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Saturday 21 May 2022
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An Overview: Wide Bandgap and Power Conversion

Wide bandgap semiconductor materials enable smaller, faster, and more dependable power electronic components. They are more efficient than silicon-based counterparts. These properties result in weight, volume, and life-cycle cost reductions in a variety of power applications.

These features enable significant energy savings in industrial processing and consumer appliances. They also aid in the widespread adoption of electric vehicles and fuel cells, as well as the integration of renewable energy into the power grid.

An Overview

Advanced power electronic device development with exceptional efficiency, reliability, functionality, and form factor will provide a competitive advantage in the deployment of advanced energy technologies.

To achieve high power conversion efficiency, low loss power semiconductor switches are required. Metal oxide field effect transistors (MOSFETs), IGBTs, and thyristors are examples of current power silicon-based switch technology.

Image courtesy of Analog Devices

A number of limitations exist in silicon-based power semiconductor devices. High voltage devices with a significant critical thickness are required due to the relatively low bandgap and low critical electric field. The thicker devices have higher resistance and associated conduction losses, resulting in higher losses.

In addition, in the majority of cases, the achievable switching frequency is low. Silicon’s relatively low bandgap contributes to high intrinsic carrier concentrations in silicon-based devices, resulting in high leakage current at high temperatures.

As a result of the development of wide bandgap semiconductor devices, new opportunities for increased efficiency have emerged. These are motivated by fundamental differences in material properties between silicon and semiconductors such as silicon carbide (SiC) and gallium nitride (GaN).

Higher critical electric fields in these WBG materials allow for thinner, more highly doped voltage blocking layers, which can reduce on resistance in majority carrier architectures by orders of magnitude. Because of the high breakdown electric field and low conduction loss, WBG materials can achieve the same blocking voltage and on resistance while having a smaller form factor.

The high frequency operation in WBG devices is made possible by the reduced capacitance value. The low intrinsic carrier concentration of WBG materials enables reduced leakage currents and robust high temperature performance. WBG semiconductors  therefore provide a pathway to more efficient, lighter, high temperature capable and smaller form factor power converters.

WBG Semiconductors allow devices to operate at significantly higher temperatures, voltages, and frequencies. This contributes to power electronic modules that are significantly more powerful and energy efficient than conventional semiconductor-based modules. To realize the full potential of WBG-based devices, however, intensive and systematic research and development efforts at every stage of the power electronics value chain, as depicted in Figure 1, are required.

Figure 1. Power electronics value chain.

SiC and GaN Based Power Semiconductors

When compared to silicon-based devices, the use of silicon carbide (SiC) can reduce on-state resistance by about two orders of magnitude. When used in power conversion systems, it can significantly reduce power loss.

SiC devices, such as power semiconductor switches, work in tandem with rectifier devices. Because of recent advances in substrate quality, epitaxy improvements, optimized device design, advances in increasing channel mobility with nitridation annealing, and optimization of device fabrication processes, commercial production of SiC-based devices is now feasible.

Silicon-based semiconductor switches have been unable to keep up with the evolution of the power electronics industry. This necessitates the use of another semiconductor material whose performance is comparable to that of newer systems, namely gallium nitride (GaN).

It is a high electron mobility (HEMT) semiconductor that is expected to see significant improvements in the coming years. GaN is typically grown on top of a silicon substrate, and the end result is known to be a fundamentally simple, elegant, and cost-effective solution for power switching.

The fact that GaN can be grown on top of silicon wafers, that it has the advantage of self-isolation, which allows efficient monolithic power integrated circuits to be fabricated economically, and that enhancement and depletion modes are available are just a few of the key features that make GaN so effective.

GaN’s exceptional electron mobility and low temperature coefficient enable it to have very low on-state resistance. This enables tasks that benefit from extremely fast switching speeds to be handled.