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Japan startup reports first normally-off gallium-oxide MOSFET

Technology News |
By Peter Clarke

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?


The company was ambiguous about the nature of the material used for the p-type inversion layer within the alpha-Ga2O3 MOSFET. This material could be an alternative transition metal oxide that is more commonly used in wafer fabs.

The gate threshold voltage extrapolated from I-V curve was 7.9V. The device is made of a novel p-type corundum semiconductor which functions as an inversion layer, the company said. Without a p-type material it would have been hard to realize a normally-off MOSFET.

Figure 1. I-V curve of normally-off Ga2O3 MOSFET. Source: Flosfia Inc.

The company was ambiguous about the nature of the material used for the p-type inversion layer within the alpha-Ga2O3 MOSFET. This material could be an alternative transition metal oxide that is more commonly used in wafer fabs.

Figure 2. Cross-sectional schematic of device. Source: Flosfia Inc.

Figure 3. Optical micrograph of normally-off Ga2O3 MOSFET. Source: Flosfia Inc.

Flosfia said it plans to manufacture alpha-Ga2O3 power devices under the GaO series name starting with SBDs and MOSFETs for use in AC adapters, motor drivers for motors in robots, electric vehicles and domestic equipment, power conditioning circuits for solar cells. Flosfia claims that GaO has the potential to shrink inverter size tenfold and to halve cost while maximizing conversion efficiency.

Related links and articles:

www.flosfia.com

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