OLED Driving TFT Layout for Low-Gray Current Stability
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Solution Overview
Problem
Existing organic light emitting display devices using hybrid thin film transistors with polycrystalline and oxide semiconductor layers face process complexity due to separate formation requirements and high current fluctuation in polycrystalline semiconductor-based driving thin film transistors, leading to low grayscale expression and large current variation.
Innovation Solution
The display device incorporates a driving transistor with a first oxide semiconductor pattern and a switching transistor with a second oxide semiconductor pattern, featuring a first light blocking layer overlapped with the first oxide semiconductor pattern and a second light blocking layer with specific distance configurations, along with a storage capacitor design to stabilize current and reduce parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a polycrystalline semiconductor layer is used in the driving thin film transistor to achieve fast driving speed, then the driving speed is improved, but the current fluctuation rate increases and grayscale expression deteriorates
Solution Approach 1:
The patent changes the material parameter of the semiconductor layer from polycrystalline to oxide semiconductor, which fundamentally alters the electrical characteristics. This parameter change reduces the current fluctuation rate and improves grayscale expression while maintaining adequate driving speed for the application
2Adaptability or versatility
If hybrid thin film transistors with different semiconductor layers (polycrystalline and oxide semiconductor) are used, then the functional requirements are met, but the process complexity increases
Solution Approach 1:
The patent applies homogeneity by using oxide semiconductor material for all thin film transistors in the display device, including both driving and switching transistors. This eliminates the need for separate polycrystalline and oxide semiconductor fabrication processes, significantly reducing process complexity while maintaining the required functional performance through uniform material characteristics
Data Source
AI summary
The present invention relates to a hybrid organic light emitting display device including a driving thin film transistor having an oxide semiconductor pattern and a switching thin film transistor having an oxide semiconductor pattern or a polycrystalline semiconductor pattern in a driving device unit for driving a unit pixel, in which a light blocking layer below an active layer is electrically connected to a source electrode to form the driving thin film transistor with wide control range at low gradation and the light blocking layer is disposed as close as possible to the active layer to broaden the control range of the driving thin film transistor.