III-Nitride Multi-Wavelength LED Arrays With Tunnel Junction Etch Stops
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Solution Overview
Problem
Current methods for manufacturing microLED displays are inefficient due to the complexity of the pick-and-place process and the need for separate epitaxy recipes for different colors, which increases cost and complexity, and introduce conductivity type conversion issues during dry etching, leading to ohmic contact challenges and increased operating voltage.
Innovation Solution
The use of III-nitride layers with tunnel junctions in a monolithic fabrication method allows for the integration of multiple color active regions on a single wafer, enabling independent electrical contacts and reducing the number of epitaxy recipes needed, while avoiding the conductivity type conversion issues associated with dry etching by making contacts to n-type GaN layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If pick-and-place approach is used to assemble microLED displays, then individual microLEDs can be precisely positioned, but the assembly process becomes slow and complex with manufacturing errors
Solution Approach 1:
The patent merges multiple microLEDs of different colors (red, green, blue) onto a single substrate in a monolithic structure, eliminating the need for separate pick-and-place operations for each color. The integrated device allows all color microLEDs to be positioned and assembled simultaneously in one fabrication process, resolving the contradiction between positioning precision and assembly speed.
2Reliability
If separate epitaxy recipes are used for different color microLEDs, then each color can be optimized independently, but the manufacturing cost and complexity increase
Solution Approach 1:
The patent employs a universal epitaxy recipe that can grow all three color active regions (red, green, blue) in sequence on the same substrate. The single epitaxy process integrates multiple functions by sequentially forming different quantum well structures with varying compositions (InGaN for blue, InAlGaN for green, AlInGaN for red) without requiring separate optimization recipes, thus reducing process complexity while maintaining color performance.
3Manufacturing precision
If dry etching is used to create mesas, then precise patterning is achieved, but conductivity type conversion occurs leading to ohmic contact challenges
Solution Approach 1:
The patent introduces an intermediary wet etching process using selective chemistry (NH4F-based solution) that etches through sacrificial layers and p-type GaN without causing conductivity type conversion. This wet etching mediator preserves the n-type conductivity of the underlying GaN layers, ensuring reliable ohmic contacts can be formed without the electrical contact issues caused by dry etching-induced conversion.
4Adaptability or versatility
If multiple separate fabrication processes are used for different color microLEDs, then each color can be independently manufactured, but the overall manufacturing time and cost increase
Solution Approach 1:
The patent performs preliminary actions by sequentially forming all three color active regions (blue, green, red) within a single epitaxy growth process before any separation or assembly steps. The red color active region is formed first, followed by green, then blue, with each layer prepared in advance on the substrate. This preliminary integration of all color layers eliminates the need for separate manufacturing cycles for each color, significantly reducing total manufacturing time while maintaining the ability to independently control each color's properties.
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 simplifies the manufacturing process, reduces costs, eliminates the need for pick-and-place operations, and achieves lower operating voltage and higher efficiency by allowing whole wafer-level transfer of pixels and making ohmic contacts to n-type GaN layers without damaging the active region.
Implementation Method 1
The method comprises forming a first color active region, forming a first etch stop layer comprising a first n-type III-nitride layer with a first Al mole fraction, forming a second color active region, forming a second etch stop layer comprising a second n-type III-nitride layer with a second Al mole fraction
Implementation Method 2
at least a first LED including a first p-type layer, a first n-type layer and a first color active region and a first tunnel junction on the first LED
Data Source
AI summary
An LED array comprises a first mesa comprising a top surface, at least a first LED including a first p-type layer, a first n-type layer and a first color active region and a tunnel junction on the first LED, a second n-type layer on the tunnel junction, the second n-type layer comprising at least one n-type III-nitride layer with >10% Al mole fraction and at least one n-type III-nitride layer with <10% Al mole fraction. The LED array further comprises an adjacent mesa comprising a top surface, the first LED, a second LED including the second n-type layer, a second p-type layer and a second color active region. A first trench separates the first mesa and the adjacent mesa, cathode metallization in the first trench and in electrical contact with the first and the second color active regions of the adjacent mesa, and anode metallization contacts on the n-type layer of the first mesa and on the anode layer of the adjacent mesa. The devices and methods for their manufacture include a thin film transistor (TFT).