Active Matrix Substrate with Stacked Oxide Semiconductor Layers
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Solution Overview
Problem
Existing active matrix substrates using oxide semiconductor TFTs face reliability issues due to metal element dispersion in the oxide semiconductor layer, leading to unstable TFT characteristics, and fail to differentiate threshold voltages for circuit and pixel TFTs, affecting their performance and power consumption.
Innovation Solution
An active matrix substrate with a stacked oxide semiconductor layer structure, where the first TFT has a higher threshold voltage than the second TFT, achieved by varying the composition and number of semiconductor layers, and using a Cu-containing electrode structure to minimize Cu dispersion, ensuring stable characteristics for both types of TFTs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-layer oxide semiconductor structure is used for both circuit TFT and pixel TFT, then the manufacturing process is simplified, but the threshold voltages cannot be differentiated and characteristics become unstable due to metal dispersion
Solution Approach 1:
The oxide semiconductor layer is segmented into multiple sub-layers (first oxide semiconductor layer, second oxide semiconductor layer, and third oxide semiconductor layer) with different compositions and thicknesses. This segmentation allows different regions of the semiconductor layer to serve different functions: the first layer provides high mobility for pixel TFTs, the second layer suppresses metal dispersion, and the third layer enables threshold voltage differentiation, thereby resolving the contradiction between manufacturing simplicity and characteristic stability.
Solution Approach 2:
The patent employs composite oxide semiconductor structures where different oxide semiconductor materials (such as In-Ga-Zn-O, In-Zn-O, Ga-Zn-O) are combined in a stacked configuration. Each material layer contributes different properties: high electron mobility, metal dispersion resistance, and threshold voltage control. This composite approach maintains manufacturing feasibility while achieving stable and differentiated TFT characteristics.
2Productivity
If the same oxide semiconductor layer is used for both circuit TFT and pixel TFT, then production is simplified, but power consumption increases and performance is compromised due to inability to differentiate threshold voltages
Solution Approach 1:
The patent applies local quality by creating regions with different oxide semiconductor compositions within the same device structure. The first oxide semiconductor layer has specific composition ratios optimized for high mobility in pixel TFTs, while the second and third layers have compositions optimized for threshold voltage control in circuit TFTs. This local differentiation allows each TFT type to operate at optimal performance and power efficiency while maintaining a unified manufacturing process.
Data Source
AI summary
An active matrix substrate includes a first TFT (10), a second TFT (20) disposed per pixel, and a circuit including the first TFT. The first and second TFTs each include a gate electrode (102A, 102B), a gate insulating layer (103), an oxide semiconductor layer (104A, 104B), and source and drain electrodes in contact with an upper surface of the oxide semiconductor layer. The oxide semiconductor layer (104A, 104B) has a stacked structure including a first semiconductor layer (104e, 104c) in contact with the source and drain electrodes and a second semiconductor layer that is disposed on a substrate-side of the first semiconductor layer and that has a smaller energy gap than the first semiconductor layer. The oxide semiconductor layers (104A) and (104B) are different from each other in terms of the composition and/or the number of stacked layers. The first TFT has a larger threshold voltage than the second TFT.