Oxide TFT-OLED Display Layout With Fewer Photomasks
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Solution Overview
Problem
The production of active matrix display devices is hindered by the need for multiple photomasks and the variability in crystallinity of polycrystalline silicon films, leading to deteriorated display quality and complex structure requirements for oxide semiconductor transistors, particularly in achieving precise carrier concentration control and integrating them with organic electroluminescence elements.
Innovation Solution
A transistor structure is developed with a dual gate oxide semiconductor layer, utilizing a multi-gradation photomask to reduce the number of photomasks needed, and incorporating a back gate to control carrier concentration, which includes a first and second gate electrode partially overlapping with insulating layers and transparent conductive layers to form a channel without offset regions, enhancing on-current and frequency characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple photomasks are used for producing oxide semiconductor transistors, then manufacturing precision can be improved, but device complexity and production cost increase
Solution Approach 1:
The patent combines multiple photomask functions into a single multi-gradation photomask that can form both the transistor active region pattern and the offset region pattern in one exposure step. This merging approach reduces the total number of photomasks from multiple separate masks to one integrated multi-gradation mask, thereby simplifying the manufacturing process while maintaining the ability to precisely control carrier concentration through the formed offset regions.
Solution Approach 2:
The patent segments the single photomask into different transmission rate regions (gradation regions) that correspond to different pattern formation requirements. The multi-gradation photomask contains first, second, and third transmission rate regions that selectively form different structures (offset regions, active regions, etc.) with different carrier concentrations, allowing precise control without needing multiple separate photomasks.
2Manufacturing precision
If offset regions are formed in oxide semiconductor transistors, then manufacturing precision improves, but device complexity increases due to additional structure requirements
Solution Approach 1:
The patent merges the formation of offset regions and active regions into a single photolithography step using a multi-gradation photomask. The offset regions are formed as integrated parts of the transistor structure during the same exposure and development process that creates the active region, eliminating the need for separate processing steps and reducing overall device complexity despite the added functional sophistication.
3Productivity
If polycrystalline silicon films are used, then productivity improves, but display quality deteriorates due to crystallinity variability
Solution Approach 1:
The patent changes the material parameter from polycrystalline silicon to oxide semiconductor, which fundamentally alters the semiconductor layer's properties. Oxide semiconductors can be deposited at lower temperatures and form more uniform films with consistent electrical characteristics, thereby improving display quality while maintaining the productivity benefits of thin-film deposition techniques.
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A display device includes a transistor includes an oxide semiconductor layer (112a), a first gate electrode (104a), a first insulating layer (106), and a transparent conductive layer (108a), and an organic EL element (130) includes a first electrode (146) being light-transmissive, and a second electrode (158), a light emitting layer (152), and an electron transfer layer (144). The first gate electrode including a region overlapping the oxide semiconductor layer, the first insulating layer provided between the first gate electrode and the oxide semiconductor layer, the transparent conductive layer provided between the first insulating layer and the oxide semiconductor layer, and at least including a region in contact with the oxide semiconductor layer, the first electrode including a region overlapping the second electrode, the light emitting layer and the electron transfer layer provided between the first electrode and the second electrode, the electron transfer layer provided between the first electrode and the light emitting layer, and the first electrode is continuous from the transparent conductive layer.