Nonvolatile Memory Read Retry Voltage Optimization
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Solution Overview
Problem
Nonvolatile memory devices face challenges in accurately reading data due to shifts or broadening of threshold voltage distributions, leading to read failures and increased read time, as conventional retry methods extend the time required to successfully read data.
Innovation Solution
A method is introduced where a read operation is performed with a first read voltage, followed by a retry to determine an optimal read level regardless of error-correctability, which is then used for subsequent read operations, reducing average read time and latency by selectively performing retries based on error correction capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional read retry operations are performed by iteratively increasing read voltage levels, then read failures due to threshold voltage shifts can be corrected, but the average read time and read latency increase significantly
Solution Approach 1:
The patent performs a read retry operation proactively to determine an optimal read voltage level before executing subsequent read operations. This preliminary action establishes a corrected reference voltage that accounts for threshold voltage shifts, enabling future reads to be performed accurately without requiring iterative retry attempts. The optimal read voltage is determined by performing a read retry regardless of whether the initial read data is correctable, and then applying this determined voltage to subsequent read operations.
2Loss of time
If read retry operations are performed only when error correction fails, then read time is reduced, but threshold voltage shifts may go uncorrected leading to future read failures
Solution Approach 1:
The patent implements a feedback mechanism where the result of each read operation (whether data is correctable or not) is used to adjust the read voltage level for subsequent operations. When read data is found to be incorrect or uncorrectable, the system performs a read retry to determine a corrected read voltage level, then applies this corrected voltage to future read operations. This feedback loop ensures that threshold voltage shifts are continuously compensated for, maintaining high read accuracy while minimizing the frequency of retry operations.
Data Source
AI summary
In a method of reading data from a nonvolatile memory device, a first read operation for memory cells coupled to a first word line is performed by applying a first read voltage to the first word line, a first read retry is performed to obtain an optimal read level regardless or independent of whether data read by the first read operation is error-correctable, and the optimal read level is stored to perform a subsequent second read operation using the optimal read level. Related methods and devices are also discussed.