Double-Gate Thin Film Transistors for Subthreshold Swing Control
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Solution Overview
Problem
Conventional thin film transistors face challenges in scaling down to smaller dimensions due to limitations in subthreshold swing and variability in fabrication processes, making it difficult to extend their performance into the 10 nm or sub-10 nm range, necessitating new methodologies or technologies for future technology nodes.
Innovation Solution
The introduction of double gate thin film transistors with a second gate on top of the channel material layer to improve electrostatic gate control and ON/OFF ratio, and the use of non-planar architectures to increase effective gate width and drive strength, enhancing performance and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional single-gate transistor structures are used, then fabrication processes are simpler and manufacturing is easier, but gate control is insufficient and subthreshold swing cannot be improved below the theoretical limit
Solution Approach 1:
The transistor gate is segmented into two separate gates (first gate and second gate) positioned at opposite sides of the channel. This segmentation allows independent control of the channel from both sides, improving electrostatic control and subthreshold swing performance while maintaining a relatively simple planar structure that is compatible with conventional fabrication processes
2Productivity
If transistor dimensions are scaled down to increase density, then more devices fit on chip, but fabrication process variability increases and performance control becomes difficult
Solution Approach 1:
The invention changes the electrical parameters of the transistor by introducing a second gate that can independently control the channel. This allows tuning of the threshold voltage and subthreshold swing through the second gate voltage, providing an additional degree of freedom to optimize device performance and compensate for fabrication variations even at scaled dimensions
3Reliability
If conventional single-gate structures are used, then device complexity is lower, but ON/OFF ratio and performance are limited
Solution Approach 1:
The gate function is segmented between two independent gates positioned at opposite sides of the channel. The first gate provides basic control while the second gate enhances the ON/OFF ratio by providing additional control over the channel conductivity, achieving superior performance without requiring complex three-dimensional structures
Solution Approach 2:
The dual-gate configuration provides multi-functionality where the first gate can control basic operation and the second gate can independently adjust threshold voltage and enhance switching characteristics. This universal control mechanism improves ON/OFF ratio while maintaining compatibility with standard fabrication processes
Data Source
AI summary
Thin film transistors having double gates are described. In an example, an integrated circuit structure includes an insulator layer above a substrate. A first gate stack is on the insulator layer. A polycrystalline channel material layer is on the first gate stack. A second gate stack is on a first portion of the polycrystalline channel material layer, the second gate stack having a first side opposite a second side. A first conductive contact is adjacent the first side of the second gate stack, the first conductive contact on a second portion of the channel material layer. A second conductive contact is adjacent the second side of the second gate stack, the second conductive contact on a third portion of the channel material layer.