Micro-LED Epitaxy Strain Balancing for Low-Bow Wafers
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Solution Overview
Problem
Micro-LED wafers with epitaxial layers experience significant wafer bow due to compressive strain, which complicates bonding with backplanes and affects efficiency.
Innovation Solution
The use of tensile-strained epitaxial layers and compressive-strained epitaxial layers to balance strain in micro-LED wafers, reducing wafer bow and improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compressive-strained epitaxial layers are used in micro-LED wafers, then the efficiency at high operating current densities is improved, but significant wafer bow occurs that complicates bonding with backplanes
Solution Approach 1:
The patent introduces tensile-strained semiconductor layers as counterbalancing elements to offset the compressive strain in the active region and other compressive layers. This strain balancing approach reduces the net wafer bow while preserving the efficiency benefits of compressive strain in the light-emitting active region. The tensile layers act as a counterweight force that compensates for the bowing effect without eliminating the compressive strain needed for high efficiency operation.
Solution Approach 2:
The patent applies different strain characteristics to different regions of the epitaxial structure. The active region maintains compressive strain for high efficiency, while specific semiconductor layers (such as the p-type cladding layer or n-type layer) are designed with tensile strain to balance the overall wafer curvature. This localized differentiation of strain quality allows simultaneous optimization of both efficiency and bonding capability.
2Productivity
If compressive strain is applied to the active region, then efficiency at high current densities improves, but wafer bow increases making bonding difficult
Solution Approach 1:
Tensile-strained semiconductor layers are strategically positioned in the epitaxial structure to provide a counterbalancing effect that reduces wafer bow to acceptable levels for bonding, while the active region maintains its compressive strain for high efficiency operation. This allows the manufacturing process to achieve both high productivity through efficient LEDs and ease of bonding through reduced wafer curvature.
Solution Approach 2:
The patent modifies the strain parameter of specific semiconductor layers by selecting materials and compositions that exhibit tensile strain characteristics. By changing the strain parameter from compressive to tensile in specific layers (such as using appropriate AlGaInP compositions or adjusting layer thicknesses), the overall wafer bow is reduced to enable bonding while preserving the compressive strain needed for high efficiency in the active region.
3Ease of manufacture
If tensile-strained layers are added to balance strain, then wafer bow is reduced facilitating bonding, but the structure becomes more complex
Solution Approach 1:
Rather than uniformly complicating the entire epitaxial structure, the patent applies tensile strain locally to specific semiconductor layers where it provides the most effective counterbalancing. This localized approach to strain management reduces wafer bow with minimal additional structural complexity, maintaining simplicity in regions where compressive strain is already present and beneficial for efficiency.
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 strain balancing technique reduces wafer bow, facilitating easier and stronger bonding with backplanes, and enhances the efficiency of micro-LEDs at high operating current densities and elevated temperatures.
Implementation Method 1
using tensile-strained epitaxial layers and compressive-strained epitaxial layers to balance strain in the epitaxial layers, thereby reducing wafer bow and improving efficiencies of micro-LEDs
Implementation Method 2
The active region may include a compressive-strained quantum well layer and compressive-strained quantum barrier layers
Implementation Method 3
an n-type semiconductor layer grown on the substrate, an active region grown on the n-type semiconductor layer, and a p-type semiconductor layer grown on the active region
Data Source
AI summary
A micro-light emitting diode (micro-LED) wafer includes a substrate, an n-type semiconductor layer grown on the substrate, an active region grown on the n-type semiconductor layer and configured to emit visible light, and a p-type semiconductor layer grown on the active region. The active region includes a compressive-strained quantum well layer and compressive-strained quantum barrier layers. At least one of the p-type semiconductor layer or the n-type semiconductor layer includes a tensile-strained layer having a thickness greater than about 50 nm, such that the tensile-strained layers can counter the compressive strain of the active region, thereby reducing the overall strain and bow of the micro-LED wafer.