Researchers Develop Paper-Thin Gallium Oxide Transistor That Can Withstand Over 8,000 Volts Before Breaking Down

Researchers at the University of Buffalo (UB) have developed a breakthrough in power electronics, a lateral gallium oxide-based transistor that can withstand more than 8,000 volts while being thinner than a sheet of paper.

With research funding from the United States Air Force Office of Research, the University of Buffalo‘s department of electrical engineering has been able to study potential gallium oxide applications over that last couple of years. In 2018, Dr. Uttam Singisetti, an associate professor of electrical engineering at the UB school of engineering and applied sciences, discovered a new type of transistor could be created for high-voltage power electronics. They established a lateral gallium oxide field-plated transistor that yielded a breakdown voltage of 1.85 kV. 

Device schematic (a), optical microscope image of MOSFET (b), optical microscope image of MOSFET after a breakdown. Image (modified) used courtesy of the University of Buffalo.

 

After this study, Dr. Singisetti concluded that if they were to increase the gate-to-drain distance of the layer (LGD) they would obtain an increase in breakdown voltage. From 2018 to now, the researching team led by Dr. Singisetti was able to finalize testing and simulations just weeks before they were shut down due to COVID-19. The new study had evolved and brought results that showed gallium oxide transistors could handle 8,032 volts before breaking down. 

This significant change from 1.85 kV to 8.032 kV was due to an increase in the LGD from 2 micrometers to 70 micrometers, coupled with the fact that the gallium oxide holds a wide-bandgap. The material’s bandgap measures how much energy is required to jolt an electron across into a conducting state. The ultra-wide bandgap provides high electric field density, good electron mobility, and good RF performance. 

Systems made with wide-bandgap materials can be thinner, lighter, and stronger to handle more power than systems with lower bandgaps. This could be a pivotal change for the semiconductor industry towards power electronics and allow devices to become lightweight with transistors still having fast-switching capabilities at high voltages.

 

Gallium Oxide Transistors 

The proposed gallium oxide transistor utilizes the chemical process known as passivation, which involves coating the device to reduce the chemical reactivity of its surface. Dr. Singisetti and his team added a layer of SU-8, a light-sensitive epoxy-based polymer material commonly used in microelectronics. SU-8 is hard-baked at 200 degrees Celsius for 10 minutes. 

 

Comparison of non-passivated and passivated transistors, reference data for GaN devices. Image (modified) used courtesy of University of Buffalo.

 

“The passivation layer is a simple, efficient, and cost-effective way to boost the performance of gallium oxide transistors,” stated Dr. Singisetti.

Results concluded, a SU-8 polymer passivation scheme held a significant increase in breakdown voltage at a given gate-drain separation and no effects on the input or output of the device. It is left with a lightweight passivated transistor with an actual thickness of 5 micrometers, to put it into perspective, the thickness of a standard sheet of paper is 100 micrometers. 

 

Automotive Applications 

Small and powerful electrical components like the gallium oxide transistor become an ideal solution for larger power loads without increasing the actual size of the electronics. Dr. Singisetti discussed the importance of his research, “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 electronic systems.”

For automotive applications, electric vehicles require high energy density batteries which usually have heavy batteries, some weighing over 1,000 pounds. The extreme battery weight is in correlation with cars being designed to go a longer distance before needing to charge. Some vehicles, such as the Tesla 3, can travel 310 miles before needing to charge, this is with industry-standard silicon materials. Now, if companies like Tesla were to incorporate gallium oxide transistors for controls and power management, the system could potentially double the traveling distance. 

 

Future Gallium Oxide Power Devices

The most commonly used material in power electronics is silicon. Silicon yields bandgap energy of 1.1 electron volts while gallium oxide holds bandgap energy of 4.8 electron volts. Introducing gallium oxide-based transistors into power electronics could allow developers to create lighter and more efficient electronic systems that can control and convert electric power. 

With the passivation layer, gallium oxide transistors can potentially meet or even exceed the performance of silicon and typical widegap semiconductors such as SiC or GaN for ultrahigh‐voltage power switching applications.