Flip-Chip LED Reflective Layer Design
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Solution Overview
Problem
Flip-chip LEDs face challenges in luminance due to the limitations of metallic silver mirrors, which are prone to migration and cannot be disposed between N-type and P-type electrodes, restricting light emission efficiency.
Innovation Solution
Incorporating a distributed Bragg reflector on the P-type layer to enhance reflectance and isolate the N-type and P-type layers, combined with an anti-diffusion layer to prevent silver mirror migration, and using a silver reflective layer fully covered by the anti-diffusion layer to improve light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If metallic silver is used as a reflective layer, then light reflection is enhanced, but the silver mirror is prone to migration and instability
Solution Approach 1:
An anti-diffusion layer is introduced as an intermediary between the silver reflective layer and the surrounding environment. This mediator prevents direct contact between the silver and potential contaminants or moisture, thereby preventing migration while preserving the reflective properties of the silver layer.
Solution Approach 2:
The reflective structure is transformed from a single material (metallic silver) to a composite structure consisting of multiple layers including the silver reflective layer and the anti-diffusion protective layer. This composite approach combines the high reflectivity of silver with the protective properties of the anti-diffusion layer, simultaneously achieving both light reflection enhancement and stability.
2Reliability
If the silver mirror is fully covered by anti-diffusion layer, then migration is prevented, but the manufacturing complexity increases
Solution Approach 1:
The thickness and material composition of the anti-diffusion layer are optimized to achieve the minimum required protection while maintaining manufacturing feasibility. By carefully controlling the layer parameters, the patent prevents migration without excessively complicating the manufacturing process.
3Illumination intensity
If distributed Bragg reflector is added to increase reflectance, then luminance is improved, but the device structure becomes more complex
Solution Approach 1:
The distributed Bragg reflector utilizes optical interference effects in a multi-layer structure to achieve enhanced reflectance. By adding layers with alternating refractive indices, the system exploits the dimensional aspect of light wave interference to improve luminance without requiring significant lateral expansion or complex mechanical structures.
4Ease of operation
If silver mirror is disposed on P-type gallium nitride surface, then electrodeless light blocking is achieved, but the silver cannot be disposed between N-type electrode and PN junction
Solution Approach 1:
The silver reflective layer is strategically positioned only on the P-type gallium nitride surface where electrodeless light blocking is needed, rather than attempting to place it in other locations. This localized approach maintains the beneficial electrodeless light blocking property while avoiding the technical constraints of other positioning options.
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
The solution significantly increases the luminance of flip-chip LEDs by enhancing the reflective surface area and ensuring the stability of the silver mirror, thereby improving the reliability and light emission efficiency.
Implementation Method 1
the at least one distributed Bragg reflector is formed on the P-type layer to improve the reflectance of a non-covered area of a P-type layer of the flip-chip
Implementation Method 2
the current popular flip-chip LED in the market utilizes high-reflection metallic silver as a silver mirror to achieve light reflection
Data Source
AI summary
A flip-chip of light emitting diode includes at least one reflective layer, at least one N-type electrode, at least one P-type electrode, at least one distributed Bragg reflector, and an epitaxial unit. The epitaxial unit includes a substrate, an N-type layer, an active layer, and a P-type layer, wherein the substrate, the N-type layer, the active layer, and the P-type are sequentially stacked. The epitaxial unit has at least one N-type layer exposed portion, which is extended from the outer side surface of the P-type layer to the N-type layer via the active layer. The at least one reflective layer is formed on the P-type layer, wherein the at least one distributed Bragg reflector is integrally bonded to the N-type layer, the active layer, the P-type layer, and the at least one reflective layer. The at least one N-type electrode is electrically connected with the N-type layer and the at least one P-type electrode is electrically connected with the P-type layer.