RF Nitro debuts GaN HEMT transistors RF Nitro Communications, a manufacturer of GaN products based in Charlotte, North Carolina, has introduced its first AlGaN/GaN transistors (see ). The company first demonstrated GaN-based VCOs in February of this year, and has now made available for evaluation prototype transistors fabricated on either sapphire or semi-insulating SiC substrates. Applications for the company s HEMTs, which offer wide bandwidth operation and breakdown voltages approaching 100 V, include high power switching, driver amplifiers, electro-optical modulators and oscillators. To date, RF Nitro has grown GaN devices by MOVPE in an 8 2-inch production reactor (see Compound Semiconductor Sept/Oct 2000, p17). The company says that its AlGaN/GaN-on-sapphire HEMTs offer the advantages of a low cost substrate, and deliver a power density of up to 2 W/mm at 10 GHz. AlGaN/GaN-on-SiC HEMTs dissipate more heat than devices grown on sapphire, and allow higher voltage operation, in addition to a power density of 6.6 W/mm at 10 GHz. "Large-diameter sapphire costs approximately $100 per substrate, and GaN-on-sapphire offers superior insulating properties, lower defect density, higher frequency performance, and superior power performance over GaN-on-silicon approaches," said Joseph Smart, VP of advanced materials. "SiC substrates are expensive, but GaN-on-SiC offers the best combination of frequency and power performance for high-power applications." RF Nitro s NGN-125-D (Al)GaN-on-sapphire device features a coplanar design with a 1 mm periphery and gate length of 0.5 m. Available in die form, the device provides a gain of 9.7 dB and saturated output power of 29 dBm, while the third order intercept (IP3) and noise figure reach +39.5 dBm and 3.5 dB, respectively (at 2 GHz). The cut off and maximum oscillation frequencies (Ft and Fmax) are 16 and 26 GHz, respectively. The company s (Al)GaN-on-SiC HEMT (NGN-225-D series) offers similar performance and features a 1.5 mm periphery, a gain of 8.6 dB and saturated output power of 31 dBm at 10 GHz. The IP3 value is 35 dBm and Ft and Fmax are both 24 GHz. Processing facility completed RF Nitro has also completed a new facility for GaN epitaxy and wafer processing. Located at the company s headquarters in Charlotte, the facility houses class 10 and class 1000 clean rooms intended for the production of GaN-based heteroepitaxial structures and power transistors. The new facility will enable an expansion from 2 inch diameter epiwafer capability to 4 inch epitaxial growth using RF Nitro s patented high-throughput Flow Modulation Epitaxy (FME) technology. According to VP of sales and marketing, B J Lyman, RF Nitro is currently using external foundry facilities to process its chips, and will begin producing 4 inch GaN epiwafers at its Charlotte facility by 2002. "At present we have a prototype production facility that is undertaking high-frequency packaging of GaAs and GaN devices," says Lyman. "All of the NGN series of nitride products are presently at the evaluation stage, and we are now increasing the throughput of these devices to satisfy interest. In the near term, our GaN activity will evolve from discretes to MMICs, available in either chip or packaged form." "This facility is indicative of our commitment to offer our customers a low-cost and high-performance GaN IC technology," added Jeff Shealy, president and CEO. "With this new facility, we will extend our market leadership from GaN epitaxial materials to GaN devices and amplifier circuits for wireless and wireline infrastructure." Cree licenses "pendeo" patent for low-defect-density GaN growth North Carolina State University (NCSU) has granted Cree an exclusive license for patented technology that allows the growth of low-defect-density GaN layers. Cree has licensed US patent no. 6,265,289, issued to NCSU on July 24, 2001, which describes methods of fabricating GaN layers and device structures using lateral growth from sidewalls into trenches. The technique, known as pendeo-epitaxy, reduces the defect density of GaN grown on sapphire or SiC substrates. During conventional growth, lattice mismatch causes dislocations that propagate in the vertical growth direction, resulting in GaN with dislocation densities of around 108109/cm2. In pendeo-epitaxy, trenches are etched in a GaN layer and growth conditions are adjusted so that subsequent GaN growth occurs from the trench sidewalls (see Compound Semiconductor March 1999, p16). Since the dislocations do not propagate significantly in the lateral direction, defect densities are typically several orders of magnitude lower, which is important to the performance and longevity of certain devices, particularly lasers. The same effect is achieved using lateral epitaxial overgrowth (also known as LEO or ELOG), which requires the use of an SiO2 or other mask. Nitronex uses alternative technique Cree is not the only company using the pendeo-epitaxy approach. Nitronex (Raleigh, NC), which is developing GaN-on-Si devices for RF and optoelectronic applications, has trademarked the term "Pendeo" to include its entire process from epitaxial growth to device fabrication. Nitronex has a number of patents in this area, including several licensed from NCSU. A search of US patents unearths at least five documents covering pendeo-epitaxy and lateral growth recipes for GaN layers. All are assigned to NCSU, and some include authors who now work at Nitronex. While Nitronex has not revealed which patents it has licensed from NCSU, the company says there is no intellectual property overlap with Cree s technology. "There are many ways to grow lateral epitaxial layers of GaN," says Warren Weeks, who heads up Nitronex s optoelectronics division. In fact, Nitronex has filed patents on its own proprietary approach. Low-defect-density lateral growth As well as including lateral growth of GaN outwards from trench sidewalls, the patent licensed by Cree describes how further reductions in defect density can be achieved if masks with windows are subsequently deposited. The GaN layer grows upwards through these mask openings and then also grows laterally, forming an overgrowth layer of low-defect-density GaN material. Alternatively, further growth in the vertical direction can produce a plurality of trenches, which are again used to grow lateral layers of GaN. Devices can then be grown on these surfaces. "The issuance of this patent significantly extends Cree s portfolio of technology, critical in the development of high performance GaN-based devices," said president and CEO, Chuck Swoboda. "Growing low-defect layers of GaN is essential to the realization of long-lifetime GaN-based laser diodes and other high-performance devices. We believe this patent strengthens our intellectual property position immensely, since it covers use of the patented process on any substrate." Cree s first SiC Schottky diodes Cree has begun shipping sample volumes of its first SiC Schottky diode chips. These will find application in high power circuits such as high frequency power supplies and motor controls. Typically, 50% of the power loss in a silicon PIN diode-based circuit arises because of the slow switching speed of the diode. SiC is able to operate at much higher speeds, virtually eliminating this source of power loss. It is expected that this will give an overall reduction in power consumption of between 4 and 7%, allowing smaller device sizes and reduced heat sink areas. Initially two device types are being sampled, a 600 V, 1 A device and a 600 V, 4 A device. Cree are expecting to ramp up production during the first quarter of fiscal 2002, with additional products to be added over the next year. In further news, a joint program with Kansai Electric Power Company has yielded record results for several high-power devices. A 6 kV MOSFET and a 5.5 kV JFET had on-resistances that were only 1/25 and 1/65, respectively, of the theoretical limit for the equivalent silicon devices. High voltage SiC PIN diodes have also been demonstrated with blocking voltages up to 19 kV, 50% over the previous record and double that from commercially available silicon devices.