Silicon Carbide: Promising Technology on the Precipice

This post is in a series on the technology Valley of Death. Find the other posts here.

You will eventually find silicon carbide in every single electric vehicle, computer power supply, solar inverter, and battery charger. These devices will be everywhere. These are multi billion-dollar markets. The question is…which companies will survive that long?

As Clayton Christensen wrote in the Innovator’s Dilemma and Geoffrey Moore wrote in Crossing the Chasm, there is a large gap between the early adopters of a technology and widespread commercial adoption (also know as “success”). It takes millions of dollars, years of hard work, and patience for a company to bridge that gap. In this post I’ll describe why silicon carbide is important in the renewable energy industry and how far it still needs to trek to get to the next watering hole.

Introduction to Silicon Carbide — Why It’s Important

I explained in an this earlier post that every renewable energy system required power conversion. The power switches inside the power converters are the single component that generates the most energy losses. They’re also the third least-reliable component in the entire system (only capacitors and circuit boards are less reliable). I provided insight from the key power switch suppliers, in this post.

One of the most promising, “game-changing” technologies in the renewable energy industry is silicon carbide. Instead of making the power switches out of silicon (the same material that’s used to make the chips inside your computer), it’s also possible — but still difficult — to make them out of a much harder material, silicon carbide. Silicon carbide is already used in many ways, including LEDs, lightning arresters, astronomical telescope mirrors, heating elements, jewelry. It’s great for power semiconductor switches because it can operate at 300°C (as compared to 150°C for silicon-based devices), can withstand 20,000 Volts (versus 6,000 Volts), and generates 1/3 the energy losses at high voltages.

The drawback is that silicon carbide is an incredibly hard material. It’s nearly as hard as diamond, which is why it’s also used in cutting tools, Porsche disk brakes, and bullet-proof vests. This means it’s difficult to work with in manufacturing. Since the manufacturing process hasn’t yet been fully worked out, the materials have many defects, especially basal plane dislocations, which can’t be detected by visual inspection. If these defects are present, they gradually cause bipolar devices to fail over a matter of weeks or months. You can rule out mass market adoption of bipolar devices until these issues are worked out! Unipolar devices, such as Schottky diodes, JBS diodes, and JFETs do not suffer from the degradation caused by the basal plan defects, but they can be impacted by other materials defects.

The sweet spots for silicon carbide applications are:

  1. Residential-scale solar inverters – silicon carbide can be used for high-voltage MOSFETs, which reduce power losses, and reduce the system’s size by switching faster and operating at higher temperature. Why is this useful? Image being able to easily lift a small inverter up a ladder and onto your roof and install it next to the solar panels…instead of having to run DC cables all the way to your basement to a heavier wall-mounted inverter.
  2. Computer server power supplies – silicon carbide MOSFETs. Here, efficiency is the main gain.
  3. Electric vehicle power converters – Current Tesla’s have an air intake on the hood with two fans blowing directly onto the inverters. Imagine the cost and size reductions if vehicle manufacturers had highly-compact hardware that could survive in the hot under-the-hood temperatures without special cooling.
  4. Utility-scale power converters – The future “smart grid” will have power converters that intelligently route power to avoid brownouts and minimize blackouts. High-voltage silicon carbide thyristors will make these systems more practical.

Silicon carbide products are made in the following steps. Currently, each step still has reliability and yield issues that need to be worked out:

  1. Epitaxy growth – take a silicon carbide wafer and then grow additional crystals on top.
  2. Device fabrication – take the epitaxy, etch it with chemicals, blast it with ions, expose it to specialized gases, and deposit metals to create a power semiconductor switch.
  3. Packaging – take the finished device, attach  miniscule wires, and surround it with plastic to create a “brick” with 4 electrical terminals.
  4. System integration – take the packaged brick, attach 2 wires for triggering the switch, and 2 heavier cables for the input and output power connections.

U.S. companies working on silicon carbide:

Overseas companies working on silicon carbide (incomplete list):

U.S. universities and government agencies working on silicon carbide:

A Promising Start

DARPA, which is the government’s agency that funds “far out” technology ideas,” funded silicon carbide research throughout the late 80’s, 90’s, and early 2000’s…but then the funding started to dry up. DARPA’s feedback to the research community was: “The technology is advanced enough…now go find some actual applications and deploy SiC as a product.”

So, some startup companies raised money from angel investors and seed money from VCs and started developing SiC-based products. They and other research-focused companies started figuring out how to package the devices so that they could actually be installed inside a larger system.  They partnered with other universities that were developing power converters for electric vehicles and built a prototype residential-scale solar inverter.

The simplest and easiest to manufacture of the silicon carbide products are diodes, so two or three large companies successfully developed silicon carbide-based diodes, launched these products through a major electronics distributor, and saw strong sales.

The Valley of Death

What about all the other promising power semiconductor products? This technology is supposed to be a game changer applicable to all aspects of the renewable energy and electric vehicle markets! Hundreds of millions of research dollars and decades of work resulted in just one mainstream line of products?? The three problems are:

  1. Cost, cost, cost – due to low manufacturing yields and low manufacturing volumes, silicon carbide devices are 10’s to 100’s of times more expensive than existing mass-market silicon devices.
  2. Reliabilityinvisible defects make it impossible to know which devices will fail in the field.
  3. Integration – researchers have been so focused on making the devices work (in the lab) that many of the packaging and triggering issues, required to make silicon carbide work in an actual renewable energy product, haven’t been fully addressed.

Silicon carbide has passed its “proof-of-concept” phase. Early prototypes are under testing. Next comes widespread commercialization…and here we come across a barren landscape riddled with gaping financing holes and prickly technology risks.

Take a look at the figure below; the black vertical bar illustrated the technology Valley of Death. DARPA funded the “Technology Creation” of silicon carbide. The simple silicon carbide diodes — with the backing of large, established companies — successfully crossed the chasm and are being bought by the “Early Majority.”

Startups — funded by angels, seed-stage VCs, Dept. of Energy, and other Dept. of Defense grants — were the “Innovators,” who started packaging silicon carbide and inserting it into actual applications. Due to the issues listed above, however, the “Earl Adopters” are having difficulty using the devices. Working out the remaining issues will take millions and millions of dollars. That black chasm is huge.

Credit: Dept. of Energy. Found here.

The Valley of Death is vast and can be encountered on multiple different paths — both at the start of a company and again when it attempts to commercialize. This National Renewable Energy Lab article and the Renewable Energy World podcast (see the 9/14/2010 entry) have argued that the entire clean tech industry is facing the valley of death. Dot-com startup just need a computer, internet connection, and a desk to get started with coding a new website. Clean tech companies, in contrast, need to spend millions of dollars to build cleanroom fab facilities or high-voltage test facilities…just to get started. The finance industry and both state and federal agencies have recognized this problem and started developing solutions. I’ll discuss these ideas in a subsequent post, but I’ve already provided some links here.

In the meantime…an immensely promising technology is on the precipice. Silicon carbide will eventually inhabit countless vehicles, computers, and renewable energy installations. Which companies do you think will survive long enough to reap the profits?

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5 responses to “Silicon Carbide: Promising Technology on the Precipice

  1. Pingback: R&D100 Award Winner | Entrepreneurial Energy

  2. Pingback: R&D 100 Award Winner « Energy.BlogNotions - Thoughts from Industry Experts

  3. What you don’t mention anywhere in this otherwise very useful and insightful piece is the emergence of gallium nitride (GaN) as a real competitor to SiC. Especially GaN built on silicon substrates, which Bridgelux will soon introduce to the LED market in large numbers.

    GaN is expected to more rapidly lower costs, leveraging volume manufacturing expected from the emergence of solid-state lighting. In addition, GaN research is more rapily advancing than that of SiC, again due in part to focus on LED lighting. Lastly, GaN should have less reliability issues than SiC.

    GaN is still behind SiC, but it is arguably catching up quickly. Either way, I agree some combination of these two wide bandgap semiconductors should make a real impact in the power electronics world!

    • GaN MaN,

      Thanks for your helpful suggestion. While I have heard about GaN, I haven’t encountered any companies with mature GaN power semiconductors, especially not in the 1200V – 6000 V, 20 A – 300 A range. My impression is that GaN power semiconductor is 5-10 years behind SiC devices, which themselves still have a ways to go.

      What makes GaN more reliable? SiC micropipes have been pretty much resolved; basal plane defects are still a challenge for SiC.

      I’m very interested in hearing your thoughts on how GaN fits into the power semiconductor market. Feel free to contact me directly at elimpaecher@gmail.com.

      Best regards, Erik

  4. hi… im a student in one university at malaysia… and now im a final year student which is taking final year project as to complete my degree level… i have a question.. can i use silicon carbide in making cutting tools?since there is not much article about silicon carbide for making cutting tools, so i don’t know how to proceed my fyp… wht are the othermaterials have to be mix in making cutting tools using silicon carbide as a matrix.. thank you

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