Selecting the Optimal Wide Bandgap Semiconductor for Your Specific Needs
Grasping the distinct benefits of silicon carbide (SiC) and gallium nitride (GaN) is key to choosing the best wide bandgap technology that aligns with your product's power specifications, thermal management needs, and form factor constraints.
Wide bandgap (WBG) semiconductors are increasingly popular in the automotive sector, particularly for electric vehicle (EV) charging systems, as depicted in Figure 1. However, their unique properties also render them highly adaptable for various energy management applications beyond just automotive.
Figure 1. Electric vehicle charging can benefit from wide bandgap technology.
In any application, the goal of power electronics is to efficiently transfer as much power as possible to the load. The critical hurdles in achieving this are effectively managing the system's heat and minimizing switching losses.
To overcome these challenges, strategies that enhance heat conduction and dissipation, as well as those that lower switching losses, are essential. Both silicon carbide (SiC) and gallium nitride (GaN), which are wide bandgap (WBG) technologies, have emerged as robust contenders to traditional silicon (Si) semiconductors, offering improved performance in these key areas.
The Bandgap Explained
In physics, the bandgap is the energy gap between the conduction band's lowest unoccupied state and the valence band's highest occupied state of a material. This gap is crucial because it dictates the amount of energy required for electrons in the valence band to be excited enough to jump into the conduction band.
The Potential of SiC and GaN to Supersede Silicon
Traditional silicon-based materials generally possess a bandgap around 1.5 electron volts (eV). In contrast, the bandgaps of wide bandgap (WBG) semiconductors like GaN and SiC are significantly larger, at 3.2 eV and 3.4 eV respectively, aligning with the 'wide' aspect of their name.
Owing to their wider bandgaps, WBG semiconductor power devices can withstand higher voltages, operate at elevated temperatures, and manage more power. These attributes render them highly suitable for use in automotive applications, including energy storage solutions.
While both SiC and GaN offer advancements over traditional silicon, they also have distinct differences from one another. Understanding these differences is crucial when determining which wide bandgap semiconductor to incorporate into power electronics designs.
SiC Scores High on Reliability and Heat Dissipation
A primary benefit of SiC power semiconductors is their superior gate-oxide reliability. SiC employs vertical transistor concepts, whereas GaN transistors have lateral conduction like most silicon devices.
Figure 2. Silicon carbide wafer. Image used courtesy of Infineon Technologies
Other benefits of SiC include efficiency gains through advancements in miniaturization, decreased cooling requirements, and lower overall system costs compared to Si for power applications.
With the thermal properties allowing for high thermal efficiency, SiC shines the most in Onboard Chargers (OBCs) for EVs. SiC employs vertical transistors, and in an OBC, heat gets dissipated through the transistor. When the heat hits the SiC layer, it disperses uniformly—only a diamond could do it better (an expensive proposition).
An OBC is an example of an application in which the maximum power needs to be pumped safely into a limited space without thermally overloading the transistor. SiC is ideal for an OBC because it’s in a sealed, confined space where heat is a factor. The dissipation allows the OBC to charge the vehicle faster while keeping a handle on the heat in a tight space.
The proliferation of fast-charging EV infrastructure requires putting equipment in many different environments as vehicle-to-grid (V2G) and vehicle-to-home (V2H) applications become more widely adopted, two other areas where SiC excels.
Beyond battery charging, SiC’s ability to dissipate in a high-power environment extends to other energy management infrastructures, such as solar power storage systems.
GaN Delivers Density and Fast Switching
GaN distinguishes itself as a lateral transistor that supports fast switching and works well where power density is highly desirable. While SiC offers density at the IC level, GaN allows you to achieve higher power density at the board level.
In a power application, GaN allows for much faster switching for reduced switching losses. As a byproduct of a fast-switching power supply, the higher frequency reduces the size of the magnetics, which also reduces board density and increases system efficiency.
Because of its effective density at the board level and fast switching, GaN is an excellent choice for consumer electronics charging use cases where the goal is quick charging from a low-power state to full power. Examples of applications include battery chargers for laptops and USB-C-type wall plugs. Another ideal application for GaN is switched-mode power supplies in data centers.
Choose the Optimal Wide Bandgap Solution
You might think that selecting your preferred WBG technology and sticking with it is your best bet, but you would want to mix and match SiC and GaN, depending on the application. You may also continue to use legacy silicon, as it still has its place.
As illustrated in Figure 3, SiC is ideal for the highest power applications but is limited in switching frequency. GaN is better suited for high-frequency switching applications.
Figure 3. SiC and GaN applications as a function of power and frequency. Image used courtesy of Infineon Technologies (click to enlarge)
Employing SiC can help you manage the thermal properties, while GaN will reduce your switching losses to almost zero. Sorting through the many application scenarios and selecting the right WBG technologies can be streamlined by reaching out to a vendor who can outline the available options and help you choose the best one for your application.
Given the many use cases for WBG technologies and the continued need for legacy silicon, it’s unlikely that either GaN or SiC will become the sole go-to technology. Infineon’s approach to WBG is to steer customers to the most appropriate choice for their power requirements while maximizing performance. Infineon Technologies has strategically invested in WBG technologies with both front-end and back-end facilities to support fabrication, assembly, and testing.
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