Toshiba Announces Gallium Nitride Power FET with World's Highest Output Power in Ku-band

Toshiba Corporation today announced that it has developed a
gallium nitride (GaN) power field effect transistor (FET) for the
Ku-band (12GHz to 18GHz) frequency range that achieves an output power
of 65.4W at 14.5GHz, the highest level of performance yet reported at
this frequency band. The main application of the new transistor will
be in base stations for satellite microwave communications, which
carry high-capacity signals, including high-definition broadcasts.
Toshiba plans to start sample shipment of the new power FET by the end
of 2007 and to go into mass production by the end of March 2008.

Advances in Ku-band microwave amplifiers focus on replacing the
electron tubes conventionally used at this bandwidth with
semiconductors, particularly GaN devices, which offer advantageous
high power characteristics at higher microwave frequencies.

The new power FET has a high electron mobility transistor (HEMT)
structure that Toshiba has optimized for the Ku-band. The company
replaced source wire bonding with via hole technology(1) to reduce
parasitic inductance, and also improved overall design of the matching
circuit for practical application at Ku-band frequencies.

Demand for GaN power FET for radars and satellite microwave
communications base stations is growing steadily, both for new
equipment and replacement of electron tubes. Toshiba will meet this
demand with early commercialization of its new Ku-band power FET.

Full details of the new GaN power FET will be presented at the
European Microwave Conference 2007, in Munich, Germany from October 8
to 12.

Background and development aims

Ever increasing communications flows in satellite microwave
communications are driving demand for higher output power in signal
amplifying devices, as is development of more powerful radar systems.
Demand is particularly strong for GaN devices, which offer advantages
over conventional gallium arsenide devices in heat dissipation and
high power performance characteristics at high frequency.

Toshiba has taken the lead in applying GaN technology to power FET
for microwave frequency applications. The company directed its initial
efforts to the development and marketing of power FET for the 6GHz
band (2005) and 9.5GHz (2006) band, and developed devices that
achieved the worlds highest output power at those frequencies. The
company has now extended its line-up to 14.5GHz. Toshiba will continue
development for the 18GHz to 30GHz frequencies (Ka-band) and beyond.

Outline of development

1. Device technology

Toshiba achieved the outstanding performance of the new FET by
optimizing the composition and thickness of the AlGaN and GaN layers
formed on the highly heat-conductive silicon carbide (SiC) substrate
of the HEMT structure. To assure high performance at Ku-band
frequencies, Toshiba has applied a shorter gate length of below 0.3
microns, and optimized the shape of each electrode and element
configuration to enhance heat dissipation.

2. Process technology

To reduce the parasitic inductance and improve higher frequency
performance, Toshiba developed a unique technology for forming via
holes, which pass from the surface source electrode through the chip
to the ground. Success in forming via holes in SiC substrate,
recognized as a highly demanding process, is a breakthrough in
development of the new FET.

As gate lengths shorten, suppression of current leakage at the
gate electrode is essential for achieving high level performance. A
unique overcoat process applied around each gate electrode contributes
to suppressing gate leakage to 1/30 that of Toshiba's conventional
approaches. Electron beam exposure technology is applied in order to
secure stable processing of gate lengths below 0.3 micron meters.

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*T
Key characteristics
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Linear gain 8.2dB
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Saturation power 65.4W
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Drain voltage 30V
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Operating frequency 14.5GHz
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Chip size 3.4mm x 0.53mm
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Package size 21.0mm x 12.9mm (external dimension)
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*T

(1) A technology of forming through hole and filling metal
electrode in the hole for connecting surface source electrodes to the
backside ground electrode, that enables to reduce the parasitic
inductance, and thus, to improve high frequency performance.

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