Automated Valley Detection for NAND Read Offset Tracking
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Solution Overview
Problem
The reliability of memory devices is compromised due to threshold voltage (Vth) distribution shifts, leading to read failures as pre-defined read levels fail to accurately track the Vth distribution, especially in high-density NAND memory devices.
Innovation Solution
Implement automated valley detection (AVD) to perform sensing operations on memory cells, generating a read offset that includes a read voltage or read develop time, which is stored in the memory device's SRAM to improve read operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-defined read levels are used for reading memory cells, then the read operation is simple and fast, but the reliability deteriorates due to threshold voltage distribution shifts causing read failures
Solution Approach 1:
The system performs sensing operations and identifies read offsets (voltage or develop time) in advance before actual read operations. These read offsets are determined based on threshold voltage distribution characteristics and are stored for subsequent use, allowing the read operation to adapt to Vth shifts without adding complexity during the actual read process
Solution Approach 2:
The system uses sensing operations to detect the actual threshold voltage distribution state of memory cells and generates feedback in the form of read offsets. This feedback mechanism allows the system to automatically adjust read parameters based on detected Vth distribution, improving reliability while maintaining operational simplicity
2Reliability
If sensing operations are performed to track Vth distribution, then read reliability improves, but the operation time increases
Solution Approach 1:
Sensing operations and read offset identification are performed in advance during idle periods or alongside other memory operations. The determined read offsets are stored and reused for multiple subsequent read operations, amortizing the time cost of sensing over many reads rather than performing sensing before every read operation
Solution Approach 2:
The memory device performs self-diagnosis through sensing operations to automatically determine its own read parameters (read offsets) based on its actual threshold voltage distribution state. This self-service capability eliminates the need for external calibration procedures and allows the device to adapt to its own aging and degradation characteristics
Data Source
AI summary
The present disclosure relates to methods and devices for performing a read operation in a memory. In one example, a method for operating a memory device includes performing sensing operations on memory cells of the memory device based on at least one voltage or at least one develop time. The memory cells are coupled to a word line. The method further includes identifying a read offset based on results of the sensing operations. The read offset can include a read voltage selected from the at least one voltage, or a read develop time selected from the at least one develop time. The method further includes storing the read offset in the memory device to be directly applied in a read operation on the memory cells.