Demand continues to grow for silicon carbide technology that maximizes the efficiency of today’s power systems while reducing their size and cost...
Demand continues to grow for silicon carbide (SiC) technology that maximizes the efficiency of today’s power systems while simultaneously reducing their size, weight, and cost. But SiC solutions are not drop-in replacements for silicon, and they are not all created alike. To realize the promise of SiC technology, developers must carefully evaluate product and supplier options based on quality, supply, and support, and they must understand how to optimize the integration of these disruptive SiC power components into their end systems.
SiC technology is on a steep upward adoption curve. Product availability has increased along with the breadth of choices from multiple component suppliers. The market has doubled over the last three years and is projected to grow 20-fold to more than $10 billion in value within the next 10 years. Adoption is extending beyond onboard hybrid and electric vehicle (H/EV) applications to nonautomotive power and motor control systems within trains, heavy duty vehicles, industrial equipment, and the EV charging infrastructure. Aerospace and defense suppliers are also pushing SiC quality and reliability to meet these sectors’ notoriously stringent demands on component ruggedness.
A key part of a SiC development program is validating SiC device reliability and ruggedness, as this greatly differs between suppliers. With the increasing trend to a total system focus, designers also need to evaluate the scope of the supplier’s product offering. It is important designers work with suppliers that offer flexible solutions such as die, discrete, and module options that are backed by global distribution and support, and comprehensive design simulation and development tools. Developers looking to future-proof their designs will also need to explore the latest capabilities such as digital programmable gate drivers that solve earlier implementation issues while enabling system performance ‘tuning’ with a keystroke.
First step: three key tests
A trio of tests provides the data to evaluate SiC device reliability: avalanche capability; the ability to withstand short circuits; and the reliability of the SiC MOSFET body diode.
Adequate avalanche capability is critical: even a minor malfunction by a passive may cause transient voltage spikes that exceed rated breakdown voltage, ultimately resulting in failure of the device or, possibly, the entire system. SiC MOSFETs with adequate avalanche capability reduce the need for snubber circuits and extend application lifetimes. The best-rated options demonstrate high UIS capability of up to 25 joules per square centimeter (J/cm2). These devices show little parametric degradation even after 100,000 cycles of repetitive UIS (RUIS) testing.
The second key test is short circuit withstand time (SCWT), or the maximum time before device failure under a rail-to-rail short condition. The result should be close to that of IGBTs used in power conversion applications, most of which have a 5- to 10-microsecond (us) SCWT. Ensuring sufficient SCWT allows systems the opportunity to service fault conditions without system damage.
A third key metric is forward voltage stability of the SiC MOSFET’s intrinsic body diode. This can vary substantially from one supplier to another. Without proper device design, processing and materials, the conductivity of this diode may degrade during operation, leading to an increase in on-state drain-source resistance (RDSon). Figure 1 sheds some light on the differences that exist. In a study undertaken by Ohio State University, MOSFETs from three suppliers were evaluated. On one end of the results, all devices from Supplier B showed degradation in forward current, while on the other, no degradation was observed in MOSFETs from Supplier C.
Once device reliability is validated, the next step is evaluating the ecosystem surrounding these devices, including breadth of product options, a solid supply chain, and design support.
Supply, support, and system-level design
With a growing number of SiC suppliers, today’s SiC companies can vary in device options — in addition to experience and infrastructure offered to support and supply many stringent SiC markets such as automotive and aerospace and defense.
Power system designs go through continuous improvement over time and within different generations of that design. SiC applications are no different. Early generations of designs may use widely available and standard discrete power products within very standard through-hole or surface mount package options. As the number of applications grow and designers focus on reducing size, weight, and cost, they typically move their designs to integrated power modules or may choose a three-party partnership. These three-party partnerships include the end-product design team, a module manufacturer, and a SiC die supplier. Each plays a critical role in achieving the overall design goals.
Supply chain issues are a key and legitimate concern in the rapidly growing SiC market. SiC substrate material is the most costly material within the manufacturing flow of the SiC die. In addition, SiC manufacturing requires high-temperature fabrication equipment that isn’t required for developing silicon-based power products and ICs. Designers must ensure SiC suppliers have a strong supply chain model including multiple manufacturing locations in case of natural disasters or major yield issues to ensure supply can always meet demand. Many component suppliers also end-of-life (EOL) older generations of devices, forcing designers to spend time and resources on a redesign of an existing application instead of developing new innovative designs that will help lower end-product costs and grow revenue.
Design support is also critical, including simulation tools and reference designs that help reduce development cycle times. With solutions for addressing the control and drive of SiC devices, developers can explore new capabilities like augmented switching to realize the full value of a total system approach. Figure 2 shows a SIC-based system design with an integrated digital programmable gate driver that further accelerates time to production while creating new ways to optimize designs.
New options for design optimization
Digital programmable gate drive options maximize SiC benefits through augmented switching. They allow easy configuration of SiC MOSFET turn on/turn off times and voltage levels so designers can speed switching and increase system efficiencies while lowering the time and complexity associated with gate driver development. Rather than manually altering the PCB, developers can instead use configuration software to optimize their SiC-based designs with a keystroke, future-proofing them while accelerating time to market and boosting efficiency and fault protection.
Early SiC adopters are already realizing benefits in the automotive, industrial, and aerospace and defense sectors as adoption grows in broader applications. Success will continue to rely on the ability to validate SiC device reliability and ruggedness. As developers adopt a total solution strategy, they will need access to comprehensive portfolios supported by a complete and reliable global supply chain and all necessary design simulation and development tools. They will also have new opportunities to future-proof investments through new capabilities of software-configurable design optimization enabled by digital programmable gate driving.
— Orlando Esparza is strategic marketing manager of Microchip