Mind the Gap! – Wide Band Gap Semiconductors are Gaining Importance


Dr. Peter Friedrichs, Senior Director SiC at Infineon
Steffen Metzger, Senior Project Director GaN at Infineon

Dr. Peter Friedrichs
Steffen Metzger

Designers of power supplies, motor control and inverter systems, RF circuitry, photovoltaic circuits and a variety of other power switching schemes are under unprecedented pressure to improve application performance while increasing power density, reducing board space and driving down component count. To address these seemingly conflicting challenges, engineers are increasingly looking to deploy solutions based on wide band gap (WBG) materials such as silicon carbide (SiC) and gallium nitride (GaN).

The attraction of using WBG materials is clear. Switching at higher frequencies than conventional silicon can improve power density by shrinking the size of passive components. It can also help to save energy on cooling the overall system. Low charge and excellent dynamic performance in reverse conduction compared to silicon alternatives can enable more efficient operation in today´s applications at existing frequencies. And the much higher breakdown field strength and thermal conductivity of SiC devices allows manufacturers to create devices that outperform silicon alternatives across a range of temperatures – a key concern in areas such as photovoltaics, industrial motor drives, traction and electromobility.

But before WBG materials start to gain a significant share in the market, engineers need to take stock of a number of important issues. These range from the technology itself, through large scale manufacturing and supply chains to the support infrastructure that is behind it.

Silicon-based semiconductors may have been around for almost sixty years but they are not ready to be written off just yet. Manufacturers continue to invest heavily in silicon R&D and a large proportion of power applications can still be addressed using the latest advances around this ‘conventional’, reliable and highly cost-effective technology. 

That said, there is no doubt that there are a growing number of demanding applications where silicon devices can simply no longer address the target requirements. Take, for instance, RF power.

Many RF applications are now heading towards frequencies where the efficiency of silicon devices is no longer good enough. To address this, semiconductor manufacturers are developing WBG solutions designed specifically for RF applications. Solutions such as Infineon’s comprehensive family of GaN-on-SiC RF power transistors that operate at frequencies of 1.8GHz and higher. These devices enable cellular amplifier designers to build smaller, more powerful and more flexible transmitters. And as the world moves towards 5G infrastructures, the role that GaN technology can play in this field is set to become even more important.

RF power is actually a relatively well-established market for WBG solutions when compared to the market for more general switching power applications including power supplies and inverters. And, as with many less mature markets, a lot of startups and small players are emerging with highly innovative solutions that compete in the key areas of price and performance. However, price and performance are far from the only issues to consider. Alongside the issue of not yet having manufacturing capabilities at a larger scale or an established supply chain and support infrastructure, a key challenge for some of these smaller companies is reluctance on the part of OEMs to buy a yet relatively unproven technology. Part of this reluctance relates to unknowns regarding product reliability.

Indeed, careful consideration of reliability should be at the forefront of the engineer’s mind when evaluating technologies for a power application that will be expected to operate, trouble-free, for many years. One of the issues is that a GaN structure, for example, is fundamentally different to a superjunction silicon structure. Because of this it is likely to exhibit different failure modes. This, in turn, means that the established tests for reliability such as those based around the JEDEC standards may no longer offer a fair reflection of lifetime reliability. 

In order for GaN to achieve widespread acceptance and credibility in the market for power applications it will be absolutely vital for the industry to identify and support relevant, new reliability standards. Infineon, as one of the most established players in the GaN sector, is pushing for such standards at the same time as providing its own reliability data for its WBG portfolio to ensure that customers understand exactly how devices will operate in real-life applications. 

Looking to the future, advances in silicon will ensure that this remains the dominant semiconductor material for at least the next ten years and, in most likelihood, a lot longer. SiC will continue to increase its market share – especially with the availability of SiC MOSFETs raising the benefits from SiC technology to a new level. New solutions supporting energy savings will be realized by the designers in many applications, among them photovoltaic inverters, energy storage systems and chargers for electromobility. And GaN will consolidate its position with respect to RF power and see future growth in more general power switching applications – especially as more robust reliability tests come online.

Within this market, we believe that Infineon occupies a unique position. As a supplier of both silicon and WBG semiconductors, the company is ‘material-agnostic’ and can take a holistic view when it comes to identifying the optimum solutions for customers in terms of performance, price and reliability. A strong history in silicon means an in-depth understanding of silicon’s sustainability and the future possibilities and limitations of conventional semiconductors.

At the same time, the company has well-established and proven SiC and GaN capabilities built up over many years. Infineon will actively improve the cost/performance ratio of WBG technologies and accelerate the market introduction of WBG-based products. Because, after all, we are aiming at making life easier, safer and greener – with technology that achieves more, consumes less and is accessible to everyone.
 

Source: Bodo's Power Systems, March 2017