Uneven DBR Reflective Layer for Dicing Crack Control in LEDs
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Solution Overview
Problem
Conventional light-emitting devices face issues with light absorption and reliability due to cracks in the reflective layer during the dicing process, which can lead to moisture penetration and reduced device reliability.
Innovation Solution
A light-emitting device design featuring a substrate with a dicing street and an uneven reflective layer with a Distributed Bragg Reflector structure, where the reflective layer has an uneven thickness adjacent to the substrate sidewall, and a cap layer formed by chemical vapor deposition to enhance film quality and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional reflective layer is used during dicing process, then the device structure is simple, but cracks occur in the reflective layer leading to moisture penetration and reduced reliability
Solution Approach 1:
The reflective layer is divided into a first reflective layer and a second reflective layer with different functions. The first reflective layer provides optical reflection, while the second reflective layer serves as a protective barrier against moisture penetration through cracks. This segmentation allows each layer to be optimized for its specific function, improving overall device reliability without excessive complexity.
Solution Approach 2:
The patent uses a composite structure combining multiple reflective layers with different material properties. The first reflective layer (e.g., metal-based) provides high reflectivity, while the second reflective layer (e.g., dielectric-based) provides crack resistance and moisture barrier properties. This composite approach resolves the contradiction by integrating multiple functions into a unified structure that maintains reliability while managing complexity.
2Reliability
If the reflective layer is made thicker to prevent cracks, then reliability improves, but light extraction efficiency decreases due to increased absorption
Solution Approach 1:
The reflective layer is segmented into two distinct layers with different thicknesses and material compositions. The first reflective layer is optimized for light reflection with appropriate thickness for optical performance, while the second reflective layer is specifically designed as a thin protective barrier that prevents crack propagation and moisture penetration without significantly increasing light absorption. This segmentation allows independent optimization of each layer's thickness for its specific function.
Solution Approach 2:
Different regions of the reflective layer structure are assigned different qualities and thicknesses. The first reflective layer has properties optimized for optical reflection, while the second reflective layer has properties optimized for mechanical protection and moisture barrier functions. This local differentiation allows the structure to achieve both high reliability and low light absorption by placing the right material properties in the right locations.
3Reliability
If a uniform reflective layer is used, then manufacturing is simpler, but cracks occur at the sidewall region during dicing process
Solution Approach 1:
The reflective layer structure implements local quality by having different layer configurations in different regions. The first reflective layer provides base reflection, while the second reflective layer is specifically positioned to protect the sidewall region and dicing street areas where cracks are most likely to occur. This localized protection approach prevents cracks at critical regions without requiring complex manufacturing processes across the entire device.
Solution Approach 2:
The second reflective layer is applied in advance as a protective barrier before the dicing process. This preliminary protective layer prevents crack formation and propagation during subsequent manufacturing steps, addressing the reliability issue before it can manifest. The preliminary action of adding this protective layer simplifies the overall manufacturing process by preventing defects rather than requiring complex repair or rework steps.
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 design improves light extraction efficiency and reduces the risk of moisture penetration, enhancing the reliability and performance of the light-emitting device by minimizing cracks and ensuring better film coating characteristics.
Implementation Method 1
a reflective layer comprising a Distributed Bragg Reflector structure covering the protective layer
Implementation Method 2
a cap layer covering the reflective layer, wherein the reflective layer comprises an uneven portion adjacent to the sidewall of the substrate
Data Source
AI summary
A light-emitting device comprises a substrate comprising a top surface and a sidewall; a semiconductor stack formed on the top surface of the substrate comprising a first semiconductor layer, an active layer and a second semiconductor layer; a dicing street surrounding the semiconductor stack and exposing the top surface of the substrate; a protective layer covering the semiconductor stack and the dicing street; a reflective layer comprising a Distributed Bragg Reflector structure and covering the protective layer; and a cap layer covering the reflective layer, wherein the reflective layer comprises an uneven portion adjacent to the sidewall of the substrate, and the uneven portion comprises an uneven thickness.