Japan startup reports first normally-off gallium-oxide MOSFET

July 17, 2018 // By Peter Clarke
Flosfia Inc. (Kyoto, Japan), a 2011 spin off from Kyoto University, has demonstrated a normally-off gallium-oxide (Ga2O3) power transistor, which it claims paves the way to the use of gallium-oxide as a standard material for power semiconductors.

The company has said it plans to develop its own production lines with a view to launching commercial production of gallium-oxide power devices in 2018.

Silicon is the dominant material for power semiconductors, which are responsible for about $20 billion on annual component sales. Because of the inherent inefficiencies in silicon switching, in recent years silicon-carbide and gallium nitride are starting to be used for power transistor applications.

Gallium oxide is another promising material that happens to come in five different phases. The alpha phase, with a corundum (aluminium-oxide) crystal structure has the most attractive material properties and Kyoto University was demonstrated the first single-crystal growth of corundum alpha-Ga2O3 on a sapphire substrate in 2008.

Flosfia was spun off in 2011 and uses mist chemical vapor deposition – under the name Mistdry – to produce thin films of compound semiconductors.

Flosfia fabricated an alpha-Ga2O3 Schotty barrier diode (SBD) showing specific on-resistance of 0.1mΩcm2, the lowest specific on-resistance ever, according to the company. Flosfia then offered engineering samples of the alpha-Ga2O3 Schotty barrier diode (SBD) in a TO220 package.

In 2016, Flosfia and Kyoto University jointly discovered p-type iridium-oxide (Ir2O3), which has the same corundum structure as alpha-Ga2O3 and could be used within an alpha-Ga2O3 MOSFET.

Flosfia has now manufactured an alpha-Ga2O3 metal-oxide-semiconductor field effect transistor (MOSFET) comprising an n+ source/drain layer, p-type well layer, gate insulator, and electrodes. The device was made on a sapphire substrate.

Next: What is the p-well material?

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