Flash Memory Pass Word Lines for Program Disturb Reduction
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Solution Overview
Problem
Flash memory devices face challenges in maintaining uniform program and erase speeds across memory cells, particularly at the outermost positions, leading to increased program disturb and threshold voltage variations, which degrade operating characteristics and reliability due to high integration density and interference capacitive coupling.
Innovation Solution
Incorporating pass word lines between select lines and word lines, and controlling the bias voltages applied to these pass word lines during program and erase operations to minimize speed differences and maintain channel boosting levels, thereby reducing program disturb and threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high integration density is increased to improve storage capacity, then storage capacity is improved, but program disturb and threshold voltage variations increase
Solution Approach 1:
The patent segments the word line structure by inserting pass word lines between the select line and the main word lines. This segmentation creates distinct functional zones that isolate the channel region, preventing capacitive coupling from propagating to outermost memory cells and reducing program disturb while maintaining high integration density.
Solution Approach 2:
The pass word lines act as intermediary elements between the select line and the main word lines. These intermediary structures control the electrical field distribution and prevent direct capacitive coupling between the select line and outermost word lines, thereby reducing program disturb in high-density configurations.
2Productivity
If pass voltage is applied to unselected word lines to maintain channel boosting, then program speed is improved, but threshold voltage variations increase
Solution Approach 1:
The patent applies different voltage conditions to different word line regions. The pass word lines receive specific voltages (Vpass or ground voltage) that are optimized for their local position between the select line and main word lines. This local quality control ensures uniform channel boosting without causing threshold voltage variations in outermost cells, thereby maintaining both program speed and precision.
3Area of stationary object
If outermost word lines are positioned closer to select line to improve integration, then integration density is improved, but program disturb increases
Solution Approach 1:
The pass word lines serve as intermediary structures that physically and electrically separate the select line from the outermost main word lines. Even when outermost word lines are positioned close to the select line for high integration density, the pass word lines intercept and control the electrical field, preventing direct capacitive coupling and reducing program disturb.
4Reliability
If channel boosting level is increased to improve program margin, then program margin is improved, but program disturb in outermost cells increases
Solution Approach 1:
The patent segments the voltage application strategy by using pass word lines to create controlled potential barriers. This segmentation allows channel boosting to be maintained in the active channel region for improved program margin, while simultaneously preventing excessive voltage propagation to outermost cells, thereby reducing program disturb.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the operating characteristics and reliability of flash memory devices by maintaining consistent program and erase speeds, reducing channel resistance, and improving patterning uniformity and cell current, while preventing unwanted program disturbances.
Implementation Method 1
high integration density and interference capacitive coupling
Data Source
AI summary
A method for operating a flash memory device includes applying a pass voltage to a drain pass word line, a source pass word line, and unselected word lines. The drain pass word line is provided between a drain select line and a word line. The drain pass word line has a structure in the same manner as the word lines. The source pass word line is provided between a source select line and a word line. The source pass word line has a structure in the same manner as the word lines. A program voltage is applied to a selected word line associated with a selected memory cell block. A ground voltage is applied to drain pass word lines and source pass word lines. Word lines associated with unselected memory cell blocks are set to a floating state.