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Compound Semiconductor Devices Offer New Driving Experiences

With increasing electronic content and applications in cars, the automotive industry offers great potential for III-V device manufacturers. Richard Stevenson reports.
Detroit auto giant General Motors predicts that global car sales will reach a new record of 60 million vehicles in 2004, a rise of 3% on the previous year. Sales of semiconductor components within the automotive industry were valued at $12.6 billion in 2003, according to market analyst company Strategy Analytics. Today, electronic content equates to approximately 25% of the costs of car production, and market research firm Frost & Sullivan expects this figure to rise to 40% by 2010. Opportunities to take a cut of this revenue have not escaped the notice of the compound semiconductor industry, with a wide variety of products attempting to penetrate the automobile market.

Predictably, silicon dominates the automobile semiconductor market, but several applications use compound semiconductors. Many of today s cars contain CD players and use LEDs for various interior lighting applications, while some also have optical communication systems driven with LEDs. Luxury models may have DVD players, and advanced driving features such as automotive radar, based on GaAs technology (figure 1). In the future, cars may even include photocatalyst-based air purifiers containing ultraviolet LEDs, and in-car communication using laser diodes. Although these luxury model products will become commonplace, changes will not occur overnight. Unlike the consumer electronics sector, where new product cycles unfold quickly, penetration of the automotive industry takes approximately seven years.

Growth in auto LED marketThe most prominent area that has already been penetrated by compound semiconductors is LED lighting. Sales of LEDs to the automotive sector reached $392 million in 2003 and will grow about 15% this year to around $450 million, says Strategies Unlimited. The industry uses a wide range of LEDs for a whole host of applications. For example, the Audi A3 contains 210 LEDs, with nearly half used for dashboard lighting, followed by radio, climate control, switch and other applications. While LEDs are widely used for interior lighting and displays, they are yet to replace incandescent sources in car headlamps.

Ron Steen, director of lighting R&D at Schefenacker, based in Germany, calculates that today s total headlamp market is 100 million units. He predicts that LED headlamp sales will only reach 1 million units in 2010. This view is shared by Burkard Wördenweber (recently R&D director at Hella KG Hueck & Co, based in Germany). "Commercialization of LED headlamps is still a long way away from the technical and financial goals," said Wördenweber. He believes that hybrid lamps containing both LEDs and other sources will be the next step, and that developments will first emerge in Asia.

Recent advances have seen LED-based daytime running lamps appearing on a variety of concept cars, and more recently on a production vehicle, the Audi A8 6.0. "Today the car industry realizes the advantages that LEDs offer mainly in one application, the center high-mounted stop lamps [that are usually placed above the rear windscreen]," said Wördenweber. "In order for LEDs to spread to the other signal lighting functions, automotive manufacturers have to acknowledge the overall savings possible through packaging (e.g. thin rear lamps). In addition, the designers have to realize the advantages that LEDs offer, such as longer lifetimes, cold-light sources and fast rise times."

In-car communicationLEDs are used as the light source for in-car fiber-optic communication systems, based on a data bus protocol known as media-orientated system transport (MOST) bus systems. These systems are already fitted in over 20 production vehicles, including models manufactured by Mercedes, Porsche, Audi, Citroën, Renault and BMW. Infineon currently has 95% of the market share for MOST transmitters and receivers, although the company has just announced the sale of its fiber-optics business unit to Finisar, a US manufacturer of optical subsystems and test gear. Suitable for data rates of up to 50 Mbit/s, the transmitter is based on a 650 nm LED. The systems connect in-car electronic devices such as CD and DVD players, car navigation systems and video-gaming consoles. MOST systems offer high operating bandwidth, increased transmission security, low weight, immunity to electromagnetic interference, and ease of handling and installation.

Today s MOST systems use 650 nm LEDs and inexpensive plastic optical fiber (POF). However, with the ever-increasing number of gadgets and systems present in cars, such as real-time video cameras for reversing, faster data transmission rates are required. Next-generation systems will comply with the IDB-1394 protocol, the automotive version of the IEEE-1394 standard, also known as FireWire, which targets higher-speed data transfer rates of up to 400 Mbit/s.

At least two different transceiver solutions are under development targeting the IDB-1394 standard. ULM Photonics, based in Germany, is investigating the combination of optical fiber and 850 nm VCSELs, capable of data transfer rates in the region of at least 1 Gbit/s (figure 2). Firecomms of Ireland is instead using resonant-cavity LEDs (RCLEDs), emitting at 650 nm, and POF. Burghard Schneider, the general manager of ULM Photonics, aims to have VSCEL-based systems in cars by 2009. "In addition to low transmission speeds, existing LED-based MOST systems deliver poor performance at higher temperatures," he explained. "Above 105 °C, a typical ambient temperature for automotive applications, POF transmission degrades and LED power output is low."

ULM Photonics has invested a great deal of effort in researching VSCEL reliability, including 85% humidity and temperature shock tests. Schneider believes that the company is capable of producing VSCELs that do not require hermetic sealing, yet will still exhibit excellent temperature behavior with good stability over time. Although the device lifetime required for the car industry is only 12,000 h, failure of any device is unacceptable.

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