Nonvolatile Memory Programming via Local Word Line Segmentation
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Solution Overview
Problem
Flash memory devices experience program disturbances due to the application of program voltage to both selected and unselected memory cells, leading to accidental programming of unselected cells, especially in multi-level cells where high program voltages are applied, which affects data retention and storage capacity.
Innovation Solution
The method involves using local word lines to divide memory cell strings into areas with different pass voltages, turning off cell transistors, and applying specific voltages to selected and unselected word lines to isolate channels and prevent electron transfer, thereby reducing the likelihood of program disturbances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a program voltage is applied to a selected word line to program a selected memory cell, then the threshold voltage of the selected memory cell is increased, but the program voltage is also applied to unselected memory cells connected to the selected word line, causing program disturbance
Solution Approach 1:
The memory cell array is divided into multiple blocks, and within each block, word lines are segmented into selected and unselected groups. Different voltage levels are applied to different segments: a high program voltage (e.g., 20V) is applied to the selected word line, while unselected word lines receive a lower pass voltage (e.g., 5V). This segmentation prevents program disturbance in unselected cells while maintaining programming accuracy in selected cells.
Solution Approach 2:
Different voltage conditions are applied to different spatial regions of the memory array. The selected word line and its connected memory cells receive high voltage for programming, while unselected word lines and their connected cells receive low voltage to maintain their state. This local differentiation of voltage quality ensures that only the intended memory cells are programmed while protecting adjacent cells from accidental programming.
2Productivity
If a high program voltage is applied to program memory cells, then the programming speed and efficiency are improved, but the program disturbance in unselected memory cells becomes more severe
Solution Approach 1:
The word lines are segmented into selected and unselected categories, with the selected word line receiving high program voltage for fast programming while unselected word lines receive low pass voltage to prevent disturbance. This segmentation allows high-speed programming of target cells without compromising the integrity of neighboring cells.
Solution Approach 2:
High voltage is locally applied only to the selected word line and its connected memory cells, while unselected regions maintain low voltage conditions. This localized high-voltage application achieves fast programming speed in the target area while preventing program disturbance in other areas of the memory array.
3Reliability
If pass voltage is applied to unselected word lines to prevent program disturbance, then the reliability is improved, but the boosting efficiency of channel voltages decreases
Solution Approach 1:
Instead of applying pass voltage to all unselected word lines, the invention applies pass voltage only to a subset of unselected word lines that are adjacent to or near the selected word line. Word lines farther away receive no additional voltage. This partial application of pass voltage provides sufficient protection against program disturbance while minimizing the negative impact on channel voltage boosting efficiency.
Solution Approach 2:
Pass voltage is applied locally to specific unselected word lines that are most susceptible to program disturbance (those adjacent to the selected word line), while other unselected word lines maintain their normal voltage levels. This localized approach protects vulnerable cells from disturbance while preserving the boosting efficiency of channel voltages in less vulnerable regions.
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 boosting efficiency of channel voltages, minimizes accidental programming of unselected cells, and maintains data integrity, particularly in multi-level cells, by controlling electron density and voltage levels across the memory cell array.
Implementation Method 1
prevent electron transfer
Implementation Method 2
driving word lines of the first area by a first pass voltage and driving word lines of the second area by a second pass voltage higher than the first pass voltage
Data Source
AI summary
Provided is a method for programming a nonvolatile memory device. The nonvolatile memory device includes a local word line to divide a memory cell string into a first area including a selected word line and a second area not including the selected word line. In the method, word lines of the first area are driven by a first pass voltage and word lines of the second area driven by a second pass voltage higher than the first pass voltage. A cell transistor corresponding to the local word line is turned off after the first pass voltage and the second pass voltage are applied. The selected word line is driven by a program voltage after the cell transistor is turned off.