Oxide Semiconductor TFT Aperture Ratio in LCDs
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Solution Overview
Problem
Liquid crystal display devices face challenges in achieving a high aperture ratio, especially in higher resolution displays like 3D or 4K2K, due to the limitations of thin film transistors made from amorphous silicon and the complexity of using crystalline silicon, which affects the field effect mobility and suitability for larger substrates.
Innovation Solution
The use of an oxide semiconductor layer in thin film transistors, extended beyond the edge of the wiring region and overlapping with pixel electrodes, enhances the aperture ratio by reducing the area occupied by non-light-transmitting components and improving field effect mobility, allowing for higher definition displays without reducing the display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a thin film transistor is manufactured using amorphous silicon, then it can be formed over a larger glass substrate, but the field effect mobility is low
Solution Approach 1:
The patent changes the material parameter from amorphous silicon to oxide semiconductor, which fundamentally alters the electrical properties and enables high field effect mobility while maintaining compatibility with large substrate manufacturing processes
Solution Approach 2:
The patent employs a composite structure combining oxide semiconductor layer with gate insulating film and electrode layers, creating a thin film transistor that achieves both high mobility and manufacturing feasibility on large substrates
2Reliability
If a thin film transistor is manufactured using crystalline silicon, then the field effect mobility is high, but it needs a crystallization step such as laser annealing and is not always suitable for a larger glass substrate
Solution Approach 1:
The patent changes the material phase from crystalline silicon to oxide semiconductor, eliminating the need for high-temperature crystallization steps like laser annealing while maintaining high field effect mobility and enabling direct deposition on large glass substrates
Solution Approach 2:
The patent replaces the mechanical/thermal crystallization process with a deposition-based oxide semiconductor formation process, substituting complex thermal treatment with simpler film deposition techniques suitable for large substrate manufacturing
3Measurement precision
If the area per pixel is decreased for higher resolution displays, then the definition is improved, but the aperture ratio decreases
Solution Approach 1:
The patent changes the transistor material to oxide semiconductor, which enables smaller transistor area for the same driving capability, thereby allowing higher pixel density without sacrificing aperture ratio
Solution Approach 2:
The patent segments the transistor structure into distinct functional layers (gate insulating film, oxide semiconductor layer, electrode layers), allowing optimized spatial arrangement that minimizes the area occupied by non-light-transmitting components
Data Source
AI summary
An object is to provide a liquid crystal display device in which a pixel including a thin film transistor using an oxide semiconductor has a high aperture ratio. The liquid crystal display device includes a plurality of pixels each including a thin film transistor and a pixel electrode. The pixel is electrically connected to a first wiring functioning as a scan line. The thin film transistor includes an oxide semiconductor layer over the first wiring with a gate insulating film therebetween. The oxide semiconductor layer is extended beyond the edge of a region where the first wiring is provided. The pixel electrode and the oxide semiconductor layer overlap with each other.