Dual-Gate Oxide TFT Display Structure for Threshold Stability
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Solution Overview
Problem
The existing display apparatus using oxide semiconductor layers for thin film transistors is sensitive to threshold voltage changes, leading to current variation issues and defects in low gray level regions due to complex processing requirements and sensitivity to chemical gases, affecting image quality and reliability.
Innovation Solution
A display apparatus is designed with a substrate having multiple oxide semiconductor layers and insulating layers, including a dual-gate structure for transistors to reduce current variation and improve performance by controlling the capacitance between the semiconductor layers and gate electrodes, using inorganic insulating layers that do not contain hydrogen to enhance reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin film transistor using an oxide semiconductor layer is used, then leakage current blocking is improved, but threshold voltage change sensitivity increases causing current variation and image defects
Solution Approach 1:
The patent changes the material parameter of the insulating layer from hydrogen-containing to hydrogen-free (or hydrogen-deficient) materials. This parameter change reduces the sensitivity of the oxide semiconductor transistor to threshold voltage shifts, thereby stabilizing current characteristics and preventing image defects while maintaining low leakage current properties
Solution Approach 2:
The patent introduces an intermediary solution by using a dual-gate transistor structure where the second gate can compensate for threshold voltage variations. The insulating layer acts as a mediator that reduces the direct harmful interaction between chemical gases and the oxide semiconductor, thereby stabilizing the transistor operation
2Reliability
If separate processes are used for forming polycrystalline semiconductor layer and oxide semiconductor layer, then transistor performance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent merges the formation processes of different semiconductor layers by using a unified oxide semiconductor layer that can serve multiple transistor types (first, second, and third transistors). This combining approach maintains the performance benefits of oxide semiconductors while simplifying the manufacturing process by eliminating separate processing steps for different semiconductor materials
3Measurement precision
If oxide semiconductor layer is used, then current control precision is improved, but current variation due to current stress increases
Solution Approach 1:
The patent changes the environmental parameter by eliminating hydrogen-containing insulating layers, which reduces the sensitivity of oxide semiconductor transistors to current stress. This parameter change stabilizes the threshold voltage and reduces current variation, thereby improving current stability while maintaining precise current control capability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces current variation and improves the uniformity of initial luminance, addressing the sensitivity to threshold voltage changes and enhancing the display apparatus's performance and reliability by simplifying the manufacturing process and reducing defects in low gray level regions.
Implementation Method 1
a fourth insulating layer disposed on the third insulating layer, wherein the third insulating layer and the fourth insulating layer are inorganic insulating layers that do not include hydrogen
Data Source
AI summary
A display apparatus include a substrate including a display area and a non-display area, a first transistor including a first oxide semiconductor layer on the substrate, a first insulating layer on the first oxide semiconductor layer and a first gate electrode on the first insulating layer, a second transistor including a second oxide semiconductor layer on the substrate, a second gate electrode on the first insulating layer and a second insulating layer on the second gate electrode, and a third transistor including a third oxide semiconductor layer on the substrate and a third gate electrode on the second insulating layer.