Toshiba Corp. announced this week it has developed a gallium nitride (GaN) power field effect transistor (FET) for the Ku-band (12 to 18 GHz) frequency range with an output power of 65.4 at 14.5 GHz, the highest performance level reported at that 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 said it plans to start sample shipments of the FET by the end of 2007 and to begin mass production by the end of March.

"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," Toshiba said in a statement.

"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 said. "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."

The new power FET has a high electron mobility transistor (HEMT) structure that Toshiba has optimized for the Ku band. It said it optimized 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, it applied a shorter gate length -- below 0.3 µm -- and optimized the shape of each electrode and element configuration to enhance heat dissipation.

To reduce parasitic inductance and improve higher frequency performance, Toshiba said it developed a technology for forming via holes that 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," it said. "As gate lengths shorten, suppression of current leakage at the gate electrode is essential for achieving high-level performance."
 
An overcoat process applied around each gate electrode contributes to suppressing gate leakage to 1/30 that of Toshiba's conventional approaches, it said. Electron beam exposure technology is applied to secure stable processing of gate lengths under 0.3-µm meters.

The company said it will continue development for the 18 to 30 GHz frequencies (Ka band) and beyond. It will present details about the new FET at the European Microwave Conference 2007, to be held Oct. 8-12 in Munich, Germany.

For more information, visit: www.toshiba.com