Bottom-Gate TFT Pixel Structure for OLED Aperture Ratio
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Solution Overview
Problem
Conventional active matrix organic electroluminescent devices face issues such as current leakage due to sunlight exposure, cleaning process defects, and reduced aperture ratio due to storage capacitor and power line occupation, which affect the stability and efficiency of OLED displays.
Innovation Solution
The system incorporates a switching thin film transistor with a first conductive layer acting as a floating gate and light-shielding layer, and a driving thin film transistor with a bottom gate configuration, along with a multilayer storage capacitor design that reduces pixel area occupation, enhancing current control and aperture ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If top gate thin film transistors are used for switching transistor, then device size is reduced and fabrication is simplified, but cleaning process sensitivity increases causing mura defects
Solution Approach 1:
The patent inverts the conventional top-gate transistor structure to a bottom-gate structure for the switching transistor. This inversion places the gate electrode at the bottom instead of the top, which fundamentally changes the device characteristics and makes the switching transistor less sensitive to cleaning process variations, thereby eliminating mura defects while maintaining simple fabrication.
2Ease of operation
If top gate thin film transistors are exposed to sunlight, then device operation is maintained, but current leakage occurs in the channel region
Solution Approach 1:
By inverting the gate structure from top-gate to bottom-gate configuration, the patent changes the electrical characteristics of the switching transistor. The bottom-gate structure provides better current control in the channel region, preventing leakage currents even when exposed to sunlight, thereby improving operational reliability.
3Adaptability or versatility
If storage capacitor and power line are included in pixel structure, then device functionality is complete, but aperture ratio is reduced
Solution Approach 1:
The patent merges the storage capacitor into the pixel structure in a space-efficient manner, and integrates the power line function into the bottom-gate structure of the switching transistor. This combining of functions reduces the overall area occupied by supporting structures, thereby increasing the aperture ratio while maintaining complete device functionality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration improves current leakage resistance, prevents cleaning defects, and increases the aperture ratio of the pixel structure, leading to more stable and efficient OLED display performance.
Implementation Method 1
a first conductive layer disposed under the channel layer... serving as a floating gate and light-shielding layer
Data Source
AI summary
An exemplary embodiment of a system comprises an active matrix organic electroluminescent device, having a substrate, and a plurality of scan lines and data lines disposed on the substrate, for defining a plurality of pixel regions. Each pixel structure comprises: a switching thin film transistor, a driving thin film transistor, and a storage capacitor. The switching TFT has a light-shielding layer adapted for preventing the sunlight from being incident into the switching TFT. The driving TFT is a bottom gate thin film transistor and have advantages of precisely controlling the current provided to the organic electroluminescent diode. Further, since the storage capacitor has a multilayer structure and occupies a reduced pixel area, the aperture ratio of the pixel structure can be increased.