Microdisplay LED Mesa Structure for Higher Light Extraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in fabricating micro-LEDs for high-resolution display systems is the difficulty in precisely aligning and bonding small-pitch micro-LED arrays to CMOS drive circuits, which affects the light extraction efficiency and beam profiles.
Innovation Solution
The approach involves bonding a micro-LED wafer to a backplane wafer using alignment-free metal-to-metal bonding, followed by etching to form mesa structures with inwardly tilted sidewalls. The mesa structures are then modified with outwardly tilted sidewalls and a reflective layer, along with a high-refractive index material, to enhance light extraction efficiency and beam collimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If alignment-free metal-to-metal bonding is used to bond micro-LED wafer to backplane wafer, then bonding difficulty is reduced, but manufacturing precision of mesa structures deteriorates
Solution Approach 1:
The patent applies preliminary action by forming mesa structures with inwardly tilted sidewalls during the wafer bonding process before final device completion. This preliminary structuring enables subsequent modification to outwardly tilted sidewalls with reflective layers, achieving high precision light extraction without requiring ultra-precise initial alignment during bonding.
2Use of energy by moving object
If mesa structures are modified with outwardly tilted sidewalls and reflective layers, then light extraction efficiency is improved, but device complexity increases
Solution Approach 1:
The patent applies dimensionality change by transitioning from inwardly tilted mesa sidewalls to outwardly tilted sidewalls with integrated reflective layers. This geometric transformation in the radial dimension creates enhanced light extraction pathways without adding significant vertical complexity, effectively managing the trade-off between performance and device complexity.
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 method improves the light extraction efficiency and beam profiles of micro-LEDs by modifying the mesa structures to have outwardly tilted sidewalls and a reflective layer, effectively addressing the alignment and bonding challenges in existing technologies.
Implementation Method 1
a high-refractive index material region (e.g., with a refractive index greater than about 1.75 for visible light) surrounding the semiconductor epitaxial layers of the mesa structure
Implementation Method 2
a reflective layer on the outwardly tilted sidewalls of the high-refractive index material region
Data Source
AI summary
A light source comprises a backplane wafer with electrical circuits fabricated thereon, and an array of LEDs coupled to the backplane wafer. Each LED of the array of LEDs comprises a mesa structure including semiconductor epitaxial layers and characterized by inwardly tilted mesa sidewalls, a high-refractive index material region (e.g., with a refractive index greater than about 1.75, such as equal to or greater than a refractive index of the semiconductor epitaxial layers) surrounding the semiconductor epitaxial layers of the mesa structure and including outwardly tilted sidewalls, and a reflective layer on the outwardly tilted sidewalls of the high-refractive index material region. In one example, each LED of the array of LEDs also include a passivation layer on the inwardly tilted mesa sidewalls of the mesa structure.