Gallium nitride innovations promise to improve the efficiency and size of power-management systems


Imagine an electric-vehicle charger that gets you on the road twice as fast as chargers used today or a motor drive that takes half the space and offers more efficiency than current applications or a laptop computer power adapter that fits in your pocket.

The future of electronics depends on power-management innovations.

Or consider this: Every simple Internet search query uses enough electricity to burn a 60-watt light bulb for about 17 seconds. Now multiply that by billions of queries happening every day and you end up with billions of kilowatt hours of energy consumption.

The challenge to manage energy more efficiently and squeeze more power into smaller spaces continues unabated. New innovations such as gallium nitride (GaN) promise to significantly improve many aspects of power management, generation and delivery. It’s expected that power electronics will manage about 80 percent of energy by 2030, up from 30 percent in 2005.1 This amounts to more than 3 billion kilowatt hours of energy savings. That’s enough electricity to power more than 300,000 homes for a year.

Anything that gets its power directly from the grid – from smartphone chargers to data centers – or that deals with high voltages up to hundreds of volts can benefit from technologies such as GaN that will improve the efficiency and size of power-management systems. (Read our new white paper: GaN drives energy efficiency to the next level.)

The search for a perfect switch

Ahmad BahaiThe centerpiece of any power-management system is a switch, which turns power on and off. It’s like a light switch on your wall, except millions of times faster and smaller. Efficiency (low losses), reliability, integration and affordability are critical attributes of a semiconductor power switch.

The search for the ideal switch is ongoing. The ideal switch conducts current with little “on” resistance and blocks the current with as little as possible leakage current while blocking significant voltage across its terminals in the off state. A higher switching frequency also means that engineers can design smaller overall power-conversion solutions. Above all, semiconductor switches must be reliable and able to be manufactured cost-effectively.

Silicon power switches have been improving in power efficiency, switching speed and reliability over several decades. These devices have successfully addressed efficiency and switching frequency in low voltage – below 100 volts – or high-voltage tolerance (IGBTs and super-junction devices). However, due to the limitation of silicon, all these features cannot be offered in a single silicon power FET. Wide bandgap power transistors such as GaN and silicon carbide (SiC) promise to offer high power efficiency at high voltages and high switching frequencies above and beyond silicon MOSFET offerings.

What GaN can do for you

An efficient high-frequency switch can reduce the size of power modules by three to 10 times, depending on the application, but requires an optimized driver and controller topology. The totem pole AC/DC converter is a topology, not viable in silicon, that can benefit from GaN’s low on resistance, fast switching and low-output capacitance to offer three times higher power density. Resonant architectures such as zero voltage and zero current switching that mitigate switching losses and improve overall efficiency can also benefit from GaN’s superior switching characteristics.

Many applications require power conversion from relatively high voltage – in the hundreds of volts – to low voltages supplied to circuit components such as processors. Switched-mode power converters with a high input-to-output voltage ratio offer lower efficiencies. These power-management blocks usually involve multiple stages of conversion. Direct conversion from intermediate 54/48 volt bus to the processor core voltage can reduce costs and improve efficiency. GaN, with its unique switching properties, is a strong candidate for direct conversion architectures. Direct conversion is currently being studied for the power management of servers in data center applications.

Also, applications such as laser drivers for LIDAR in autonomous vehicles, wireless charging, and envelope tracking by high-efficiency power amplifiers in 5G base stations can benefit from the efficiency and fast switching of GaN technology.

The reduced conduction loss of GaN power devices, in conjunction with a higher switching frequency, results in much higher power density. But thermal management and parasitics do not scale! Concentrating more power in a smaller volume creates new challenges for heat dissipation and packaging. A smaller die surface area limits the efficiency of traditional packaging techniques. Three-dimensional heat spreading is a promising option for GaN packaging.

Living greener

In order to break the cycle of cost and mass adoption, a new power semiconductor technology needs to address some of the shortcomings of incumbent devices in the most compelling applications. GaN is opening the door to drive power scaling beyond what silicon can offer in high-voltage applications. An inverter for an industrial motor drive or a grid-tied energy storage system can immensely benefit from the higher density offered by GaN devices.

GaN offers other unique, untapped properties that can deliver new values and opportunities for future power management. The bidirectional structure of a GaN device, unlike a typical PN junction MOSFET, can control the current flow with a dual-gate structure. A matrix converter for motor drives can potentially reduce the number of switches by taking advantage of a bidirectional device. Furthermore, GaN devices can operate at higher temperatures than silicon devices, which make it an attractive choice for many hot applications, such as integrated motor drives.
 
The long-term implications of groundbreaking technologies such as GaN are significant: The lower power loss will mean we won’t need as many new power plants to meet increasing demands for electricity. Higher power density will mean more integration. Battery-powered circuits – such as those in electric vehicles, drones and robots – can run longer and more efficiently. Data centers with their thousands of servers that help us connect with friends and colleagues will operate more efficiently. We’ll be able to live greener lives.

Additional resources:


1- Power Electronics for Distributed Energy Systems and Transmission and Distribution Applications, ORNL, 2005