LED Reflective Opening Geometry to Prevent Mirror Layer Cracking
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Solution Overview
Problem
Current light-emitting devices face challenges in optimizing the reflective structure design, which affects the light extraction efficiency and reliability due to issues with the metal reflective layer coverage and cracking, leading to suboptimal performance in terms of brightness and voltage.
Innovation Solution
The design incorporates a reflective structure with an insulating reflective mirror and layer, featuring a specific geometry of reflective structure openings with varying side surface lengths and angles, and a metal reflective layer that fills these openings, improving adhesion and even coverage to enhance reflection and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a metal reflective layer is applied to improve light extraction efficiency, then the brightness performance is improved, but the metal reflective layer may crack due to thermal expansion mismatch, worsening the reliability
Solution Approach 1:
The patent applies a composite reflective structure consisting of an insulating reflective mirror layer (e.g., ITO, IZO, or ZnO) combined with a metal reflective layer (e.g., Al, Ag, or Au). The insulating layer serves as a buffer to reduce thermal expansion mismatch stress, preventing cracking of the metal layer while maintaining high reflectivity for improved light extraction efficiency and brightness.
Solution Approach 2:
The insulating reflective mirror layer acts as an intermediary between the semiconductor substrate and the metal reflective layer. This intermediate layer absorbs and distributes thermal stress, protecting the metal layer from cracking while still providing reflective functionality to enhance light extraction.
2Illumination intensity
If the reflective structure opening geometry is optimized to increase reflection area, then light extraction efficiency is improved, but the manufacturing precision required increases due to specific side surface length ratios
Solution Approach 1:
The patent specifies different geometric characteristics for different parts of the reflective structure opening. The first side surface has a specific length ratio (0.5-2.0 times the second side surface length) and specific angle ranges (15-45 degrees for first side surface, 30-60 degrees for second side surface). This local optimization of geometry ensures adequate light extraction efficiency while providing clear manufacturing guidelines to maintain precision.
3Illumination intensity
If the metal reflective layer coverage is increased to improve reflection, then light extraction efficiency is improved, but the adhesion and evenness of coverage become problematic, leading to cracking
Solution Approach 1:
The patent uses a composite structure where the insulating reflective mirror layer provides a stable adhesion interface for the metal reflective layer. This composite approach allows the metal layer to be applied with adequate coverage for high reflection while the insulating layer ensures uniform adhesion and prevents cracking by accommodating thermal stress.
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 configuration increases the effective reflection area, improves light extraction efficiency, and enhances the reliability of the light-emitting device by preventing metal reflective layer cracking, thereby optimizing brightness and voltage performance.
Implementation Method 1
a metal reflective layer covering the connection layer and filling into the reflective structure opening... increases the effective reflection area, improves light extraction efficiency
Data Source
AI summary
A light-emitting device comprises a first semiconductor layer; a semiconductor mesa, comprising an active layer and a second semiconductor layer and comprising an inclined surface connected to the first semiconductor layer; a contact electrode covering the second semiconductor layer and comprising an upper surface; a reflective structure comprising a reflective structure opening having a first side surface and a second side surface; a connection layer covering the reflective structure; and a metal reflective layer covering the connection layer; wherein in a cross-sectional view of the light-emitting device, a first portion of a projection of the first side surface to the upper surface of the contact electrode comprises a first length, a second portion of a projection of the second side surface to the upper surface of the contact electrode comprises a second length, and the first length is smaller than the second length.