3D Non-Volatile Memory Write Control for Threshold Voltage Stability
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Solution Overview
Problem
Existing non-volatile semiconductor memory devices face challenges in maintaining a narrow distribution width of threshold values, which affects data retention and reliability.
Innovation Solution
A non-volatile semiconductor memory device with a three-dimensional structure that includes multiple memory cell transistors, each capable of being set to different threshold voltages, and a control circuit that performs specific voltage operations during write operations to manage the distribution width.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple memory cell transistors are arranged three-dimensionally to increase capacity, then storage density is improved, but threshold voltage distribution width increases
Solution Approach 1:
The memory cell transistors are divided into multiple groups based on their threshold voltage characteristics. By segmenting the memory cells into distinct groups with controlled threshold voltage ranges, the patent manages the inherent variation in threshold voltages that arises from three-dimensional stacking, thereby maintaining narrow distribution width while preserving high storage capacity.
Solution Approach 2:
The patent utilizes different voltage levels (first voltage and second voltage) applied to control gates to dynamically adjust and differentiate the threshold voltages of memory cell transistors. By changing voltage parameters during write operations, the system can set and maintain precise threshold voltage values for each memory cell group, counteracting the spreading effect of three-dimensional arrangement.
2Reliability
If threshold voltage distribution width increases, then data retention and reliability deteriorate
Solution Approach 1:
The control circuit performs write operations by applying specific voltages to control gates based on the desired threshold voltage for each memory cell group. This controlled voltage application acts as a feedback mechanism that actively maintains threshold voltage within target ranges, preventing distribution width from increasing and thereby preserving data retention and reliability.
Solution Approach 2:
The patent establishes target threshold voltages for different memory cell groups before actual data storage operations. By pre-defining and controlling the threshold voltage distribution through structured write operations, the system proactively prevents threshold voltage spread from degrading reliability, rather than attempting to correct it afterward.
Data Source
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AI summary
A non-volatile semiconductor memory device includes a first semiconductor layer including a first memory cell transistor including a first channel, a second semiconductor layer including a second memory cell transistor including a second channel, a third semiconductor layer including a third memory cell transistor including a third channel, and a control circuit that controls the first memory cell transistor to the third memory cell transistor so that a write operation can be performed. When performing a write operation on the second memory cell transistor, the control circuit supplies a first voltage that is a reference voltage to the second channel, supplies a second voltage that is greater than the first voltage to the first channel, and then supplies the second voltage to the third channel, thereby boosting the voltage supplied to the first channel to a third voltage that is greater than the second voltage.