Flip Chip Red LED with Branched Electrode and Etch Stop Layer
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Solution Overview
Problem
The challenge lies in manufacturing flip chip type light emitting diodes (LEDs) with AlGaInP, which requires removing the GaAs substrate to prevent light absorption, but conventional laser lift-off processes are inefficient, limiting most LEDs to vertical types.
Innovation Solution
A light emitting device design featuring a light transmitting substrate, a light emitting structure with specific semiconductor layers, an insulating layer, and electrodes configured for optimal light extraction and current distribution, including a second ohmic electrode with a pad electrode and branched electrodes, and an optical layer to enhance light output and contact efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional laser lift-off process is used to remove GaAs substrate, then substrate removal is achieved, but the process is inefficient and difficult to implement
Solution Approach 1:
The patent extracts the GaAs substrate removal step from the conventional laser lift-off process by introducing a dedicated etch stop layer that can be selectively removed. This separates the substrate removal function from the LED structure fabrication, making the process more controllable and efficient.
Solution Approach 2:
The etch stop layer is formed in advance during the LED structure fabrication process, before substrate removal is needed. This preliminary action enables efficient substrate removal later by providing a pre-defined removal interface, avoiding the need for complex laser lift-off procedures.
2Ease of manufacture
If GaAs substrate is not removed, then manufacturing is simpler, but light absorption occurs reducing LED efficiency
Solution Approach 1:
The patent introduces an etch stop layer as an intermediary between the GaAs substrate and the LED structure. This layer serves as a mediator that allows the substrate to remain during manufacturing (maintaining simplicity) while providing a clean removal interface when needed (preventing light absorption in the final device).
3Ease of manufacture
If vertical type LED structure is used, then manufacturing is easier, but light extraction efficiency is limited
Solution Approach 1:
The patent enables flip-chip type LED structure where the LED is inverted and mounted with the substrate face up. This inversion, made possible by the etch stop layer technique, improves light extraction efficiency by allowing light to exit from the top surface where the semiconductor layers are thinner, while still maintaining manufacturing feasibility through the standardized fabrication process.
4Reliability
If second ohmic electrode area is increased, then ohmic contact is improved, but light extraction efficiency may be reduced
Solution Approach 1:
The patent applies local quality by creating a branched electrode structure where different regions of the second ohmic electrode serve different functions. The pad electrode at the center provides strong ohmic contact, while the branched electrodes extending outward minimize light absorption in the light extraction path. This localized differentiation optimizes both electrical contact and optical performance in their respective regions.
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
Enables the production of flip chip type red LEDs with improved light extraction efficiency and ohmic contact, allowing for high brightness and color reproduction in displays by using LEDs as subpixels.
Implementation Method 1
a light emitting structure including a second conductive semiconductor layer disposed on the light transmitting substrate, a first conductive semiconductor layer disposed on the second conductive semiconductor layer, and an active layer disposed between the second conductive semiconductor layer and the first conductive semiconductor layer; the active layer emits light in a red wavelength band
Implementation Method 2
there is a need to remove the GaAs substrate in order to prevent light absorption. However, there is a problem in that it is difficult to remove the GaAs substrate using a conventional laser lift-off (LLO) process
Data Source
AI summary
An embodiment discloses a light emitting device and a display comprising the same. The light emitting device includes: a light transmitting substrate; a light emitting structure including a second conductive semiconductor layer disposed on the light transmitting substrate, a first conductive semiconductor layer disposed on the second conductive semiconductor layer, and an active layer disposed between the second conductive semiconductor layer and the first conductive semiconductor layer; an insulating layer covering the light emitting structure; a first ohmic electrode electrically connected to the first conductive semiconductor layer; a second ohmic electrode disposed on one side of the second conductive semiconductor layer facing the light transmitting substrate and electrically connected to the second conductive semiconductor layer; a first electrode electrically connected to the first ohmic electrode through the insulating layer; and a second electrode electrically connected to the second ohmic electrode through the insulating layer and the light emitting structure, wherein the active layer emits light of a red wavelength band, the second ohmic electrode includes a pad electrode disposed at the center of the second conductive semiconductor layer and a plurality of branched electrodes extending outward from the center of the second conductive semiconductor layer.