Silicon Carbide’s Potential to Improve Power Density and Efficiency
Silicon carbide (SiC) devices belong to the group of wide bandgap semiconductors and have several characteristics that make them attractive for a wide range of power applications.
Compared to silicon devices, SiC components have higher voltage and current capacity, lower losses, larger breakdown field strength, faster-switching, and ability to withstand high-temperature conditions.
Construction, characteristics, and benefits of SiC power devices
The SiC devices are designed and built almost like the normal Si counterparts, apart from a few differences such as the semiconductor material. Unlike the Si which uses silicon, the SiC has additional carbon atoms.
When it comes to the device construction, the SiC devices have thinner drift layer and higher impurity concentrations that give them lower electrical resistance and consequently less conduction and switching power losses.
Some of the features that make Silicon carbide devices superior include:
- A wider bandgap that gives them the ability to operate withstand higher voltages than Silicon. It has the ability to work with higher voltages with typical device ratings of 600V and 1200V.
- Better control of the p- ad n-type regions during construction
- Higher breakdown strength of about 10 times that of silicon
- Low ON resistance that translates to higher electrical conductivity
- Thermal conductivity is 3 times greater the silicon.
Benefits of SiC devices
These SiC devices have benefits such as better power efficiency, reduced losses and energy savings hence lower operating costs and environmental damage.
Due to their higher power density, the devices are smaller in physical size and this translates to space and weight savings. The high operating frequencies allow the use of smaller passive components such as the capacitors and inductors.
Other benefits include;
- Ability to withstand high voltages of about 10 times what traditional silicon can handle. For this reason, only a few series devices are required in high voltage applications and this reduces costs and circuit complexity.
- SiC components have higher energy bandgaps which make them stronger to withstand the effects of heat, radiation, strong electromagnetic fields and other factors that affect stability and performance. This makes them suitable for automotive, aerospace, military, and other sensitive and demanding applications in harsh environments.
- High current capacity reduces circuit components, cost, and complexity.
- Ability to operate and withstand higher junction operating temperatures reduces cooling requirements, costs, and complexity
- SiC devices are more reliable, have a longer service life and ability to withstand harsh environments.
Typical Silicon Carbide devices
Generally, the common SiC power devices are the SiC MOSFET and SiC Schottky diode as well as hybrid and All SiC power modules. The devices often share the same nomenclature as the Si equivalents. For example, the SiC MOSFET still has the gate, drain, and source terminals.
SiC MOSFET
SiC MOSFET is a revolutionary power device that has several benefits over traditional silicon equivalent. These range from low ON resistance and switching losses to better thermal conductivity and high figure of merit.
Today, the SiC MOSFET device is attracting a lot of attention and slowly replacing the IGBT because of its superior overall performance. In particular, the device is reliable, energy-efficient, rugged and able to support higher switching frequencies and operating voltages. The high power density devices have simple designs that require fewer and smaller sized external components.
SIC MOSFETs are suitable for a wide range of electronics power system switching applications. Their semiconductor material and construction process enable them to support a combination of high voltage and fast switching operations that traditional power transistors cannot achieve.
Generally, the wide gap semiconductors are suitable for the high power densities applications, low consumption high operational voltage applications as well as high RF output applications in wireless communications.
Current and potential applications include power systems in the automotive, airplane, traction drives, industrial drives, induction heating, server power supplies, battery chargers, inverters, etc.
SiC Schottky Barrier Diodes
Compared to the Si counterparts, the SiC Schottky Barrier Diodes (SBDs) have superior electrical and thermal conductivity. Generally, the SiC SBDs have higher forward current capacities and low forward voltage drops over their operating temperature range.
Also, the SiC Schottky barrier diodes have higher reverse voltage ratings, short reverse recovery time, and low switching losses. Other properties include better surge current handling capability, less EMI during switching operations, a stable switching behavior independent of the temperature, and more.
Some of the diodes have junction barrier Schottky (JBS) structures that ensure very low leakage currents and ability to handle high surge currents - which are necessary properties for switched-mode power supply systems.
The SiC Schottky diodes deliver better power conversion compared to the silicon devices and are, therefore, more suitable for electric vehicle charging stations, battery chargers, solar power systems, hybrid power storage systems, and more. Their fast switching speeds and low voltage operation makes them suitable for TTL and CMOS logic gates. Other applications include signal conditioning and switching.
SiC power modules — All SiC and hybrid modules
Semiconductor switching devices achieve high power densities either in standalone or hybrid modules. The traditional power modules for larger currents are the silicon IGBTs combined with the fast recovery diodes (FRDs). However, these have limitations such as lower switching frequencies and operating voltages in addition to higher power losses. Some manufacturers are today integrating various SiC components in different configurations to enhance the power handling capacities and properties.
Typical combinations include
- Hybrid modules that combine Silicon IGBT and SiC diodes
- All SiC power modules that combine SiC MOSFETS and SIC SBDs
Integrating the SiC diodes with the IGBTs greatly enhances their capabilities by reducing the turn-on losses hence increasing current handling ability and switching frequencies than what the IGBT/FRD module delivers. In particular, they significantly reduce the switching losses that occur due to IGBT tail current and FRD recovery loss.
The All SiC modules deliver better efficiencies and high-frequency performance than the standalone devices and are suitable for power supplies for industrial equipment such as hybrid power storage system, the induction heating applications, etc.
SiC power devices applications
The ability to operate at higher temperatures means that they require less thermal cooling and this makes them suitable for a wide range of applications for normal and harsh environments. Some application includes automotive, aircraft, mining and military electronics and especially the power systems. Typical application areas include the DC/DC converters, drive train inverters, and EV chargers.
Application of SiC power devices in Automotive
In hybrid or electric vehicles, SiC devices can reduce losses and improve efficiency and battery performance. Several vehicle manufacturers are today using SiC-based power devices in inverters, convertors, drivetrains and infotainment as a way of reducing energy use and extending the battery life while reducing charging requirements.
Low power losses and better efficiency translate to the delivery of more energy to the load as compared to the silicon devices. For example, higher inverter output translates to rapid acceleration and better speed through the race.
For example, replacing the silicon IGBT with SiC MOSFETs and modules has seen a significant improvement in performance and energy savings in the Formula E electric vehicle inverters. The resulting higher efficiency delivers benefits such as a possible 10% power increase, less weight and consequently extended battery range.
Using SiC enables higher frequencies of up to 24KHz vs. the 16kHz IGBT achieves while weight and volume drop from 15Kg to 9Kg and from 14 to 10 liters respectively.
SiC Aircraft applications
The higher power density, ability to operate at higher temperatures and under harsh conditions are desirable features in the aircraft power supplies. This means low weight, smaller size, higher efficiency and consequently lower fuel consumption and emissions.
Challenges and future of SiC power devices
- Requires specific gate drives: The SiC switching devices requires specific gate drivers different from those that drive the IGBTs. The IGBT drivers cannot support the fast switching speeds and fault response necessary to protect the SiC when there is a short circuit. Also, managing the gate drive conditioning circuit is usually a challenge for some power applications such as motor drives.
- Packaging challenges: As the device’s physical size shrinks, the loss power density increases and the packaging material must have the ability to deal with this excess heat. Also, since the device can operate at higher junction temperature, the die interconnections, attach, and encapsulation must have the capacity to handle these.
- Difficult and expensive manufacturing processes
Despite its higher price, the device offers many more benefits that outweigh its cost in the long term. The demand for SIC is rapidly increasing and set to rise higher as material costs continue to fall. Specifically, the SIC MOSFET, which is one of the most popular among many other components, is likely to see huge commercial deployments due to the role it plays in conserving energy and environmental benefits it delivers.
