Dynamic Read Voltage Determination for Nonvolatile Memory Cells
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The accuracy of data read from nonvolatile memory cells, such as those in 3D NAND flash memory, is affected by charge leakage in the gate dielectric layer over time, leading to incorrect differentiation between adjacent memory states during read operations.
Innovation Solution
An operating method for a memory system that involves obtaining sets of read voltages with initial and offset values, performing read operations based on these voltages, counting memory cells meeting set conditions, determining differences between quantities for adjacent voltage values, and calculating an optimal read voltage to accurately distinguish between adjacent memory states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a preset read voltage is used to read memory cells, then the reading operation can be performed, but the accuracy of distinguishing adjacent memory states deteriorates due to charge leakage and threshold voltage shifts
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed preset read voltage to a dynamic read voltage determination process. The system performs multiple read operations at different voltage values (initial voltage plus offset values) and dynamically selects the optimal read voltage based on the distribution characteristics of read results, allowing the read voltage to adapt to charge leakage and threshold voltage shifts in real-time
Solution Approach 2:
The patent changes the parameter of read voltage from a static preset value to a variable value that is determined based on read result distributions. By adjusting the read voltage according to the actual distribution characteristics of memory cell states, the system compensates for charge leakage effects and maintains accurate state differentiation
2Measurement precision
If multiple read voltages are tested to determine optimal read voltage, then the accuracy of distinguishing memory states is improved, but the time consumption increases
Solution Approach 1:
The patent applies preliminary action by pre-defining a set of candidate read voltages consisting of an initial voltage and multiple offset values. This pre-prepared voltage set eliminates the need for exhaustive voltage scanning during actual operation, reducing time consumption while maintaining accurate state differentiation through the predetermined voltage candidates
Solution Approach 2:
The system implements feedback by using the distribution characteristics of read results at different voltage values to determine the optimal read voltage. The read results from multiple voltage tests provide feedback that guides the selection of the optimal voltage, creating a closed-loop optimization process that balances accuracy and efficiency
Data Source
AI summary
A memory device includes. a memory controller configured to send a first command, and a memory coupled to the memory controller. The memory is configured to in response to the first command, perform first read operations based on a first set of read voltages. The first set of read voltages includes first read voltages. Any two adjacent first read voltages have an equal offset with a first value. Each first read operation is performed based on one first read voltage. The memory is also configured to obtain first quantities of memory cells meeting set conditions, each of which corresponds to a read result of one first read operation. The memory is further configured to send first information corresponding to the first quantities of memory cells meeting the set conditions to the memory controller. The memory controller is further configured to obtain first differences each between two first quantities corresponding to two adjacent first read voltages with the first information received from the memory, determine an optimal read voltage based on the first differences, and send one or more second commands to the memory indicating the memory to perform read operations based on the optimal read voltage.