Oxide TFT Display Structure Against Moisture and Hydrogen Ingress
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Solution Overview
Problem
Display devices using oxide semiconductor transistors for both pixel and driver circuit regions face reliability issues due to moisture and hydrogen ingress, leading to changes in electrical characteristics, especially in high temperature and high humidity environments.
Innovation Solution
A display device structure is implemented where an oxide semiconductor film is used for the channel formation region of transistors, and a planarization film with an organic insulating material is used over the transistors, with a specific structure that prevents hydrogen or moisture from entering the oxide semiconductor film, particularly in the driver circuit region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a transistor using oxide semiconductor for semiconductor layer is used to integrate pixel transistor and driver circuit, then field-effect mobility is improved and manufacturing is simplified, but reliability deteriorates due to entry of impurities such as hydrogen or moisture
Solution Approach 1:
A barrier layer is introduced as an intermediary between the oxide semiconductor layer and the gate insulating film. This barrier layer specifically blocks hydrogen and moisture from entering the oxide semiconductor layer while allowing the transistor to maintain its high field-effect mobility characteristics. The barrier layer acts as a mediator that protects the oxide semiconductor from impurity contamination without affecting its electrical performance.
Solution Approach 2:
The harmful elements (hydrogen and moisture) are extracted or removed from the system by introducing a barrier layer that specifically blocks these impurities. The barrier layer takes out the problematic impurity entry pathway while preserving the beneficial high mobility characteristics of the oxide semiconductor transistor.
2Device complexity
If driver circuit is integrated with pixel transistor on the same substrate, then frame width and peripheral IC cost are reduced, but transistor reliability is compromised due to impurity entry
Solution Approach 1:
The barrier layer is selectively formed only in the driver circuit region where oxide semiconductor transistors are used, rather than uniformly across the entire display device. This local application provides targeted protection against impurity entry in the integrated driver circuit area while maintaining the simplified integrated structure. The barrier layer is positioned specifically where the oxide semiconductor layer is present in the driver circuit.
3Ease of manufacture
If oxide semiconductor film is used for channel formation region, then manufacturing steps are simplified compared to polycrystalline silicon, but electrical characteristics change due to impurity entry
Solution Approach 1:
The barrier layer is formed preliminarily before the oxide semiconductor layer is deposited. This preliminary action prevents hydrogen and moisture from entering the oxide semiconductor layer during subsequent manufacturing processes, ensuring that the electrical characteristics remain stable throughout production. The barrier layer is prepared in advance to protect the oxide semiconductor from impurity contamination.
Data Source
AI summary
The display device includes a first substrate provided with a driver circuit region that is located outside and adjacent to a pixel region and includes at least one second transistor which supplies a signal to the first transistor in each of the pixels in the pixel region, a second substrate facing the first substrate, a liquid crystal layer between the first substrate and the second substrate, a first interlayer insulating film including an inorganic insulating material over the first transistor and the second transistor, a second interlayer insulating film including an organic insulating material over the first interlayer insulating film, and a third interlayer insulating film including an inorganic insulating material over the second interlayer insulating film. The third interlayer insulating film is provided in part of an upper region of the pixel region, and has an edge portion on an inner side than the driver circuit region.