Wide Bandgap Devices for Power Converters — Part 2

Wide bandgap (WBG) semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) are known to provide superior performance compared to silicon. These include higher efficiency, higher switching frequency, higher operating temperature, and higher operating voltage. 

 

Electron band separation in semiconducting substances. Image courtesy of All About Circuits

 

WBG semiconductors greatly enhance the efficiency of the power conversion stages by acting as a valid substitute for silicon in the manufacturing of voltage converters, power switches and high efficiency diodes. Compared to the conventional silicon based technology, WBG semiconductors allow to obtain important improvements such as greater power efficiency, smaller size, lighter weight and lower overall cost [2]. Read on to learn more about the basics of wide bandgap devices and understand the benefits offered by employing them in power electronic systems.

 

An Overview

The first power semiconductors were launched in 1952. Since then silicon has been and remains the main semiconductor material in switched mode power conversion applications. However, WBG materials have been considered to be the next logical step since the mid 20th century. The first SiC WBG semiconductor was commercially available only in 2001. 

In recent days, GaN WBG semiconductor material is also more readily available. The semiconductor material that was employed mostly in light emitting diode applications has now arrived as a serious replacement for silicon technology in the power conversion applications space. The market growth of these WBG (especially SiC and GaN) reflects the superior characteristics of these semiconductor materials with respect to silicon. The key characteristics are lower conduction loss, lower switching loss and high temperature operation.

WBG materials generally have a large energy bandgap. This is the energy gap existing between the upper limit of the valence bond and the lower limit of the conduction band. Bandgap allows the semiconductors to switch between conduction (ON) and interdiction (OFF) states based on electrical parameters controllable from outside. A wider band gap implies a greater electric breakdown field but also the chance of operating at higher temperatures, voltages and frequencies. A wide bandgap also means higher breakdown electric field and therefore higher breakdown voltage. Overcoming the theoretical limits of silicon, WBG semiconductors like SiC and GaN offer significant performance improvements and allow operating with efficiency and reliability even in the most severe conditions.

 

Benefits of WBG Semiconductors

WBG semiconductors are expected to pave the way for exciting innovations in power electronics, solid-state lighting and other diverse applications across multiple industrial and clean energy sectors with vastly superior performance compared to the current technology [3]. The key benefits of incorporating WBG devices is the elimination of up to 90% of the power losses that currently occur during ac to dc and dc to ac power conversion. The high power performance can be enhanced by the use of WBG devices and is known to be up to 10 times higher than silicon based devices.The system reliability can be enhanced by enabling operation at higher maximum temperatures.

The systems developed using WBG devices are known to be smaller and lighter in comparison with the silicon based devices. Also, the life cycle energy use is reduced and paves the way for opportunities with new applications. Due to operation at higher frequencies than silicon based devices, compact and less expensive product designs can be identified. Note that as manufacturing capabilities improve and market based applications expand, the cost of WBG based devices is known to reduce further. 

In order to achieve the voltage and current ratings required in specific applications, novel device designs need to be implemented. These designs should be capable of exploiting the properties of the WBG materials to the maximum extent as possible [4]. Alternative packaging materials or designs are required in order to withstand the high temperatures in WBG. That said, existing systems may have to be redesigned to integrate the WBG devices in ways that help deliver their unique capabilities.

SiC and GaN are known to be the next generation materials for high performance power conversion and electric vehicles. Highest reliability is offered by employing WBG based devices that provide superior robustness for harsh environmental conditions. Robustness and ruggedness are also achievable by use of WBG based devices [5]. In summary, compared to silicon the crucial benefits offered by WBG materials include lower on resistance, higher breakdown voltage, higher thermal conductivity, operation at higher temperatures, greater reliability, near zero reverse recovery time and excellent high frequency performance.

 

Key references:

1. Isik et. al., Wide band-gap semiconductor based power electronics for energy efficiency, 2018.
2. Power Management Chapter 11: Wide Bandgap Semiconductors
3. Wide Bandgap Solutions
4. Hernandez et. al., On the integration of wide band-gap semiconductors in single phase boost PFC converters, 2015.