Micro-Display Bonding Interface for Low-CTE Walk-Off
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Solution Overview
Problem
Conventional micro-LED display technologies face challenges in integrating LEDs with control circuits due to the large number of metal bumps required, leading to degraded performance and reduced integration density, as well as issues with thermal expansion mismatch causing 'walk-off' during bonding.
Innovation Solution
A thin-film transistor (TFT) layer is deposited on the LED substrate with a reduced number of metal bonds to the backplane, incorporating selector, modulation, and memory circuits, and using materials with lower melting points to minimize thermal expansion mismatch and allow for denser LED packaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional micro-LED display technologies are used with traditional integration methods, then electrical connectivity is achieved, but the large number of metal bumps required degrades performance and reduces integration density
Solution Approach 1:
The patent segments the electrical connection function by dividing the array of LEDs into groups that share common electrical connections. Instead of requiring individual metal bumps for each LED, multiple LEDs are electrically connected through shared conductive pathways in the substrate, significantly reducing the total number of metal bumps needed while maintaining proper electrical connectivity across the display array
Solution Approach 2:
The substrate is designed with multi-functional conductive structures that serve multiple purposes: providing electrical connectivity for groups of LEDs, acting as alignment references for bonding, and serving as thermal management pathways. This universal design reduces the number of dedicated components needed, thereby reducing overall device complexity
2Stability of the object's composition
If conventional bonding methods are used, then LED array is attached to substrate, but thermal expansion mismatch causes 'walk-off' during bonding
Solution Approach 1:
The patent employs a multi-stage bonding process with progressively increasing temperature and pressure parameters. By carefully controlling and gradually changing these parameters rather than applying them all at once, the thermal expansion mismatch between dissimilar materials is minimized, preventing walk-off while achieving stable bonding
Solution Approach 2:
Alignment marks and fiducial features are pre-formed on both the LED array and substrate before the bonding process. These preliminary structural features serve as guides that maintain alignment throughout the bonding process, compensating for thermal expansion differences and preventing walk-off
3Ease of operation
If more metal bonds are used to control each LED individually, then precise control is achieved, but integration density is reduced
Solution Approach 1:
The patent introduces addressable control through multiple dimensions: spatial grouping of LEDs connected to common lines, temporal multiplexing through sequential row/column addressing, and logical addressing schemes. This multi-dimensional control approach enables precise individual LED control without requiring individual physical connections for each LED, thereby maintaining integration density
Data Source
AI summary
For small, high-resolution, light-emitting diode (LED) displays, such as for a near-eye display in an artificial-reality headset, LEDs are spaced closely together. A backplane can be used to drive an array of LEDs in an LED display. A plurality of interconnects electrically couple the backplane with the array of LEDs. The backplane can have a different coefficient of thermal expansion (CTE) than the array of LEDs. During bonding of the backplane to the array of LEDs, CTE mismatch can cause misalignment of bonding sites. The higher the bonding temperature, the greater the misalignment of bonding sites. Lower temperature bonding, using materials with lower melting or bonding temperatures, can be used to mitigate misalignment during bonding so that interconnects can be more closely spaced, which can allow LEDs to be more closely spaced, to enable a higher-resolution display.