Reflective Pixel Electrode Layout for Higher LED Out-Coupling
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Solution Overview
Problem
Display devices face challenges in preventing damage to pixel electrodes and improving out-coupling efficiency, particularly in light-emitting diode (LED) structures where light emission is affected by electrode design and material properties.
Innovation Solution
The display device incorporates a pixel electrode with a reflective electrode layer, an upper electrode layer in a polycrystalline phase, and a contact electrode of specific materials to ensure efficient light emission by aligning the contact electrode with light-emitting elements and using materials like polycrystalline ITO, ZnO, and copper to prevent light absorption and etching of the reflective electrode layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a contact electrode is disposed on a pixel electrode in a conventional display device, then electrical connection is established, but the contact electrode may absorb light and reduce out-coupling efficiency
Solution Approach 1:
The contact electrode is segmented into a first contact layer and a second contact layer with different materials and functions. The first contact layer (ITO or IZO) provides electrical connection with lower light absorption, while the second contact layer (Cu or Au) provides excellent electrical conductivity. This segmentation allows the device to achieve both reliable electrical connection and reduced light absorption by distributing these functions across different layers.
Solution Approach 2:
The patent changes the material parameters of the contact electrode by using transparent conducting oxide materials (ITO or IZO) instead of conventional metals. These materials have different optical and electrical properties - they maintain good electrical conductivity while having significantly reduced light absorption in the visible range, thereby improving out-coupling efficiency without sacrificing electrical connection reliability.
2Manufacturing precision
If an etching process is used to form contact electrodes, then precise patterning is achieved, but the reflective electrode layer may be damaged or etched
Solution Approach 1:
The upper electrode layer is formed in advance as a protective layer over the reflective electrode layer before the etching process. This preliminary action creates a barrier that prevents the etchant from directly contacting and damaging the reflective electrode layer, while still allowing precise patterning of the contact electrode to be achieved through the upper electrode layer.
Solution Approach 2:
The upper electrode layer acts as an intermediary between the etching process and the reflective electrode layer. It serves as a protective barrier that mediates the interaction between the etchant and the sensitive reflective layer, allowing the etching process to proceed with precise patterning without causing damage to the underlying reflective electrode structure.
3Productivity
If light-emitting elements are disposed close to each other to increase pixel density, then display resolution is improved, but light emission may be blocked or out-coupling efficiency reduced
Solution Approach 1:
The contact electrode structure is optimized with local quality by using different materials at different locations. The first contact layer uses transparent conducting oxide materials that are transparent to light, allowing light to pass through to the light-emitting elements below. The second contact layer uses highly conductive metals for electrical connection. This localized material optimization allows close spacing of light-emitting elements without light blocking, thereby increasing pixel density while maintaining light emission efficiency.
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 out-coupling efficiency by reflecting light upward and preventing absorption, while the polycrystalline upper electrode layer protects the reflective layer from etching, thereby improving the overall performance and longevity of the display device.
Implementation Method 1
each of the pixel electrodes may include a reflective electrode layer, and thus light emitted from light-emitting elements can be reflected upward
Implementation Method 2
the upper electrode layer is disposed on the reflective electrode layer and may be in a polycrystalline phase... the polycrystalline upper electrode layer protects the reflective layer from etching
Data Source
AI summary
A display device includes a pixel electrode disposed on a substrate and including a reflective electrode layer and an upper electrode layer, a contact electrode disposed on the pixel electrode, light-emitting elements disposed on the contact electrode and disposed perpendicular to the pixel electrode, a planarization layer disposed on the pixel electrode, the planarization layer filling a space between the light-emitting elements, and a common electrode disposed on the planarization layer and the light-emitting elements, and a size of the contact electrode is equal to a size of each of the light-emitting elements in a plan view, and the upper electrode layer is disposed on the reflective electrode layer and is in a polycrystalline phase.