Transparent-Substrate LED Array With Current-Spreading Layer
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Solution Overview
Problem
In LED assemblies used in virtual and augmented reality systems, current crowding occurs due to uneven current distribution from n-contacts to LEDs located far from these contacts, leading to significant voltage differences between edge and center LEDs, which is undesirable for both backplanes and integration.
Innovation Solution
A current spreading layer made of conductive material, such as indium tin oxide (ITO), is formed on the substrate surface to reduce voltage differences by evenly distributing current across the LED array, potentially patterned or with openings for improved light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current flows from n-contacts through substrate to LEDs, then LEDs can be driven to emit light, but current crowding occurs and voltage difference increases between close and far LEDs
Solution Approach 1:
A current spreading layer made of conductive material (e.g., ITO, graphene, metal) is introduced as an intermediary between the n-contacts and the LEDs. This layer acts as a mediator to redistribute current laterally across the substrate, ensuring uniform current density to all LEDs regardless of their distance from the n-contacts, thereby reducing voltage differences and improving power efficiency
Solution Approach 2:
The current spreading layer extends the current distribution path from a vertical dimension (direct substrate conduction) to a two-dimensional lateral distribution network. By creating a conductive plane that spans across the substrate surface, the system transforms point-source current injection into areal current distribution, eliminating distance-dependent voltage drops
2Reliability
If current spreading layer is formed as continuous layer, then current distribution is improved, but light extraction may be reduced
Solution Approach 1:
The current spreading layer is segmented into multiple discrete conductive traces or patterns instead of a continuous film. These segmented conductors are strategically positioned to deliver current to different LED regions, maintaining effective current distribution while creating optical pathways between segments that allow light to escape without being blocked by a continuous conductive layer
Solution Approach 2:
The current spreading layer exhibits spatially varying properties: in regions where current distribution is critical, the layer is more dense or conductive; in regions where light extraction is prioritized, the layer is thinner, patterned, or absent. This local optimization allows simultaneous achievement of uniform current delivery and high light extraction efficiency
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 conductive layer effectively reduces voltage differences between LEDs, improving operational efficiency and reducing power consumption by ensuring consistent current flow, while also enhancing light extraction and maintaining a compact LED array design.
Implementation Method 1
a current spreading layer having a conductive material (e.g., a conductive oxide) may be formed on a surface of the substrate of the LED assembly, in order to spread current more evenly through the LED assembly
Data Source
AI summary
In a flip-chip LED assembly having an array of LEDs formed on the same substrate, different LEDs of the array have different distances to the n-contacts of the assembly. This may cause current crowding as current has to spread from the n-contacts through the substrate to each the farthest LEDs of the LED array, requiring LEDs that are farther away to be driven with a higher voltage in order to receive a desired amount of current. To spread current more evenly through the LED assembly and reduce a voltage difference between the closest and farthest LEDs of the array, a current spreading layer having a conductive material (e.g., a conductive oxide) is formed on a surface of the substrate of the LED assembly. The current spreading layer may be a bulk layer or be patterned to increase light extraction from the LEDs of the array.