The Wide Bandgap Challenge

About a year ago, I had a great idea. Set up a blog to go with our website. Fast forward to now and we’ve managed to post just one article – and that was at the start. The last year has been a blur of fund-raising efforts and getting technology programmes up and running – both have been successful and we are full speed ahead.

During the fund-raising effort, a question that was asked time and time again was why do we think diamond can make an impact when so much investment has already been made in other materials, in particular silicon carbide (SiC) and gallium nitride (GaN)? The glib technical answer is just look at the respective physical properties of the materials and make your own conclusions. However the real answer is more complex and takes some time to explain.

For a start, the real competitor is silicon. It has become a commodity market. The base material is manufactured using a liquid process and wafers up to 450mm diameter can be processed – that’s a lot of devices on a single crystal piece of silicon. Also despite people attempting to write silicon off with regular monotony for the last 20 years, it has constantly found ways to push the material to its absolute limits. But now, finally, consensus is that 2021, or so, will see feature sizes finally hit the buffers of what is possible – however already thoughts are moving to things like vertical architectures, 3D architectures and hybrid approaches with 2D compounds and the like.

All this should be happy days for those looking beyond silicon at electronics based on materials that simply by replacing silicon with them could yield an order of magnitude improvement in performance. But here’s the rub. The fact is that the majority of the electronics market is a commodity market relying on the economies of scale. Anyone trying to compete with this has to either have something that is so compelling on performance that people will happily pay a premium or it can be made more cheaply than silicon is today (and ideally deliver the former as well).

Let’s look at the second point first. Just about all wide bandgap semiconductor materials are produced from the vapour or gas phase – this is significantly more energy intensive than is required to produce silicon and is at least an order of magnitude slower to grow. So the substrate materials are themselves expensive – although this is somewhat compensated by the fact that you generally need less wide bandgap material to make devices. You also then need to process that material to make devices. Here wafer size does matter, the cost of putting a 300mm or 450mm diameter wafer through a fabrication process is not significantly more than the cost of putting a 100mm or 200mm diameter wafer through a process (notwithstanding the eye watering costs of the infrastructure as you scale up).

Going back to the first point on performance, you also need to outperform silicon. That devices based on SiC and GaN can deliver this is not in dispute. However they have yet to yield the performance advantages that justify their current premiums, except in specialised applications where their use can yield overall savings in the bigger picture. Put simply, it is now possible to make a laptop supply that would be a quarter of the size of the one you currently use and it runs significantly cooler too, but would you pay a 3 to 4 times premium for it?

This is the problem that GaN and SiC now face. The devices that are being made are largely competing with ones where there is an equivalent in silicon that is 10%-20% of the cost to produce. Both materials have struggled to deliver a compelling case, and the outcome is huge investments in infrastructure to try to achieve the economies of scaled mass production in order to compensate for the fact that they can only deliver a good but not compelling case for replacing silicon. And their current roadmaps don’t look like they are going to deliver something that will generate clear blue water over silicon anytime soon either.

Already there are signs that both material technologies are consolidating. Take Infineon’s recent acquisition of Cree’s SiC power electronics business and International Rectifier for GaN devices (and complementary silicon devices), and Transphorm’s effective acquisition of Fujitsu’s GaN interests. Tacit admission that there is limited leeway for both these materials to make a dent into silicon?

When you crunch the numbers GaN, SiC and diamond at scaled production are, carat for carat, not that dissimilar in cost to produce. So the question boils down to how much starting material you need; how expensive is the manufacturing process; and, most importantly, is there a compelling performance advantage over silicon?

In the case of (single crystal) diamond, we need around a one fifth of the material that GaN and SiC need to achieve the same rating. The technology that Evince is developing has an inherent elegant simplicity that has less than half the manufacturing steps needed to make a conventional semiconductor device. Finally, where we are heading is towards a family of devices and applications that go where silicon, GaN and SiC presently just can’t go. This is where diamond will achieve early success and sustainability as it makes the journey towards commercial mass production.

Is the diamond electronics revolution is coming? You bet!

Why Grids Need Diamond To Be Their Best Friend

by Gareth Taylor CEO

A couple of weeks ago I was invited to give a talk on innovation to a group of people from the distribution system end of the electrical utilities sector. It was an interesting opportunity to discuss the subject in an industry that is famed for its conservatism, where the word “innovation” is usually tempered with only so long as the technology/service/practice is already well proven so that the prime directive (“keep the lights on”) is not compromised.

In preparing my talk I was reminded of how my own sojourn into diamond began 18 years ago, not in a lab but from strategy development for the international electrical substations manufacturer I worked for at the time. My brief was to look at how electricity transmission and distribution networks might evolve over the next few decades and to present this to the main board. The outcome was the creation of three scenarios, for which a strategy was developed for each one. These are summarised in the figure below, which highlights the general flow of electricity through the network.

Energy Scenarios

The first scenario was called “Status Quo” – the core assumption being that we would continue to build large gigawatt scale power stations and use the transmission networks as the main conduit for shipping energy to where it was needed. The strategy resulting from this pretty much aligned with where the business was focused, so a happy board – although not for long. The second scenario was called “The Age of Sustainability” – the core assumption here being that other fuel vectors e.g. gas are actually cheaper and more efficient to transport than electricity and growth of renewable generation plant would lead to more distributed generation at the tens to low hundreds of MW level closer to the point of use. The final scenario was called “The User Rebellion” – a scenario where domestic and commercial users, possibly due to worsening quality of supply, took matters into their own hands and installed high levels of embedded generation most of at significantly below the 1MW level.

In the latter two cases this meant that the challenges (and hence new business opportunities) were all going to stem at the distribution network level on systems that were never designed to cope with large amounts of bidirectional power flow or contribute to the national security of the electricity system. The recommendation to the board was that of the three scenarios put forward, Status Quo was the one least likely to happen. Despite acknowledging the validity of this assertion the board choose to subscribe to the Titanic school of management and ignore the impending the threat to its primary business. The outcome? Subsumed as part of a bigger global concern 12 years ago.

With the benefit of hindsight, those scenarios weren’t all that bad. Only today when you look at the energy mix the outcome is that we have a melange of some of the principles that drove The Age of Sustainability and The User Rebellion. And while we correctly predicted that what have become known as Smart Grids would be necessary, what we failed to anticipate was the degree of burden that international government policies towards renewables would further place on already distressed distribution networks. The simple fact is that the intermittency of renewables has yet to be properly addressed.

Going back to the talk I gave, one of my themes was therefore that change and the rapidity of change is becoming something that utilities cannot just react to or engage in programmes that start when the production roll-out of that technology/service/practice is at completion. In fact there are some enabling pieces in the jigsaw that are so fundamental that they enable and drive profound change across a whole swathe of how you might operate electricity networks, boiling down to a handful of enabling component technologies. These I term “horseshoe nail technologies” – for those familiar with the proverb.

So cue Elon Musk’s recent announcement of Tesla’s Powerwall domestic energy storage system highlighting that certainly the The User Rebellion is very much alive– even though he acknowledged it is currently twice the cost that could seen as sustainable. All serving to re-open the vexed question of just who should pay for energy storage – despite the fact that it is recognised as one of the horseshoe nails necessary to cope with the intermittency of all that solar and wind we’re being encouraged to embrace. Ask a renewables developer, ask a grid operator, neither wants to take on the responsibility of energy storage.

While the Powerwall undoubtedly uses some very clever battery technology, actually what makes it really work is the power electronic system that interfaces the battery to the grid and controls the charge and discharge of the battery. Going back to those strategy scenarios what I recognised was that power electronics would play a massively increased role in energy systems not only for energy storage, but the way we connect generators to the grid, the way we control the flow of electricity and the way we use that energy – especially at the utility distribution voltage level. Like energy storage, power electronics continues to be twice the cost that many would see as sustainable. Unlike energy storage, power electronics does justify its cost in many scenarios, so much so that 120GW of power electronic systems designed to control >1MW of energy are manufactured per annum (for comparison UK electrical plant capacity is around 60GW).

The cost of power electronics is not going to come down until a replacement for the silicon transistors that lie at the heart of these systems is found. Only then can large swathes of costs to be taken of power electronic systems. Gallium Nitride and Silicon Carbide continue to make slow but steady advances, albeit at the sub 1800V level. However the real energy challenge lies at the 11kV to 33kV that most distribution networks operate at and this requires devices able to switch at those sorts of voltages. Only then can power electronic systems come to the fore, permitting fully dynamic stabilisation of the grid. And this is where diamond comes in. All those many years ago there was a nagging feel that GaN and Sic would struggle to deliver clear blue water over silicon and so it has, so far, proven to be.

Of all the electronic materials, diamond offers the most compelling case as the material most able to enable and deliver the power electronics needed to make a truly smart power grid. The past 18 years have been a long and necessarily intermittent journey, but with major advances in the materials technology, the recognition that carbon is likely to be to the 21st century what silicon was to the 20th, the technology we are now starting to demonstrate at Evince is truly a breakthrough in bringing fully synthetic diamond based electronics into the mainstream.

And my final message in that talk to the utilities? Most things you may get away with on a purely reactive strategy, but when it comes to those horseshoe nails it may be better to embrace and nurture them from an early stage rather than act in denial until its too late. As Elon Musk is showing, one exceptionally wealthy man can rewrite the rules, think what a few more joining in could do.

Welcome

Welcome to Evince Technology’s blog space. Thoughts and musings on the challenges of bringing diamond electronics into the mainstream will be posted here.