New GaN technologies bring high frequency switching to an expanding range of applications
01 April 2021
The key to taking the essential next step toward an energy efficient world lies in the use of new materials, such as wide bandgap semiconductors, which enable greater power efficiency, smaller size, lighter weight, lower overall cost – or all these factors combined.
The full version of this article was originally featured in the April 2021 issue of EPDT magazine [read the digital issue]. Sign up to receive your own copy each month.
Though silicon technology can lay claim to maturity and cost-effectiveness, attention is now turning to materials such as gallium nitride (GaN) to improve the performance of power-delivery circuitry. Here, Adrian Cotterill, Senior Global Product Manager – Discrete Semiconductor & Patricio Gomez Bello, Senior Global Product Manager – Power Management, Mixed Signal at electronic component distributor, Farnell explain how leading semiconductor manufacturers, including Infineon Technologies, Nexperia & NXP, are designing solutions to help engineers overcome the challenges of a new technology and build the benefits of GaN technology into their designs.
Silicon field-effect transistor (FET) technology has been first choice for numerous power applications for decades. During that time, manufacturers have made great strides in cutting on-resistance while improving breakdown voltage to cut losses and boost safety margins, respectively. Through the use of innovative manufacturing techniques, such as vertical architectures that make full use of the silicon wafer, vendors have been able to improve on switching frequency that pays off in higher switching frequencies. This, in turn, makes it possible to reduce power-supply size and weight with smaller magnetic and passive support components. However, losses encountered when the transistor state changes are difficult to avoid because the properties of silicon lead to carriers taking time to be cleared when the channel is switched off. Trade-offs also have to be made in the process design between on-resistance and the breakdown voltage.
Though silicon technology can lay claim to maturity and cost-effectiveness, attention is now turning to materials such as gallium nitride (GaN) to improve the performance of power-delivery circuitry. A key advantage of GaN lies in its bandgap energy of 3.4eV, several times higher than the 1.1eV of silicon. This property leads to a higher breakdown voltage, which designers can translate into smaller transistor dimensions. This can yield lower gate and output capacitances, helping boost switching frequencies into the megahertz range.
The second key attribute of GaN is its intrinsically higher carrier mobility. The electron mobility of GaN is almost 40% greater than that of silicon. The high mobility results from the way in which a two-dimensional electron gas forms at the interfaces between the component materials, a feature intrinsic to high electron mobility transistors (HEMTs) and found in other materials, such as gallium arsenide (GaAs). The high mobility further enables low on-resistance, suiting high-current operation.
Compared to silicon, GaN devices are able to operate in high-temperature conditions that would be challenging to silicon devices, which makes it possible to employ smaller heatsinks, helping further shrink the volume and weight of power electronics.
Design considerations for GaN devices
Although the performance of GaN devices offers key advantages over comparable silicon, there are important design considerations. Rapid switching brings benefits in terms of size and efficiency; however, high changes in current and the time, combined with parasitic inductances, can create unwanted transient voltages within the PCB. These transients can
interfere with the gate and driver circuitry of the device, and potentially lead to sustained oscillation that should be suppressed for safe operation. Designers can control these conditions through PCB-level techniques that minimise parasitic inductances, and the application of snubber components, such as capacitors with a low equivalent series resistance...
Read the full article in EPDT's April 2021 issue...
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