Memory Device Selection Transistor Threshold Control
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Solution Overview
Problem
Existing memory devices face challenges in finely controlling selection transistors to properly select and access memory cells, requiring precise management of threshold voltages to ensure accurate data storage and retrieval.
Innovation Solution
The implementation of a method that includes pre-program, erase, and fine program operations on selection transistors within memory blocks, utilizing a control circuit to adjust and verify threshold voltages of source and drain selection transistors, ensuring optimal turn-on and turn-off states for efficient data access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If selection transistors are controlled similarly to memory cells using the same control scheme, then the control structure is simple, but the selection precision and ability to properly select desired memory cells deteriorates
Solution Approach 1:
The patent segments the control process for selection transistors into distinct phases: pre-program operation to establish initial threshold voltage distribution, erase operation to reset, and fine program operation to precisely adjust. This segmentation allows different control strategies for different operational stages, achieving both structural simplicity and selection precision by dividing the control function into manageable segments rather than applying a single uniform control scheme throughout.
Solution Approach 2:
The patent applies preliminary action by performing a pre-program operation on selection transistors before they are used for memory cell selection. This preliminary programming establishes an appropriate threshold voltage distribution in the selection transistors beforehand, ensuring they are ready for precise control during subsequent erase and fine program operations. The preliminary action prepares the selection transistors to achieve fine control without requiring complex real-time adjustment mechanisms.
2Measurement precision
If multiple operations (pre-program, erase, fine program) are performed on selection transistors, then the selection control precision is improved, but the operation time and process complexity increases
Solution Approach 1:
The pre-program operation is performed as a preliminary action that establishes the foundation for subsequent precise control. By programming the selection transistors in advance with appropriate threshold voltage characteristics, the patent reduces the need for extensive real-time adjustment during actual memory access operations, thereby minimizing overall operation time while maintaining precision.
Solution Approach 2:
The control process is segmented into three distinct operations with specific purposes: pre-program for initial setup, erase for resetting, and fine program for precise adjustment. This segmentation allows each operation to be optimized independently and executed efficiently, avoiding redundant operations and reducing total processing time compared to a single monolithic control process.
Solution Approach 3:
The patent utilizes parameter changes by adjusting the threshold voltage of selection transistors through controlled programming operations. By changing the threshold voltage parameter in specific steps during pre-program, erase, and fine program operations, the system achieves precise control over transistor switching behavior. This parameter-based control approach is more efficient than alternative control methods, reducing operation time while maintaining precision.
Data Source
AI summary
An operating method of a memory device may include performing a pre-program operation on selection transistors that are included in strings, wherein each of the strings comprises a first source selection transistor, a second source selection transistor, a plurality of memory cells, and a drain selection transistor that are sequentially coupled, and performing an erase operation and a fine program operation on at least one of the selection transistors.