Oxide TFT Through Hole Placement for Hydrogen Mitigation
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Solution Overview
Problem
The use of silicon nitride films in display devices emitting hydrogen can degrade the characteristics of oxide semiconductor TFTs, particularly when the channel length is short, leading to depletion of the TFTs, despite the essential moisture-blocking properties of SiN films.
Innovation Solution
The design involves forming specific through holes in the interlayer insulating films to connect the drain or source of TFTs, with carefully controlled distances and channel lengths to mitigate the influence of hydrogen emitted from SiN films, ensuring the channel length is either less than 4 μm when the distance between the through hole and the channel is less than 20 μm or 4 μm or more when the distance is 20 μm or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon nitride film is used to block moisture, then the moisture-blocking performance is improved, but hydrogen is emitted that degrades the oxide semiconductor TFT characteristics
Solution Approach 1:
A hydrogen barrier film is introduced as an intermediary layer between the silicon nitride film and the oxide semiconductor layer. This mediator prevents hydrogen emitted from the SiN film from reaching and degrading the oxide semiconductor, while allowing the SiN film to maintain its moisture-blocking function.
Solution Approach 2:
The protective film structure is segmented into multiple functional layers: a hydrogen barrier film specifically targeting hydrogen emission and a silicon nitride film targeting moisture blocking. This segmentation allows each layer to specialize in blocking one type of harmful substance without compromising the other.
2Productivity
If the channel length of TFT is shortened to improve device integration, then the productivity is improved, but the TFT becomes more sensitive to hydrogen emission and may be depleted
Solution Approach 1:
The hydrogen barrier film serves as a protective intermediary that enables the use of shorter channel lengths without compromising TFT stability. By blocking hydrogen from reaching the oxide semiconductor, the barrier film allows aggressive scaling while maintaining reliable operation.
3Area of stationary object
If the distance between through hole and channel is reduced to optimize layout, then the area is reduced, but hydrogen can more easily reach the channel causing depletion
Solution Approach 1:
The hydrogen barrier film acts as a mediator that decouples the distance relationship between through holes and channels. Even when through holes are positioned close to channels for area optimization, the barrier film prevents hydrogen from the SiN film from reaching the channel region.
Solution Approach 2:
The hydrogen barrier film provides localized protection specifically at the interface between the SiN film and the oxide semiconductor layer. This local quality enhancement针对性地 addresses the hydrogen emission problem without affecting other areas of the device.
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
This approach effectively suppresses the impact of hydrogen on the TFT characteristics, preventing depletion and maintaining reliable operation by optimizing the relationship between through hole placement and channel length.
Implementation Method 1
The SiN film formed by CVD emits hydrogen when it is baked
Implementation Method 2
If the hydrogen diffuses into the channel, the TFT is depleted
Implementation Method 3
the oxide semiconductor is reduced, consequently, the characteristics of the TFT changes
Data Source
AI summary
One embodiment of the invention is characterized as follows. A display device comprising: a display area including a plurality of pixels, each of the pixels has a first TFT and a second TFT, the first TFT and the second TFT comprise an oxide semiconductor, the first TFT and the second TFT are covered by an interlayer insulating film, a first through hole is formed in the in the interlayer insulating film to connect a drain of the first TFT, wherein a distance d1 between a center of the first through hole and an edge of a channel of the first TFT is shorter than a distance d2 between a center of the first through hole and an edge of a channel of the second TFT, a channel length of the first TFT is shorter than a channel length of the second TFT.