Wide-bandgap devices such as SiC are essential to modern applications.
Technology is accelerating rapidly with different drivers across a multitude of application sectors. Looking at two of the most important markets—industrial and automotive—the key trends that dominate are increased efficiency, form factor, and improved sensing using image sensing.
In the industrial sector, advances in MOSFETs and power modules are being deployed to improve the energy efficiency and system cost of a wide range of industrial systems. Two areas that have a particular benefit are EV charging infrastructure and alternative/renewable energy applications such as Solar.
Cost and performance are common threads in many industrial applications. Designers are being challenged to deliver more power from solar inverters without increasing size or to reduce cooling costs associated with energy storage. Affordable charging is seen as a gateway to the proliferation of electrified passenger vehicles. However, what is critical is the enablement of faster charging capability via DC wallbox or DC Fast charging without requiring additional cooling.
In the automotive arena, efficiency is inextricably linked to the range of the vehicle as well as the size, weight, and cost of the on-board electronics. Here, the deployment of SiC solutions over IGBT power modules in EV/HEV is providing significant performance improvements, alongside the benefits gained from enhanced power management in automotive CPUs, LED lighting, and body electronics.
The traction inverter is a key focus as it impacts overall efficiency of the vehicle and therefore defines the range. Considering driving profiles, the majority of the time a light passenger vehicle operates under light load conditions and—as such—the efficiency improvement benefits with SiC over IGBT solutions are well understood. Additionally, the on-board charger (OBC) needs to be as small as possible. Smaller form factors are achieved only with wide bandgap devices that enable high switching frequency. Every ounce of energy saved enables the vehicle to improve the overall mileage and mitigate range anxiety.
Benefits of SiC technology in modern applications
Every power conversion in automotive and industrial applications relies upon semiconductor-based switching devices and diodes to be efficient and reduce the losses of conversion. Consequently, the semiconductor industry has worked to advance the performance of silicon-based semiconductor devices used in power applications; in particular, IGBTs, MOSFETs and diodes. This, along with innovation in power conversion topologies has resulted in better performance than ever before.
With incumbent silicon-based semiconductor devices reaching the limit of their ability to continue to increase efficiency, a new material is required. So-called wide bandgap (WBG) materials such as SiC and gallium nitride (GaN) hold much promise for the future. The electrical system demand for higher performance, density, and reliability is pushing the technology envelope for SiC technology.
Whether it’s the mission profiles of automotive traction or solar inverters or electric vehicle chargers, SiC based MOSFET and diode products offer better performance and system level costs than incumbent Si-based IGBTs and rectifiers. The wide bandgap nature of SiC enables higher critical fields than silicon, translating into higher blocking voltage capability such as 1,700V and 2,000V. In addition, SiC has inherently higher electron mobility and saturation velocity than Si devices, resulting in operation at significantly higher frequency and junction temperatures, both of which are highly beneficial. Additionally, SiC-based devices can switch with relatively low losses at higher frequencies, reducing the size, weight, and cost of associated passive components, including magnetics and capacitors.
Their significantly lower conduction and switching losses mean that SiC-based power solutions generate less heat. This, along with the ability to operate at junction temperatures (Tj) as high as 175oC means that the need for thermal mitigation such as fans and heatsinks is significantly reduced, saving system size, weight, and cost as well as ensuring greater reliability even in challenging, space-constrained applications.
The need for higher voltage devices
The wide-bandgap nature of SiC enables higher critical fields than silicon, translating into higher blocking voltage capability. For a given wattage, increasing voltages would reduce the overall current capability requirements and thus overall copper losses. In renewable energy applications such as solar photovoltaic (PV) systems, the DC bus voltage from the PV panels has increased from 600V to 1,500V to enhance efficiency. Similarly, there is a transition from a 400V bus in light passenger vehicles to an 800V bus (in some cases a 1,000V bus) to drive efficiency and reduce charging times. In the past, 750V-rated devices were used for 400V bus voltages, but now higher voltages such as 1,200V and even 1,700V are required to ensure reliable operation in these applications.
Latest technology
To meet this need for increased breakdown voltages, onsemi has developed a range of 1,700V M1 planar EliteSiC MOSFET devices that are optimized for fast switching applications. One of the first devices available is the NTH4L028N170M1 that has a VDSS of 1,700V and an extended VGS of -15/+25V. This device has an excellent typical RDS(ON) value of just 28mΩ.
The new 1,700V MOSFETs can operate with junction temperatures (Tj) as high as 175oC, allowing any heatsinking to be significantly smaller or removed entirely. The NTH4L028N170M1 includes a Kelvin source connection on the fourth pin (TO-247-4L package) that improves turn-on power dissipation and gate noise. Also available is a D2PAK–7L configuration, which further reduces package parasitics in devices such as the NTBG028N170M1.
Soon to be available is a 1,700V 1000mΩ SiC MOSFET in TO-247-3L and D2PAK-7L packaging for highly reliable auxiliary power supply units within EV charging and renewable applications.
Alongside the MOSFETs, onsemi has also developed a range of 1,700V SiC Schottky diodes. With this rating, devices in the D1 family will offer more voltage margin between VRRM and the peak repetitive reverse voltage of the diode. In particular, the new devices will deliver lower VFM, maximum forward voltage, and excellent reverse leakage current, even at high temperature, thereby allowing designers to achieve stable high voltage operation at elevated temperatures.
The new devices (NDSH25170A & NDSH10170A) are available in a TO-247-2L package and as bare die, along with a 100A version that is not available packaged.
Supply chain considerations
With component availability hampering supply chains in some sectors, it is very important that—when selecting new devices/technologies—the ability to supply is taken into consideration. To ensure reliable supply to customers to support rapid growth, onsemi recently acquired GTAT. Not only does this bolster its supply chain, but it also allows onsemi to leverage GTAT’s technical experience.
Currently, onsemi is the only large-scale supplier with end-to-end supply capability, which includes volume SiC boule growth, substrate, epitaxy, device fabrication, best-in-class integrated modules, and discrete package solutions.
To support the anticipated growth in SiC over the next few years, onsemi plans to increase the capacity of substrate operations fivefold and make substantial investments in expanding the company’s device and module capacity to double across all of its sites by 2023. This will be followed by nearly doubling capacity again by 2024, with the capability to double capacity again in the future.