Memory Cell Programming with Adjacent-Wordline Voltage Compensation
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Solution Overview
Problem
Memory devices experience a decrease in reliability due to changes in threshold voltage distribution of memory cells caused by short time retention after program operations, necessitating a scheme to compensate for this decrease.
Innovation Solution
A memory device and method that includes a control logic to perform a first program voltage apply operation, verify program states, and a second program voltage apply operation based on bit line voltages determined by adjacent memory cells, with a peripheral circuit to precharge bit lines and increase threshold voltages of successfully verified cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a program operation is performed on memory cells, then data can be stored in the memory cells, but the threshold voltage distribution changes due to short time retention, decreasing reliability
Solution Approach 1:
The patent applies preliminary action by performing a compensation program operation immediately after the initial program operation, before the threshold voltage distribution changes significantly due to retention. This second program operation pre-compensates for the expected threshold voltage shift, ensuring the threshold voltage distribution remains narrow and stable, thereby maintaining reliability.
2Reliability
If a compensation program operation is performed on memory cells, then threshold voltage distribution stability is improved, but the program operation time is extended
Solution Approach 1:
The patent applies partial action by performing the compensation program operation only on a subset of memory cells (specifically, cells where the verify operation succeeded in the first program operation). This selective approach compensates for threshold voltage changes in the necessary cells while avoiding unnecessary operations on all cells, thus extending reliability without excessively increasing the overall program operation time.
3Measurement precision
If verify operation is performed on memory cells, then program state is confirmed, but additional time is required for verification
Solution Approach 1:
The patent applies feedback by using the verify operation results to determine whether the compensation program operation should be performed. The control logic receives feedback from the verify operation (success or failure) and uses this information to decide on the subsequent compensation operation. This feedback mechanism ensures that verification time is not wasted on cells that already have stable threshold voltages, optimizing the balance between measurement precision and time consumption.
Data Source
AI summary
A memory device may include a memory cell array including a plurality of memory cells connected to word lines and bit lines, a peripheral circuit configured to perform a first program voltage apply operation of increasing threshold voltages of selected memory cells and a verify operation of verifying program states of the selected memory cells based on the increased threshold voltages, and a control logic configured to, after the verify operation has succeeded, control the peripheral circuit to determine a bit line voltage by which a bit line connected to the memory cell having succeeded in a verify operation is precharged, based on threshold voltages of memory cells connected to one or more adjacent word lines, and perform a second program voltage apply operation of increasing a threshold voltage of the memory cell having succeeded in the verify operation based on determined bit line voltage.