Bandgap is the term used for the amount of energy needed to release electrons in semiconductor materials so that the electrons can move freely, enabling the flow of electricity. Wide Bandgap (WBG) semiconductors such as gallium-nitride (GaN) and silicon-carbide (SiC) have bandgaps significantly greater than those of silicon semiconductors. WBG materials have several characteristics that make them useful compared to lower bandgap materials: WBG semiconductors are able to operate at higher voltages and power densities than silicon-based semiconductors. WBG semiconductors also can operate at higher frequencies, which help to simplify system circuitry and reduce system costs. Further, WBG semiconductors tolerate heat better than silicon so WBG-based power electronic chips can operate in harsher conditions without degrading the semiconductor material, reducing the need for bulky insulation and additional cooling equipment.
Harnessing WBG device capabilities can potentially lead to dramatic energy savings in consumer appliances and industrial processes, accelerate widespread use of electric vehicles and fuel cells, and help integrate renewable energy onto the electric grid. But realizing the potential of WBG semiconductors will require the development of cutting edge manufacturing processes that can produce high-quality WBG materials, devices and modules at an affordable cost.
One venture created in 2014 to accelerate WBG development is the PowerAmerica Institute (PA), a private-public partnership between the U.S. Department of Energy, industry and academia. It is comprised of corporate entities (e.g., ABB, Cree, Lockheed-Martin, Monolith Semi, Transphorm, Toshiba), universities (led by North Carolina State University) and laboratories. Headquartered in Raleigh, North Carolina, PA is a $146 million program, with $70 million provided by the U.S. Department of Energy and $76 million provided by industry, state and academia through cost sharing.
PA recently released a call for projects to advance WBG semiconductor manufacturing and to accelerate the adoption of WBG semiconductors in power electronics applications.
PA’s call for projects is primarily focused on development of advanced WBG power semiconductor technologies, converter and inverter architectures, and packaging and manufacturing processes with the potential to improve the performance and lower the cost of power converters and power management systems.
The call for projects requests proposals that aim to:
Four categories of WBG power semiconductor devices for power electronics applications will be considered:
Voltage Category 1 seeks to scale up manufacturing of WBG power semiconductor devices with blocking voltage in the range of 650 V to 1700 V. Major applications include home appliances, HVAC, building automation, transportation applications such as traction drives for cars and trucks and light rail systems. Industrial applications include automated production lines, robotics, food processing, packaging and logistics. Data center applications include power factor correction circuits and DC/DC converters. Power generation applications include photovoltaic inverters and wind turbine inverters.
Voltage Category 2 covers WBG power semiconductor devices with blocking voltage in a range of 3300 V to 6500 V. Major applications include medium voltage motor drives in mining, oil and gas exploration and refining, chemical, water and sewage plants, lumber processing, wind turbine inverters, locomotive traction drives and HVDC power transmission. PowerAmerica points out that silicon power devices operating in this voltage range typically are significantly de-rated (often by 50%) to improve their reliability. Inverters and motor drives used at these voltage levels also have high power ratings that require the ability to dissipate large amount of heat. Consequently, power semiconductor modules, which contain multiple semiconductor die, have had to feature a large baseplate that can be mounted to heatsink or other cooling devices thus enabling an efficient path for dissipation of up to several kW of heat.
Voltage Category 3 includes WBG power semiconductor devices with blocking voltage of 10 kV and higher. PowerAmerica acknowledges that there are no commercial high power silicon transistors in this voltage range, that the domain of power semiconductor devices has been extended to 10 kV and beyond with the advent of SiC MOSFETs and Schottky diodes. They point out that devices in this category may be able to connect to a medium voltage distribution power grid without a step down transformer. PA further notes that many applications could improve efficiency and performance by changing power circuit topology and replacing multiple power blocks using devices from Category 2 with reduced count of Category 3 devices. This project category will require power modules with high power dissipation capability similar to those in Category 2 combined with high blocking voltage, higher creepage and clearance requirements and partial arc discharge prevention to ensure reliable operation. PA characterizes market adoption for WBG power semiconductor devices in this category as " the most difficult."
Voltage Category 4 seeks to commercialize WBG applications at voltages < 600 V where it has been assumed that silicon devices would continue to dominate because of cost. According to the PA project announcement "this may be changing due to the high switching frequency of WBG devices which results in the use of smaller passive components, and the potential for higher efficiency which potentially results in lower joule heating, and the ability to operate at higher temperatures." Since voltage Category 4 devices operate at lower voltages the associated power electronics applications have less critical reliability requirements. Developing products in Voltage Category 4 could potentially "create volume for GaN/Si epitaxial and wafers that may assist in improving the overall material quality for higher voltage applications."
PA states that it is focused on leveraging interest in this area to assist in the development of a GaN open foundry model for Voltage Category 1.
According to PA’s call for projects announcement application proposals:
Applying organizations will be required to match PA’s funding. A project registration form can be found here . (https://docs.google.com/forms/d/1t0Jhsdu9eCrNATwdhCqrrQT1mQvc_jQ-YCmJYZMQ9WQ/viewform).