Micro-LED Backplane Bonding Architecture With Alignment-Free Contacts
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Solution Overview
Problem
The challenge in fabricating micro-LED display panels lies in precisely aligning and bonding small-pitch micro-LED arrays to CMOS drive circuits, which is difficult due to the small dimensions and high misalignment tolerance of the bonding pads.
Innovation Solution
The solution involves using alignment-free hybrid bonding of a micro-LED wafer to a backplane wafer, followed by post-bonding micro-LED singulation and mesa formation. This method utilizes dielectric-to-dielectric bonding at room temperature and subsequent metal contact pad bonding at a low annealing temperature, eliminating the need for precise alignment and minimizing metal etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional alignment-based bonding is used to bond micro-LED arrays to CMOS drive circuits, then precise electrical connection can be achieved, but the manufacturing complexity and misalignment risk increase significantly due to small pad dimensions
Solution Approach 1:
The bonding process is divided into two independent stages: first bonding the micro-LED array to the carrier substrate, then bonding the carrier substrate to the CMOS drive circuit. This segmentation allows each bonding step to be optimized independently, reducing overall process complexity while maintaining precision.
Solution Approach 2:
A carrier substrate is introduced as an intermediary between the micro-LED array and the CMOS drive circuit. This carrier substrate provides a stable platform for mounting micro-LEDs and facilitates the bonding process by enabling indirect connection, thereby reducing the alignment difficulty between the small micro-LED pads and the larger CMOS pads.
2Reliability
If high-pitch bonding pads are used to increase misalignment tolerance, then bonding reliability improves, but the display resolution and packing density decrease
Solution Approach 1:
The bonding interface is extended from a direct one-to-one pad-to-pad connection to a many-to-one connection where multiple micro-LED bonding pads connect to a single larger CMOS bonding pad through the carrier substrate. This dimensional change in the bonding topology allows smaller micro-LED pads to be used without compromising alignment tolerance.
Solution Approach 2:
The carrier substrate serves multiple functions: it provides mechanical support for the micro-LED array, acts as a bonding interface that accommodates pad size mismatches, and enables electrical connection to the CMOS drive circuit. This multi-functionality allows the system to maintain high resolution while ensuring bonding reliability.
3Manufacturing precision
If metal etching is performed to form contact holes for bonding, then electrical connection can be established, but contamination of the active region increases and quantum efficiency decreases
Solution Approach 1:
The bonding pads and contact structures are prepared in advance on the carrier substrate before the micro-LED array is mounted. This preliminary preparation allows the bonding interface to be established without requiring subsequent etching operations that could contaminate the micro-LED active region.
Solution Approach 2:
The metal etching operation is extracted and eliminated from the bonding process. Instead of etching contact holes through the micro-LED structure, the connection is established through pre-formed contact pads on the carrier substrate, thereby removing the source of contamination and preserving the quantum efficiency of the micro-LEDs.
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 enables high-density and high-performance bonding of micro-LEDs to drive circuits with improved light extraction efficiency and quantum efficiency, as it avoids metal etching and reduces contamination of the active region.
Implementation Method 1
bonding the second bonding layer to the first bonding layer, where the second dielectric layer is bonded to the first dielectric layer
Implementation Method 2
subsequent metal contact pad bonding at a low annealing temperature
Implementation Method 3
the second bonding layer is configured to diffuse incident light emitted by the active region
Data Source
AI summary
Disclosed herein are a light source for a display system and methods of fabricating the light source. The light source includes a backplane wafer including a first bonding layer that includes an array of pixel contact pads in a first dielectric layer; a second bonding layer including an array of small metal contact pads in a second dielectric layer; and an array of mesa structures on the second bonding layer and configured to emit light. The second dielectric layer is bonded to the first dielectric layer such that each pixel contact pad of the array of pixel contact pads is in contact with two or more small metal contact pads that are electrically coupled to a same mesa structure of the array of mesa structures.