Gallium oxide MOSFET sees record 8kV breakdown

June 01, 2020 //By Nick Flaherty
A lateral gallium oxide MOSFET developed at the University of Buffalo uses a polymer passivation layer to achieve a breakdown voltage over 8kV.
A lateral gallium oxide MOSFET transistor developed at the University of Buffalo uses a polymer passivation layer to achieve a breakdown voltage over 8kV.

Researchers at the University of Buffalo in the US have developed a lateral Gallium Oxide transistor with a breakdown voltage as high as 8kV for high voltage power electronics.

“To really push these technologies into the future, we need next-generation electronic components that can handle greater power loads without increasing the size of power electronics systems,” said lead researcher Uttam Singisetti, associate professor of electrical engineering at the UB School of Engineering. The transistor could also benefit microgrid technologies and solid-state transformers.

The bandgp of a gallium oxide transistor is electron volts, placing it ahead of other wide bandgap silicon carbide (3.4eV) and gallium nitride (3.3eV) for high voltage power and high frequency switching applications.

The Ga 2O3 MOSFET uses SU-8, an epoxy-based polymer commonly used in microelectronics, as the passivation layer to achieve the high breakdown voltage.  The team achieved a  record high breakdown voltage of 6.72 kV for a MOSFET with a gate length (Lgd) of 40μm, giving an average field strength of 1.69 MV/cm. The peak drain current is 3 mA/mm for a 2μm device with a gate source separation of 3 μm . The on-resistance for the device (Ron) is 13kΩ. mm, giving a Figure of Merit of 7.73 kW/cm 2 . This high on resistance comes from plasma induced damage of channel and access regions. A key finding is that the Ron and on-current density remain unchanged after passivation. The breakdown increases with the gate length up to 70 μm , giving a maximum breakdown voltage of 8.03 kV.

“The higher the breakdown voltage, the more power a device can handle,” says Singisetti. “The passivation layer is a simple, efficient and cost-effective way to boost the performance of gallium oxide transistors.”

Simulations show the transistor has a field strength of more than 10MV/cm. “These simulated field strengths are impressive. However, they need to be verified by direct experimental measurements,” said Singisetti.

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