Nonvolatile Memory Read Method Selective Bit Line Precharging
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Solution Overview
Problem
The existing nonvolatile memory devices consume excessive operating current and experience a source line bouncing phenomenon due to unnecessary precharging of all bit lines during read operations, especially in multi-level cell and triple level cell programming methods.
Innovation Solution
A method where bit lines are precharged only for memory cells whose data has not been determined in previous read operations, using specific reference voltages to differentiate between memory cells with different threshold voltages, thereby reducing unnecessary precharging and current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If precharging is performed for all memory cells every time during read operations, then the read operation can be completed for all memory cells, but the consumption of operating current increases and source line bouncing phenomenon occurs
Solution Approach 1:
The patent applies local quality by differentiating the precharging operation between two groups of memory cells: first memory cells that require precharging and second memory cells that do not require precharging. This is achieved by controlling page buffers to selectively precharge bit lines coupled to first memory cells based on threshold voltage characteristics, while avoiding precharging for second memory cells. This selective approach reduces overall operating current consumption while maintaining reliable read operations for all memory cells.
2Reliability
If precharging is performed for all memory cells every time during read operations, then the read operation can be completed for all memory cells, but source line bouncing phenomenon occurs where a lot of current flows through source line
Solution Approach 1:
The patent eliminates source line bouncing phenomenon by applying local quality control to the precharging process. Page buffers are controlled to precharge bit lines only for first memory cells (those requiring precharging based on threshold voltage) while avoiding precharging for second memory cells. This localized approach prevents excessive current flow through the source line that would otherwise occur during universal precharging, thereby eliminating the bouncing phenomenon while maintaining complete read operation capability.
3Ease of operation
If precharging is performed for all memory cells every time during read operations, then uniform read operation can be performed, but the threshold voltage distribution of the memory cells is widened
Solution Approach 1:
The patent resolves the contradiction between uniform operation and threshold voltage distribution by implementing local quality control. Different precharging strategies are applied to different memory cell groups: first memory cells receive precharging to ensure uniform read operation, while second memory cells skip precharging to preserve their threshold voltage characteristics. This differentiated approach maintains ease of operation for cells requiring it while preventing threshold voltage distribution widening in cells that would be adversely affected.
Data Source
AI summary
A read method of a nonvolatile memory device according to an exemplary embodiment of this disclosure includes precharging bit lines coupled to memory cells, performing a first read operation by supplying a first reference voltage to the memory cells in order to determine the data stored in the memory cells, precharging bit lines coupled to undetermined memory cells whose data has not been determined by the first read operation, and performing a second read operation by supplying a second reference voltage to the memory cells in order to determine data stored in the undetermined memory cells.