Semiconductor Memory Device LSB MSB Programming Interference
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Solution Overview
Problem
Interference between neighboring memory cells in semiconductor memory devices, particularly during programming operations, leads to unreliable data storage and read operations, especially in multi-level cell configurations, due to threshold voltage distribution shifts caused by high program voltages.
Innovation Solution
The proposed method involves performing a least significant bit (LSB) program operation followed by increasing the threshold voltages of most significant bit (MSB) cells before executing the MSB program operation, thereby reducing interference and maintaining reliable data storage and read operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high program voltage is supplied to a selected word line during program operation, then programming speed is improved, but interference between neighboring memory cells increases causing threshold voltage distribution shifts
Solution Approach 1:
The patent applies preliminary action by performing an LSB program operation on adjacent pages before performing the MSB program operation on the target page. This preliminary programming of LSB cells in neighboring pages prevents interference from affecting the MSB threshold voltage distribution during the main programming operation, thus maintaining reliability while enabling high-speed programming.
Solution Approach 2:
The patent segments the programming operation into two distinct phases: LSB program operation and MSB program operation. By dividing the programming process into separate stages with different voltage conditions, the patent eliminates interference between neighboring cells during MSB programming while maintaining efficient programming speed through the structured two-phase approach.
2Manufacturing precision
If incremental step pulse programming is used to prevent threshold voltage widening, then programming precision is improved, but programming time increases
Solution Approach 1:
The patent segments programming into LSB and MSB operations that can be performed in parallel on different pages. The LSB operation uses incremental step pulse programming for precision, while the MSB operation benefits from the preliminary LSB programming that prevents interference. This segmentation allows precise threshold voltage control without excessive programming time penalty.
Solution Approach 2:
By performing LSB programming as a preliminary action on adjacent pages, the patent prepares the memory cells in advance to prevent interference during the subsequent MSB programming. This preliminary action reduces the need for multiple verify-and-reprogram cycles, thereby reducing total programming time while maintaining precision.
Data Source
AI summary
A program method of a semiconductor memory device includes performing a least significant bit (LSB) program operation for target LSB program cells of a selected page, increasing the threshold voltages of target most significant bit (MSB) program cells of the selected page before performing an MSB operation for the target MSB program cells, and performing the MSB program operation for the target MSB program cells after the increasing of the threshold voltages of the target MSB program cells.