LED Contact Structures Using Plating for Metal Reduction
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Solution Overview
Problem
Conventional deposition processes for forming contact layers in light emitting devices result in excessive metal consumption and reduced light output due to metal deposition on secondary surfaces and areas that do not contribute to light emission, necessitating additional reclamation processes.
Innovation Solution
A plating process using a bi-layer mask structure and a seed layer sandwiched between two resist layers, where the seed layer is only exposed in desired areas for plating, allowing for precise deposition of a conductive contact layer that is smoother and more reflective than traditional methods, reducing metal consumption by over 90% and enhancing light output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If conventional deposition processes are used to form contact layers, then complete coverage is achieved, but metal consumption increases and light output decreases
Solution Approach 1:
The patent applies local quality by making the contact layer's surface properties non-uniform: the top surface is smooth and reflective for light emission, while the bottom surface conforms to the rough substrate topology for good electrical contact. This is achieved through conformal deposition followed by selective planarization, allowing different regions of the contact layer to serve different functions - electrical conduction at the interface and light reflection at the top surface.
Solution Approach 2:
The contact layer formation is segmented into multiple stages: first forming a conformal layer that follows the substrate topology, then selectively removing or planarizing portions to create a smooth top surface. This segmentation allows the contact structure to achieve both complete coverage for electrical contact and smooth surfaces for light emission, resolving the contradiction between coverage and precision.
2Illumination intensity
If metal is deposited on all surfaces including secondary surfaces, then complete coverage is achieved, but light output is reduced due to metal blocking light emission areas
Solution Approach 1:
The contact layer is designed with spatially varying properties: it maintains full coverage and conforms to the rough substrate surface in areas where electrical contact is needed, while having a smooth, planar top surface in areas where light emission occurs. This local differentiation allows the same structure to fulfill both electrical and optical functions without compromise.
Solution Approach 2:
The patent performs preliminary planarization or selective removal of the contact layer before final device assembly, creating a smooth top surface in advance. This preliminary action ensures that when the device is complete, the light emission areas are already optimized for light output, preventing the need for later reclamation processes and reducing metal in light paths.
3Productivity
If conventional deposition is used, then simple process is maintained, but additional reclamation processes are required
Solution Approach 1:
The patent performs the planarization or selective removal of metal layers as a preliminary action during the fabrication process, before final device assembly and testing. By addressing the surface topology issue early in the process flow, the need for subsequent reclamation processes is eliminated, streamlining the overall fabrication sequence and improving productivity.
Solution Approach 2:
The patent extracts or removes the problematic rough surface topology from the light emission areas through selective planarization or removal of the contact layer in specific regions. This extraction of the unwanted surface feature eliminates the need for later reclamation processes, as the smooth surface is built-in from the start rather than requiring subsequent correction.
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 reduces metal consumption and improves light output by ensuring the contact layer is only deposited on necessary areas, resulting in a smoother, more reflective surface that enhances light emission and eliminates the need for reclamation processes.
Implementation Method 1
a surface of the plated contact layer may have a greater reflectivity with respect to the light emission than that of the seed layer
Implementation Method 2
an electrically conductive contact structure including at least one plated layer on the surface
Data Source
AI summary
A light emitting device includes an active layer configured to provide light emission due to carrier recombination therein, a surface on the active layer, and an electrically conductive contact structure on the surface. The contact structure includes at least one plated contact layer. The contact structure may include a sublayer that conforms to the surface roughness of the underlying surface, and the plated contact layer may be substantially free of the surface roughness of the underlying surface. The surface of the plated contact layer may be substantially planar and/or otherwise configured to reflect the light emission from the active layer. Related fabrication methods are also discussed.