Patterned Metal Shunting Layer for LED Light Extraction
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Solution Overview
Problem
Conventional LED shunting designs face a tradeoff between minimizing current crowding and light blockage, with high contact resistance at the interface of metal shunting strips and current spreading layers, leading to non-uniform current distribution and light extraction issues.
Innovation Solution
A patterned metal shunting layer comprising an array of circular or polygonal dots with diameters between 2Lt and 10Lt, interconnected by thin metal connectors, reduces contact resistance and light blockage, ensuring uniform current distribution and efficient light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If narrow metal shunting strips are used to minimize light blockage, then light extraction is improved, but contact resistance increases
Solution Approach 1:
The shunting layer is segmented into multiple discrete metal dots arranged in a pattern rather than continuous strips. This segmentation allows each dot to have sufficient width for low contact resistance while the overall pattern maintains low light blockage by optimizing the number, size, and spacing of individual dots.
Solution Approach 2:
The metal dots are strategically positioned and sized to provide locally optimized electrical contact properties at the interface with the current spreading layer, while the overall distribution pattern ensures minimal impact on light extraction. Each dot's dimensions are tuned to balance contact resistance and light blockage locally.
2Reliability
If wide metal shunting strips are used to reduce contact resistance, then current distribution uniformity is improved, but light blockage increases
Solution Approach 1:
Instead of using wide continuous strips that block light, the shunting function is achieved through multiple segmented metal dots. The collective effect of many smaller dots provides sufficient current distribution uniformity without the light blockage penalty of wide continuous strips.
Solution Approach 2:
The shunting structure transitions from two-dimensional continuous strips to a pattern of discrete dots, effectively using the third dimension (vertical stacking of current paths through multiple dots) to achieve low contact resistance without increasing the planar footprint that blocks light.
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 achieves lower overall contact resistance and reduced light blockage, improving the efficiency of LED light emission by maintaining uniform current distribution and maximizing light extraction without increasing contact resistance.
Implementation Method 1
a low-resistance metal shunting layer 32 is patterned to extend across the current spreading layer 28
Implementation Method 2
The top surface of the LED die 10 is roughened to increase light extraction
Data Source
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AI summary
A shunting pattern on a surface of an LED die comprises an array of metal dots having widths that are on the order of 2Lt-5Lt (where Lt is transfer length) so as not to block a significant amount of light, yet have low contact resistance to the semiconductor current spreading layer. Contact resistance is not significantly reduced with widths greater than 2Lt. Each dot represents a current injection area. For a minimum 2Lt width and 50 square dots per mm2, the top surface area of an LED die will have about 1% of its surface covered by the dots. To cause the current to be evenly distributed over the top surface of the LED, the dots are connected with a grid of very thin metal connectors, having widths much less than 2Lt. In one embodiment, a wire bond electrode is formed near the middle of the top surface of the LED to create a more uniform current distribution.