LED Display Structures Eliminating Deep Etching
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Solution Overview
Problem
Conventional light emitting diode (LED) and micro-LED technologies face efficiency reduction as pixel sizes decrease, primarily due to surface damage from deep etching processes, which are necessary for electrical isolation, current spreading, and light extraction, but these processes introduce defects and limitations in scalability and light extraction efficiency.
Innovation Solution
The proposed solution involves a fabrication method that reduces or eliminates deep etching by using an active matrix addressing architecture, integrating light extraction features on unpatterned or minimally patterned structures, and placing a current spreading layer on the underside of the LED after separation from the substrate, allowing for efficient electrical isolation and improved light extraction without damaging the sensitive regions of the LED stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If deep etching processes are used for electrical isolation and light extraction, then light extraction efficiency is improved, but surface damage and defects increase reducing electroluminescence efficiency
Solution Approach 1:
The patent extracts the light extraction function from the deep etching process by placing microlens arrays on the backside of the LED after substrate removal. This separates the light extraction mechanism from the potentially damaging etching process, allowing efficient light extraction without compromising the electroluminescence efficiency of the LED structure.
Solution Approach 2:
Instead of etching the front surface or sidewalls of the LED for light extraction, the patent inverts the approach by placing light extraction features (microlens arrays) on the backside of the LED. This reverse engineering approach avoids damage to the sensitive electroluminescence regions while achieving superior light extraction.
2Reliability
If deep etching is performed to create isolated islands for electrical isolation, then charge conduction isolation is improved, but manufacturing complexity and process difficulty increase
Solution Approach 1:
The patent extracts the electrical isolation function from deep etching by removing the substrate entirely and forming isolation trenches in the released LED structure. This separates the isolation process from the sensitive LED growth process, simplifying fabrication while maintaining effective electrical isolation between adjacent LEDs.
Solution Approach 2:
The patent performs preliminary substrate removal before forming isolation structures. By removing the substrate first, the LED is released and can be easily patterned with isolation trenches using standard photolithography, avoiding the need for complex deep etching processes that would be required if isolation structures were formed during the growth phase.
3Area of moving object
If pixel size is reduced to increase display resolution, then device density is improved, but surface damage from etching increases reducing efficiency
Solution Approach 1:
The patent extracts all deep etching operations from the pixel fabrication process. By removing the substrate and placing light extraction features on the backside, the front surface of small pixels remains intact without etching damage, maintaining high electroluminescence efficiency even at reduced pixel sizes for high-resolution displays.
Solution Approach 2:
The patent moves light extraction functionality from the lateral dimensions (sidewall etching) to the vertical dimension (backside microlens arrays). This dimensional shift allows small pixels to maintain their integrity without lateral etching damage, enabling high-density pixel arrays with preserved efficiency.
Data Source
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AI summary
LED structures (e.g., LED arrays) and fabrication methods can reduce or even eliminate deep etching, and associated defect formation, proximate sites of individual LEDs. Such approaches can achieve desired electrical isolation without deep etching, provide a high conductivity current spreading layer, and, or reduce losses otherwise associated with conventional fabrication approaches. Some implementations advantageously lift off or separate an insulating substrate from a wafer to expose a bottom surface of the epitaxial LED layer and forms a backside contact (e.g., ground plane) overlying the bottom surface. Other implementations isolate deep etching away from sensitive regions and locate the backside contact on a top surface of the epitaxial LED layer. Some implementations form light extraction features (e.g., photonic crystals) on the exposed bottom surface. The top surface of the epitaxial LED layer may be un-doped to improve electrical isolation. The bottom surface of may be shallow etched to improve light extraction.