As the name suggests, wide bandgap power electronics have a larger bandgap, meaning WBG devices have a higher breakdown voltageFor power electronics applications, silicon has long been the technology of choice, offering a proven, reliable, and cost-effective solution. But over the last few years, a new technology has grown in popularity: wide bandgap (WBG) semiconductors.
While there are a variety of WBG materials available, the two most widely used in power devices are silicon carbide (SiC) and gallium nitride (GaN) across multiple types of transistor and diode-based devices — including SiC MOSFETs, SiC Schottky diodes, and GaN FETs.
In this article, we focus on the advantages of WBG devices and what that means for power system designers. We start by briefly looking at the material properties of WBG semiconductors and their advantages in power applications. We then discuss how these material properties give WBG components their advantages at a device level and how this leads to benefits at a board and system level.
Material properties of wide bandgap semiconductors
Without diving too deep into quantum physics, it’s enough to know that the ‘bandgap’ in WBG refers to the difference in energy levels between the different possible states for electrons. To conduct electricity, an electron must cross this gap to a higher energy state. In silicon, this gap is relatively small (1.1 eV), but it’s larger in WBG materials like SiC and GaN (typically 3.3 eV and 3.4 eV, respectively) — this is what gives these materials their properties.
What are the implications of having a larger bandgap?
First, the larger bandgap means WBG devices can have a higher breakdown voltage, as a greater electric field is needed to release electrons that can carry charge.
Also, SiC devices have much better thermal conductivity than silicon, while for GaN devices the thermal conductivity is similar to silicon. While not directly a consequence of the wider band gap, it’s true to say that WBG materials tend to have greater electron mobility than silicon — and GaN has greater electron mobility than SiC. WBG devices also have a greater saturated electron drift velocity, which means electrons move faster, enabling higher frequency operation.
There are several different forms of SiC, with their atoms arranged differently. The most widely used variant in power semiconductors is the ‘4H’ variant due to better anisotropic electron mobility.
Device-level properties of wide bandgap semiconductors
What implications do these material properties have for the characteristics of semiconductor devices? For power electronics, we’re interested in switching devices, and how close they come to an idealised perfect switch that can change between its two states instantaneously with no power losses.
Realistically, there will always be some losses, but WBG semiconductors can help minimise them and maximise efficiency. Compared to silicon technologies, such as MOSFETs and IGBTs, WBG devices have a number of attractive electrical properties, including:
- no reverse recovery effects for GaN
- shorter switch-off times
- lower capacitance, helping to enable faster switching
- low gate charge, reducing losses and hence power consumption
- low forward voltage drop
- robust intrinsic body diode
Technology
Power: designing solutions with power at the core
We provide you with the right insights and expertise when you need it most, so you can make the right decisions for your product, and your business.
With the ongoing shift to renewable energy and the electrification of transport and industry, the demand for higher power and greater energy efficiency in electronics is increasing. Wide bandgap technologies including SiC and GaN bring many advantages.
WBG OVERVIEWThe drain-to-source on resistance, or RDS(on), is an important characteristic of semiconductors. Devices with a lower RDS(on) offer lower conduction resistance. WBG devices typically have lower RDS(on) than their silicon counterparts, which means they dissipate less heat and have lower power losses when conducting.
What about thermal characteristics? With their smaller bandgap, silicon devices are more easily affected by higher temperatures than WBG parts, with less thermal energy needed to move electrons across the bandgap. In practice, this means that silicon parts are typically limited to operating temperatures of about 100°C, while WBG devices can, in theory, be used at much higher temperatures of around 300°C.
It's worth mentioning that different substrate possibilities exist, such as SiC-on-Si, GaN-on-Si and GaN-on-SiC. These bring different properties and varying manufacturing challenges.
LOOKING FOR SUPPORT? CONTACT OUR POWER EXPERTS
Board-level advantages of wide bandgap semiconductors
These material- and device-level properties lead to some clear advantages when considering a power solution at the board level.
First, higher electron mobility gives WBG semiconductors higher switching frequency, thus improving efficiency and enabling lighter devices with a smaller footprint. This efficiency also means less heat is dissipated, so the cooling requirements are lower than for silicon-based devices. WBG devices also offer good current stability over a wide operating temperature range.
The higher breakdown voltage, mentioned above, enables higher operating voltages and hence higher power operation for SiC devices, with SiC MOSFETs rated at up to 2000 V.
While many, if not most, power conversion applications only require conversion in one fixed direction, there are certain topologies where bi-directional operation is required, such as Vehicle-to-Grid configurations in electric vehicles (EVs). WBG devices are well-suited to these applications, providing the efficiency and power density required.
System-level advantages of wide bandgap semiconductors
Looking at a system level, one of the key advantages of WBG devices over silicon is their higher efficiency, therefore lower energy losses, related to higher switching frequencies. This means they are well suited to use cases where efficiency is critical, such as in EVs and renewables. With greater efficiency and less wastage, the cost of supplying and storing energy — such as in lithium batteries — can be reduced.
These high switching frequencies also mean the inductors and capacitors used in a power supply can be much smaller and lighter. Combined with the smaller footprint of WBG devices themselves, this enables higher power density systems. These weight and space savings are attractive in compact and portable applications, such as power supplies for laptops and portable consumer electronics.
SiC components can operate at elevated temperatures, making them ideal for automotive, industrial, or military uses in harsh environments. WBG devices also offer the ability to handle high surge voltages and high currents, making them suitable for more demanding industrial applications.
The electrical properties can enable simpler converter topologies with fewer external components — for example, their lower switching losses reduce the need for complicated voltage balancing.1
Challenges of wide bandgap technologies
SiC and GaN are transforming power electronics, but they bring new challenges and design considerations — and are not simply a drop-in replacement for silicon components.
For starters, their high switching frequencies mean noise and EMI can be challenging, requiring appropriate filtering. Parasitic capacitance and inductance are also potential problems, needing careful PCB layout.
Heat dissipation is another issue to consider, with the higher power density of WBG devices. However, in some systems the greater efficiency of WBG can make thermal management easier — less waste heat means smaller heatsinks can be used. The higher thermal conductivity of WBGs also helps heat dissipation, while using top-side cooled (TSC) packages for WBG devices enables them to lose heat effectively from the top surface of their package.
Making the right choice for your application
There’s a lot to think about if you’re considering SiC or GaN for your next power design. As explained in this article, they can deliver invaluable benefits, including higher efficiency and greater power density. On the other hand, they can typically be more expensive than silicon alternatives, and the reliability of WBGs has been a concern in some applications.
Whatever your requirements, we’re here to help. Avnet Silica’s FAEs and power engineers can provide comprehensive information and expert guidance to help you make the right design choices.
Reference
Working on a power project?
Our experts bring insights that extend beyond the datasheet, availability and price. The combined experience contained within our network covers thousands of projects across different customers, markets, regions and technologies. We will pull together the right team from our collective expertise to focus on your application, providing valuable ideas and recommendations to improve your product and accelerate its journey from the initial concept out into the world.
Like what you see?
Follow us on LinkedIn
Follow our dedicated power page on LinkedIn for the latest power updates and news from our team of power experts.