Oki Starts Sample Provisioning of Gallium Nitride Power Transistor for Wireless Base Stations

Tokyo, Japan, January 12, 2005 -- Oki Electric Industry Co., Ltd. (TSE: 6703) today announced it has started sample provisioning of Gallium Nitride(*1) High Electron Mobility Transistor(*2) (GaN-HEMT), a high frequency wave power transistor (high output amps) for wireless base stations, using gallium nitride material. With this transistor, base stations for 3G mobile phones and PHS, and wireless telecom base stations for wireless Metropolitan Area Network (MAN)(*3) can reduce its size and power consumption.

Because GaN-HEMT has a high output power density (output power by gate width) of 3 to 10W/mm, ten-folds higher than conventional gallium arsenide HEMT (GaAs-HEMT), the size of the transistors can be reduced. Traditionally, electric power was combined with multiple transistors to receive high output. However, with GaN-HEMT, a smaller size can be achieved because the output power per transistor is large, which reduces the number of transistors, transmission circuit components and peripheral circuits.

"As smaller size and lower power consumption base stations have been longed for, I believe Oki's Gan-HEMT will impact the GaN high frequency power device market," said Harushige Sugimoto, Chief Technology Officer at Oki Electric. "Going forward, we will work on reducing the size, lowering the cost and achieving higher output by bringing in customer needs and work on commercializing products for 3G mobile phone base stations and wireless MAN products."

As mobile phone service becomes more sophisticated and in variety, the amount of data communication increases, which results in the need for a higher output power. In order to secure a high output power, it is necessary to enlarge the power transistor and as the number of base stations increase, it has been a challenge to expand the size of the base stations and ensure higher power consumption. To avoid power loss in high-frequency cables, most base stations are becoming to utilize tower-top configuration, placing a high frequency amplifier near the antenna. Because of this, it is necessary to make the amplifier chassis small. In addition, in order to reduce the loss of direct current from power cables, higher power voltage is necessary. In particular, the power transistor in the transmitter is required to be smaller and higher voltage as it holds a large portion in package size and power consumption of the amplifier box.

GaN-HEMT can operate at over three to five times higher voltage than that of GaAs-HEMT, which enables higher voltage power. On the other hand, the power loss in peripheral component (ohm loss) is reduced because the operating current can be decreased by 1/3 to 1/5, which contributes to lowering the power consumption of the entire circuit. Because of these advantages, a product for high output wireless and wireless base stations using GaN-HEMT are highly demanded.

By operating in high output power density of 7.8W/mm, in this sample Oki was able to achieve a high output saturation power(*4) of 50.2W and a significant reduction in size, 1/9 of the products from other companies in volume ratio. In addition, the Adjacent Channel leakage Power Ratio (ACPR)(*5), one of the power transistor performance indicator, achieves a low figure of -55dBC (when back off of 10dB in saturation power and 5MHz in W-CDMA(*6) signal input), which is 1/10 of the spec required for the signal amplifier for 3G mobile phone base stations.

Oki plans sample shipment from early 2006, after prior evaluations with specific customers, and volume production from the latter half of 2006. By 2008, Oki aims to achiever 30% of the GaN high frequency power device market in the world.

[Features for the sample GaN-HEMT]

[Glossary]

*1 Gallium Nitride (GaN)

A type of compound semiconductor with a band gap (forbidden band: Eg) of 3.4eV, which is 3 times larger than the conventional semiconductor silicon material of 1.1 eV. Because it has an AlGaN/GaN structure, it can induce high-speed two-dimensional electron gas. GaN is expected to enable a high output wireless base station device that requires super high-speed operation because of its high breakdown voltage.

*2 High Electron Mobility Transistor (HEMT)

A field-effect transistor (FET) used as a channel for two-dimensional electron gas (2DEG) that is induced by hetero junction such as AlGaAs/GaAs and AlGaN/GaN. The 2DEG is high in electron concentration and the mobility range is large. These characteristics enable high transmission gain and high-speed high frequency wave FET performance.

*3 Wireless Metropolitan Area Network (Wireless MAN)

Wireless MAN is one of some types of networks using wireless media. MANs are large computer networks usually spanning a campus or a city. Standardization such as IEEE 802.16a, and industry associations such as WiMAX Forum are being established for practical use.

*4 Saturation power

When input power of high frequency wave is increased in transistors, the output power is also increased, while the increment decreases and the amount saturates. Saturation power is the output power at this time.

*5 Adjacent Channel leakage Power Ratio (ACPR)

In wireless communication systems, frequency wave is separated in certain width (channel) when used. For example, 3G mobile phones (W-CDMA) use 5MHz channels in one carrier. Usually, wireless output is conducted so a signal would fit into a channel width. When the output power increases, wireless output amp deforms and thus cannot fit into a channel, which results in leaking to the adjacent channel. The ratio of this is known as ACPR. Because the leakage affects the communication in the adjacent channel, the smaller the ACPR is the better output device it is.

*6 Wideband - Code Division Multiple Access (W-CDMA)

A standard for communication in 3G mobile phones, in which data can be transmitted in a range of 144kbps to 2Mbps. This enables real-time communication of video and voice. It is efficient because CDMA enables to share a single frequency wave with multiple users. Commercial service is provided mainly in Japan.

Notes:

• Names of companies and products are trademarks or registered trademarks of the respective companies.

Press Contact: