1200V GaN Switches on Sapphire Substrate

We present results on 1200V GaN switches made with HEMTs on sapphire substrates. These are fast-switching, low loss devices extending the high performance of GaN switches to higher voltage levels. The insulating nature of sapphire substrates can help to extend the rated voltage of GaN HEMTs to 1200V and beyond, while simultaneously using a much thinner buffer layer compared to GaN-on-Si for similar voltages. Using a 70 mΩ GaN-on-sapphire 2-chip normally-off GaN FET in TO-247 package, we obtained >99% efficiency for a 900:450V buck converter operating at 50kHz. The GaN die has R
ON,sp
of 6.1mΩ.cm
²
and the device shows excellent switching FOMs with R
ON
.Q
G
= 0.9 Ω.nC, and R
ON
.Q
RR
= 11 Ω.nC. The sapphire substrate is thinned to below 200μm to give a thermal resistance comparable to that of packaged GaN-on-Si switches. These results indicate that a correctly engineered GaN-on-sapphire technology can be a very competitive platform for the 1200V power device market.