits programmed in MLCs. This preliminary action allows the system to prepare appropriate read voltages in advance, preventing read errors caused by charge loss while maintaining efficient data retrieval
Solution Approach 2:
The patent implements a feedback mechanism where the sensing operation result (indicating the number of programmed bits) is used to dynamically select the appropriate read voltage. This feedback loop ensures that the read operation uses optimal voltages based on the actual state of MLCs, thereby maintaining high accuracy without requiring multiple read attempts
2Reliability
If multiple sensing operations are performed on flag cells, then data read accuracy is improved, but operation complexity increases
Solution Approach 1:
The patent applies different read voltages (first read voltage and second read voltage) to different states of the flag cell based on the number of bits programmed in MLCs. This localized approach ensures that each sensing operation uses the most appropriate voltage for the specific state being detected, improving accuracy while keeping the complexity manageable through voltage differentiation
3Measurement precision
If read voltage level is increased, then detection capability is improved, but charge loss in flag cells increases
Solution Approach 1:
The patent dynamically changes the read voltage parameter based on the detected state of the flag cell. When the flag cell indicates a certain number of programmed bits, the system switches between first read voltage and second read voltage levels. This parameter adaptation allows the system to maintain high detection capability while minimizing charge loss by using lower voltages when sufficient for detection
Data Source
AI summary
A method is provided for reading data in a nonvolatile memory device. The method includes performing a first read operation on multiple multi-level memory cells (MLCs), performing a first sensing operation on at least one flag cell corresponding to the MLCs, selectively performing a second read operation on the MLCs based on a result of the first sensing operation, and performing a second sensing operation on the at least one flag cell when the second read operation is performed. Read data is output based on results of the first read operation and the first sensing operation when the second read operation is not performed, and the read data is output based on result of the first read operation, the first sensing operation, the second read operation and the second sensing operation when the second read operation is performed. The read data corresponds to programmed data in the MLCs.