“Silicon carbide (SiC) technology can significantly improve the efficiency of current power systems while reducing their size, weight and cost, so the market demand continues to rise. But SiC solutions are not a drop-in replacement for silicon-based solutions, they are not identical. To realize the vision of SiC technology, developers must carefully evaluate multiple products and suppliers in terms of product quality, availability and service support, and understand how to optimize the integration of different SiC power components into their final system.
Author: Orlando Esparza
Silicon carbide (SiC) technology can significantly improve the efficiency of current power systems while reducing their size, weight and cost, so the market demand continues to rise. But SiC solutions are not a drop-in replacement for silicon-based solutions, they are not identical. To realize the vision of SiC technology, developers must carefully evaluate multiple products and suppliers in terms of product quality, availability and service support, and understand how to optimize the integration of different SiC power components into their final system.
An ever-expanding range of applications
The use of SiC technology is rising dramatically. With the continuous increase of suppliers, the selection of products is also increasingly rich. The silicon carbide market has doubled in the past three years and is expected to grow 20-fold over the next 10 years, with a market cap of over $10 billion. Silicon carbide applications are expanding from on-board applications in hybrid and electric vehicles (H/EVs) to non-automotive power and motor control systems in trains, heavy-duty vehicles, industrial equipment, and EV charging infrastructure. Suppliers in aerospace and defense are also continuously improving the quality and reliability of SiC to meet the stringent requirements of these industries for product robustness.
A key part of the SiC development program is validating the reliability and robustness of SiC devices, as products from different suppliers vary widely. With the increasing focus on the overall system, designers also need to evaluate suppliers’ product offerings. It is important that designers work with suppliers that offer flexible solutions such as die, discrete component and module options, as well as global distribution, support, and comprehensive design simulation and development tools. Developers who want their designs to be future-proof will also need to explore new capabilities, such as digitally programmable gate drivers. These drivers address early implementation issues while enabling one-click “tuning” of system performance.
Three key tests
These three tests provide data to evaluate the reliability of SiC devices (avalanche resistance, short-circuit withstand capability) and the reliability of SiC MOSFET body diodes.
Adequate avalanche immunity is critical because even minor failures of passive components can cause transient voltage spikes to exceed the rated breakdown voltage, which can eventually cause the device or entire system to fail. SiC MOSFETs with adequate avalanche resistance reduce the need for snubber circuits, extending application life. Top products can deliver UIS performance up to 25 joules per square centimeter (J/cm2). Even after 100,000 repeated UIS (RUIS) tests, the parametric degradation of these devices is small.
The second key test is short-circuit withstand time (SCWT), or the extremely long time the device can withstand under rail-to-rail short-circuit conditions before it fails. Test results should be close to IGBTs used in power conversion applications, most of which have 5 to 10 microsecond (µs) SCWT. A long enough SCWT gives the system a chance to troubleshoot the failure without damaging the system.
The third key metric is the forward voltage stability of the SiC MOSFET intrinsic body diode. This metric varies widely from supplier to supplier. Without proper device design, processing, and materials, the diode’s conductivity may decrease during operation, increasing the on-state drain-source resistance (RDS(on)). Figure 1 shows this difference. In a study conducted at The Ohio State University, MOSFETs from three suppliers were evaluated. On the one hand, all devices from supplier B showed degradation in forward current, while on the other hand, no degradation was observed in the MOSFET from supplier C.
Figure 1: Forward characteristics of SiC MOSFETs, showing differences in body diode degradation from different suppliers. (Image credit: Dr. Anant Agarwal and Dr. Min Seok Kang of The Ohio State University)
After device reliability has been verified, the next step is to evaluate the ecosystem of these devices, including the richness of product selection, reliable supply chain and design support.
Supply, Support and System Level Design
Among the growing number of SiC suppliers, today’s SiC companies, in addition to their different experience and infrastructure, can offer different device options to support and supply numerous demanding SiC markets such as automotive, aerospace and defense.
Over time, the design of power systems undergoes continuous improvement across generations. SiC applications are no exception. Early designs may use very standard through-hole or surface mount package options for a variety of common standard discrete power products on the market. As the number of applications increases, designers begin to focus on reducing size, weight and cost, so they usually turn their attention to integrated power modules or choose third-party partners. These third-party partners include end-product design teams, module manufacturers, and SiC chip suppliers, all of whom play a critical role in achieving the overall design goals.
In the fast-growing SiC market, supply chain issues are a key issue that cannot be ignored. The SiC base material is an extremely expensive material in the SiC chip manufacturing process. In addition, SiC manufacturing requires high-temperature manufacturing equipment, which is not required for manufacturing silicon-based power products and ICs. Designers must ensure that SiC suppliers have a stable supply chain model, including multiple manufacturing plants in different locations, to ensure that supply can always meet demand in the event of a natural disaster or major production issue. Many component suppliers also end-of-life (EOL) previous-generation devices, forcing designers to spend time and resources redesigning existing applications rather than developing innovative designs that help reduce end-product cost and increase revenue.
Design support is also important, including simulation tools and reference designs that help shorten development cycles. With solutions to control and drive SiC devices, developers can explore new capabilities such as Augmented Switching to realize the full value of a holistic system approach. Figure 2 shows a SiC-based system design that integrates digitally programmable gate drivers to further speed up production while creating new ways to optimize the design.
Figure 2: The modular interposer combined with the gate driver core provides a platform to rapidly evaluate and optimize new SiC power devices with enhanced switching. (Image source: Microchip)
New options for optimized design
Digitally programmable gate drivers maximize the benefits of SiC with enhanced switching. They allow easy configuration of SiC MOSFET turn-on/off times and voltage levels, so designers can increase switching speed and system efficiency, while reducing the time and complexity required for gate driver development. Rather than manually changing the PCB, developers can use configuration software to optimize SiC-based designs with one click, increasing efficiency and fault protection while speeding time to market.
Table 1: Implementing a new enhanced switching technology using digitally programmable gate drivers can help address SiC noise, speed up short-circuit response, help manage voltage overshoot, and minimize overheating.
As SiC applications expand, early SiC adopters are already gaining ground in the automotive, industrial, aerospace and defense sectors. Future success will continue to depend on the ability to verify the reliability and robustness of SiC devices. As developers begin to adopt a total solution strategy, they will need access to a comprehensive portfolio of resources, supported by a complete and reliable global supply chain and all necessary design simulation and development tools.
They will also have new opportunities to make future-proof investments with software-configurable design optimizations enabled by digitally programmable gate drivers.