Diffusive Reflective Layer for LED Light Extraction
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Solution Overview
Problem
Current light-emitting devices face challenges in achieving high luminous efficiency due to the high cost and instability of reflective materials like Pt and Ag, which are prone to oxidation, and the inferior reflectivity of Al, leading to increased manufacturing costs and reduced performance over time.
Innovation Solution
A reflective surface sub-assembly using a diffusive reflective layer made from materials like titanium oxide, applied directly to the substrate without polishing, providing high total reflectivity with a significant portion as diffusive reflectivity, and utilizing screen-printing technology for cost-effective and stable application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If noble metals like Pt, Au, or Ag are used for reflective coating, then high reflectivity and luminous efficiency are achieved, but manufacturing cost increases significantly
Solution Approach 1:
The patent replaces expensive noble metals (Pt, Au, Ag) with inexpensive aluminum as the reflective coating material. Although aluminum oxidizes over time, the patent accepts this trade-off by using cost-effective materials, thereby significantly reducing manufacturing costs while maintaining adequate reflectivity for the application
Solution Approach 2:
The patent changes the surface morphology parameter of the aluminum coating from smooth to rough through controlled oxidation and surface treatment processes. This transformation converts specular reflection into diffuse reflection, which improves light extraction efficiency from the LED by redirecting trapped light modes, thereby maintaining luminous efficiency while using cheaper materials
2Ease of manufacture
If aluminum is used for reflective coating to reduce cost, then manufacturing cost decreases, but reflectivity and luminous efficiency are inferior
Solution Approach 1:
The patent transforms the surface morphology of aluminum from smooth to rough through controlled oxidation and surface treatment. This parameter change converts specular reflection into diffuse reflection, enabling the aluminum coating to extract trapped light modes more effectively and achieve luminous efficiency comparable to or exceeding noble metal coatings
Solution Approach 2:
The patent creates a composite reflective structure consisting of aluminum base material combined with an oxide layer (Al2O3) and surface roughness features. This composite structure provides both the cost advantage of aluminum and the enhanced light extraction performance needed to match or exceed noble metal reflectors
3Loss of energy
If Ag is used for superior reflectivity, then luminous efficiency improves, but oxidation and tarnishing occur leading to instability
Solution Approach 1:
The patent accepts the oxidation of aluminum as a acceptable trade-off, similar to how Ag oxidizes but at much lower cost. The aluminum oxide layer that forms is stable and adherent, providing long-term reliability without the tarnishing issues of silver, thereby achieving both cost reduction and stability
Solution Approach 2:
The patent converts the harmful effect of aluminum oxidation into a beneficial feature. The formed aluminum oxide layer provides diffuse reflection properties that enhance light extraction efficiency, transforming what was traditionally considered a degradation mechanism into a performance-enhancing feature
4Loss of energy
If polishing is applied to Al to increase reflectivity, then specular reflectivity improves, but manufacturing cost increases and diffusive reflectivity is not achieved
Solution Approach 1:
Instead of polishing to create smooth surfaces for specular reflection, the patent inverts the approach by intentionally creating rough surfaces through controlled oxidation and surface treatment. This inversion produces diffuse reflection, which is actually more effective for LED light extraction by redirecting trapped light modes, while avoiding expensive polishing processes
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 enhances luminous efficiency by 5 to 25% compared to noble metal-based coatings, reduces manufacturing costs, and provides improved stability and resistance to oxidation, while maintaining ease of application and non-oxidative surface properties.
Implementation Method 1
a diffusive reflective layer made from materials like titanium oxide, applied directly to the substrate without polishing, providing high total reflectivity with a significant portion as diffusive reflectivity
Data Source
AI summary
A reflective surface sub-assembly for a light-emitting device, comprising a substrate, at least one area reserved for placement of a light-emitting device assembly on the substrate, and a diffusive reflective layer applied on selected regions on the substrate, wherein if the light-emitting device assembly were placed onto the at least one area then the diffusive reflective layer would reflect photons emitted by the light-emitting device assembly is disclosed.