Author:
Didier Balocco, onsemi
Date
06/12/2024
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Figure 1: onsemi’s end-to-end SiC production
For applications such as electric vehicles (EV) and solar panels, engineers face the challenges of sensitive electronic components having to provide continuous, reliable operation within harsh environments. To further the adoption of these sustainable solutions, we need innovation at the component level to help elevate the overall system efficiency while providing increased robustness. One technology which is rapidly coming to the forefront as a technology capable of delivering these necessary advances is Silicon Carbide (SiC) semiconductors.
As part of the third generation of semiconductor technology, SiC solutions feature a wide bandgap (WBG) and deliver elevated levels of performance. This larger energy gap between layers (compared to previous generations of semiconductors) increases the energy required to switch the semiconductor from insulating to conducting. For comparison, first and second-generation semiconductors required values of between 0.6 eV to 1.5eV to switch, whereas third generation have values 2.3 eV to 3.3eV. In performance terms, WBG semiconductors exhibit a ten times higher breakdown voltage and are less activated by thermal energy. This translates to higher stability, increased reliability, better efficiency through reduced power loss and a much higher temperature ceiling.
For EV and inverter manufacturers that require excellent high power, high temperature and high frequency capabilities, SiC semiconductors represent an exciting prospect. But, in real terms, how does this performance translate and how is the semiconductor industry readying to keep up with the potential demand?
Within an EV and the accompanying charging network, high-performance semiconductors are core to the AC-DC charging stations, DC-DC fast chargers, motor inverter systems and vehicle high-voltage DC to low-voltage DC transformers. It is these systems that SiC semiconductors will look to optimize, delivering increased efficiency, higher performance ceilings and faster switching, contributing to quicker charging times, as well as a better utilization of the batteries’ capacity. This can allow for an increase in EV range or a reduction in the battery’s size, decreasing the vehicle’s mass and production costs, while improving the performance aiding widespread adoption.
Despite running cooler than their ICE powered counterparts, EVs still represent an incredibly harsh environment for power electronics with thermal management a key consideration for designers. For many earlier silicon and insulated-gate bipolar transistor (IGBT) devices, the running conditions inside an EV can lead to failure within the vehicle’s expected lifetime. With SiC solutions, the thermal limit is considerably higher and thermal conductivity is 3x higher on average, allowing for an easier transmission of heat to the surrounding environment. This translates to an increased reliability, permitting a reduction in the cooling requirements, further decreasing the weight and removing packaging considerations.
The improved peak voltage rating and surge capacity granted by SiC technology also supports manufacturers aiming to reduce charging times and vehicle weight. Typically, most EVs infrastructures have been in the 200 V to 450 V range, but automakers are seeking further performance gains by moving to 800 V. The first vehicle to implement this change was the premium-level Porsche Taycan, but more manufacturers are following suit with Hyundai’s recently announced Ioniq 5 now featuring 800 V charging, at a considerably lower retail price.
But what is the reason behind this move? Well, 800 V systems deliver several benefits, such as faster charging time, a reduction in cable size (due to lower current) and a decrease in conduction losses, all of which save production costs and improve performance. Currently, fast charging systems are reliant on expensive water-cooled cables which could be eliminated, while within vehicles smaller gauge cables would save significant weight, increasing the vehicle’s range. For some, the move to 800 V is paramount for creating the performance gain needed to convince consumers to adopt EVs, but this development is only possible through utilizing SiC semiconductors. Existing second-generation semiconductors simply lack the performance and reliability to operate at such voltages within the harsh environment of EVs and their charging infrastructure.
Beyond EVs, there are further growing sectors that will benefit from the performance delivered by the new generation of SiC semiconductors. Renewable energy is seeing rapid expansion and as a result solar/wind farm inverters and decentralized energy storage solutions (ESS), which are both reliant on semiconductor technology, are seeing a projected compound annual growth rate (CAGR) of 13% and 17% respectively. (source: Global Solar Central Inverters Market 2022-2026)
In a similar move to the EV market’s shift upwards in vehicle voltage, SiC technology allows solar farms to increase their string voltage. Existing installations typically operate at 1000 V to 1100 V, but newer central inverters leveraging SiC semiconductors will enable 1500 V. This allows for a reduction in the string cable size (as the current is lower) and in the number of inverters, due to each device permitting a greater number of solar panels. As some of the larger hardware expenses in solar farms, reducing the number of inverters and cable size can significantly reduce the overall project cost.
The benefits delivered by SiC technology to renewable energy applications extends beyond merely supporting higher voltages. For example, onsemi’s 1200 V EliteSiC M3S MOSFETs feature up to 20% power loss reduction in hard switching applications such as those seen in solar inverters, when compared to industry leading competition. Such savings can have a considerable impact when you consider the scale of the operations affected – in Europe alone, there are 208.9GW of solar farms. (source: Global Solar Central Inverters Market 2022-2026)
In terms of reliability, solar farms and offshore wind power represent incredibly challenging environments for electrical components, and it is in these surroundings that SiC technology will once again outperform existing solutions. By permitting higher temperatures, voltages and power densities, engineers can design more reliable, smaller and lighter systems than existing silicon solutions. Inverter enclosures can be reduced, and many surrounding electronic and thermal management components eliminated. While the higher-frequency operation permitted by SiC allows for smaller magnets, further reducing the system cost, weight and size.
It is clear that for EVs and sustainable energy generation, SiC semiconductors represent a step improvement in just about every aspect. Well implemented SiC MOSFETs and diodes can improve the efficiency of an entire operation, while reducing the design considerations, and in many cases reducing the overall project cost. But, as with any pioneering technology, there will be extensive demand. A question for many electronic engineers is whether SiC manufacturing is ready for widespread adoption and if production will remain reliable as quantities increase.
Fundamentally, one of the main issues with SiC is its construction. While silicon carbide is in abundance in space, it is unfortunately incredibly rare on Earth. So, it needs to be synthesized by combining silica sand and carbon in a graphite electric resistance furnace at temperatures between 1600°C and 2500°C. This process develops a SiC crystal boule, which needs further machining to ultimately shape a SiC semiconductor. Each step of production requires incredibly tight quality control to ensure the final product meets stringent testing standards. To maintain quality, onsemi has adopted a unique approach. As the industry’s only end-to-end SiC manufacturer, it controls every step of the process from the substrate to the final module (Figure 2).
Within its facilities, silicon and carbon are combined within furnaces before being CNC machined into cylindrical pucks and sliced into thin wafers. Depending on the required breakdown voltage, a specific epitaxy wafer layer (Figure 3) is grown before the wafer is diced into individual dies and packaged. By controlling the process from start to finish, onsemi has been able to create an effective production system ready for the increasing SiC demand.
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Figure 2: A SiC epitaxy wafer layer
While onsemi utilized its experience gained from producing silicon-based technologies, there are many challenges specific to SiC materials that must be appreciated to guarantee a high-quality and robust final product. For instance, many aspects of existing industry standards designed for silicon technology needed to be exceeded to create a reliable end product. Understanding any potential failure mechanisms is key to maintaining quality and, through extensive collaboration with universities and research centers, onsemi was able to identify the characterization and reliability of SiC under a range of conditions. The result of the research was a comprehensive methodology which could be applied to SiC processes.
For sustainable technologies to have the real-world impact necessary to help us meet global climate targets, efficiency, reliability and cost-effectiveness are key. Historically, finding component level solutions which can deliver on all three has been nearly impossible, but for many applications, this is what’s on offer with SiC technology. While global supply shortages have somewhat slowed SiC semiconductors’ arrival, it is clear we are now going to see a rapid uptake in the technology.
There are still challenges that large scale SiC adoption will face, such as semiconductor manufacturers keeping pace with demand and ensuring reliability is maintained. But through collaboration and research, the industry should be able to ensure standards are kept high and manufacturing efficiency optimized. In terms of deployment, it is important to remember that first and second-generation semiconductors will still have their place.
