News: LEDs
3 October 2024
Polar Light partners with Finetech to connect pyramidal GaN micro-LEDs
For display applications, Polar Light Technologies (PLT) — which stems from research by founder professor Per-Olof Holtz and his team at Sweden’s Linköping University — has created novel gallium nitride (GaN) pyramidal micro-LEDs that are directly bonded to indium pads on a silicon chip. This new method, where LEDs are built from the bottom up, avoids the surface damage seen in traditional top-down methods, resulting in much better optical performance.
The pyramidal shape allows the creation of very small LEDs that are brighter and more efficient at emitting light by reducing energy losses and increasing energy efficiency.
To connect these pyramidal micro-LEDs to silicon substrates, Polar Light has teamed up with Finetech of Berlin, Germany (a supplier of sub-micron and high-accuracy die bonding solutions) to develop a cold bonding technique that ensures accurate alignment with the electronics. In early trials, the method showed an 85% success rate, proving its potential for large-scale manufacturing.
Pyramidal micro-LED to enable smaller, brighter and more efficient light emitters
Polar Light’s approach to making display front panels involves a bottom-up fabrication method using atomic layer regrowth. They grow GaN micro-LEDs in the shape of pyramids on a silicon carbide (SiC) substrate. This produces high-quality micro-LEDs as small as 300nm, without the damage caused by traditional top-down methods. As a result, the devices have near-perfect surfaces, which is crucial for optical properties.
The micro-LED displays can fit the resolution of a full TV screen into an area smaller than 5mm², with about 1000 x 1000 connection points spaced just 5µm apart. Polar Light’s design also significantly reduces energy use, making the micro-LEDs highly efficient for next-generation micro-displays.
Compared with regular LEDs, the pyramidal micro-LEDs improve augmented-reality (AR) system efficiency by 50-200 times thanks to better internal and external quantum efficiencies and enhanced light utilization. By minimizing internal electric field interference and optimizing the interaction between charge carriers in the quantum wells, the micro-LEDs produce more light with sharper, narrower emission. This makes them suitable for applications like AR and micro-projectors, where precise light control is important, says Polar Light.
Finetech develops cold compression bonding process for pyramidal micro-LEDs
A complete micro-LED display consists of three main parts: the front panel (the actual display), the back panel (which includes all the electronics), and the connection between the two. For the process of connecting the front panel to the back panel made of silicon, a modified flip-chip bonding method was used in which the metallized GaN pyramids are precisely aligned and bonded to the indium pads on the silicon back panel.
Because of differences in how silicon carbide and silicon expand with heat, no heat could be used during the bonding process. Finetech and Polar Light developed a cold compression bonding method for aligning and bonding micro-LED arrays using an automated FINEPLACER femto 2 sub-micron die bonder. This machine is claimed to ensure excellent process control, with high accuracy in flatness, alignment and bonding force, which is crucial for connecting the fine-pitch indium bumps for high-performance displays.
In addition to its precision, the FINEPLACER die bonder is flexible enough to scale up production and adapt to new micro-LED technologies. Finetech also provides solutions for handling materials and cleaning with chemical or atmospheric plasma to avoid damage or contamination. This system allows for easy flipping of delicate indium bump arrays without tweezers, and it ensures that the materials are treated before bonding to improve overall quality.
Polar Light and Finetech at MicroLEDConnect 2024
At MicroLEDConnect 2024 in Eindhoven, The Netherlands (25-26 September), both companies presented their latest innovations for micro-LED display technology.
Finetech showcased solutions that improve accuracy, reduce costs and enable smooth scaling from R&D to large-scale micro-LED production.
The firm also presented a live session on Indium Bump Interconnect Flip Chip Bonding, showing how the technology is particularly beneficial for high-density flip-chip applications and can significantly enhance the reliability and efficiency of micro-LED devices.
Linköping micro-LED spin-off Polar Light Technologies appoints CEO
