MicroLED Mesa Passivation With DBR for Sidewall Recombination Loss
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Solution Overview
Problem
MicroLEDs face challenges in efficient operation due to high surface recombination effects, which reduce light output, and current industrial processes struggle to scale effectively for miniaturized chips with complex geometries and high aspect ratios, necessitating improved passivation methods.
Innovation Solution
A light emitting diode (LED) device with a conformal passivation layer comprising a low-refractive index material and a distributed Bragg reflector (DBR) is developed, applied to the sidewalls and top surface of the mesa, along with specific contact formations to enhance electrical and optical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional passivation methods are used on microLEDs, then manufacturing is simpler, but surface recombination increases and light output decreases
Solution Approach 1:
The passivation structure is segmented into multiple functional layers: a conformal base passivation layer that follows the mesa geometry, and an additional planarized passivation layer that provides a flat surface. This segmentation allows each layer to perform its specific function optimally while reducing overall surface recombination.
Solution Approach 2:
The passivation structure implements local quality by providing different characteristics at different locations: the conformal base layer provides excellent surface coverage and field effect passivation at the mesa sidewalls, while the planarized top layer provides a flat surface for subsequent processing. This localized optimization reduces surface recombination across the entire device.
2Manufacturing precision
If miniaturized microLED chips are used for high-density displays, then display resolution improves, but photolithographic process capabilities are exceeded and manufacturing becomes difficult
Solution Approach 1:
The conformal base passivation layer is deposited beforehand to define the mesa sidewall geometry and provide electrical passivation before subsequent processing steps. This preliminary action establishes precise dimensional boundaries that guide later photolithographic steps, enabling better control over miniaturized features.
Solution Approach 2:
The solution transitions from a single-layer planar passivation approach to a multi-layer three-dimensional conformal structure. This dimensional change allows the passivation to follow the vertical sidewalls of high aspect ratio mesas, providing effective passivation without requiring proportional increases in lateral processing precision.
3Reliability
If complex mirror and electrical contact geometries are used for efficient microLED operation, then device performance improves, but manufacturing complexity increases
Solution Approach 1:
The conformal base passivation layer serves multiple functions simultaneously: it provides electrical field effect passivation to reduce surface recombination, defines the mesa sidewall geometry for subsequent processing, and creates a uniform surface for contact formation. This multi-functionality reduces the need for separate complex structural elements.
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
The solution reduces surface recombination, increases reflectivity, and confines light within the semiconductor pixel area, improving luminance and reducing crosstalk between pixels, thus addressing the limitations of existing technologies in microLED display applications.
Implementation Method 1
MicroLEDs face challenges in efficient operation due to high surface recombination effects, which reduce light output
Implementation Method 2
a passivation layer on the at least one side wall and on the top surface of the mesa, the passivation layer comprising one or more a low-refractive index material and distributed Bragg reflector (DBR)
Implementation Method 3
The solution reduces surface recombination, increases reflectivity, and confines light within the semiconductor pixel area, improving luminance and reducing crosstalk between pixels
Data Source
AI summary
Described are light emitting diode (LED) devices comprising a mesa with semiconductor layers, the semiconductor layers including an N-type layer, an active layer, and a P-type layer. The mesa has a top surface and at least one side wall, the at least one side wall defining a trench having a bottom surface. A passivation layer is on the at least one side wall and on the top surface of the mesa, the passivation layer comprises one or more a low-refractive index material and distributed Bragg reflector (DBR). A p-type contact is on the top surface of the mesa, and an n-type contact on the bottom surface of the trench.