11 October 2016

German project yields demonstration model of high-resolution LED headlights with adaptive forward lighting

A German research alliance has developed the basis for smart, high-resolution LED headlights involving adaptive forward lighting. The demonstration model was developed by overall project manager Osram of Munich, Germany in collaboration with project partners Daimler AG, Fraunhofer Gesellschaft, Hella KGaA Hueck & Co and Infineon Technologies.

Both headlights contain three LED light sources, each with 1024 individually controllable light points (pixels). The headlight can therefore be adapted very precisely to suit the respective traffic situation to ensure optimum light conditions at all times without dazzling other drivers. The light can be adapted to take account of every bend in the road so that there are no dark peripheral areas. In addition, with the aid of sensors in the vehicle, the surroundings can be analyzed in order to illuminate oncoming traffic. This allows the driver to see these vehicles more clearly. At the same time, the light beam does not shine into the eyes of oncoming drivers, so they are not dazzled. As a result, such shifting headlights no longer have to be dimmed on country roads.

Picture: The new LED chip with 1024 individually controllable pixels. The combination of three such chips allows a resolution of 3072 pixels per headlight. (picture: OSRAM Licht AG).

Funded by the German Federal Ministry of Education and Research (BMBF), the project has now been completed after three and a half years with the production and field test of headlight demonstrators. For the implementation, Osram Opto Semiconductors, Infineon and the Fraunhofer Institute for Reliability and Microintegration (IZM) in Berlin, Germany developed an LED chip with 1024 individually controllable pixels. In the current generation of adaptive headlights on the market, several LED components are installed in the headlights side by side and on top of each other. Additional electronic components are required to switch light segments on and off. The number of segments is limited due to the restricted space in the headlight. In the new approach, electronic activation of the LED is integrated in the chip, resulting in much higher resolution, while still meeting limited space requirements. For the high-resolution, smart automotive lighting, in a second step the Osram Specialty Lighting unit developed an LED module featuring an electrical and thermal interface that enables direct connection to the vehicle's electronics.

The project has now demonstrated the feasibility of the system. When a smart, high-resolution headlight is used, driving and weather conditions are continuously analyzed: what is the course of the road, how fast is the car driving, is there oncoming traffic, and what is the distance between the car and other vehicles? Based on these conditions, the variable, adaptive light distribution ensures tailor-made lighting in every situation, e.g. at high speeds, the light beam's range is increased automatically. In city traffic, on the other hand, wider light distribution improves safety as, in addition to the road, also the sidewalk and peripheral areas are illuminated better. These functions are implemented fully electronically with no mechanical actuators. With glare-free full beam the driver always has the best possible light at night – with no adverse effects for other drivers. For motorists this is a benefit in terms of awareness, helping to reduce the risk of accidents when driving at night.

"We now want to develop this new type of high-resolution LED light source so that it's ready for serial production and we see enormous potential for its use in headlights," says Osram Licht AG's chief technology officer Stefan Kampmann.

Infineon developed the intelligent driver circuitry in the LED chip. This allows each of the 1024 pixels to be controlled individually. The semiconductor maker managed to design it in such a way that it can be connected directly with the light-emitting LED array above it. The technical challenge lay in reconciling the special requirements for this with the manufacturing technologies for LED drivers. With the intelligent driver circuitry and its broad automotive application expertise, Infineon is supporting the trend toward adaptive front-lighting systems (AFS).

Hella specified the main technical requirements for the light source based on the functional requirements from Daimler. The light and electronics firm developed the entire optical system for the light modules and its cooling concept as well as the prototype headlights. As well as being efficient, they generate a very homogeneous light pattern and, in addition, the individual pixels have good lighting quality. The different light patterns can thus be generated purely electronically with no mechanical actuators (representing a step towards digitization in the lighting industry).

In the research project, Daimler specified the functional requirements and the future vehicle properties for the complete headlight system. This was the basis for the components and module properties for the overall headlight system, which calculates the best light distribution with consideration of future sensors and vehicle architectures and passes this information on to the pixel headlights. Regarding future electric vehicles, energy efficiency is an important requirement for the newly developed LEDs. A vehicle from Daimler with the smart LED headlights was used for the field trials under real traffic conditions.

The existing Mercedes-Benz E-Class car contains MULTIBEAM LED headlights from Hella which each have 84 individually controllable Osram LEDs. Daimler is continuing to develop LED headlights with a greater number of increasingly finer pixels.

Fraunhofer contributed to the project its competence in connection technology (LED & ICs) and materials as well as in the detection and isolation of defects. The high resolution was achieved through even finer structuring with miniaturized connection technology. For this purpose, at the Fraunhofer Institute for Reliability and Microintegration (IZM), LED arrays from Osram with 1024 pixels were assembled on an active driver circuit from Infineon that controls each pixel individually. Aided by effective cooling, the chips were assembled to enable micron-sized height differences to be balanced out.

Two different assembly techniques were investigated: thermos-compression bonding with porous gold nano-sponge and reflow soldering with highly reliable gold-tin. Both assembly techniques proved to be successful with a high yield and a robust interface for the subsequent LED processes.

One of the technical challenges of the high-resolution LED headlight is the comparatively large chip with 1024 individually controllable pixels. This is because, as the LED chip size increases, it raises the risk of failure or decreased luminosity of the individual pixels in the pixel matrix during the production process. To overcome this problem, the Fraunhofer Institute for Applied Solid State Physics IAF in Freiburg, Germany developed new technology to repair defects. It is based on ultraviolet laser micromachining and enables defects in LED chips to be repaired during the production process. The microscopic defects are identified and removed with a UV laser through careful material removal or are electrically isolated without the laser inadvertently causing new defects (leakage current paths). When they have been repaired, the pixels regain their full luminosity – the luminescence pattern is homogeneous again.

The economic benefits of laser micromachining from the Fraunhofer IAF are not only in reducing defects during production and thus lowering production discard and costs for large LED chips. The process can also increase the average life of the LEDs (an important competitive advantage).

Supported by the German Federal Ministry of Education and Research (BMBF) under funding ID 13N12510, the μAFS project ran from February 2013 to September 2016, and achieved the aim to develop a smart lighting solution as the technical basis for a new class of energy-efficient LED headlights with additional road safety functions. Adaptive front-lighting systems (AFS) can be developed from this, enhancing safety for drivers, passengers and other road users.

See related items:

Osram's Oslon Compact LEDs used for adaptive headlights on new Mercedes Benz CLS Class

Osram launches Ostar Headlamp Pro as first LED for Advanced Forward Lighting Systems

German research project focuses on intelligent LED headlamps

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