Nonvolatile Memory Control Circuit for 3D Stacked Cell Voltage Stability
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Solution Overview
Problem
Existing nonvolatile semiconductor memory devices face challenges in efficiently programming and retaining data due to threshold voltage distribution issues, particularly in three-dimensional stacked memory cells, where adjacent cells' voltage distributions can lead to data corruption over time.
Innovation Solution
The implementation of a control circuit that applies specific threshold voltage distributions to memory cells, including a first program operation for a target cell and a second program operation for adjacent cells, using a charge storage film to retain multiple levels of data, and executing an E′ distribution program to maintain positive voltage distributions and prevent electron-hole recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple memory cells are stacked three-dimensionally to increase storage capacity, then the storage density is improved, but the threshold voltage distribution becomes unstable due to adjacent cell interference
Solution Approach 1:
The patent divides the programming operation into two distinct segments: a first program operation for the target memory cell and a second program operation for adjacent memory cells. This segmentation allows independent control of voltage distribution in different cell groups, preventing threshold voltage instability caused by adjacent cell interference while maintaining high storage density through three-dimensional stacking.
2Device complexity
If a single program operation is applied to all memory cells, then the programming process is simplified, but data retention deteriorates due to electron-hole recombination from improper voltage distribution
Solution Approach 1:
The patent performs a preliminary second program operation on adjacent memory cells before or during the first program operation on target cells. This preliminary action establishes proper positive threshold voltage distributions in adjacent cells, preventing electron-hole recombination and ensuring long-term data retention, while the control circuit manages the complexity of coordinating these operations.
3Reliability
If threshold voltage is increased to improve data retention, then programming efficiency decreases due to longer programming times and repeated operations
Solution Approach 1:
The patent dynamically changes voltage parameters by applying different voltage distributions to different memory cell groups. The control circuit adjusts the threshold voltage parameters selectively - maintaining higher voltages for data retention in adjacent cells while optimizing programming voltage for target cells, thereby achieving both reliable data retention and efficient programming without requiring repeated operations.
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 data retention by stabilizing threshold voltage distributions, reducing the risk of data corruption and improving programming efficiency in three-dimensional memory cell arrays.
Implementation Method 1
Each of the memory cells includes a charge storage film for storing charge
Implementation Method 2
the control circuit is configured to provide an at least partially negative threshold voltage distribution to the memory cells, thereby erasing retained data of the memory cells, and to provide multiple levels of positive threshold voltage distributions to the memory cells, thereby writing multiple levels of data to the memory cells
Data Source
AI summary
A control circuit provides an at least partially negative threshold voltage distribution to a memory cell, thereby erasing retained data of the memory cell, and provides multiple levels of positive threshold voltage distributions thereto, thereby programming multiple levels of data to the memory cell. The control circuit, when executing a program operation to the memory cell, executes a first program operation that provides the multiple levels of positive threshold voltage distributions to a first memory cell which is a memory cell subject to program, and executes a second program operation that provides a positive threshold voltage distribution, to a second memory cell adjacent to the first memory cell, irrespective of (regardless of) whether data to be programmed to the second memory cell is (already) present in the second memory cell or not.