1200V GaN uses hafnium gate

Sandia National Laboratories in the US has demonstrated a high power 1200V MOSFET using gallium nitride (GaN) using a hafnium gate with a high-K electric. 

The 1200V MOSFET uses a 100nm hafnium dioxide (HfO2) gate dielectric to achieve a current density of  330 mA/mm at a drain bias of five volts, over ten times that of other 1.2 kV class GaN or even silicon carbide (SiC) MOSFETs.

This is key for automotive designs, and the research was conducted as part of the Electric Drivetrain Consortium, sponsored by the DOE Vehicle Technologies Office. Using GaN for high votlage 880V and 1000V inverter designs can increase efficiency to boost range and reduce costs compared to silicon carbide (SiC) designs. 

The thick HfO2 on GaN gate also has a simultaneous low leakage current (0.5 nA at 2 MV/cm), a high breakdown strength of 5.2 MV/cm, and a high recorded dielectric constant of 22.0).

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Until now, the use of a HfO2 high-κ gate dielectric was thought to be incompatible with wide bandgap semiconductors due to high leakage and low band offset. The gate design with highly doped source layers and low contact resistance increases channel inversion and reduces channel resistance due to the increased gate capacitance associated with the large dielectric permittivity.

Sandia’s process has not only achieved record low gate leakage but also demonstrated an order of magnitude improvement in on-state current densities compared to reports from other GaN and SiC devices.

The researchers compared this to a 3.75 mΩ-cm2 SiC MOSFET fabricated at XFAB which demonstrated 27 mA/mm at a drain voltage (VDS) of 5 V and gate voltage (VGS) of 20 V. Tranphorm, part of Renesas Electronics since June 2024, has also developed a 1200V GaN MOSFET.