Memory Device Dual-Stage Programming for Threshold Voltage Distribution
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Solution Overview
Problem
Existing memory devices face challenges in achieving an optimal threshold voltage distribution during program operations, which can lead to inefficiencies and potential data loss due to changes in threshold voltage caused by disturbance between adjacent word lines.
Innovation Solution
The memory device employs a dual-programming approach, incorporating a foggy program operation and a fine program operation. The foggy program operation increases the threshold voltage to specific foggy program states, while the fine program operation further adjusts the threshold voltage to precise fine program states, thereby improving the threshold voltage distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single program operation is performed to increase threshold voltage, then program speed is improved, but threshold voltage distribution precision deteriorates due to word line disturbance
Solution Approach 1:
The program operation is divided into two distinct stages: foggy program operation that increases threshold voltage to intermediate levels, and fine program operation that precisely adjusts threshold voltage to final states. This segmentation allows each stage to optimize for its specific function, resolving the contradiction between speed and precision.
Solution Approach 2:
The foggy program operation is performed as a preliminary action before the fine program operation. This preliminary action pre-charges the threshold voltage to intermediate levels, reducing the burden on the subsequent fine program operation and enabling faster overall programming while maintaining precision.
2Productivity
If foggy program operation is performed to increase threshold voltage, then program operation speed is improved, but threshold voltage control precision deteriorates
Solution Approach 1:
The program operation is segmented into foggy program operation for rapid voltage increase and fine program operation for precise voltage control. This segmentation allows the system to achieve both high productivity in the first stage and high precision in the second stage.
Solution Approach 2:
Different control strategies are applied at different stages: the foggy program operation uses broader voltage steps for speed, while the fine program operation uses finer voltage adjustments for precision. Each stage has optimized local quality appropriate to its function.
3Reliability
If threshold voltage of memory cells is increased during program operation, then data storage capability is improved, but threshold voltage changes in adjacent memory cells occur due to disturbance
Solution Approach 1:
The foggy program operation performs preliminary threshold voltage adjustment to intermediate levels, establishing a stable foundation before the fine program operation. This preliminary action reduces the magnitude of voltage changes required in subsequent operations, minimizing disturbance to adjacent cells.
Solution Approach 2:
The program operation uses periodic verification between foggy and fine programming stages to ensure threshold voltage stability. This periodic checking and adjustment minimizes unnecessary voltage changes and reduces disturbance effects on adjacent memory cells.
Data Source
AI summary
A memory device includes: a plurality of memory cells; a peripheral circuit for performing a program operation of storing data in the plurality of memory cells; and a program operation control circuit for, in the program operation, controlling the peripheral circuit to perform a foggy program operation of increasing a threshold voltage of the plurality of memory cells to a threshold voltage corresponding to any one state among an erase state and first to sixth foggy program states, and perform a fine program operation of increasing the threshold voltage of the plurality of memory cells to any one state among the erase state and first to fifteenth fine program states.