GaN power grows and grows
01 March 2007
Two companies are looking into the feasability of Gallium Nitride (GaN) as alternative power sources, writes CAROLINE HAYES.
GaN is characterised by the reduced switching losses that can be achieved in diode and MOSFETs. This reduction can be used to increase efficiency, reduce heatsinks or reduce the transistor’s current rating. Operating frequency can also be increased to allow more smaller, passive components to be used.
As there is no high-frequency oscillation at turn-off, the RFI filter requirements are also lower when using GaN. Active snubber components can be eliminated from the design, as there is no voltage over-shoot at turn-off, typically used in optoelectronics applications and in high-power, high-frequency devices. Used in switch mode power supplies, they can deliver higher frequency power factor correction circuits, which result in increased efficiency, smaller size, lower noise and less heatsink requirements as well as higher yield.
Temperature performance is also improved.
In Tokyo, Toshiba (www.toshiba.co.jp/ index.htm) has developed a GaN field effect transistor (FET) that surpasses the performance of GaAs (gallium arsenide) FETS. Using a HEMT (high electron mobility
transistor) structure in the epitaxial layer, optimising the composition and thicknesses of the AIGaN and GaN layers and optimising the gate length and distance between the source and drain electrodes, to maximise heat dissipation and performance in the X-band, or 9.5GHz, frequencies, delivers an output power
of 81.3W at 9.5GHz. This is, claims the company, six times the power density of a GaAs FET and the world’s highest output power at the 9.5GHz frequency level. The FETs can replace GaAs versions in microwave solid-state amplifiers used in radar and satellite microwave communications, operating in the eight to 12GHz range.
Toshiba announced a GaN power FET with 174W output in the 6GHz band last year and manufacturing has begun for 50W GaN power FETs, with samples released and mass production scheduled by the end of Q2 this year.
STMicroelectronics (www.st.com) is working with GaN transistor and diode manufacturer, Velox Semiconductor in New Jersey, to introduce 600V GaN Schottky diodes.
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