There may be a new player in the semiconductor world in the form of gallium oxide technology. According to Dr. Uttam Singisetti, associate professor of electrical engineering at the School of Engineering and Applied Sciences at the University of Buffalo (UB), this material can play a key role in improving electric vehicles, solar energy and other forms of renewable energy. "We need Electronic components with more powerful and efficient power handling capabilities. Gallium oxide opens up new possibilities that we cannot achieve with existing semiconductors. "
The electronics industry is maximizing the use of silicon as much as possible, but it is still limited, which is why researchers are exploring other materials such as silicon carbide, gallium nitride, and gallium oxide. Although gallium oxide has poor thermal conductivity, its band gap (about 4.8 electron volts or eV) exceeds that of silicon carbide (about 3.4 eV), gallium nitride (about 3.3 eV), and silicon (1.1 eV).
Band gap is a measure of the energy required to bring an electron into a conducting state. Systems made of high bandgap materials can be thinner, lighter, and handle more power than systems made of materials with lower bandgap. In addition, the high band gap allows these systems to be operated at higher temperatures, reducing the need for bulky cooling systems.
5μm Ga 2 0 3 MOSFET
Professor Singisetti and his students (Ke Zang and Abhishek Vaidya) made a 5-micron metal-oxide-semiconductor field-effect transistor (MOSFET) made of gallium oxide, and a sheet of paper was about 100 microns thick.
The researchers said that the transistor's breakdown voltage was 1,850 V, more than double the record for gallium oxide semiconductors. Breakdown voltage is the amount of electricity required to convert a material, in this case gallium oxide, from an insulator to a conductor. The higher the breakdown voltage, the higher the power the device can handle.
Singisetti said that because transistors are relatively large, they are not suitable for smartphones and other small devices. But it may help regulate energy flows in large-scale operations, such as power plants that harvest solar and wind energy, as well as electric cars, trains, and airplanes.
"We increased the power handling capabilities of the transistors by adding more silicon. Unfortunately, this adds more weight, which reduces the efficiency of these devices," Singisetti said. "Gallium oxide allows us to reach and eventually exceed silicon-based devices with less material. This can lead to lighter, more fuel-efficient electric vehicles."
However, to achieve this, some challenges must be addressed, he said. In particular, gallium oxide-based systems must be designed to overcome the material's low thermal conductivity.
The research was supported by the National Science Foundation, the State University of New York's Materials and Advanced Manufacturing Excellence Network, and the University of Buffalo's Institute for Environmental and Water Research and Education (RENEW).
More gallium oxide research
Other researchers are also studying gallium oxide. In an article published by AIP Press in Applied Physics Letters, authors Higashiwaki and Jessen outline examples of the use of gallium oxide for microelectronics. The author focuses on field-effect transistors (FETs), which can benefit from the large critical electric field strength of gallium oxide. The quality that Jessen refers to enables the design of FETs with smaller geometries and aggressive doping profiles that can destroy any other FET material.
"One of the biggest weaknesses in the microelectronics world is getting the most out of power: designers always want to reduce excessive power consumption and unnecessary heat generation," said Gregg Jessen, chief electronics engineer at the Air Force Research Lab. "Usually, you can do this by downsizing the device. However, the technology currently in use is approaching the operating voltage limits required for many of its applications. They are limited by the critical electric field strength."
The material's flexibility in various applications stems from its wide range of possible electrical conductivity-due to its electric field strength, from high electrical conductivity to very insulating and high breakdown voltage capabilities. Therefore, gallium oxide can reach extreme levels. Large-area gallium oxide wafers can also be grown from the melt, reducing manufacturing costs.
"The next gallium oxide application will be a unipolar FET for power supplies," Jessen said. "Critical field strength is the key indicator here. It has excellent energy density capability. The critical field strength of gallium oxide is more than 20 times that of silicon, and more than twice that of silicon carbide and gallium nitride.
The authors discuss the fabrication methods of Ga 2 O 3 wafers, the ability to control electron density, and the challenges of hole transport. Their research shows that unipolar Ga 2 O 3 devices will dominate. Their paper also details Ga 2 O 3 applications in different types of FETs and how the material can be used in high voltage, high power, and power switching applications.
"From a research perspective, gallium oxide is really exciting," Jessen said. "We are just beginning to understand the full potential of these devices in a variety of applications, and now is a good time to participate in this space."
First gallium oxide MOSFET
FLOSFIA successfully demonstrated for the first time in Japan the possibility of using ZnO to achieve normally-off MOSFETs. This is groundbreaking because producing normally-off MOSFETs has always been considered extremely challenging. FLOSFIA plans to manufacture corundum (a crystal structure) α-Ga 2 O 3 power device, GaO series, starting with the Schottky barrier diode (SBD) in TO-220 and then MOSFET.
The first α-Ga 2 O 3 (see Figure 1) of a normally-off MOSFET consists of an N source / drain layer, a p-type well layer, a gate insulator, and an electrode (see Figures 2 and 3). The gate threshold voltage extrapolated from the I-V curve is 7.9V. The device is made of a new p-type corundum semiconductor, which functions as an inversion layer. No theoretical research predicts that p-type materials are compatible with n-type Ga 2 O 3 until the team discovered p-type Ir 2 O 3 in 2016, which was considered to be a very difficult to achieve normally-off MOSFET.
FLOSFIA, headquartered in Kyoto, Japan, is a by-product of research at Kyoto University and specializes in fog chemical vapor deposition (CVD) film formation. Using the physical properties of gallium oxide (Ga 2 O 3), FLOSFIA is committed to developing low-loss power devices. The company has successfully developed an SBD with the lowest specific on-resistance of any type currently available, enabling technology related to power reduction, which is 90% less than before. FLOSFIA will now develop its own production line, focusing on commercial production starting in 2018. It produces various thin films, enhances the MISTDRY technology, realizes the commercialization of power devices, and implements its technology in electrode materials and oxide electronics with functional characteristics Devices, plating and polymers.
In summary, gallium oxide is an emerging power semiconductor material with a band gap larger than that of silicon, gallium nitride, and silicon carbide. However, before becoming a major player in power electronics products, more research and development and advancement work are still needed.