Flip-Chip LED N-Electrode Inversion for Light Extraction
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Solution Overview
Problem
Conventional vertical LEDs suffer from light blocking due to the presence of the N-type electrode on the light-emitting surface, which hampers light extraction and efficiency.
Innovation Solution
A flip-chip LED design where the N-type electrode is moved to the support substrate, eliminating the pad electrode from the light-emitting surface, and a transparent conductive layer connects the electrode and light-emitting regions for vertical current injection, ensuring electrical isolation and improved light extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the N-type electrode is placed on the light-emitting surface in a conventional vertical LED structure, then current injection and electrical connection are achieved, but light extraction efficiency deteriorates due to light blocking by the electrode
Solution Approach 1:
The patent inverts the conventional LED structure by flipping the chip orientation. The N-type electrode that was previously on the light-emitting surface is now positioned on the back surface, away from the light extraction path. This inversion resolves the contradiction by eliminating light blocking while maintaining electrical connection through the flipped geometry.
Solution Approach 2:
The patent transitions from a planar electrode arrangement to a three-dimensional vertical structure. By stacking the P-type and N-type electrodes on opposite surfaces of the flipped chip, the solution moves the electrical connection problem to a different spatial dimension, allowing light to extract unobstructed from the top surface while electrodes remain on the bottom surface.
2Illumination intensity
If the N-type electrode blocks the light-emitting surface, then electrical connection is maintained, but light emission intensity deteriorates
Solution Approach 1:
By inverting the chip structure, the patent eliminates the need for complex transparent electrode designs or light-blocking apertures. The simple act of flipping the chip moves the opaque N-type electrode away from the light path, dramatically improving light emission intensity without adding structural complexity.
3Reliability
If wire bonding is performed on the light-emitting surface with pad electrodes present, then electrical connection is established, but bonding stability deteriorates due to light blocking and space constraints
Solution Approach 1:
The patent inverts the bonding approach by moving pad electrodes to the back surface of the flipped chip. This provides ample flat bonding area away from the light-emitting surface, improving wire bonding stability and accessibility without compromising light extraction or requiring complex bonding techniques.
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 design enhances light extraction efficiency by removing light-blocking electrodes from the emitting surface and stabilizes wire bonding, leading to improved packing and die bonding yields.
Implementation Method 1
a transparent conductive layer, which connects the electrode region and the light-emitting region, thereby realizing vertical current injection into the light-emitting epitaxial layer
Implementation Method 2
the isolation region of the n-type semiconductor layer forms an insulation portion via ion injection to realize electrical isolation between the light-emitting region and the electrode region
Data Source
AI summary
A flip-chip light emitting diode (LED) includes: a substrate having a P-type pad electrode and an N-type pad electrode; a light-emitting epitaxial layer flip-chip mounted over the substrate, including, from top down, an n-type semiconductor layer, an active layer, and a p-type semiconductor layer. The n-type semiconductor layer is divided into a light-emitting region, an isolation region, and an electrode region. The light-emitting region and the electrode region are electrically isolated by the isolation region. The active layer and the p-type semiconductor layer are below the light-emitting region. The p-type semiconductor layer connects with the P-type pad electrode. The electrode region of the n-type semiconductor layer connects with the N-type pad electrode. A conductive connection portion on the n-type semiconductor layer connects the electrode region of the n-type semiconductor layer and the light-emitting region, realizing vertical current injection into the light-emitting epitaxial layer when an external power is connected.