Feb 7 2018
For a long time, silicon has been the go-to material in the realm of semiconductor and microelectronics technology. But silicon still has some limitations, mainly with scalability for power applications. Pushing semiconductor technology to its maximum potential necessitates smaller designs at higher energy density.
This is a false-color, plan-view SEM image of a lateral gallium oxide field effect transistor with an optically defined gate. From bottom to top: the source, gate and drain electrodes. Metal is shown in yellow and orange, dark blue represents dielectric material and lighter blue denotes the gallium oxide substrate. (Image credit: AFRL Sensors Directorate at WPAFB, Ohio, US)
Transparent conductive oxides are a main emerging material in semiconductor technology, offering the unusual combination of transparency and conductivity over the visual spectrum. One conductive oxide specifically has unique properties that allow it to work well in power switching: Ga2O3, or gallium oxide, a material with an extremely large bandgap.
One of the largest shortcomings in the world of microelectronics is always good use of power: Designers are always looking to reduce excess power consumption and unnecessary heat generation. Usually, you would do this by scaling the devices. But the technologies in use today are already scaled close to their limits for the operating voltage desired in many applications. They are limited by their critical electric field strength.
Gregg Jessen, Chief Electronics Engineer - Air Force Research Laboratory
In their article published recently in Applied Physics Letters, from AIP Publishing, authors Masataka Higashiwaki and Jessen state a case for creating microelectronics using gallium oxide. The authors concentrate on field effect transistors (FETs), devices that could significantly benefit from gallium oxide's large critical electric field strength, a quality which Jessen says could enable the design of FETs with smaller geometries and aggressive doping profiles that would damage any other FET material.
The material's flexibility for a range of applications is due to its broad range of potential conductivities and high-breakdown-voltage capabilities because of its electric field strength. Therefore, gallium oxide can be scaled to a maximum degree. Large-area gallium oxide wafers can also be grown from the melt, minimizing manufacturing costs.
The next application for gallium oxide will be unipolar FETs for power supplies. Critical field strength is the key metric here, and it results in superior energy density capabilities. 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 manufacturing techniques for Ga2O3 wafers, the ability to regulate electron density, and the challenges with hole transport. Their research proposes that unipolar Ga2O3 devices will rule. Their paper also covers Ga2O3 applications in different types of FETs and how the material can be of use in high-power, high-voltage, 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 for several applications, and it's a great time to be involved in the field."