Oxide Semiconductor Transistor Insulation for Moisture Resistance
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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 interlayer insulating film structure to prevent 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 an oxide semiconductor for a semiconductor layer is used to achieve higher field-effect mobility and high-speed operation, then the transistor can operate at high speed and be suitable for integrated driver circuits, but entry of impurities such as hydrogen or moisture into the oxide semiconductor generates carriers and changes electrical characteristics of the transistor
Solution Approach 1:
The patent applies the inert atmosphere principle by providing a protective insulating film comprising a first insulating film and a second insulating film with lower hydrogen concentration. This creates a barrier that prevents hydrogen and moisture from entering the oxide semiconductor layer, thereby maintaining the transistor's electrical characteristics stability while preserving its high field-effect mobility properties
Solution Approach 2:
The patent uses a composite insulating film structure consisting of two different insulating films with complementary properties. The first insulating film provides primary protection, while the second insulating film with lower hydrogen concentration provides enhanced protection against hydrogen ingress. This composite structure effectively prevents impurity entry while maintaining the transistor's high-speed performance
2Device complexity
If transistors are integrated in both pixel region and driver circuit region to reduce frame width and cost, then the display device structure is simplified and cost is reduced, but the transistor used for driver circuit region experiences larger electrical load and requires better electrical characteristics
Solution Approach 1:
The patent applies local quality by providing the protective insulating film structure specifically over the transistor in the driver circuit region where higher electrical characteristics are required. The protective film comprises a first insulating film and a second insulating film with lower hydrogen concentration, creating a localized protection zone that ensures stable electrical characteristics for driver circuit transistors under larger electrical loads
3Ease of manufacture
If manufacturing steps of transistor using oxide semiconductor are used to achieve easier manufacturing compared to polycrystalline silicon, then manufacturing complexity is reduced, but hydrogen or moisture entry into oxide semiconductor during manufacturing changes electrical characteristics
Solution Approach 1:
The patent applies preliminary action by forming the protective insulating film structure before completing the transistor manufacturing process. The protective film comprising the first insulating film and the second insulating film with lower hydrogen concentration is prepared in advance to prevent hydrogen and moisture entry during subsequent manufacturing steps, thereby ensuring electrical characteristics control while maintaining ease of manufacture
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.