By Orlando Esparza, Senior Product Marketing Manager, Discrete & Power Management Business Unit, Microchip Technology Inc.
Silicon Carbide (SiC) technology helps modern power systems perform efficiently while also minimizing their size, weight and cost. Therefore, it is not surprising that developers are increasingly looking to adopt this technology. It is important to note that SiC solutions are not exact replacements of silicon and developers need to assess product and supplier alternatives regarding quality, supply as well as support. In addition, they must learn how to enhance the integration of these troubling SiC power components into their end systems.
High Demand for SiC Technology Adoption
With the increasing adoption of SiC technology, we have seen an increase in product availability as well. The market has doubled in the past three years and is positioned to grow at least 20 times more. Over the next decade, the market share is projected to reach $10 billion in value. Adoption is moving beyond on-board hybrid and electric vehicle (H/EV) applications and seeking non-automotive power and motor control systems within trains, heavy duty vehicles, industrial equipment and electric vehicle (EV) charging infrastructure. Certain sectors such as the aerospace and defense industry requires strict demands on component ruggedness and in response, suppliers are now placing greater emphasis on SiC quality and reliability.
However, these attributes differ from one supplier to another and assessing SiC device reliability and ruggedness has become more crucial than ever. Moreover, designers will have to review supplier’s product offering as it is essential for them to work with suppliers who can provide flexible solutions to address a wider set of requirements. For example, they could look at die, discrete and module options that are supported by global distribution, support and comprehensive design simulation and development tools. To be able to provide future-proof designs, developers should source for recent resources such as digital programmable gate drivers which can help address previous implementation issues while allowing system performance ‘tuning’ with a keystroke.
Evaluating the Reliability of SiC Device
This evaluation involves a trio of tests that will provide insights on the device’s avalanche capability, its endurance against short circuits as well as the reliability of the SiC MOSFET body diode.
- It is critical that the device prove adequate avalanche capability as a minor malfunction by a passive has the potential to trigger transient voltage spikes beyond acceptable breakdown voltage limits, therefore leading to device or system failure. As a result, SiC MOSFETs need to be evaluated and checked if they have enough avalanche capability to minimize the dependency on snubber circuits and ensure a longer application lifetime. A top-rated device in this category will typically have a high UIS capability of up to 25 Joules per square centimeter (J/cm2). Such devices show little parametric degradation even after 100,000 cycles of Repetitive UIS (RUIS) testing.
- The short circuit withstand time (SCWT) test finds the maximum time before device failure under a rail-to-rail short condition. The goal of this test is to have an outcome that is close to that of IGBTs used in power conversion applications, which typically have a 5-10 microsecond (us) SCWT. Systems with adequate SCWT have the opportunity to address and repair fault conditions without system damage.
- The third key test is forward voltage stability of the SiC MOSFET’s intrinsic body diode, though it may vary among suppliers. If a device has been built with faulty or inadequate design, processing and materials, the conductivity of this diode may be impacted resulting in damages during operation and an increase in ON-state drain–source resistance (RDSon).
Figure 1 shows the differences in MOSFETs. Ohio State University conducted a study to compare the degradation levels of MOSFETs from three different suppliers. All devices from supplier B showed degradation in forward current, while no degradation was seen in MOSFETs from supplier C.
Figure 1: Forward characteristics of SiC MOSFETs demonstrate the variances in body diode degradation by supplier. Source: Dr. Anant Agarwal and Dr. Min Seok Kang, Ohio State University.
Once the device has been checked for reliability, it is important for developers to analyze the ecosystem of the device and consider various checkpoints such as the range of product offerings, a strong supply chain and design support.
Assessing the Key Differentiators among SiC Suppliers
SiC suppliers are growing steadily. As mentioned earlier, the key parameters that differentiate these suppliers are their capabilities around system level design, support and supply. These businesses will not only offer a variety of device options but also differ in terms of experience and infrastructure capability to support and supply to SiC markets with stringent standards such as the automotive as well as aerospace and defense industries.
For power system designs, SiC applications need to be continuously improved and within various generations of the design. In the early generations of designs, the designer may have applied easily available and standard discrete power products choosing from the available options of standard through-hole or surface-mount packages. However, as the scope of the applications expand and the number of applications increase exponentially, designers will need to optimize by reducing size, weight and cost. They may choose to transition to an integrated power module or form a three-party partnership agreement. Such partnerships involve separate parties such as the end-product design team, a module manufacturer as well as a SiC die supplier. Each party is considered to be a vital role in realizing the overall design of the application.
In the increasingly growing SiC market, supply chain issues are a critical concern as SiC substrate material is the most expensive item throughout the SiC die manufacturing process. SiC manufacturing also involves high-temperature fabrication equipment that are not required for silicon-based power product and IC developments. It is essential that designers work with SiC suppliers with a strong supply chain model to cover various manufacturing locations to avoid issues related to natural disasters or major yield. In addition, numerous component suppliers also end-of-life (EOL) older generation devices which pushes designers to utilize time and resources to re-design old applications as opposed to focusing on new design with goals to minimize cost and increase revenue.
Design support is equally as critical and should encompass various tools such as simulation programs and reference designs to further speed up the development cycle. Designers can now opt for control and drive solutions that provide added capabilities such as augmented switching. Figure 2 illustrates a SIC-based system design with an integrated digital programmable gate driver that further accelerates time to production while developing new ways to enhance designs.
Figure 2: The combination of module adapter boards and gate driver cores offer a platform to efficiently evaluate and optimize new SiC power devices through augmented switching.
Design Optimization
SiC benefits are maximized by digital programmable gate drive options through augmented switching. These options make it possible to easily configure SiC MOSFET turn on/turn off times and voltage levels where designers can expedite switching and improve system efficiencies while reducing the time and difficulty related to gate driver development. Instead of physically changing the PCB, developers may employ configuration software to optimize their SiC-based designs with a keystroke. As a result, they will be able to future-proof these designs while accelerating time to market and enhancing efficiency as well as fault protection.
Figure 3: The table illustrates how the use of digital programmable gate drivers can implement the latest augmented switching techniques and offer various benefits such as solving SiC noise problems, speeding short-circuit response, managing voltage overshoot problems as well as reducing overheating.
As adoption continues to grow in a wide range of applications, early SiC adopters are understanding the benefits in industries related to automotive, industrial as well as aerospace and defense. The underlying differentiator here will still rest on their ability to prove the reliability and ruggedness of the SiC device. Ultimately, developers will require greater visibility and access to comprehensive product offerings that are enabled by a robust and reliable global supply chain as well as supported by essential design simulation and development tools. Digital programmable gate driving will help achieve software-configurable design optimization therefore creating opportunities for developers to future-proof their investments.
