Wordline Verify Voltage Offsets for Memory Cell Coupling Compensation
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Solution Overview
Problem
Memory devices experience reliability issues due to cell-to-cell coupling and lateral charge migration, leading to widened threshold voltage distributions and reduced read window budget, which affect the accuracy of memory access operations and increase bit error rates.
Innovation Solution
A wordline group dependent corrective program verify operation that adjusts program verify voltages based on cell size-related metrics and neighboring wordline programming levels to compensate for cell-to-cell coupling and lateral charge migration effects, thereby aligning threshold voltage distributions and improving read window budget.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional program verify operation is used, then operation simplicity is maintained, but reliability deteriorates due to cell-to-cell coupling and lateral charge migration
Solution Approach 1:
The patent segments the memory array into multiple wordline groups based on cell size-related metrics. Each wordline group is assigned a specific offset value to compensate for cell-to-cell coupling effects. This segmentation allows targeted correction without requiring complex operations across the entire memory array, thus improving reliability while controlling complexity.
Solution Approach 2:
The patent applies local quality by determining offset values specific to each wordline group based on their cell size characteristics. Instead of using a uniform verify voltage across all wordlines, the system adjusts the verify voltage locally for each group to account for variations in cell-to-cell coupling and lateral charge migration, thereby improving reliability without uniformly increasing operation complexity.
2Measurement precision
If higher program verify voltage is applied, then programming accuracy is improved, but harmful effects from cell-to-cell coupling and lateral migration increase
Solution Approach 1:
The patent changes the voltage parameter dynamically by applying different offset values to the program verify voltage based on wordline group characteristics. This allows the verify voltage to be adjusted precisely for each group, improving measurement precision while avoiding the harmful effects that would result from uniformly high voltage application. The parameter change is tailored to each wordline group's specific needs.
3Reliability
If uniform program verify voltage is used across all wordlines, then operation simplicity is maintained, but read window budget is reduced due to varying cell characteristics
Solution Approach 1:
The patent performs preliminary action by pre-determining offset values for each wordline group based on cell size-related metrics before the actual program verify operation. This preliminary classification and offset assignment allows the system to improve read window budget through targeted voltage adjustments without adding significant complexity during the verify operation itself, as the complex analysis has already been completed in advance.
Data Source
AI summary
A memory device includes a memory array including a set of target memory cells connected to a target wordline; and a first wordline and a second wordline, each adjacent to the target wordline; and control logic, operatively coupled with the memory array, to perform operations including causing a program operation to be initiated to program the set of target memory cells of the target wordline to a target programming level; determining, for each memory cell connected to each wordline of the memory array, a respective value of a metric that reflects a size of a memory cell; identifying a plurality of wordline groups in the memory array, wherein for each wordline group, each memory cell connected to each wordlines of a wordline group has the respective value falling in a respective threshold range; determining a first offset value corresponding to a first wordline group of the plurality of wordline groups, the first wordline group including the target wordline; identifying, based on programming level information of the first wordline, a program verify voltage offset associated with the target wordline; and causing, during a program verify time period of the program operation, a program verify voltage to be applied to the target wordline to verify programming of the set of target memory cells, wherein the program verify voltage is adjusted by the program verify voltage offset and the first offset value.