3D Memory Read Voltage Offset Table for Threshold Variation
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Solution Overview
Problem
Nonvolatile memory devices with three-dimensional (3D) memory cell arrays face challenges in ensuring reliable read operations due to variations in threshold voltage distributions across word lines, leading to read errors and performance degradation over time and different environmental conditions.
Innovation Solution
A method is introduced where a first read operation is performed using a default read voltage level, followed by a read retry operation with a second read voltage level if the initial read fails. A read offset table is determined based on the difference between these voltage levels, allowing for the selection of a third read voltage level for subsequent operations on different word lines, compensating for threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single default read voltage level is used for all word lines, then the device complexity is reduced, but read errors increase due to threshold voltage variations across different word lines
Solution Approach 1:
The patent segments the read voltage control by creating a read offset table that stores individual offset values for different word line groups. This allows each word line group to have its own optimized read voltage level, addressing threshold voltage variations without requiring complete individual control of every word line, thus balancing complexity reduction with reliability improvement
Solution Approach 2:
The patent changes the read voltage parameter dynamically by applying offsets to the default read voltage level based on word line group characteristics. The read offset table stores pre-calculated voltage offsets that are added to the default read voltage to compensate for threshold voltage variations across different word lines, improving read reliability while maintaining manageable system complexity
2Measurement precision
If read retry operations are performed with different voltage levels for each word line, then read accuracy is improved, but the time required for read operations increases
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing read voltage offsets for different word line groups in a read offset table before actual read operations. This allows the system to quickly retrieve and apply appropriate voltage offsets during read operations without performing time-consuming voltage level searches or retries, thus improving read accuracy while minimizing time loss
Solution Approach 2:
The patent implements dynamic read voltage adjustment by selecting different voltage offsets from the read offset table based on the specific word line group being accessed. This dynamic adaptation allows the system to optimize read voltage for each word line group while maintaining efficient operation through pre-computed offset values, balancing accuracy improvement with time efficiency
3Duration of action of stationary object
If read voltage offsets are determined and applied for each word line group, then performance degradation over time is reduced, but the device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent applies universality by creating a read offset table that serves multiple word line groups with similar characteristics. Instead of determining unique offsets for every single word line, the system groups word lines and applies common offsets to each group, reducing the overall complexity of the voltage control mechanism while still addressing performance degradation over time through targeted voltage compensation
Data Source
AI summary
A method of operating a nonvolatile memory device that includes a three-dimensional (3D) memory cell array is provided as follows. A first read operation is performed on first memory cells connected to a first word line by using a first read voltage level. A read retry operation is, if the first read operation fails, performed on the first memory cells so that a read retry voltage level is set to a second read voltage level. A read offset table is determined based on a difference between the first read voltage level and the second read voltage level. The read offset table stores a plurality of read voltage offsets. A second read operation is performed on second memory cells connected to a second word line by using a third read voltage level determined using the read offset table.