Transforming power electronics with a new generation of GaN-powered chips.
If the 19th century was all about industrial manufacturing and the 20th century was about information processing, then Tomás Palacios has a prediction for our century: “I believe the 21st century is going to be all about energy processing,” he says. “The future of our society depends on how we solve that challenge.” A professor of electrical engineering and computer science at MIT, Palacios puts his faith in a revolutionary new material to transform our energy future: gallium nitride (GaN). Together with his former graduate student, Bin Lu, Palacios has co-founded the company Cambridge Electronics, Inc. to unlock the potential of this wonder compound and exploit it for commercial and industrial uses.
Used in the electronics industry since the 1990s, GaN has quietly become the second-most common semiconductor in the world after silicon, mostly used in LED lightbulbs. But we’ve only just begun to explore its capabilities. “Gallium nitride is a truly amazing semiconductor material,” says Palacios. “The current flows through the material much more easily than silicon, and you can turn a switch on and off an order of magnitude faster.” With those properties, Palacios believes the potential payoff for using GaN could be huge. “If everything lines up in the right way, we are talking about saving 50 percent of the energy that would otherwise be wasted as heat,” he says.
The key to GaN’s power lies in its wide band gap, a measurement of how much energy needed to free electrons to move around a material. While silicon’s band gap is 1.1 electron volts (eV), GaN’s is 3.4 eV—more than three times as high. That means that the material can support much stronger electric field than silicon and switch between on and off much more quickly and efficiently, resulting in less energy loss. Currently, electricity is generated at high voltage at power plants, but must be converted to much lower voltages to be used by electronic devices. “It turns out that more than 50 percent of electricity generated in the world never reaches the final user,” Palacios says. “It is lost either in the transmission process or in the transformation from high voltage to low voltage or vice versa.” Using GaN to create switching devices to transform voltage could keep energy from being lost, resulting in more sustainable energy production overall.
Despite that promise, however, engineers have needed to overcome multiple challenges in order to unlock the full potential of GaN. Due to characteristics of the material, transistors using GaN tend to be “on” in the default state, while circuit designers prefer them to be “off.” Lu came up with a new way to design the transistor, using a new etching process to enable the default “off” state, which also allows creation of high-frequency devices for 5G communications. He also created three-dimensional fin-shaped structures for the transistors based on what some manufacturers were doing with silicon. “This opened up a new way of shaping the electric field in the devices,” he says, “effectively suppressing current leakage and trapping effects which slow down the speed and increase the power loss of the devices.” Together with Palacios, Lu won an award from the Institute of Electrical and Electronics Engineers (IEEE) in 2012 for the design, which allows the transistors to operate at high voltages at a small size with very low current leakage.
When Lu earned his doctorate in 2013, Palacios suggested that they take these innovations out into the world, creating Cambridge Electronics Inc. to commercialize GaN for power electronic applications. Using GaN instead of silicon could mean engineers could increase the efficiency of power electronic circuits and shrink the size. A laptop power adapter, for instance, could be shrunk to the size where the entire charger fits inside the plug. Similarly, on-board chargers inside an electric car could charge the battery faster and take up less space. Most importantly, GaN could help deal with the massive amounts of energy being used for data centers, which are growing in size exponentially. “Already 2 percent of the country’s energy is being used for data centers,” says Palacios. “Unless we do something really, really fast, we are going to run into huge problems from lack of energy.”
Lu and Palacios have already started making prototypes for new devices, developing the technology further and testing in manufacture environment with industry partners. “Our goal is to build the most versatile and robust GaN technology platform and produce devices and chips that truly unlock the potential of GaN,” says Lu. Rather than spending resources to build a fabrication facility from scratch, the company plans to take advantage of partnerships with companies with existing facilities to make GaN chips within two to three years that could be used in a variety of electronic systems. In a world of constrained resources, arguably none will be as scarce in coming years as energy. GaN can help to face that scarcity head on by helping use the energy we have much more effectively. “If Cambridge Electronics is successful, we will have a really efficient way to bring electricity exactly where you need it in the form you need to do the work you need,” says Palacios. “I think it’s fair to say that gallium nitride is the ideal material for addressing the energy revolution for the 21st century.”