Memory Device Preprogram Pulse Narrowing Threshold Voltage Distribution
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Solution Overview
Problem
In memory devices, such as 3D NAND memory devices, the accuracy of data read is affected by the distribution of threshold voltages across memory cells, leading to a limited read window. This restricts the ability to accurately distinguish between adjacent programmed states.
Innovation Solution
A memory device and system that utilize a peripheral circuit to provide preprogram pulses and increment step pulse programming (ISPP) to memory cells, allowing for the preprogramming of memory cells to be closer to their target programmed states, thereby narrowing the threshold voltage distribution and increasing the read window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional programming methods are used, then programming speed is maintained at acceptable levels, but the read window is limited due to broad threshold voltage distribution
Solution Approach 1:
The patent segments the memory cells into multiple classes based on their threshold voltage distributions and programs each class with tailored preprogram pulses. This segmentation allows different programming strategies for different cell groups, narrowing the overall threshold voltage distribution and increasing the read window while maintaining acceptable programming speed through parallel processing of multiple classes.
Solution Approach 2:
The patent applies preliminary action by introducing preprogram pulses before the main programming process. These preprogram pulses partially program memory cells to bring their threshold voltages closer to the target state, reducing the required programming dose and narrowing the final threshold voltage distribution. This preliminary action increases the read window while the subsequent main programming completes the task efficiently.
2Measurement precision
If preprogram pulses are applied to narrow threshold voltage distribution, then read window is increased, but programming process complexity increases
Solution Approach 1:
The patent divides memory cells into multiple classes based on their threshold voltage characteristics and applies segmented programming strategies. Each class receives customized preprogram pulses tailored to its specific distribution characteristics. This segmentation approach narrows the overall threshold voltage distribution and increases the read window while managing complexity through systematic classification and targeted processing.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting preprogram pulse parameters (voltage levels, pulse widths, durations) based on the specific characteristics of each memory cell class. This allows optimization of the programming process for each class, narrowing threshold voltage distributions and increasing the read window while controlling overall process complexity through parameter optimization rather than process complexity.
Data Source
AI summary
Examples of the present application disclose a memory device, a memory system, and an operation method of a memory device. In the method, prior to ISPP programming of memory cells of selected memory cells, a first preprogram pulse is first applied to a selected word line to preprogram a first class of memory cells of the selected memory cells.