Self-aligned ITO DBR p-contact for small pitch micro-LEDs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in manufacturing small micro-LEDs is the difficulty in achieving high reflectivity and low resistance due to the small size of reflective metal layers and the need for precise alignment, which can lead to leakage current and reduced efficiency, especially when the pitch of the LED array is reduced.
Innovation Solution
The use of a conductive distributed Bragg reflector (DBR) made of transparent conductive oxide layers with alternating refractive indices, which acts as both the electrical contact and back reflector, eliminating the need for a metal p-contact reflector and allowing for the same lateral size as the epitaxial layers, thereby reducing contact resistance and increasing reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reflective metal layer is used as the electrical contact, then good electrical conductivity is achieved, but the lateral size must be reduced for small pitch LEDs which increases contact resistance
Solution Approach 1:
The patent combines the electrical contact function and the back reflector function into a single conductive DBR structure. This merged structure eliminates the need for a separate reflective metal layer while providing both low contact resistance and high reflectivity, thereby resolving the contradiction between maintaining good electrical conductivity and reducing lateral size for small pitch LEDs
Solution Approach 2:
The conductive DBR structure serves multiple functions simultaneously: it acts as the electrical contact (p-contact), the back reflector, and the current spreading layer. This multi-functionality eliminates the need for separate components and maintains performance despite reduced lateral dimensions required for small pitch LEDs
2Productivity
If the pitch of LED array is reduced, then higher packing density is achieved, but alignment precision becomes more difficult which leads to leakage current
Solution Approach 1:
By merging the electrical contact and back reflector into a single conductive DBR structure formed in the same lateral area as the epitaxial layers, the patent eliminates the need for separate alignment steps between these components. This resolves the alignment precision issue that becomes critical when reducing pitch to increase packing density
Solution Approach 2:
The conductive DBR structure inherently provides both electrical contact and optical reflection functions within its own structure, eliminating the need for external alignment with separate components. The structure self-services multiple functions that would otherwise require precise alignment between multiple layers
3Reliability
If a separate metal p-contact reflector is used, then high reflectivity is achieved, but device complexity increases due to additional alignment steps
Solution Approach 1:
The patent merges the back reflector function into the conductive DBR structure itself, eliminating the need for a separate metal p-contact reflector layer. This single integrated structure provides both electrical contact and high reflectivity (>90%) while reducing device complexity by removing additional alignment steps
Solution Approach 2:
The conductive DBR structure serves as both the electrical contact and the back reflector, providing multi-functionality in a single component. This eliminates the need for separate reflector layers and their associated alignment steps, thereby reducing device complexity while maintaining high reflectivity
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 enables high total reflectance and low resistance even at small pitches, allowing for reliable fabrication of micro-LEDs with pitches less than 4 μm, and eliminates alignment issues, making the technology highly scalable for small-pitch micro-LEDs.
Implementation Method 1
a conductive distributed Bragg reflector (DBR) on the plurality of epitaxial layers
Implementation Method 2
The large refractive index contrast may help to achieve a high reflectance with a small number of ITO layers
Implementation Method 3
The conductive DBR may include a plurality of transparent conductive oxide layers and may cover at least 80%, at least 90%, or at least 95% of a full lateral area of the plurality of epitaxial layers
Data Source
AI summary
A micro-light emitting diode includes a substrate including at least a first portion of an n-type semiconductor layer, and a mesa structure on the substrate and characterized by a linear lateral dimension equal to or less than about 3 μm. The mesa structure includes a plurality of epitaxial layers, and a conductive distributed Bragg reflector (DBR) on the plurality of epitaxial layers. The conductive DBR includes a plurality of transparent conductive oxide layers and covers between about 80% and about 100% of a full lateral area of the plurality of epitaxial layers. The micro-LED also includes a dielectric layer on sidewalls of the mesa structure, a reflective metal layer on sidewalls of the dielectric layer and electrically coupled to the first portion of the n-type semiconductor layer, and a first metal electrode in direct contact with the conductive DBR.