Oki Electric Develops GaN-HEMT on Silicon Substrate with Record High Amplifying Characteristics

With plans for deployment in WiMAX products

Los Angeles, Calif. October 16, 2005 -- Oki Electric Industry Co., Ltd. (TSE: 6703) today announced the development of a power transistor with dramatically improved amplifying characteristics at the 208th Meeting of the Electrochemical Society. This Gallium Nitride High Electron Mobility Transistor (GaN-HEMT), is formed on a large diameter silicon substrate achieving a world record for transconductance rating of 350mS/mm and maximum oscillation frequency (fmax)(*1) of 115GHz. Because this GaN-HEMT is achieved on a silicon wafer --not on conventional SiC (Silicon Carbide)--, it can reduce costs by approximately 50%. This will help wireless communication systems become lower power consumption, smaller and lower cost.

"Succeeding in improving amplifying characteristics for power transistors is an exciting achievement for Oki, as the market has been in need of smaller and lower power consumption wireless communication systems," said Harushige Sugimoto, Senior Vice President and Chief Technology Officerof Oki Electric."By enhancing higher output of transistors based on this technology, we can contribute to the acceleration of WiMAX and next generation wireless communication systems. Volume shipment of such products are planned to start from 2007."

In addition to a 115GHz figure for fmax and 350mS/mm figure for transconductance, which is an indicator of amplification performance, the transistor achieved a 56GHz current gain cut-off frequency(*2). This is a significant improvement from previous GaN-HEMT on silicon substrate devices, which had a range of 70 to 80 GHz fmax, and achieves a performance equivalent to GaN-HEMT on SiC substrates.

Conventionally, power transistors using GaN were developed on a SiC substrate due to its advantage of easy crystal growth. However, there have been problems with SiC boards for its low quality, difficulty to shift to larger diameters, and expensive substrate costs. The newly developed device is a high electron mobility transistor (HEMT), which grows the AlGaN/ GaN structure on the silicon substrate with very few defects and is fifty to a hundred times lower cost than SiC.

By improving the crystal growth technology for gallium nitride on silicon substrate, Oki was able to gain high electron mobility in a high-quality thin film. Oki achieved such high ratings by developing a technology to form the gate electrode on a recessed structure(*3), reducing gate length to 0.2µm, developing a recessed structure for the ohmic electrodes, and optimizing the device structure.

This device was jointly developed with the Research Center for Micro-Structure Devices at the Nagoya Institute of Technology, and with support from The Research Promotion Bureau of Japan's Ministry of Education, Culture, Sports, Science and Technology.

Oki announced this at the 208th Meeting of the Electrochemical Society, held in Los Angeles, U.S.A., from October 16th to 21st.
Symposium Topics : L1-Nitride and Wide Band gap Semiconductors for Sensors, Photonics and Electronics VI
Title : AlGaN/GaN HEMTs with Recessed Ohmic Electrode on Si Substrates

[Glossary]

*1 Maximum oscillation frequency (fmax): Maximum performance frequency when transistor is used as power amplifier.
*2 Cut off frequency (ft): When all amplifiers are operated in a high frequency, gain is reduced. Cut off frequency is an indicator of frequency performance for devices, and determined when the gain is 1.
*3 Recessed structure:: This is a transistor structure that sets gate electrodes on the recession formed by eching. This reduces the parasitic resistance of the transistor and the leakage current, resulting in improving amplification and high frequency characteristics.

[Reference] Device Structure and Frequency Characteristic

About Oki Electric Industry Co., Ltd.

Founded in 1881, Oki Electric Industry Co., Ltd. is Japan's first telecommunications manufacturer, with its headquarters in Tokyo, Japan. With the corporate vision, Oki, "Network Solutions for a Global Society," Oki provides top-quality products, technologies and solutions to its customers through its info-telecom system business, semiconductor business and printer business. All three businesses functions as a collective force to create exciting new products and technologies that satisfy a spectrum of customer needs in various markets. Visit Oki's global web site at http://www.oki.com/.

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