In a joint R&D effort, a group of companies and research institutions have developed an LED light source with 1.024 pixels; each one of them can be selectively switched on or off. This gives automotive lighting designers the possibility to implement smart, dazzle-free lighting concepts that are significantly more precise and adaptive that today’s implementations. Plus, the novel light source makes it possible to implement adaptive cornering light as well as levelling without any mechanical elements. The high-resolution lighting can clip out any number of segments, dynamically protecting oncoming traffic and pedestrians from being dazzled. The headlight beam can be adapted to any conceivable curve characteristic, eliminating dark peripheral areas in the driver’s field of sight.
The R&D group includes Osram, Infineon, automotive lighting expert Hella, carmaker Daimler-Benz as well as two Fraunhofer institutes. Three and a half years after the project named µAFS (for “micro-structured adaptive front-lighting system”) started, the group now introduced the result of their work. In terms of technology, the system developed integrates 1024 white LEDs on a single chip along with the driver circuitry and a high-level interface that enables driver assistance systems to selectively control every single LED, or pixel. The group also introduced a headlamp containing two such active lighting units, one with a single LED chip, the other one with two of them. Daimler showcased a vehicle that has (of course) two such headlamps, adding up the resolution to 6000 LED pixels per vehicle.
Besides integrating so many high-brightness LEDs with each one capable of drawing 11 mA of current, the project also was challenging in terms of semiconductor technology, because GaN LEDs and the Silicon driver circuitry had to be integrated in a single unit, explained Osram CTO Stefan Kampmann. Here, Fraunhofer stepped in: The Fraunhofer Institute Reliability and Microintegration (IZM) contributed its competence in connecting technology for LED and ICs and the materials required.
The high-resolution structure was achieved with miniaturized connection technology and a cooling system. The institute also successfully tested two alternatives as to the assembly technique: Porous gold nano-sponge and reflow soldering with gold/tin alloy. Both proved to be feasible in terms of technology as well as economy, said Fraunhofer researcher Herbert Oppermann. Another Fraunhofer institute, Fraunhofer IAF, contributed a technology to repair pixel defects during the production process. IAF’s technology is based on ultraviolet laser micromachining. It identifies microscopic defects and removes them with an UV laser through very selective material removal. According to Kampmann, after the repair the pixels regain their full luminosity, ensuring a homogeneous luminescence pattern.
Though theoretically all pixels can be activated at the same time (drawing more the 10 A of current, with all associated heat problems), energy efficiency was a development target. Compared to a digital projector, the system has two to three times better energy efficiency. The reason: A digital projector turns on all pixels continuously and afterwards blacks out undesired pixels which is not very energy effective. The µAFS system only activates the pixels that are actually used, significantly reducing energy consumption and thus heat.
Though the development focus also took into account to enable a cost-effective volume production, the high-resolution LED headlight is not yet ready for series start. “We are now at the end of an R&D project, not at a product presentation”, said Kampmann. He expects the technology will be available in series vehicles in about four to five years, given the existing design processes in the automotive industry.
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