Powering the Energy Transition with Silicon Carbide and Wide Band-Gap Devices

With clear benefits of reduced switching losses and higher efficiency (to name a few), the fundamental advantages of SiC to the energy transition have been understood for some time [4]. However, the barriers of performance, reliability, cost, and supply chain have stood in the way of industry adoption – until now. Thanks to a confluence of factors including major advances in SiC technology, a maturing supplier ecosystem, and major public and private sector investment, Figure 1, SiC is now reaching a tipping point in the global power electronics industry to support the clean energy transition and Environmental, Social, and Governance (ESG) initiatives around the globe [5].

 

Figure 1. The sustainable investment surge that will feed SiC market growth. Image used courtesy of Bodo’s Power Systems

 

For industry players ranging from foundries to device manufacturers, and from OEM’s to equipment operators, there is a pressing need to develop their own SiC roadmap and secure their supply chain or risk being left behind. Already we are witnessing key partnerships develop across the supply chain with the intent of bringing next-generation power management products to market at accelerating speed.

 

Breakthrough performance

SiC as a material is now stable and manufacturable at scale which is translating its lab-based performance advantages to real-world conditions. ON Semiconductor’s full-SiC power modules being utilized in Delta Electronics PV inverters is a perfect example, Figure 2 [6].

 

Figure 2. Delta Electronics SiC-based PV inverter using ON Semiconductor full-SiC power modules. Image used courtesy of Bodo’s Power Systems

 

Furthermore, the developments of new SiC device architectures are showing increasing potential to supplant Silicon (Si) device architectures – particularly at higher power/voltage ratings for applications like DC microgrids [7]. For example, the on-resistance versus critical electric field for breakdown trade-off, for a given breakdown voltage, has been shown to be superior for SiC versus Si, Figure 3 [8]. Consequently, SiC Schottky Barrier Diodes (SBDs) are now being used in high-frequency applications for achieving higher energy star ratings, such as switched-mode power supplies for industrial and traction drives, where switching losses are an issue – replacing Si PiN diodes [9].

 

Figure 3. Specific on-resistance of the ideal drift region. Image used courtesy of Bodo’s Power Systems

 

SiC Schottky diodes and DMOSFETs are now poised to replace Si PiN diodes and IGBTs in applications ranging from as low as 600 V to 12 kV due to reduced switching losses at the same frequency and higher efficiency per power conversion stage (e.g. 7% higher range when using 1.2 kV SiC devices within an EV traction inverter [10]). This is a result of the advantageous unipolar nature of SiC devices that reduce the stored charge needing to be removed from the device during each switching event [11].

Our team at NoMIS is developing SiC co-packs (3.3 kV and 6.5 kV) suitable for exploring the advantages and challenges medium voltage SiC provides when it comes to devices, circuit topologies, control, other converter components, and system-level implications, Figure 4 (engineering samples made available upon request).

 

Figure 4. SiC co-pack prototype from NoMIS. Image used courtesy of Bodo’s Power Systems

 

Proven reliability

Widespread industry adoption of SiC requires proven reliability, which had remained elusive until recently due to concerns regarding performance over the operating life of SiC devices, especially in rugged conditions (i.e. short circuit and avalanche conditions) [12].

The reliability challenge is quickly being overcome with commercial SiC chips in the ranges of 600 V to 1.7 kV having passed JEDEC and automotive reliability tests over 1,000 hours [13]. This has led to the rapid rollout of SiC technology in the high-growth EV market by leading automotive manufacturers [14].

Despite the rapid adoption of SiC in automotive, one of the remaining challenges for SiC device technology stems from concerns over drift in the threshold voltage (Vth) under long-term operation caused by defects in and at the interface of the gate oxide [15]. Yet here too, a major breakthrough in the last year by Professor Kimoto at Kyoto University sets a path to improve gate oxide screening yield by using >50 nm gate oxides, while other adjacent innovations are set to overcome concerns for long-term operation [16].

Our team at NoMIS are already working with other groups to apply these scientific breakthroughs to ensure Vth shift becomes a thing of the past for SiC devices.

 

Falling costs

Historically the higher cost of SiC devices relative to Si has made companies reluctant to switch technologies despite the performance advantages. However, a step-change in investment in production capacity across the entirety of the value chain is driving down the cost of SiC and this trend is set to accelerate as economies of scale take effect [17], [18].

Thanks to the coming introduction of 200 mm (8 inch) SiC wafers and related advances in both technology and manufacturing processes, 1.2 kV SiC devices at below $0.03 per Ampere are now in reach. This is only 30% costlier than Si, meaning price-parity is much closer than many would have thought. At NoMIS, our recent award from ARPA-E as a SEED topic SBIR is focussed on bringing down the cost of SiC devices – particularly at higher voltage nodes.

Other routes to price parity are also opening up at the multi-chip power module level where SiC advantages spill over into reduced costs of other system-level components [7], [11]. As the global EV market turbocharges volume production, prices will fall further and the recent entry of players, like Foxconn, will only add to the downward trend [19].

 

Stronger supply chain

As the recent challenges in microelectronics semiconductors have shown, a robust, regional, and scalable supply chain will be critical for SiC adoption and growth. Interested companies were often hesitant to transition to SiC due to the lack of a comparably developed supply chain to Si.

But with SiC foundries established and major new entrants emerging in North America, Europe, and Asia including integrated, foundry, and fabless models, companies have multiple options to partner for their SiC transition. Furthermore, the opportunity to build production capacity by converting existing Si foundries provides an attractive route to quickly adding SiC production capacity, Figure 5.

 

Figure 5. The SiC transition for foundries and fabless players. Image used courtesy of Bodo’s Power Systems

 

However, success for stakeholders in all stages of the supply chain will require a deep understanding of the technology’s future direction in order to right-size the substantial up-front investments. It also demands a high level of collaboration and coordination, from securing substrate supply to achieving device qualification, as no single player can deliver the global-scale SiC transition alone.

As we look to the next stage of the SiC transition, our team at NoMIS Power Group are working across industry, government, and academia to bridge the remaining missing links in SiC adoption; from the breakthrough science that will power the next stage of SiC adoption, such as SiC-based CMOS platform, through to innovative device design, rapid prototyping and testing of devices, and development of process design kits that will scale-up foundry operations.

 

This article originally appeared in Bodo’s Power Systems magazine.