Ever wanted a light bulb that lasts up to 10 years, a blue laser that will quadruple the storage capacity of a compact disc or aerospace components that can operate over a wide temperature range and remain unaffected by radiation. Then a remarkable kind of semiconducting material made from gallium nitride and its close chemical cousins: aluminum nitride and indium nitride may be the answer.
"Gallium nitride is a material that few people outside of the electronics field have even heard of," said ONR Program Officer John Zolper. "But it may turn out to be one of the most important materials of the new millenium."
Gallium, aluminum, and indium are metallic elements that all reside on column three of the Period Table. By adding nitrogen atoms to their chemical structures, they become semiconducting materials that, when paired with appropriate substrate materials, can serve as next-generation transistors for advanced military and commercial applications.
The Office of Naval Research was a pioneering supporter of these nitride-based materials, dating back to the early 1970s. As the applications list above implies, they have a range of potential commercial as well as military uses.
During the last five years, some stunning breakthroughs in the production of blue and green lasers and light emitting diodes, or LEDs, with reliably extended lifetimes generated excitement in scientific circles about these nitride-based materials.
More recently, transistors with new world records in power, power density and efficiency reported by Cornell University, Cree Inc., the University of California at Santa Barbara, HRL LLC., and other laboratories have refocused attention on these materials for several electronic devices, including amplifiers.
New radar technology that can search, detect, and track smaller and faster targets in the littoral, or coastal, zones of the world where future Naval conflicts are expected to occur is a driving force behind ONR's long-term support of gallium nitride technology.
"For a Navy radar system to be effective in the littoral zone, it must be able to pick out of the clutter the signal of a missile coming out of a cave on the side of a coastal mountain," Zolper said.
Gallium nitride amplifiers will take the place of vacuum tubes in most Navy radar systems once they are available, Zolper said. Most military radar systems are still based on vacuum tubes, which have the needed power, but whose "phase noise" reduces a system's sensitivity.
Reducing phase noise is at a premium in high-clutter environments such as the coastal zones where land formations, man-made structures and human activity create a lot of background clutter.
Newer military electromagnetic systems will also require active aperture antenna arrays with a linear amplifier behind each antenna element. Gallium nitride amplifiers are expected to become the amplifier of choice for many of these applications.
Gallium nitride promises big improvements in the performance of ultra-wide bandwidth communications and radar systems because it can deliver up to 10 times as much power at microwave frequencies as the silicon and gallium-arsenide semiconductors now used in cellular telephones, military radar systems, and satellite transmitters.
The commercial market is considering this technology for wireless base stations due to its superior signal fidelity combined with higher efficiency. It is also one of two enablers for base stations that broadcast multiple beams simultaneously.
One of the most urgent commercial uses for gallium nitride transistors will be the communications satellites that serve communications users and digital satellite TV customers.
Present systems use vacuum traveling wave tubes that require high voltages (more than 2000 V), which often result in reliability problems and preclude the implementation of satellites with multiple independently targeted simultaneous beams.
Systems now under development in commercial and defense-related projects will use hundreds of low-earth orbit satellites to provide service to users anywhere on Earth.
The greater transmitting power and higher efficiencies supplied by gallium nitride materials mean that a fewer number of higher orbiting, multiple beam satellites will do the same job as many more low-earth satellites.
The nitride materials will also boost the power of the transmitting towers, giving them more coverage and versatility, thus reducing the need and expense of installing more towers. In addition, the higher "linearity" and dynamic range of these gallium nitride amplifier devices means more signals can be broadcast simultaneously without undesirable cross talk or distortion.
Due to gallium nitride's chemical composition, scientists also expect the material to exhibit greater "radiation hardness," an attribute that is highly desirable for applications in outer space where components must operate reliably in radioactive environments.
Whatever its application, the technology's biggest hurdle is the lack of an affordable substrate material. The most widely used substrates are sapphire and silicon-carbide. Sapphire is economically attractive at about $100 for a two-inch wafer versus $5,000 for a similar-sized piece of high resistivity silicon carbide.
Many of the technical difficulties have been solved for sapphire, making it an economical choice; however, the high thermal conductivity of silicon carbide makes it the preferred substrate for high-power microwave devices desired by the military because heat removal from the active device is essential to optimize performance.
Development of bulk gallium nitride substrates is also underway. A gallium nitride substrate would be ideal for LEDs and lasers but its thermal conductivity is lower than silicon-carbide's, which will probably limit its use in high-power microwave devices.
Today, at least 180 labs in and out of the United States are researching gallium nitride and related materials. The potential of this field is noteworthy, according to Strategies Unlimited, a marketing firm in Mountain View, Calif.
The company has predicted the overall gallium nitride market -- including LED and laser diodes -- to be about $3 billion annually by 2006. The transistor market by itself is less clear but could reach $436 million by 2009 for all electronic applications.
"Gallium nitride transistors are now reaching a lot of milestones that have long been predicted," Zolper said. The technology base will continue to mature over the next three-to-five years, with commercial and defense-related products being realized at the end of that time frame."
The Office of Naval Research pursues an integrated science and technology program from basic research through manufacturing technologies. Research areas include oceanography; advanced materials; sensors; electronics; surveillance; mine countermeasures; weapons; and surface ship, submarine and aircraft technologies.
Potential applications of Gallium Nitride
Office of Naval Research
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Eliminating Noise In Subspace
Los Alamos - Oct. 30, 2000
Scientists at the U.S. Department of Energy's Los Alamos National Laboratory have taken another step forward in the quest for a quantum-based computer by demonstrating the existence of a physical state immune to certain types of information-corrupting "noise," which could otherwise disrupt computations based on quantum states. The research appears in a recent issue of the journal Science.
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