Direct-Bonded Micro-LED Arrays for Sapphire Defect Removal
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Solution Overview
Problem
Current microLED (mLED) display technologies face challenges in mass production and commercialization due to high crystalline defect densities and degradation issues in GaN films on sapphire substrates, limiting their performance and efficiency compared to OLEDs.
Innovation Solution
The development of direct-bonded LED arrays involves fabricating micro-LED structures with coplanar electrical contacts on a flat bonding interface, which are then bonded to silicon driver chips using processes like ZiBond or DBI, enabling wafer-level construction and resulting in a transparent and flexible micro-LED array display with improved light output and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If microLED structures are fabricated on sapphire substrates, then high brightness and fast response times are achieved, but high crystalline defect densities and degradation issues occur
Solution Approach 1:
The patent extracts the microLED structures from the problematic sapphire substrate using laser lift-off technology. The sapphire substrate is separated from the GaN layer, allowing the microLEDs to be transferred to a flexible polymer substrate. This extraction removes the source of crystalline defects while preserving the high brightness characteristics of the GaN-based microLEDs.
Solution Approach 2:
The patent changes the substrate material parameter from rigid sapphire to flexible polymer. This parameter change fundamentally alters the thermal and mechanical properties of the system, reducing thermal stress and preventing the formation of crystalline defects that occur in GaN films on sapphire substrates.
2Ease of manufacture
If conventional LCD technology is used, then mass production is easier, but energy consumption is high and contrast is low
Solution Approach 1:
The patent employs self-emissive microLED technology where each pixel generates its own light through electroluminescence. This self-service capability eliminates the need for complex backlight systems and liquid crystal modulation layers required in LCDs, significantly reducing energy consumption while enabling direct control of each pixel for high contrast ratios.
3Illumination intensity
If microLED arrays are bonded to driver circuits, then higher brightness and efficiency are achieved, but manufacturing complexity increases
Solution Approach 1:
The patent merges the microLED array and driver circuit onto a single flexible substrate through direct bonding. This integration combines the light-emitting elements with the control electronics, eliminating the need for separate mounting and interconnection steps. The wafer-level bonding process enables parallel processing of multiple devices, reducing overall manufacturing complexity despite the advanced bonding technology required.
4Illumination intensity
If GaN films are deposited on sapphire substrates, then high overall brightness is achieved, but degradation issues and shorter product life occur
Solution Approach 1:
The patent extracts the GaN microLED layer from the sapphire substrate using laser-induced phase transformation. This extraction removes the microLEDs from the thermally stressful sapphire environment that causes degradation, allowing them to be mounted on a flexible substrate with better thermal management and mechanical compliance, thereby extending product life while maintaining high brightness.
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 enhances the brightness, contrast, and energy efficiency of mLED displays, offering higher lux per watt performance and longer product life, making them suitable for applications like automotive and virtual/augmented reality displays.
Implementation Method 1
microLEDs, also known as micro-LEDs, μLEDs, and 'mLEDs' as used herein, are gaining significant attraction as an emerging flat panel display technology
Implementation Method 2
The coplanar electrical contacts of the flat bonding interface surface are direct-bonded to electrical contacts of a driver circuit for the LED structure
Data Source
AI summary
Direct-bonded LED arrays and applications are provided. An example process fabricates a LED structure that includes coplanar electrical contacts for p-type and n-type semiconductors of the LED structure on a flat bonding interface surface of the LED structure. The coplanar electrical contacts of the flat bonding interface surface are direct-bonded to electrical contacts of a driver circuit for the LED structure. In a wafer-level process, micro-LED structures are fabricated on a first wafer, including coplanar electrical contacts for p-type and n-type semiconductors of the LED structures on the flat bonding interface surfaces of the wafer. At least the coplanar electrical contacts of the flat bonding interface are direct-bonded to electrical contacts of CMOS driver circuits on a second wafer. The process provides a transparent and flexible micro-LED array display, with each micro-LED structure having an illumination area approximately the size of a pixel or a smallest controllable element of an image represented on a high-resolution video display.