Variable Pass Voltage Control for Memory Read Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The reliability of nonvolatile memory devices is compromised due to the widening of threshold voltage distributions and increased interference between memory cells as they deteriorate, leading to errors in read operations, especially as the erase count increases, causing a shift in threshold voltage distributions and potential data loss.
Innovation Solution
A memory system that applies a variable pass voltage to unselected word lines during read operations based on the erase count of the target memory block, using a pass voltage level table to adjust the voltage levels accordingly, thereby minimizing interference and maintaining data integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed pass voltage is applied to unselected word lines during read operations, then the circuit design is simple, but the reliability of read operations deteriorates as erase count increases due to threshold voltage distribution shifts
Solution Approach 1:
The pass voltage applied to unselected word lines is changed from a fixed value to a dynamic value that varies based on the erase count of the memory block. The voltage generation circuit adjusts the pass voltage level according to the target memory block's erase count, making the voltage characteristic adaptive rather than static, thereby maintaining read reliability as the memory deteriorates
Solution Approach 2:
The pass voltage parameter is modified based on the erase count status of the target memory block. By changing the voltage level parameter dynamically according to memory block wear status, the system compensates for threshold voltage distribution shifts and maintains accurate read operations throughout the memory's lifecycle
Solution Approach 3:
The system uses the erase count information as feedback to adjust the pass voltage level. The controller determines the erase count of the target memory block and uses this information to control the voltage generation circuit to apply the appropriate pass voltage, creating a closed-loop control system that adapts to memory deterioration
2Manufacturing precision
If the pass voltage level is adjusted based on erase count, then the threshold voltage distribution shift is reduced, but the device complexity increases due to additional control logic
Solution Approach 1:
The pass voltage parameter is modified based on the erase count status of the target memory block. By changing the voltage level parameter dynamically according to memory block wear status, the system compensates for threshold voltage distribution shifts and maintains accurate read operations throughout the memory's lifecycle
Solution Approach 2:
The system uses the erase count information as feedback to adjust the pass voltage level. The controller determines the erase count of the target memory block and uses this information to control the voltage generation circuit to apply the appropriate pass voltage, creating a closed-loop control system that adapts to memory deterioration
Data Source
AI summary
A memory system includes a memory cell array including a plurality of memory cells; a peripheral circuit configured to apply a read voltage to a selected word line coupled to a selected memory cell among the memory cells, and apply a pass voltage to unselected word lines coupled to unselected memory cells other than the selected memory cell among the memory cells, during a read operation; and a controller configured to control the peripheral circuit, and apply a variable voltage level of the pass voltage based on status information of a target memory block which is the target of the read operation.