Nitride LED Substrate Removal for Thermal Dissipation
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Solution Overview
Problem
Nitride semiconductor light emitting diodes (LEDs) face challenges with heat transfer due to the use of sapphire substrates, which have low thermal conductivity, and existing methods for removing these substrates are inefficient, limiting the performance and efficiency of LED arrays used in high-power applications like vehicle lighting.
Innovation Solution
A method for manufacturing a light emitting device involves growing nitride semiconductor layers on a sapphire substrate, forming electrodes, and using laser lift-off to remove the substrate, followed by etching to create recessed portions and counter electrodes on a support substrate, allowing for improved heat dissipation and electrical separation of elements, enabling efficient serial connection of LED elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sapphire substrate is used for growth, then nitride semiconductor layers can be grown effectively, but thermal conductivity is poor leading to heat dissipation problems
Solution Approach 1:
The sapphire substrate is completely removed from the LED structure through laser lift-off and etching processes. This extraction eliminates the thermal bottleneck caused by sapphire's low thermal conductivity, allowing direct heat dissipation from the active layer to the underlying support substrate with high thermal conductivity, thereby resolving the heat dissipation problem while maintaining effective nitride semiconductor growth.
2Ease of manufacture
If sapphire substrate is removed by laser lift-off or polishing, then rear surface electrode can be formed, but the process is complex and time-consuming
Solution Approach 1:
The mechanical polishing process is replaced with a chemical etching process using selective etchants. This substitution allows for faster and more precise substrate removal with better control over the etching depth and profile, reducing manufacturing time and complexity while enabling efficient formation of rear surface electrodes.
3Productivity
If LED elements are closely arranged for high power output, then light output efficiency increases, but electrical separation between elements becomes difficult
Solution Approach 1:
Electrical separation between closely arranged LED elements is achieved by introducing insulating structures in the vertical dimension (depth) rather than relying solely on horizontal spacing. Insulating films and recessed portions are formed at the rear surface level, creating electrical isolation in the depth direction that allows elements to be closely arranged in the planar direction while maintaining reliable electrical separation.
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 the thermal conductivity and electrical separation of LED elements, leading to improved light output efficiency and reliability in high-power applications such as vehicle lighting, while also simplifying the manufacturing process.
Implementation Method 1
Recently, development has been done to remove the sapphire growth substrate by laser lift-off (LLO) or polishing.
Implementation Method 2
at least one recessed portion having a side surface exposing the fourth semiconductor layer, the second active layer and the third semiconductor layer
Data Source
AI summary
An LED device includes first and second LED elements containing a lower layer of first conductivity type, an active layer, and an upper layer of second conductivity type, wherein the second LED element has third and fourth electrodes on the lower layer, recessed portion having a side surface exposing the upper, active and lower layers, and reaching the third electrode, fifth electrode disposed on the upper layer extending on the side surface of the recessed portion, and connected with the third electrode, and groove extending from the upper layer and reaching the active layer between the third and fourth electrodes to electrically separate the third electrode from the fourth electrode.