GaN high-frequency transistors achieve record efficiency

GaN high-frequency transistors achieve record efficiency

Technology News |
By Wisse Hettinga

There are several ways to increase the power density of transistors. Researchers at Fraunhofer IAF have chosen the path of increasing the operating voltage: By scaling the transistor design vertically and laterally, they succeeded for the first time in Europe in realizing high-frequency transistors suitable for applications at an operating voltage of 100 V. These components based on the semiconductor gallium nitride (GaN) are characterized by a significantly increased power density at frequencies in the GHz range.

The performance of these newly developed components for the frequency range of 1 – 2 GHz has been demonstrated in the laboratory. Measurements showed a power density of more than 17 W/mm and a power efficiency (PAE) of 77.3 percent at a frequency of 1.0 GHz. This is the highest power efficiency achieved for 100 V operation in this frequency range ever reported. Tests have even shown that this technology has a power density of over 20 W/mm at 125 V.

“By increasing the operating voltage from 50 to 100 volts, higher power densities are possible. This means that a system can deliver more power over the same area than is possible with commercially available 50 V or 65 V technologies,” explains Sebastian Krause from Fraunhofer IAF, one of the main developers of the technology.

On the one hand, this makes it possible to produce more powerful systems of the same size. On the other hand, it will also make it possible to create more compact and lighter systems with the same performance. “By doubling the operating voltage to 100 V, the transistor has an output impedance four times higher for a given power,” explains Krause. This makes it possible to implement smaller and thus less lossy matching networks, which in turn results in higher energy efficiency of the overall system.

The long-term goal of the development is to operate at up to 10 GHz. This would make the Freiburg, Germany based Fraunhofer Institute the first source of such 100 V components based on GaN. This is of particular interest for high-performance applications such as mobile radio base station amplifiers, pulse and continuous wave radar particle accelerators, industrial microwave heaters and amplifiers for plasma generators. Usually, such systems require a lot of power while at the same time the volume requirements of the components are low – exactly what 100 V technology is supposed to enable.

Power generators for microwave heating are a large industrial application. “In the field of plasma generation, industry usually works with higher frequencies, but many users still use vacuum components such as magnetrons or klystrons. Here we are working on providing an alternative based on semiconductors, since semiconductors are much more compact and lighter and can be used to realize arrangements such as phased arrays, for example,” says Krause.

For a long time, tube-based components (e.g. traveling wave tubes) have dominated electronic systems with high power requirements. In the meantime, however, development is moving towards power semiconductors. Fraunhofer IAF scientists see 100 Volt technology based on GaN as an efficient alternative for increasing the power of microwave generators.

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