GaN – The Wide Bandgap Semiconductor that is Fundamental to a New Future
Silicon technology was the centerpiece of the technology discussion around the world in the 70’s and 80’s. Silicon devices were inventing the future thanks to Moore’s Law and a very generous dose of capital investment. If you can remember the 70’s, you can also remember that a smartphone was an impossible dream outside of the comic books. Now it’s a commodity with over one billion units sold every year. Computers used to be big boxes, now they are clouds with unbelievable computation and storage capacity accessible by virtually anyone with a phone, a tablet, or even a computer (soon a watch or glasses too!).
Still no flying cars though.
So, what’s driving the future now? Is it still silicon? Not really.
Take a look at figure 1 – it shows the growth in global semiconductor revenues since the 1980’s. This graph also shows the compounded annual growth rate of the industry for the decade of the 80’s (22%), the 90’s, (16%), and the years since the turn of the century (4%). Semiconductors are now growing at about the rate of the global economy. No longer is silicon driving the future – it’s just going with the flow.
Figure 1: Industry revenues from 1980 to the present. Compounded annual growth rates for the 1980’s, 1990’s, and for 2000 through 2013 are also shown.
In order to take charge of the future once again we need a strategic inflection. To quote Andy Grove , “a strategic inflection point is a time in the life of business when its fundamentals are about to change. That change can mean an opportunity to rise to new heights. But it may just as likely signal the beginning of the end.”
Gallium nitride is a semiconductor material that creates a strategic inflection in the semiconductor industry for two reasons; (1) it makes higher performance products, and (2) they will soon cost less to make.
Higher Performance?
There are a myriad of ways to compare device performance between silicon and GaN. In power applications where switching speed and conduction losses are very important, GaN-based transistors with 5X better performance are widely available. These are first-generation devices and Moore’s Law is just kicking in. At Efficient Power Conversion Corporation (EPC) we are readying two sequential generations for launch in 2014 and 2015 that each have a factor-of-two improvement over prior generations. This can continue for years as the theoretical difference in performance is over 1000:1 . We are just at the beginning of the learning curve!
But what about more complicated devices like analog and digital ICs? There are challenges here for GaN, but these are similar to the challenges that faced silicon 40 years ago. There are solutions that have already been demonstrated, but a clear winner has yet to emerge .
Lower Cost?
Figure 2 shows the projected cost evolution of GaN power transistors. When first launched in 2010, GaN transistors cost more. In particular, the growth of the thin epitaxial layer on top of silicon was expensive. There were some significant offsets, however; GaN transistors are smaller, so the starting silicon wafer costs less per device. GaN devices do not require packaging at voltage ratings below about 200 V. For higher voltages, it’s much smaller packaging than their aging silicon counterparts. Remember, packaging represents 50% of the cost of the average power MOSFET!
| GaN (600 V and lower) | ||
| 2010 | 2016 | |
| Starting Material | lower | lower |
| Epi Growth | higher | same |
| Wafer Fab | lower | lower |
| Assembly | lower | lower |
| Overall | higher | lower |
Figure 2: Comparison of relative manufacturing costs of a power MOSFET and a GaN transistor with similar voltage and on-resistance.
With recent advances in epi growth equipment and process, this cost is now approaching the cost of growing silicon epi. The cost advantage is rapidly shifting towards GaN. With continued die shrinks and volume increases, we are now experiencing a “virtuous cycle,” where devices cost less and perform better each year.
So let’s assume this trend continues and GaN technology continues to perform better, cost less, and can be used for more and more complex integrated circuits. How does that change the future? Let’s look at four examples where GaN transistors are already helping to invent the future.
Transforming Space
Power converters used in harsh environments, such as space, high-altitude flight, or high-reliability military applications must be resistant to damage or malfunctions caused by radiation. GaN transistors today perform 40 times better electrically while being able to withstand 10 times the radiation compared with the aging Rad Hard power MOSFET. This enables entirely new architectures for satellite power and data transmission.
Elon Musk, CEO of SpaceX, has set as his mission to reduce the cost of putting objects in space by a factor of 10. With GaN technology applied to satellites we can reduce the size of the electronics, eliminate the shielding required, and greatly improve the performance of the data communications. This greatly reduces the number of solar panels, makes the entire system smaller and lighter weight, and extends the life of the satellite. A factor of two reduction in weight is within our reach with today’s technology, whereas a factor of 10 is possible when eGaN technology is used to produce entire systems on a single chip. Multiply the impact of SpaceX with eGaN technology and we will change the way we use space and accelerate the exploration (and possible colonization?) of our universe.
Transforming the Machine Interface
LiDAR, or light detection and ranging, uses high speed pulsed lasers to rapidly create a three dimensional image or map of a surrounding area. One of the earliest adopters of this technology was the Google "driverless" car. Today’s GaN transistors are enabling new and broader applications such as 3D printing, real-time motion detection for video gaming, computers that respond to hand gestures as opposed to touch screens, and fully autonomous vehicles. As GaN technology evolves, LiDAR can be further improved in both resolution and cost. Projects are already underway to include “3D Awareness” in our cell phones. Imagine if phones could understand the space around us. We will be able to get directions in a new, more comprehensive way. An iPhone today can provide the location of the building you desire, but with LiDAR, 3-D mapping could lead you straight to a specific office.
Transforming the Use of Electricity
Wires suck. Today, we need wires to supply power to our ever-growing collection of electrically-powered gadgets. For those gadgets that are so completely indispensable, we need to take them with us at all times, and they need batteries that must be recharged all-too-frequently. Expected in 2015, wireless power systems using GaN technology will begin to unload this wired burden by providing energy wirelessly to charge cell phones and tablets. By integrating thin transmission coils in the floor tiles and the walls of buildings and homes, the need for wall sockets will be eliminated altogether! This same wireless power technology can be used to charge electric vehicles when parked over a transmitting coil embedded in the floor of a garage. A project is underway to embed wireless chargers at bus stops. Eventually, in a one-minute stop, a bus can get enough charge to drive a mile to the next bus stop. This could eliminate the need for most of the heavy batteries and overhead electrical systems that burden electric buses today.
GaN technology makes possible the efficient transmission of electricity at safe frequencies that are difficult for their silicon transistor ancestors. Taking GaN technology to higher voltages and higher frequencies extends the wireless power transfer distance. Integrating GaN technology into complete systems on a chip enable wireless power systems to be embedded into almost every device that consumes electricity.
Transforming Medicine
We are all getting older every day, and, as we age, we develop more opportunities for frailties and chronic health problems. Today there are major advances in fields such as implantable systems, imaging, and prosthetics that are enabled by GaN technology.
Wireless power is already having an impact on implantable systems such as heart pumps. Beyond just artificial hearts, many other medical systems can also benefit. As Dr. Pramod Bonde of the University of Pittsburg Medical Center speculated, “ can be leveraged to simplify sensor systems, to power medical implants and reduce electrical wiring in day-to-day care of the patients.”
But it’s not just GaN technology in wireless power that is transforming medicine. Imaging technology is also improving by leaps and bounds! The resolution of MRI machines is being enhanced through the development of smaller and more efficient sensing coils using GaN transistors and ICs. Diagnostic colonoscopies are about to become a thing of the past due to today’s GaN transistors. These types of non-invasive imaging breakthroughs significantly reduce the cost of health care through early warning and non-invasive diagnostics. As we integrate entire systems on a single GaN chip, miniaturization and image resolution improves the standard of care while medical costs come down.
How does this play out in the next few years?
In figure 3 is the revenue forecast for GaN transistors based on Efficient Power Conversion’s design-in inventory today. Note that 48% of the revenue comes from the sum of wireless power, envelope tracking, and LiDAR. These are three applications that were virtually non-existent four years ago when EPC first introduced enhancement mode power transistors. Additional new applications are popping up weekly. The predictions for growth in the power industry are all flawed because they cannot anticipate entirely new fields emerging. And the GaN journey has just begun!
Figure 5: EPC’s projected revenue by application in 2018. Almost half are projected to come from new applications such as LiDAR, Envelope Tracking, and Wireless Power.
We are at an inflection point – certainly in power conversion and quite possibly in the entire semiconductor industry. This is a most fascinating and exciting time for those involved in the change. For the rest, I borrow again from Andy Grove , “The person who is the star of previous era is often the last one to adapt to change, the last one to yield to logic of a strategic inflection point and tends to fall harder than most.”
References:
Andrew S. Grove, “Only the Paranoid Survive,” Doubleday, 1996.
A. Lidow, J.Strydom, Michael de Rooij, Yanping Ma, “GaN Transistors for Efficient Power Conversion. First Edition,” Power Conversion Press, 2012.
A. Lidow, “Fast Just Got Faster Volume 6 – The Expanding Markets for GaN Technology”, http://epc-co.com/epc/EventsandNews/FastJustGotFasterBlog/Issue6.aspx
A. Lidow, J. Strydom, and M. Rearwin, “Radiation tolerant enhancement mode gallium nitride (eGaN®) FETs for high frequency DC-DC conversion,” GOMAC Tech Conference, Charleston, South Carolina, April 2014.
