Flip-Chip LED Side Wall Electrode and Current Blocking
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Solution Overview
Problem
The luminous efficiency of flip-chip LEDs is limited due to electrode light blocking and current concentration issues, which restricts their application in general and outdoor lighting, as existing methods require etching the active layer to fabricate the n-type electrode, leading to reduced light emission from the side walls.
Innovation Solution
The n-type electrode is placed on the epitaxial side wall in combination with a current blocking layer, eliminating the need to etch the active layer, and a reflection layer is used between the substrate and p-type epitaxial layer, along with an insulating protection layer to prevent direct contact with the active layer and control current distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the n-type electrode is fabricated by etching part of the p-type layer and active layer, then the electrode can be formed on the n-type layer, but the active layer area is lost and luminous efficiency is reduced
Solution Approach 1:
The n-type electrode is moved from the traditional planar position on the n-type layer to a vertical position on the side wall of the n-type epitaxial layer. This dimensional change allows the electrode to be formed without etching away active layer material, preserving the light-emitting area while still providing electrical contact to the n-type layer.
Solution Approach 2:
The electrode structure is segmented into multiple components: the n-type electrode on the side wall, the insulating protection layer covering part of the side wall, and the current blocking layer at the edge. This segmentation allows each component to perform its specific function independently, with the insulating layer protecting the active layer from the electrode while the current blocking layer manages current distribution.
2Reliability
If the metal electrode is placed on the light emission path, then the electrode connection is achieved, but the electrode blocks and absorbs light
Solution Approach 1:
The electrode is repositioned from a horizontal plane that blocks light emission to a vertical side wall position where it does not interfere with the upward light emission path. This dimensional relocation allows the electrode to maintain its electrical connection function while eliminating its harmful light-blocking effect.
Solution Approach 2:
The LED structure adopts an asymmetric configuration where the n-type electrode is positioned only on the side wall rather than symmetrically on both top and bottom surfaces. This asymmetry allows light to emit freely from the top surface without being blocked by electrodes, while still providing necessary electrical contact through the side wall electrode.
3Device complexity
If the current blocking layer is not used, then the manufacturing process is simplified, but current concentrates on the LED edge
Solution Approach 1:
The current blocking layer is applied locally at the edge region of the LED rather than uniformly across the entire structure. This localized application prevents current concentration at the edges where it would be harmful, while leaving the central active region unaffected and maintaining overall structural simplicity.
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 luminous efficiency by preserving the active layer area and preventing current concentration on the LED edge, thereby improving light emission without losing luminous area and overcoming electrode light blocking defects.
Implementation Method 1
a reflection layer, between the substrate and the p-type epitaxial layer
Implementation Method 2
an insulating protection layer, cladding the LED side wall and exposing part of the side wall of the n-type epitaxial layer
Data Source
AI summary
A flip-chip LED includes a substrate, having a surface with a p-region metal portion and an n-region metal portion separated from each other; a p-type epitaxial layer, an active layer and an n-type epitaxial layer successively laminated on the substrate; a reflection layer between the substrate and the p-type epitaxial layer; a current blocking layer between the reflection layer and the p-type epitaxial layer and positioned to prevent the current from concentrating on the edge of the LED; an insulating protection layer cladding the LED side wall and exposing part of the side wall of the n-type epitaxial layer; a P electrode connecting the metal reflection layer and the p-region metal portion of the substrate; and an N electrode connecting the side wall of the n-type epitaxial layer and n-region metal portion of the substrate.