Thin Film Transistor Electrode Stack for Uniform Etching
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Solution Overview
Problem
Existing thin film transistors (TFTs) used in organic light-emitting displays face challenges in achieving a uniform etching profile for source and drain electrodes with a double or triple-layered metal and/or metal oxide stack structure, due to differing etching properties of the materials involved.
Innovation Solution
The TFTs incorporate a stack structure of an aluminum (Al) layer, an aluminum-nickel alloy (AlNiX) layer, and an indium tin oxide (ITO) layer, with specific compositions and thicknesses, which allows for a uniform etching profile using a single etchant, preventing junction spikes and reducing contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a double or triple-layered metal and/or metal oxide stack structure is used for source and drain electrodes, then emission direction, resistance, and contact properties are improved, but achieving a uniform etching profile becomes difficult due to different etching properties of the materials
Solution Approach 1:
The patent introduces an intermediate layer (aluminum-nickel alloy layer) between the aluminum layer and the ITO layer. This intermediate layer acts as a mediator that has etching properties intermediate between aluminum and ITO, enabling the entire stack structure to be etched uniformly by a single etchant. The intermediate layer resolves the contradiction by providing a transition zone that facilitates uniform etching while maintaining the functional benefits of the multi-layer structure.
Solution Approach 2:
The patent uses a composite stack structure consisting of aluminum layer, aluminum-nickel alloy layer, and ITO layer. Each layer is designed with specific composition and thickness to achieve both low contact resistance and uniform etching. The composite structure combines materials with different properties (aluminum for low resistance, ITO for transparency and emission control, and the alloy layer for etching uniformity) to simultaneously satisfy multiple requirements.
2Reliability
If a multi-layered stack structure is used, then contact resistance is reduced and emission properties are improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent merges multiple functions into a single integrated stack structure. The aluminum layer provides low contact resistance, the aluminum-nickel alloy layer provides uniform etching and structural stability, and the ITO layer provides transparency and emission control. By combining these layers in a specific sequence with optimized thicknesses, the patent achieves multiple functional benefits while maintaining manufacturability through a single etching process.
Solution Approach 2:
The patent optimizes specific parameters of each layer (composition ratios, thicknesses) to achieve the desired balance between performance and manufacturability. The aluminum-nickel alloy layer contains 2-10 at% nickel, which is carefully controlled to provide the right etching properties without excessive complexity. The thickness of each layer is also optimized to ensure proper functionality while maintaining uniform etching characteristics throughout the stack.
Data Source
AI summary
A thin film transistor including: a substrate; an active layer formed over the substrate; a gate insulating layer formed over the active layer; a gate electrode formed over the gate insulating layer; an interlayer insulating layer formed over the gate electrode; and source and drain electrodes that contact the active layer via the interlayer insulating layer. The source and drain electrodes may have a structure including an aluminum (Al) layer, an aluminum-nickel alloy (AlNiX) layer, and an indium tin oxide (ITO) layer, which are sequentially stacked.