Multi-Layer Gate Electrode for Back-Gate TFT Work Function Control
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Solution Overview
Problem
Conventional back gate thin film transistors face challenges in meeting demands for low resistivity, high work function, and surface roughness control with a single gate material.
Innovation Solution
A transistor design incorporating a gate electrode composed of multiple layers, including a first gate material layer with low resistivity and a second gate material layer with high work function and low surface roughness, ensuring stable control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single gate material is used, then device complexity is reduced, but it is difficult to meet all demands regarding work function, resistivity, and surface roughness control
Solution Approach 1:
The gate electrode is divided into multiple layers, each with specific functions: a first gate material layer (e.g., tungsten) provides low resistivity and high work function, while a second gate material layer (e.g., molybdenum nitride) provides low surface roughness. This segmentation allows each layer to optimize for its specific function, collectively meeting all performance demands that a single material cannot satisfy.
Solution Approach 2:
The gate electrode uses a composite structure combining different materials (e.g., tungsten and molybdenum nitride) to achieve properties that neither material could provide alone. The composite structure integrates the low resistivity and high work function of tungsten with the low surface roughness of molybdenum nitride, creating a gate electrode that meets multiple conflicting requirements simultaneously.
2Reliability
If gate material layers are added to meet multiple demands, then performance requirements are satisfied, but manufacturing process complexity increases
Solution Approach 1:
The patent employs preliminary actions in the manufacturing process by first forming the first gate material layer (tungsten) with specific properties, then selectively removing portions, and finally forming the second gate material layer (molybdenum nitride) in the remaining openings. This sequential preliminary preparation ensures that each layer is deposited under optimal conditions, facilitating subsequent processing steps and improving overall manufacturability despite the multi-layer complexity.
3Ease of operation
If portions of gate material layers are selectively removed, then desired gate electrode structure is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent introduces an intermediary approach by using a two-step selective removal process: first removing portions of the first gate material layer to form openings, then removing portions of the second gate material layer in the same openings. This intermediary sequential removal allows for better control and alignment, reducing the precision burden on a single step while achieving the desired gate electrode structure with improved ease of operation.
Data Source
AI summary
A transistor includes a gate electrode, a gate dielectric, a channel layer and a source line and bit line. The gate electrode includes a first gate material layer and a second gate material layer disposed on the first gate material layer, wherein a work function of the first gate material layer is lower than a work function of the second gate material layer. The gate dielectric is disposed on the gate electrode. The channel layer is disposed on the gate dielectric. The source line and bit line are disposed on and connected to the channel layer.