Micro LED Backplane Bonding With Reflectors for Color Purity
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Solution Overview
Problem
The misalignment of micro LEDs with semiconductor elements due to differences in thermal expansion coefficients between the wafer and the backplane substrate during the transfer process leads to contact failures, which is exacerbated by the need for precise alignment in high-resolution displays.
Innovation Solution
Forming LEDs directly on the backplane substrate by bonding an epitaxial layer to semiconductor elements, eliminating the transfer process and ensuring precise alignment, and incorporating reflectors between LEDs to improve light extraction efficiency and prevent color mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LEDs are transferred to the backplane substrate using thermocompression at high temperature, then the LEDs can be bonded to the backplane substrate, but misalignment occurs between the LEDs and semiconductor elements due to different thermal expansion coefficients
Solution Approach 1:
The patent applies preliminary action by performing the alignment of LEDs with semiconductor elements before the high-temperature bonding process. The LEDs are pre-aligned on the wafer with the backplane substrate at lower temperature, and then the bonding is performed. This ensures that the alignment is established before thermal expansion differences can cause misalignment during the high-temperature bonding process.
2Measurement precision
If the size of LEDs is reduced to achieve high-resolution display, then the display resolution is improved, but the alignment precision requirement becomes more stringent
Solution Approach 1:
The patent performs alignment before the high-temperature bonding process, when the wafer and backplane substrate are at lower temperature and have minimal thermal expansion. This preliminary alignment ensures that even for micro-sized LEDs required for high-resolution displays, the alignment precision can be achieved before thermal effects cause misalignment during bonding.
3Ease of operation
If the transfer process is performed after LED alignment, then the LEDs can be positioned on the backplane substrate, but contact failure occurs due to alignment shift from thermal expansion difference
Solution Approach 1:
The patent performs the alignment action before the high-temperature bonding process. The LEDs are aligned with the semiconductor elements on the backplane substrate while the wafer is still at lower temperature, and then the bonding is performed. This preliminary alignment ensures that the alignment is established before thermal expansion differences can cause misalignment during the bonding process, preventing contact failure.
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 method enhances alignment accuracy, reduces processing time, and improves light extraction efficiency while minimizing color mixture, resulting in a high-resolution display device.
Implementation Method 1
the thermal expansion coefficient of the wafer on which the LEDs are grown is different from that of the backplane substrate. Accordingly, the degree of expansion of the wafer and the degree of expansion of the backplane substrate may be different from each other when high-temperature heat is applied during the transferring process
Data Source
AI summary
There is provided a display device. The display device includes a plurality of semiconductor elements disposed on a substrate; a plurality of LEDs disposed on the plurality of semiconductor elements and electrically connected to the plurality of semiconductor elements, respectively; and a plurality of reflectors disposed above the semiconductor elements and each located between every two of the LEDs. The plurality of LEDs may include a plurality of respective light-emitting layers disposed on the plurality of semiconductor elements, and a common electrode disposed on the plurality of light-emitting layers. The reflectors are disposed between the LEDs, so that light emitted from LEDs does not travel toward the side portions of the LEDs but toward the above of the substrate, thereby improving the light extraction efficiency and suppressing color mixture.