Micro LED Contact Structure for Light Extraction and Reflectivity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional micro light emitting diode (LED) systems face challenges in achieving high light extraction efficiency due to issues with ohmic contact, limited reflectivity, and total reflection effects, particularly in flip-chip LED structures, which hinder the development of efficient display panels for applications like augmented reality and automotive displays.
Innovation Solution
The proposed solution involves a micro LED structure with a bottom conductive layer, a light emitting layer, a top conductive structure, and a conductive side arm, along with a thin ohmic contact layer and a composite reflective dielectric layer, designed to enhance light extraction efficiency by optimizing the contact area and reflectivity, and using transparent materials to minimize light shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick metal electrode is used to achieve good ohmic contact, then the contact resistance is reduced, but the light transmittance is blocked
Solution Approach 1:
The electrode structure is divided into multiple functional layers (transparent conductive layer, reflective layer, and additional transparent conductive layer) rather than using a single thick metal layer. This segmentation allows each layer to perform its specific function: the transparent layers maintain light transmittance while the reflective layer provides the necessary electrical contact and light reflection.
Solution Approach 2:
The electrode uses a composite structure combining transparent conductive materials (such as ITO, IZO, or ZnO) with a reflective layer (such as Al or Ag). This composite material approach allows the electrode to simultaneously achieve good electrical contact properties and high light transmittance, resolving the contradiction between contact quality and light transmission.
2Illumination intensity
If a thin metal electrode is used to maintain light transmittance, then the light blocking is reduced, but the current diffusion becomes non-uniform causing local overheating
Solution Approach 1:
The electrode is segmented into multiple layers where the transparent conductive layers handle current distribution uniformly across the surface while the reflective layer provides concentrated ohmic contact. This segmentation allows thin transparent layers to maintain light transmittance while still ensuring uniform current diffusion through the conductive properties of the transparent material.
Solution Approach 2:
Different regions of the electrode structure have different properties: the transparent conductive layers have high light transmittance and uniform current distribution properties, while the reflective layer has high electrical conductivity and light reflection properties. This local quality differentiation allows the electrode as a whole to achieve both good current diffusion and light transmittance.
3Illumination intensity
If the contact area between metal electrode and semiconductor material is decreased to add back reflective structure, then the reflectivity is improved, but the ohmic contact resistance dramatically increases
Solution Approach 1:
The electrode structure is segmented so that the reflective layer can be positioned beneath the transparent conductive layer, allowing the reflective layer to provide high reflectivity while the transparent conductive layer maintains full contact area with the semiconductor for low ohmic contact resistance. This segmentation enables both high reflectivity and low contact resistance to coexist.
Solution Approach 2:
The transparent conductive layer acts as an intermediary between the reflective layer and the semiconductor material. It allows the reflective layer to perform its light reflection function while maintaining electrical contact with the semiconductor, thus mediating between the conflicting requirements of high reflectivity and low contact resistance.
4Illumination intensity
If a Bragg mirror is used to improve reflectivity, then the normal incident light reflectance is improved, but the oblique incident light reflectance remains low preventing total reflection
Solution Approach 1:
The patent changes the parameter of reflectivity from the Bragg mirror's wavelength-specific, angle-dependent reflection to the metal reflective layer's broad-spectrum, high-angle reflection. By using a metal reflective layer (Al or Ag) instead of a Bragg mirror, the system achieves high reflectivity for both normal and oblique incident light, enabling total reflection capability.
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 configuration achieves light extraction efficiencies of at least 20%, significantly improving the performance of micro LED systems by increasing the light emergent area and reflectivity, addressing the limitations of conventional LED structures.
Implementation Method 1
Light emitting diode (LED) is a junction luminescent device, and the main structure of LED is a P-N junction. Under a forward bias, the P-N junction emits visual light or infrared light.
Implementation Method 2
the limitation of the total reflection effect has not been overcome yet, which limits the improving of the light extraction efficiency
Data Source
AI summary
A micro light emitting diode (LED) having a high light extraction efficiency includes a bottom conductive layer, a light emitting layer on the bottom conductive layer, and a top conductive structure on the light emitting layer. The micro LED additionally includes a conductive side arm electrically connecting the sidewall of the light emitting layer with the bottom conductive layer, and a reflective bottom dielectric layer arranged under the light emitting layer and above the bottom conductive layer. In some embodiments, the micro LED further includes an ohmic contact between the top conductive structure and the light emitting layer that has a small area and is transparent, thereby increasing the light emergent area and improving the light extraction efficiency.