Vertical LED Wafer Bonding Thermal Stress Reduction
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Solution Overview
Problem
Vertical type LEDs face reliability issues due to thermal stress caused by differences in thermal expansion coefficients between heterogeneous growth and support substrates, leading to potential cracking or debonding during the wafer bonding process.
Innovation Solution
The method involves forming a complex structure with wafer bonding layers and sacrificial separation layers, where the thermal expansion coefficients of the bonded structures are matched to prevent cracking, and using a laser lift-off or etching scheme to separate the growth substrate, followed by the formation of passivation and electrode layers to enhance the LED's structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wafer bonding scheme is used to form support substrate under second conductive semiconductor layer, then reliability of LED is improved, but manufacturing process becomes complicated
Solution Approach 1:
A buffer layer is introduced as an intermediary between the growth substrate and the support substrate. This buffer layer has thermal expansion coefficients matched with both substrates, serving as a mediator that reduces thermal stress during bonding while maintaining the reliability benefits of the wafer bonding scheme without requiring complex heterogeneous material bonding
Solution Approach 2:
The thermal expansion coefficient parameter is controlled by selecting appropriate materials for the buffer layer that match both the growth substrate and support substrate. This parameter matching reduces thermal stress and enables reliable bonding while simplifying the manufacturing process
2Ease of manufacture
If growth substrate and support substrate are made from heterogeneous materials, then LED can be manufactured, but crack or debonding may occur due to thermal stress caused by difference in thermal expansion coefficient
Solution Approach 1:
The buffer layer is designed with homogeneous thermal expansion properties that are matched to both the growth substrate and support substrate. This creates a homogeneous thermal stress environment that prevents cracking and debonding while enabling the manufacturing of LEDs with heterogeneous substrate materials
Solution Approach 2:
A composite structure is formed with the buffer layer positioned between the growth substrate and support substrate. This composite material approach allows the use of heterogeneous materials for the outer substrates while the intermediate buffer layer provides thermal expansion matching to prevent structural failures
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 improves the reliability of vertical type LEDs by reducing thermal stress-induced defects and maintaining light efficiency while simplifying the manufacturing process.
Implementation Method 1
separate the growth substrate by irradiating a laser beam thereon
Implementation Method 2
the active layer generates light according to current applied thereto
Data Source
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AI summary
A light emitting device according to the embodiment includes a support substrate; a reflective layer over the support substrate; an ohmic contact layer over the reflective layer; a light emitting semiconductor layer including a second conductive semiconductor layer, an active layer and a first conductive semiconductor layer over the ohmic contact layer; a first passivation layer surrounding a lateral side of the light emitting semiconductor layer; and a second passivation layer surrounding lateral sides of the first passivation layer and the reflective layer.