LED Fabrication Using AAO Shadow Masks for Light Extraction
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Solution Overview
Problem
Current methods for fabricating light emitting diodes (LEDs) face challenges in enhancing light efficiency due to light loss within the device, particularly due to total reflection at the interface between the active layer and the substrate, and the complexity of forming patterns on substrates using conventional mask techniques, which limits productivity and versatility.
Innovation Solution
The use of an anodic aluminum oxide (AAO) layer with a large number of holes as a shadow mask to form patterns on substrates, allowing for the etching of semiconductor layers and creation of scattering centers that reduce light loss by increasing the amount of light emitted externally, while simplifying the fabrication process and improving electrode pad formation in vertical LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional photolithography methods are used to form patterns on substrates, then pattern formation is achieved, but the fabrication process becomes complex and productivity decreases
Solution Approach 1:
The patent extracts the pattern formation function from the complex photolithography process by using AAO layers with pre-formed hole patterns as direct shadow masks. This eliminates multiple photolithography steps (photoresist coating, exposure, development, etching) and replaces them with a single anodization process that directly creates the desired patterns on metal layers, thereby simplifying the fabrication process and improving productivity while maintaining pattern precision
Solution Approach 2:
The patent applies preliminary action by pre-forming the AAO layer with controlled hole patterns through anodization before the actual pattern transfer to semiconductor layers. The AAO layer serves as a pre-prepared shadow mask that defines the final pattern geometry, allowing subsequent etching processes to directly replicate these pre-determined patterns without requiring complex in-situ pattern formation steps
2Use of energy by moving object
If light is emitted at angles greater than the critical angle at the interface between active layer and substrate, then light generation occurs, but total reflection confines the light inside the LED reducing light efficiency
Solution Approach 1:
The patent applies local quality by creating localized patterned structures (scattering centers or extraction gratings) at specific locations within the LED device - either on the substrate surface or within the active layer. These localized structures have different optical properties than the surrounding areas, creating regions that specifically address light extraction at critical angles while leaving other regions intact for their original functions, thereby reducing total reflection losses without compromising light generation efficiency
Solution Approach 2:
The patent addresses the two-dimensional light propagation problem by introducing vertical dimensionality through patterned structures that extend into the light path. The periodic or random patterns create additional light extraction pathways in the vertical dimension, allowing light that would normally be confined by total internal reflection at the planar interface to escape through the patterned structures, effectively adding a third dimension to light extraction geometry
3Manufacturing precision
If the semiconductor layer thickness is increased to accommodate large pattern sizes, then pattern formation is possible, but the semiconductor layer thickness becomes greater than necessary for light emitting function
Solution Approach 1:
The patent applies segmentation by dividing the pattern formation process into two independent stages: (1) forming the AAO shadow mask with the desired large pattern dimensions, and (2) transferring this pattern to the semiconductor layer through etching. This segmentation allows the pattern size to be determined by the AAO layer geometry rather than being constrained by semiconductor layer thickness, enabling large patterns to be formed on appropriately thin semiconductor layers without requiring excessive thickness accommodation
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 approach enhances light emitting efficiency by increasing the amount of light reflected and emitted externally, reduces the thickness of semiconductor layers, and simplifies the fabrication process, leading to higher productivity and the ability to form various pattern shapes, thus addressing the limitations of conventional methods.
Implementation Method 1
forming an anodic aluminum oxide (AAO) layer with a large number of holes by performing anodizing treatment of the aluminum layer
Data Source
AI summary
The present invention relates to a method of fabricating a patterned substrate for fabricating a light emitting diode (LED), the method including forming an aluminum layer on a substrate, forming an anodic aluminum oxide (AAO) layer having a large number of holes formed therein by performing an anodizing treatment of the aluminum layer, partially etching a surface of the substrate using the aluminum layer with the large number of the holes as a shadow mask, thereby forming patterns, and removing the aluminum layer from the substrate.