Stacked TFT and White OLED for High Aperture Ratio
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Solution Overview
Problem
Active matrix organic light emitting displays (AMOLEDs) face challenges in increasing aperture ratio due to the presence of thin film transistors and capacitors, which decrease the display's efficiency and require innovative solutions to enhance display effect.
Innovation Solution
The implementation of a second thin film transistor and a white light emitting element on top of the first thin film transistor, along with a micro-cavity structure formed by reflective and transflective electrodes, increases the aperture ratio and improves display efficiency by converting non-display regions into display areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thin film transistors and capacitors are disposed in the pixel design, then the display can be driven by current, but the aperture ratio decreases
Solution Approach 1:
The patent stacks the second thin film transistor and second light emitting element vertically on top of the first thin film transistor, transitioning from a planar layout to a three-dimensional stacked architecture. This vertical arrangement allows the pixel circuit components to occupy the z-dimension rather than consuming lateral display area, thereby maintaining high aperture ratio while preserving current driving functionality.
Solution Approach 2:
The patent embeds the second thin film transistor and second light emitting element within the vertical structure of the first light emitting element assembly. The stacked configuration creates a nested arrangement where multiple functional layers are integrated vertically, allowing circuit components to be housed within the pixel structure without expanding the lateral footprint.
2Reliability
If metal climbing structure is used around the via hole, then the risk of short circuit is reduced, but the aperture ratio becomes low
Solution Approach 1:
The patent relocates the metal climbing structure from a lateral arrangement around the via hole to a vertical configuration extending along the z-axis. This vertical metal structure provides equivalent electrical isolation and short circuit prevention while occupying minimal lateral space, thereby maintaining high aperture ratio.
Solution Approach 2:
The patent concentrates the metal climbing structure specifically at critical isolation points where short circuit prevention is most needed, rather than using extensive lateral metal barriers. This localized vertical metal arrangement provides targeted protection while minimizing impact on the display area.
3Area of stationary object
If a second light emitting element emitting white light is disposed on the second thin film transistor, then the original non-display region becomes a display region, but the device structure becomes more complex
Solution Approach 1:
The stacked thin film transistors and light emitting elements share common structural components, such as the substrate, buffer layers, and encapsulation structures. This multi-functional integration allows the pixel to simultaneously achieve high aperture ratio, improved display effect, and maintained manufacturing feasibility through standardized process steps.
Solution Approach 2:
The patent resolves structural complexity by organizing multiple light emitting elements and transistors in the vertical dimension rather than spreading them laterally. This stacked architecture consolidates multiple functions into a compact vertical stack, reducing the overall device footprint and simplifying the lateral structure while expanding display area.
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 enhances the aperture ratio and display effect by increasing light extraction efficiency and brightness, achieving a higher PPI (Pixels Per Inch) of at least 1.5 times, thereby improving the overall display performance.
Implementation Method 1
one of the first electrode and the second electrode is a reflective layer, and the other is a transflective layer, so as to form a micro-cavity structure
Data Source
AI summary
An organic electroluminescent display device and a manufacturing method thereof are disclosed. The organic electroluminescent display device includes a substrate, a first thin film transistor disposed on the substrate, a second thin film transistor disposed on the first thin film transistor, a first light emitting element electrically connected with a drain of the first thin film transistor, wherein the first light emitting element comprises a first electrode, a first light emitting layer and a second electrode which are stacked, a second light emitting element electrically connected with a drain of the second thin film transistor, wherein the second light emitting element is disposed on the second thin film transistor and comprises a third electrode, a second light emitting layer and a fourth electrode, wherein the second light emitting element is configured to emit white light. By forming the second light emitting element on the second thin film transistor, an original non-display region of the organic electroluminescent display device becomes a display region, as a result, an aperture ratio of the organic electroluminescent display device is increased, and the display effect of the organic electroluminescent display device is improved.