OLED Storage Capacitor Design for Aperture Ratio
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Solution Overview
Problem
Large-sized OLED displays face issues with voltage drop in front light emitting types due to high resistance materials and low aperture ratios in rear light emitting types, where circuit wires obstruct light emission.
Innovation Solution
The OLED display incorporates a storage capacitor with overlapping plates and a specific layer structure for the driving voltage line, reducing the occupied area and enhancing the aperture ratio by allowing a larger pixel opening.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the common electrode is made of transparent material in front light emitting type, then light emission is enabled, but voltage drop occurs due to high resistance
Solution Approach 1:
The patent inverts the light emitting direction from front emission to rear emission. The OLED display is configured to emit light from the rear side through the substrate, allowing the common electrode to be made of low-resistance opaque material while still achieving light emission through the substrate, thus resolving the contradiction between light emission and voltage stability.
2Reliability
If circuit wires are placed to not overlap pixel electrode in rear light emitting type, then voltage stability is improved, but aperture ratio becomes low due to wire obstruction
Solution Approach 1:
The patent moves the storage capacitor from the planar area to a vertical dimension by positioning it to overlap the driving voltage line in the cross-sectional view. This three-dimensional arrangement allows the capacitor to occupy space without blocking the light emission area, thus improving aperture ratio while maintaining voltage stability through proper wiring configuration.
3Area of moving object
If storage capacitor area is reduced, then aperture ratio is improved, but capacitor functionality may be compromised
Solution Approach 1:
The patent embeds the storage capacitor structure within the existing wiring and electrode layers. The capacitor plates are positioned to overlap the driving voltage line, utilizing the vertical space and existing structural elements to create the capacitor function without requiring additional planar area, thus maintaining both aperture ratio and capacitor 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 the aperture ratio by minimizing the storage capacitor's area, enabling a wider pixel opening and addressing the limitations of existing OLED display types.
Implementation Method 1
Electrons injected from one of the two electrodes (for example, the common electrode, or cathode) are combined with holes injected from the other of the two electrodes (for example, the pixel electrode, or anode) in the organic emission layer, thus forming excitons. The excitons emit light while radiating energy.
Data Source
AI summary
An organic light emitting diode (OLED) display is disclosed. The OLED display includes a substrate, a scan line on the substrate and configured to transfer a scan signal, a data line crossing the scan line and configured to transfer a data signal, a driving voltage line crossing the scan line or the data line and configured to transfer a driving voltage, a switching thin film transistor (TFT) connected to the scan line and the data line, a driving TFT connected to the switching TFT and the driving voltage line, an OLED connected to the driving TFT, and a storage capacitor connected to the driving voltage line and a driving gate electrode of the driving TFT. The storage capacitor includes a first storage capacitor plate that overlaps the driving voltage line.