Semiconductor Memory Source Select Transistor Threshold Control
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Solution Overview
Problem
Semiconductor memory devices face challenges in effectively controlling the threshold voltages of source select transistors, leading to reduced current flow and unintended leakage, which affects the reliability and efficiency of memory operations.
Innovation Solution
The operating method involves programming and reprogramming the second source select transistor by applying specific voltages to bit lines and source select transistors, decoupling from the common source line, and adjusting threshold voltages to desired levels through a peripheral circuit, ensuring effective control of source select transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If source select transistor threshold voltages are not properly controlled, then memory device complexity is reduced, but current leakage increases and reliability deteriorates
Solution Approach 1:
The source select line is divided into multiple segments (first source select line SSL1 and second source select line SSL2), each controlling separate source select transistors (SST1 and SST2). This segmentation allows independent threshold voltage control for each transistor through dedicated programming operations, enabling precise leakage control without requiring complex global control mechanisms.
Solution Approach 2:
The patent applies preliminary programming operations to set the threshold voltages of source select transistors before normal memory operations begin. The peripheral circuit performs preliminary voltage applications to SST1 and SST2 to establish appropriate threshold voltages that prevent leakage, ensuring reliable operation from the start without requiring complex real-time adjustment mechanisms.
2Manufacturing precision
If threshold voltage control is simplified, then device complexity is reduced, but current flow control precision deteriorates
Solution Approach 1:
The patent applies different threshold voltage control strategies to different source select transistors based on their specific locations and functions. SSL1 and SST1 are programmed with one set of voltage conditions while SSL2 and SST2 receive different voltage conditions, allowing each transistor to have optimized threshold voltage characteristics suited to its specific role in the memory array.
Solution Approach 2:
The patent changes voltage parameters (applying different voltages to SSL1, SSL2, CSL, and BL during programming) to achieve precise threshold voltage control. By varying the voltage applied to different lines during programming operations, the peripheral circuit can independently adjust the threshold voltages of SST1 and SST2 to precise target values, ensuring accurate current flow control.
3Reliability
If multiple source select transistors are used per cell string, then current leakage is reduced, but device complexity increases
Solution Approach 1:
The patent merges the control of multiple source select transistors (SST1 and SST2) under a unified peripheral circuit architecture. The same peripheral circuit that controls memory cells also manages the threshold voltage programming for both SST1 and SST2, combining multiple control functions into a single integrated system rather than requiring separate control circuits for each transistor.
Solution Approach 2:
The peripheral circuit is designed with multi-functionality, serving both as the control circuit for memory cell operations and as the programming circuit for source select transistors. The same circuitry that applies voltages during read/write operations also performs threshold voltage programming for SST1 and SST2, eliminating the need for dedicated programming circuits and reducing overall device complexity.
Data Source
AI summary
An operating method of a semiconductor device is provided. The operating method of the semiconductor memory device includes programming a second source select transistor electrically coupled to a common source line through a first source select transistor; reprogramming the second source select transistor when a threshold voltage of the second source select transistor is less than a target voltage, and ending a program for the second source select transistor when the threshold voltage of the second source select transistor is greater than or equal to the target voltage. The programming includes electrically decoupling the second source select transistor from the common source line by turning off the first source select transistor.