Enhancing the power of Gallium Nitride
26 February 2016
Gallium nitride (GaN) has been around as a semiconductor material for high performance wireless transistors for many years thanks to its wide band gap and high temperature capabilities.
Many RF engineers are used to hearing about it, if not necessarily using it. A challenge is that RF CMOS processes have been pushing into the mid-range wireless applications dominated by GaAs technology, and potentially squeezing out GaN devices as a result, largely entrusting GaN for use in Government programs and other applications that need the performance and can afford the cost.
In recent years a new approach to GaN has made the technology much more accessible. It is now starting to make significant inroads into several other market areas as well as change the design trade-offs for developers of RF systems.
The emergence of enhancement-mode GaN has changed the cost/performance trade-off for many designs. This approach grows a GaN layer on top of a silicon substrate, bringing the economies of scale of silicon processing to the higher performance of pure GaN. Since the first commercial enhancement-mode GaN devices were launched in 2010, the RF transistor market has benefited from the lower cost for HEMT transistors and MESFETs in the 2.5 to 6GHz range. Made by companies such as Cree, Macom, Qorvo and Microsemi, these are increasingly being adopted in cellular phone power amplifiers and other high frequency, high power wireless applications. This allows designers to produce smaller, more efficient 3G and 4G base stations and 5G prototypes.
The power market is also taking advantage of this process change, particularly with the high temperature performance. Enhancement mode GaN MOSFETs from transistor suppliers such as Macom and EPC are being adopted in power switching designs with a faster, more linear rise and fall than CMOS devices.
Unfortunately just having better performance in an individual component is not enough. The increased use is also due to the fact that the silicon controllers have caught up in speed. To get the most out of the enhancement-mode GaN devices, these controllers need to be able to support power switching above 1MHz with cycles under 100ns. The latest CMOS silicon controllers make this cost effective by allowing multiple enhancement-mode GaN MOSFETs to be used in a single package. This can dramatically reduce the size of power supplies and increase the efficiency making them more cost effective.
This higher performance is also providing benefits in high-end consumer applications. The higher frequency response, faster switching and higher efficiency is even driving the technology into the audio market for Class D amplifiers and portable, battery powered designs. This provides a longer battery life and better quality audio for high end systems.
While GaN devices have been around for many years, the emerging applications brought about by new manufacturing techniques are driving multiple new design opportunities. With the ability to support higher switched speeds and higher temperatures, power designs can be made more efficient, systems can be made smaller, and audio systems can have higher quality sound and longer battery life.
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