Oxide Semiconductor Driving Transistor for Display Uniformity
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Solution Overview
Problem
Current light emitting display apparatuses face challenges in achieving uniform picture quality due to threshold voltage deviations in driving transistors, which affect current flow and gradation, especially as resolution increases in mobile and virtual image display applications.
Innovation Solution
The implementation of an oxide-based driving transistor in a bottom gate mode with a back channel etch (BCE) process, minimizing mask processes and layout area, and optimizing subthreshold swing factor (S-factor) to enhance turn-on and off-current characteristics, thereby improving pixel circuit performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a general driving transistor is used in light emitting display apparatus, then the device can be manufactured with standard processes, but threshold voltage deviation causes non-uniform picture quality and poor gradation
Solution Approach 1:
The patent changes the material parameter of the driving transistor from conventional semiconductor to oxide semiconductor, which fundamentally alters the electrical characteristics to achieve low threshold voltage deviation and excellent off-current characteristics, thereby improving picture quality uniformity
Solution Approach 2:
The patent employs a composite structure combining oxide semiconductor layer with conventional semiconductor layers in a dual-layer configuration, where the oxide semiconductor provides stable electrical characteristics for the driving transistor while conventional semiconductor handles high-speed switching functions
2Measurement precision
If resolution is increased in light emitting display apparatus, then picture quality is improved, but threshold voltage deviation and gradation problems become more severe
Solution Approach 1:
By changing to oxide semiconductor material, the patent achieves extremely low threshold voltage deviation that remains stable even as pixel size decreases for higher resolution displays, enabling fine gradation control at high resolutions
Solution Approach 2:
The patent uses oxide semiconductor which can be formed through low-temperature processes, making it suitable for flexible substrates and high-resolution displays where conventional high-temperature processed semiconductors would be impractical
3Ease of manufacture
If mask processes are minimized in transistor fabrication, then manufacturing complexity is reduced, but transistor performance may be compromised
Solution Approach 1:
The patent combines the gate electrode formation with the source and drain electrode formation into a single mask process step, where the gate electrode serves dual purposes as both the transistor gate and one electrode of the storage capacitor, thereby reducing mask processes while maintaining performance
Solution Approach 2:
The gate electrode of the driving transistor is designed to simultaneously function as an electrode for the storage capacitor, making it a multi-functional component that reduces overall device complexity and manufacturing steps
4Area of stationary object
If layout area of pixel circuit is minimized, then resolution can be increased, but transistor characteristics may deteriorate
Solution Approach 1:
The patent utilizes a dual-layer circuit structure where the first circuit layer contains transistors with gate electrodes on the substrate, and the second circuit layer contains transistors with gate electrodes on the first circuit layer, enabling three-dimensional integration that reduces planar area while maintaining transistor performance
Solution Approach 2:
The patent implements a nested arrangement where the storage capacitor is formed using the gate electrode of the driving transistor as one electrode, and the source electrode of the driving transistor as the other electrode, nesting functional elements within each other to minimize area
Data Source
AI summary
A display apparatus can include a first transistor disposed on a substrate, the first transistor including a first active layer made of low temperature polycrystalline silicon (LTPS); a circuit insulating layer disposed on the first transistor; a second transistor disposed on the circuit insulating layer, the second transistor including a second active layer made of an oxide semiconductor; a driving transistor disposed on the circuit insulating layer, the driving transistor having a back channel etch structure (BCE) and an active layer made of the oxide semiconductor; and a light emitting diode electrically connected to the driving transistor, in which the circuit insulating layer is disposed between the first transistor and the driving and second transistors.