Nonvolatile Memory String Selection Voltage Adjustment
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Solution Overview
Problem
In semiconductor memory devices, particularly nonvolatile memory systems, there is a challenge in accurately selecting and programming cell strings due to variations in threshold voltages of string selection transistors, which can lead to leakage currents and reduced reliability.
Innovation Solution
An operating method is introduced that involves detecting the threshold voltages of string selection transistors and adjusting the voltages supplied to these transistors during programming operations, ensuring they fall within specific ranges to stabilize selection and minimize leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed voltages are applied to string selection transistors in three-dimensional nonvolatile memory, then device structure is simplified, but selection accuracy deteriorates due to threshold voltage variations
Solution Approach 1:
The patent applies dynamics by transitioning from fixed voltage application to dynamic voltage adjustment. The system detects threshold voltages of string selection transistors and adjusts programming voltages accordingly, making the voltage supply adaptive rather than static. This resolves the contradiction by maintaining simple detection circuitry while achieving accurate selection through real-time voltage modulation based on transistor characteristics.
Solution Approach 2:
The patent changes the voltage parameter dynamically based on threshold voltage measurements. By detecting whether threshold voltages fall within specified ranges and adjusting programming voltages accordingly, the system optimizes selection accuracy without complicating the overall device structure. This parameter adaptation allows the same hardware to achieve both simplicity and precision.
2Measurement precision
If threshold voltage detection and adjustment is implemented, then selection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by implementing threshold voltage detection and adjustment only for string selection transistors where it is most needed, rather than uniformly across all transistors. The system selectively detects and adjusts voltages based on specific range criteria, concentrating complexity only where threshold variations significantly impact selection accuracy, thereby maintaining overall system simplicity.
Solution Approach 2:
The patent implements feedback by detecting threshold voltages and using this information to adjust programming voltages in subsequent operations. This closed-loop approach improves selection accuracy by continuously adapting to transistor characteristics while keeping the feedback mechanism simple - only comparing detected voltages against predefined ranges and making corresponding adjustments.
3Ease of operation
If uniform programming voltage is applied to all cell strings, then operation is simplified, but leakage current increases due to threshold voltage variations
Solution Approach 1:
The patent changes programming voltage parameters based on detected threshold voltage ranges. By adjusting voltages dynamically - applying higher voltages to transistors with higher thresholds and lower voltages to those with lower thresholds - the system eliminates leakage current while maintaining operational simplicity. The voltage adjustment is automatically determined by the detection circuitry, requiring no additional operational complexity from the user.
Data Source
AI summary
An operating method of a nonvolatile memory, which includes a plurality of cell strings, each cell string having a plurality of memory cells and a string selection transistor stacked on a substrate, includes detecting threshold voltages of the string selection transistors of the plurality of cell strings; adjusting voltages to be supplied to the string selection transistors according to the detected threshold voltages; and applying the adjusted voltages to the string selection transistors to select or unselect the plurality of cell strings during a programming operation.