Ajay Sattu, onsemi
Components based on wide-bandgap (WBG) technologies such as SiC are crucial to improve efficiency in industrial, automotive and renewable energy applications. In this article, onsemi considers how next-generation SiC devices will evolve to enable even higher efficiency and smaller form factors and also discusses why having a robust supply chain is critical for companies switching to SiC technology.
Advances in MOSFET technology, discrete packages, and power modules are helping to improve energy efficiency and reduce costs in a wide range of industrial systems such as EV charging infrastructure and renewable energy systems such as solar photovoltaic (PV) applications. However, balancing cost and performance is an ongoing challenge for designers who must deliver more power without increasing the size of solar inverters or their cooling costs. This is necessary because affordable charging will be a crucial driver for the increased uptake of electric vehicles.
An automobile’s efficiency is linked to the size, weight and cost of onboard electronics, which impact vehicle range. Using SiC instead of IGBT power modules in an EV/HEV can deliver significant performance improvements, especially in the traction inverter, as this significantly contributes to a vehicle’s overall efficiency. A light passenger vehicle mainly operates under low-load conditions where the efficiency advantages of SiC over IGBT are most apparent. The size and weight of the onboard charger (OBC) also impact vehicle range; therefore, it must be designed to be as small as possible - the higher switching frequency of WBG devices plays a vital role in enabling this.
The Benefits of SiC Technology
Minimizing power conversion losses requires using semiconductor power switches that offer best figures of merit. Improvements in the performance of silicon-based semiconductor devices used in power applications (IGBTs, MOSFETs and diodes), combined with innovation in power conversion topologies, have led to significant efficiency improvements. However, having been pushed close to their theoretical limits, they are now being replaced by wide bandgap (WBG) semiconductors such as SiC and gallium nitride (GaN) in new applications.
The demand for higher performance, greater power density, and better reliability pushes the envelope even for SiC. Its wide-bandgap property allows it to withstand higher voltages (1700V to 2000V) than silicon. At the same time, it also has inherently higher electron mobility and saturation velocity. This allows it to operate at significantly higher frequencies and junction temperatures, both highly desirable properties for power applications. Additionally, SiC-based devices can switch with relatively low losses meaning the size, weight, and cost of required passive components are lowered.
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Figure 2: SiC brings many benefits to power systems
The lower conduction and switching losses of SiC devices would require less heat dissipation. This, combined with its ability to operate at junction temperatures (Tj) up to 175°C results in less requirement for thermal mitigation measures such as fans and heatsinks. This also reduces system size, weight and cost and ensures greater reliability in space-constrained applications.
Need for Higher Voltages
Reducing losses at a required power level can be achieved by increasing voltage to reduce current. For this reason, the DC bus voltage from the PV panels has increased from 600 V to 1500 V over the last several years. Similarly, the 400 V DC bus in light passenger vehicles can be increased to 800 V bus (and, in some cases, to 1000 V). In the past, 750 V-rated devices were used for 400 V bus voltages. Now, devices with even higher voltage ratings (1200 V up to 1700 V) are required to ensure these applications operate safely and reliably.
Latest Developments in SiC
To meet this need for devices with higher breakdown voltages, onsemi has developed the 1700V M1 planar EliteSiC MOSFET products optimized for fast-switching applications. The NTH4L028N170M1 is one of the first devices to be released and has a VDSS of 1700 V, an extended VGS of -15/+25 V, and a typical RDS(ON) value of just 28 mΩ.
These 1700 V MOSFETs can operate at junction temperatures (Tj) up to 175°C, meaning they can work with much smaller or sometimes even no heatsinks. In addition, the NTH4L028N170M1 has a Kelvin source connection on the fourth pin (TO-247-4L package) to improve power dissipation turn-on and reduce gate noise. These switches are also available in a D2PAK–7L package with lower package parasitics.
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Figure 3: New 1700 V EliteSiC MOSFETs from onsemi
A 1700 V 1000 mΩ SiC MOSFET in TO-247-3L and D2PAK-7L packages for highly reliable auxiliary power supply units in EV charging and renewable applications has also been released to production.
onsemi has developed the D1 range of 1700 V SiC Schottky diodes. This voltage rating gives devices more voltage margin between VRRM and the peak repetitive reverse voltage. The devices have a lower VFM (maximum forward voltage) and excellent reverse leakage current – meaning designers can achieve stable high-voltage operation, even at high temperatures.
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Figure 4: New 1700 V Schottky diodes from onsemi
The NDSH25170A & NDSH10170A devices are available in a TO-247-2 package or as a bare die, with 100A variants (unpackaged) also available.
Supply Chain Considerations
A shortage of available components has hampered production in some electronics industry sectors. Therefore, when selecting a supplier for a new technology, it is critical to consider their ability to fulfil orders on time. To guarantee customer supply, onsemi recently acquired GT Advanced Technology (GTAT) to take advantage of its logistics expertise. onsemi is currently the only large-scale SiC supplier with end-to-end capability, including volume boule growth, substrate, epitaxy, device fabrication, best-in-class integrated modules and discrete packaging solutions. To meet the anticipated growth in SiC applications, onsemi is planning a multifold increase in the capacity of its substrate operations and increasing its device and module capacity by 2024 while also allowing for further future expansion.
The features of SiC devices enable engineers to meet the power density and thermal design challenges in evolving automotive, renewables and industrial applications. With its 1700 V range of SiC MOSFETs and diodes, onsemi has addressed the requirement for devices with higher breakdown voltages. It is also developing a 2000V SiC MOSFET technology for emerging solar, solid-state transformer, and solid-state circuit breaker applications.