Uniroyal unveils high output power LEDs Uniroyal Optoelectronics has demonstrated high-brightness blue LED chips with an output of 3.5 to 4 mW. When conventionally packaged, the lamp power output is expected to be between 8 and 10 mW, making these emitters suitable for outdoor displays, in addition to enabling a number of LED-based biomedical and dental procedures. This high output power elevates these devices into the league of other LED manufacturers such as Nichia and Osram Opto Semiconductors; the latter company produces a shaped blue InGaN chip that offers 8 mW when packaged (see Compound Semiconductor February 2001, p7). Uniroyal has also begun shipping 450 and 470 nm InGaN-on-sapphire blue LEDs with a minimum power output of 2 mW in die form. When conventionally packaged, these devices are expected to result in output power levels between 4 and 5 mW. The 450 nm LED can be combined with a phosphor coating to make white lamps for niche applications such as flashlights and nightlights, while the 470 nm emitter is designed for outdoor video displays, biomedical applications and instrumentation. "Uniroyal Optoelectronics is producing increasingly higher quality products from its facilities in Tampa, Florida," said president and chief operating officer Robert Soran. "We recently doubled the capacity of our high-brightness blue and green LEDs, and we are also nearing completion of the build out of additional capacity for these devices." NorLux lighting subsidiary In further news, Uniroyal has formed NorLux, a subsidiary which has been set up to design custom lighting solutions and applications that leverage high-brightness LEDs. Based in Carol Stream, IL, NorLux is equipped with high-capacity, prototype design and test equipment in a class 10 000 clean room. The new subsidiary aims to speed up the development of solid-state lighting-based applications. LumiLeds LEDs optimize backlights LumiLeds Lighting has introduced a backlight source optimized around its new Luxeon LEDs, a range of large-area, high-power devices employing high-flux chips (see Compound Semiconductor March 2001, p11). LumiLeds packaged LEDs now offer outputs upward of 20 lumens in certain colors (such as its 540 nm green device), and these emitters are being employed in the new backlighting system to enable features not currently available with conventional backlighting technology, says the company. In addition, this is the first source that targets medium to large LCD displays, including those used in PCs. LumiLeds is already working with LCD panel manufacturers and hopes to introduce Luxeon-powered backlights by the end of the year. LEDs offer a number of advantages over conventional light sources for this application. Solid-state emitters are more durable than fragile cold cathode fluorescent lamp (CCFL) sources, and at around 10 V their power operation is low enough to significantly reduce electromagnetic interference. LEDs also appear brighter, resulting in NTSC values of up to 130% being produced in the backlight. The NTSC is the color chart definition for typical cathode ray tube screens that defines color saturation e.g. how "red" an object appears. CCFLs exhibit only around 80% of the ideal NTSC value, resulting in paler colors. Added to this is the ability to "color sequence" the LEDs as a result of the Luxeon s very fast (100 ns) switching times. A higher resolution is afforded by the fast modulation and sequencing of the red, green and blue LEDs. Energy requirements are also reduced: in CCFL sources, filters are needed to display the required colors, and the LCD display has three different areas per pixel that open and close to show red, green and blue. This makes the LCD display more expensive and power hungry. As LED displays already consist of individual color-separated emitters, the LCD panel requires just one area that opens/closes per pixel and consumes less power. "This solid-state backlighting solution will allow the LCD display market to go head-to-head with the incumbent cathode ray tube market," explained Mark Pugh, LumiLeds vice-president of strategic marketing. GELcore set to expand LED range GELcore, the joint venture between GE Lighting and Emcore, has introduced new blue, green and blue-green high-brightness LEDs. These InGaN-based devices add to the company s existing white, 620 nm red, 620 nm red-orange, 605 nm Portland orange and 588 nm yellow amber AlInGaP LEDs introduced last year (Compound Semiconductor August 2000, p19). Applications for the new devices, which are housed in clear standard 5 mm packages, include variable messaging, traffic signals, exit signage and specialty lighting applications. Several viewing angles offering different luminous intensities are available. GELcore was set up two years ago to develop solid-state lighting systems. The company subcontracts epiwafer growth, chip fabrication and the manufacturing of LED lamps and lighting systems. Sterling develops SiC diodes with General Electric Sterling Semiconductor, a subsidiary of Uniroyal Technology, has expanded its R&D contract with General Electric Corporate Research & Development (GE CRD) to include the development and evaluation of silicon carbide Schottky diodes. These devices are "building blocks" that support a wide range of consumer and industrial products, including wireless communications, portable computing and automobiles. Si-based Schottky diodes are sold in quantities of 500 million units per year in North America alone. SiC-based devices offer the advantage of being able to operate at much higher voltages and temperatures and with greater efficiencies than silicon devices, allowing for simplified electronic designs and packaging in products that use Schottky diodes. Under its contract with Sterling, General Electric will demonstrate Schottky diodes using Sterling s SiC wafers and epitaxy, applying GE technology developed in part under previous initiatives such as the "Megawatt" device program sponsored by the Defense Advanced Research Projects Agency. The effort is focused on perfecting device design and demonstrating the relationship between device performance and yield, and the characteristics of silicon carbide wafers. The R&D contract with GE CRD is a subcontract to a grant awarded to Sterling in 1999 by the US Defense Department to develop technology for SiC wafer production under Title III of the Defense Production Act. The GE CRDSterling relationship is non-exclusive for both parties. Japanese groups boost SiC MOSFETs The electronics technology research laboratory of the Ministry of Economy, Trade and Industry has developed a silicon carbide MOSFET with one-tenth the internal resistance of previous devices. The lab lowered the internal resistance by reducing the defects in transistor gates and devising a structure that facilitates current flow deep within the substrate, eliminating resistance due to surface defects. Lowering internal resistance in turn reduces energy loss, a significant factor in the development of SiC MOSFETs for applications such as electric vehicles and industrial power generation equipment. The Electrotechnical Laboratory and the Research and Development Association for Future Electron Devices have jointly developed a silicon carbide MOSFET, which achieves a channel mobility of 140 cm2/Vs. The joint research group has devised a new oxide film formation technique and a unique buried channel structure to boost the flow of electrons. The group has also developed an ultra-high-temperature, ultra-speed thermal processor that incorporates a unique post-ion-implantation thermal processing system, and has succeeded in reducing the source drain s sheet resistance to 38 . The prototype SiC MOSFET will pave the way to significantly reducing power losses in SiC-based large power converters. The Power Electronics Research Center of the National Institute of Advanced Industrial Science and Technology has successfully fabricated an interface-controlled enhancement buried-channel 4H-SiC MOSFET that achieves a channel mobility of 140 cm2/Vs at a threshold voltage of 0.3 V. The MOSFET has a thermally grown gate oxide in 4H-SiC, which is prepared by dry oxidation with H2O annealing. The buried channel region was created by nitrogen ion implantation at room temperature followed by annealing at 1500C. The lab has found the optimum doping depth of the buried channel region at 0.2 m. SiC is expected to be used as a next-generation power electronics semiconductor material, which should achieve resistance levels less than 1/100 of those of conventional silicon devices. Cree unveils new 3 inch 4H-SiC wafers Cree has introduced a new 3 inch diameter n-type 4H-SiC wafer to complement its existing 3 inch n-type 6H-SiC wafers. In addition, Cree has demonstrated a 3 inch semi-insulating 4H-SiC substrate, which it says will allow scaling of RF and microwave products for commercial production. The availability of 3 inch wafers more than doubles the available device area per wafer compared to existing 2 inch SiC wafers, and is expected to significantly reduce the cost of devices made from SiC. "The addition of n-type 4H to our 3 inch product family, and the demonstration of 3 inch semi-insulating wafer capability, results from Cree s commitment to converting world-class research into products that respond to the needs of the commercial market," commented Robert Glass, general manager of Cree s materials business.