How WBG switching devices are starting to redefine power system development

The merits of wide-bandgap (WBG) semiconductor technology have been talked about extensively for much of the last decade. Though so far they have only made relatively small inroads in terms of unit volumes shipped each year, there are dynamics now emerging that seem certain to turn things up by orders of magnitude in the near future. This will shift WBG devices from being a novelty which is confined to disparate niche applications into larger-scale mainstream use.

Whichever industry analysts’ reports you choose to look at, the overall outcome that they predict is much the same. The WBG business is going to see a major ramp-up over the course of the coming years. Data Bridge, for example, expects there to be a compound annual growth rate (CAGR) of 54% witnessed here up to 2028.¹ Technavio is equally confident that there will be a significant increase in WBG revenue.² It projects that annual figures of close to $2.9 billion will be reached by 2024, which equates to a >36% CAGR between now and then.

The advantages of WBG

What differentiates WBG materials, like silicon carbide (SiC) or gallium nitride (GaN), from conventional semiconductor materials like silicon (Si) is the more extensive gap that lies between the valence band and conduction band. While Si has a gap that is just 1.1 eV, for SiC it is 3.26 eV and for GaN it is 3.4 eV. Because of this, WBG devices will possess a breakdown voltage level that is an order of magnitude higher than that of Si. This means that devices fabricated from it can be used in circuits that have far higher voltages involved. In addition, WBG technology offers markedly better electron saturation velocity and this allows much faster switching speeds to be supported. Figure 1 illustrates the important differences between Si and WBG.

Figure 1: Comparison of the key characteristics of wide-bandgap materials with those of Si.

As WBG devices can achieve high blocking voltages in much smaller dies, there are only low internal device capacitances to contend with. This has several plus points for switching operations, as switching speeds can be further accelerated and gate drive power requirements are markedly lower. Faster edge rates, along with intrinsically lower on-resistance and minimal gate leakage (thanks to elevated breakdown voltages), all result in less power loss and greater conversion efficiencies.

The greater thermal conductivity of SiC specifically is another valuable attribute, as heat can be dissipated far more effectively from the die of a SiC device than from a Si one. Because of this, the higher junction temperatures that can be supported is another important attribute. It allows SiC devices to be deployed into more challenging application environments than their Si counterparts.

The principal market drivers

Because of the faster switching and lower losses involved in this process, WBG technology has a lot of appeal in industry sectors where it is paramount that the highest possible efficiency levels are attained. Among the ones where WBG is already starting to see traction are:

• Solar inverters — with the greater efficiency of GaN and SiC power switches meaning that more of the electrical energy coming from photovoltaic cells can actually be supplied into the grid;
• EV charging infrastructure — resulting in vehicles being able to travel longer distances between recharges, as well as allowing faster charge times;
• Data centres — enabling more densely packed server racks with lower power budgets and less complex thermal management;
• Industrial motor drives — leading to miniaturisation and greater efficiency.

Implementing WBG designs

Though the attributes of WBG can enable power conversion efficiencies to be boosted, it is not simply a matter of swapping conventional Si devices for WBG alternatives. The substitution of a Si-based MOSFET with a SiC one, for instance, will successfully speed up switching and curb the losses involved. However, once installed, the likelihood is that there will be greater electromagnetic interference (EMI) associated with it. This will call for additional snubbing and filtering, which will cause losses too — so the problem is just shifted around rather than actually being solved.

Cascodes provide a way of leveraging the operational advantages of SiC, without having to carry out extensive re-engineering work. These hybrids each feature the respective functionality of a SiC JFET and a Si-based MOSFET in combination with one another. As a result, they can deliver the heightened switching speed capabilities that are an inherent part of SiC, while also being easy to drive. These devices have already proved very popular in EV powertrains (including onboard chargers and DC/DC converters).

Rather than using WBG devices as drop-in replacements for previous Si-based devices, ideally systems should be fully designed from scratch in order to accommodate this technology in a proper manner. Key to this is increasing the operating frequency to a point where switching losses are still low, but savings are also achieved in relation to the external passive components (such as inductors and transformers). If higher frequencies are used then the size of these components can be shrunk — with bill-of-materials (BoM) costs thereby being reduced, as well as less board real estate being needed.

Supplied in SOT227B packages, the IXFN130N90SK MOSFET transistor modules from IXYS offer a straightforward route for engineers to migrate to WBG technology. With dual N-channel operation, these devices have a 900 V rating and their on-resistance is only 10 mΩ.

Based on SiC Schottky diode technology, the SKKE60S12 rectifier modules from Semicron are aimed at high-frequency rectification work. These 1.2 kV units are housed in the company’s SEMIPACK 2 packaging format. Heat is dissipated via their aluminium oxide baseplates (which are ceramic insulated). A junction temperature range of -40°C to +125°C is supported.

Covering use cases that range from solar inverters and battery chargers through to industrial motor drives, the LSIC1MO120E0080 N-channel MOSFET from Littelfuse relies on SiC technology. This device exhibits low gate charge (95 nC) and output capacitance (75 pF) parameters. Its gate leakage current is a maximum of 100 nA, with its gate resistance being only 1.0Ω.

Figure 2: Littelfuse’s LSIC1MO120E0080 SiC MOSFET.

GeneSiC’s G3R160MT17D SiC MOSFET also has a 1.7 kV rating. Targeted at high-density system designs, its thermal resistance is typically just 0.64°C/W. This device is housed in a compact TO-247 package. Its typical on-resistance value is only 160 mΩ, which helps to curb the power losses experienced.

Figure 3: The GeneSiC G3R160MT17D.

Conclusion

It is clear that WBG devices are going to become an essential element of contemporary power switching designs — delivering substantial boosts in terms of conversion efficiencies through faster switch speeds, elevated voltages and reduced losses. If industry sectors are to fully realise all the benefits that can be derived from such technology, and market traction is to be maximised, then a robust supply channel capable of offering an expansive portfolio of products will be essential.

By working with leading suppliers in power discrete technology, Transfer Multisort Elektronik (TME) is able to provide engineers with access to all the latest innovations in SiC semiconductors. It can also provide the engineering support necessary to help engineers looking to move from Si-based systems to next-generation SiC-based systems.

References

1. https://www.databridgemarketresearch.com/reports/global-wide-bandgap-wbg-power-semiconductor-devices-market
2. https://www.technavio.com/report/wide-bandgap-wbg-power-semiconductor-devices-market-industry-analysis

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