String Driver Bias Emulation for Memory Threshold Variation
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Solution Overview
Problem
The neighbor bias effect and coupling effects between adjacent transistors in scaled semiconductor devices, particularly string drivers, lead to significant variations in threshold voltage and increased leakage currents, impacting the reliability and efficiency of memory operations.
Innovation Solution
Incorporation of a five nodes string driver device (SDF) with dummy transistors biased at Vpass to emulate neighbor bias effects, simulating the interactions and voltage variations in a controlled environment, using a program switch voltage regulator circuit to manage these effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device scaling is continued to improve integration density, then productivity increases, but neighbor bias and coupling effects between adjacent transistors worsen, leading to threshold voltage variations and increased leakage currents
Solution Approach 1:
The patent introduces dummy transistors that copy the electrical characteristics of actual adjacent transistors. These dummy transistors are identical in structure and bias conditions to the real adjacent transistors, allowing them to replicate the neighbor bias and coupling effects without being part of the functional circuit. This copying approach enables accurate modeling and analysis of scaling effects while maintaining circuit functionality.
Solution Approach 2:
The dummy transistors act as intermediaries between the actual transistors and the analysis system. By placing dummy transistors at strategic locations, they mediate the measurement and analysis processes, allowing researchers to observe and quantify neighbor bias effects without directly measuring the complex interactions between actual transistors. This intermediary approach simplifies the analysis while maintaining accuracy.
2Productivity
If device scaling is continued to improve integration density, then productivity increases, but coupling effects between adjacent transistors worsen, causing increased leakage currents
Solution Approach 1:
The dummy transistors copy the leakage characteristics of actual adjacent transistors by being biased under identical conditions. This allows the patent to measure and analyze coupling-induced leakage currents through the dummy transistors, which replicate the harmful effects without contributing to the functional circuit's leakage. The copying approach enables quantitative analysis of scaling-related leakage issues.
3Measurement precision
If dummy transistors are added to emulate neighbor bias effects, then measurement precision improves, but device complexity increases
Solution Approach 1:
The dummy transistors are created as simple copies of actual transistors with identical structure and biasing. This copying approach maintains measurement precision by accurately replicating neighbor bias effects while minimizing the increase in device complexity. The dummy transistors use the same fabrication processes and design rules as the functional transistors, avoiding the need for complex additional structures.
Solution Approach 2:
The patent applies local quality by placing dummy transistors only at specific locations where neighbor bias effects are most significant. Rather than adding dummy transistors throughout the entire circuit, the approach selectively places them at strategic positions to model local interactions. This localized approach improves measurement precision for critical areas while minimizing overall device complexity.
Data Source
AI summary
A semiconductor device is described in this disclosure. The semiconductor device includes a first semiconductor channel, a second semiconductor channel parallel to the first semiconductor channel, and a gate disposed above the first semiconductor channel and the second semiconductor channel. In addition, the semiconductor device includes a string driver and dummy devices coupled to the string driver, wherein dummy devices are biased at Vpass to better emulate transistor bias behavior of the string driver by capturing the Vt/Dvt modulating effect of the Vpass on the neighbor devices. Further, the semiconductor device is coupled with a program voltage regulator circuit to emulate neighbor bias effort on the string driver.