Emerging wide bandgap (WBG) semiconductors hold the potential to revolutionize the
electronics world, promising to advance the global industry in much the same way as the
invention of the silicon (Si) chip over 50 years ago enabled the modern computer era.
The electronic bandgap is what allows semiconductor devices to switch currents on and
off to achieve a desired electrical function, and WBG materials, the category of
electronic materials in which the bandgap energy exceeds approximately 2 electronvolts
(eV), exhibit characteristics and processes that make them superior to Si for many
applications. The most mature and developed WBG materials to date are silicon carbide
(SiC) and gallium nitride (GaN), which possess bandgaps of 3.3 eV and 3.4 eV
respectively, whereas Si has a bandgap of 1.1eV. SiC and GaN devices are starting to
become more commercially available. Smaller, faster, and more efficient than counterpart
Si-based components, these WBG devices also offer greater expected reliability in
tougher operating conditions.
Advantages of WBG semiconductors over Si in power electronics include lower losses for
higher efficiency, higher switching frequencies for more compact designs, higher
operating temperature (far beyond 150° C, the approximate maximum of Si), robustness in
harsh environments, and high breakdown voltages. Diverse applications range from
industrial functions, such as motor drives and power supplies, to automotive and
transportation systems including hybrid and electric vehicles, aircraft, ships, and
traction, to wireless communications, military systems, space programs, and clean energy
generation from solar inverters and wind turbines.
A characteristic of WBG materials is the ability to emit light in the visible
spectrum. This has allowed innovation in the solid-state lighting industry, where
developments in WBG-based light emitting diodes (LEDs) have resulted in devices with
greater lighting efficiency and much longer lifetimes than incandescent bulbs. In
fact, LEDs provide light output on the order 160 lumens per watt, with a service
life between 35,000 to 50,000 hours, while incandescent lights provide less than 20
lumens per watt and last between 1,000 to 2,000 hours. WBG technology is also used
in laser diodes, with next generation DVD players, including Blu-ray and HD DVD
formats, employing GaN-based blue lasers.
SiC is by far the most mature WBG technology, attributable in part to its excellent
thermal conductivity. Due to SiC’s ability to effectively transfer generated heat
away from itself, SiC is especially well suited for the highest power applications
such as photovoltaic systems and wind turbines, as well as high temperature
operating environments like down-hole drilling where temperatures can exceed 200° C.
GaN is popular as a more cost-effective alternative to SiC, but given that today’s
GaN is bonded over a Si or SiC substrate as opposed to grown on a bulk-GaN substrate
for cost reasons, GaN is not as thermally conductive as SiC or even standard Si. The
WBG benefits of GaN, such as high voltage operation, high switching frequencies, and
outstanding reliability - coupled with expectations that GaN will reach price parity
with Si equivalents by 2015, keep it as a front-running choice for power electronics
up to 900 V, as well as a superb choice for next generation consumer electronics,
where size, efficiency, and price greatly matter.
The power electronics industry is ushering in a new era marked by the emerging
availability of wide bandgap (WBG) semiconductors. With power device innovations in
conventional silicon (Si) nearly reaching their theoretical limits and the new WBG
materials offering important advantages over Si, the power electronics industry is
heralding opportunities previously not thought possible, as well as anticipating
significant improvement in existing applications.
The advantages of SiC over Si for power devices include lower losses for higher
efficiency, higher switching frequencies for more compact designs, robustness in harsh
environments, and high breakdown voltages. SiC also exhibits significantly higher
thermal conductivity than Si, with temperature having little influence on its switching
and thermal characteristics. This allows operation of SiC devices in temperatures far
beyond 150° C, the maximum operating temperature of Si, as well as a reduction in
thermal management requirements for lower cost and smaller form factors.
SiC is the most maturely developed of the WBG technologies, culminating in the recent
commercial availability of SiC power electronics. SiC-based power discretes,
including diodes, rectifiers, super junction transistors (SiC BJTs), JFETs, MOSFETs
and thyristors are now in production by a number of manufacturers, including Cree,
GeneSic, Infineon, ROHM, STMicroelectronics, Semelab/TT Electronics, and Central
The SiC Schottky diode is currently the most prevalent type of SiC power device, with
variants available today for operation up to 1700 V, in temperatures up to 250° C.
Schottky diodes are known for their lower forward voltage drops than standard
diodes, making them beneficial in high efficiency applications such as photovoltaic
(PV) systems. SiC Schottky diodes offer a much lower reverse leakage current, and
higher reverse voltage than Si Schottky diodes, improving the efficiency and
reliability of new PV systems. In standalone (off-grid) systems, the diodes prevent
batteries from discharging through the solar panels at night. In grid-connected
systems, the diodes prevent reverse current from flowing between adjacent strings.
Not surprisingly, the first confirmed end products using SiC power electronics are
Schottky diodes are also known for very fast switching, making them useful in
applications such as switch mode power supplies (SMPS). High speed switching allows
the use of small inductors and capacitors for smaller form factors, without trading
off efficiency. Hence, SiC Schottky diodes, offering the industry’s highest
switching speeds, will enable the next generation of smaller, lighter switch mode
Power modules incorporating SiC diodes are available to simplify design efforts. SiC
diodes are often coupled with IGBTs, so modules combining the two exist, such as the
GB100XCP IGBT/SiC diode co-pack from GeneSic. There are also modules which combine
SiC diodes and SiC MOSFETs, such as Cree’s CAS100H12AM1 1.2 kV, 100 A SiC
A more recent entrant (in the last couple of years) in the SiC world of power devices
is the "super" junction transistor (SJT), or super-high current gain SiC-based BJT.
These power switches target 1.2kV (now) to 10 kV (future), high temperature (>300°
C), and high-efficiency medium to high-frequency power conversion applications, such
as SMPS, Uninterruptible Power Supply (UPS), aerospace, defense, down-hole oil
drilling, geothermal, Hybrid Electric Vehicle (HEV) and inverter applications. The
SiC SJTs offer significant benefits over Si IGBTs, SiC MOSFETs and JFETs including
reduction in power losses for improved system efficiency, and reduction in thermal
management requirements to lower cost and size. SiC SJTs are also a direct
replacement for Si IGBTs, so they can be driven using the standard IGBT/MOSFET gate
drivers, whereas SiC MOSFETs and JFETs require specialized gate drivers.
As a nascent technology, SiC presents a higher purchasing cost than Si, spawning
investigation into less expensive WBG materials and leading to developments in
gallium nitride (GaN). Power devices using GaN material bonded over a Si or SiC
substrate (generally still referred to as simply GaN) are more cost effective than
SiC, and anticipated to become more widely available in the near future. While
otherwise preserving the same performance benefits over Si as SiC, the mismatch in
substrate (bulk-GaN as a substrate is currently prohibitively expensive) actually
reduces GaN’s high theoretical thermal conductivity to slightly lower than Si.
Therefore GaN-based devices are targeted at less temperature stringent applications.
The price of GaN –based devices is expected to be comparable to Si equivalent
counterparts by 2015, making GaN an excellent choice for next generation power
applications and end products.
Target applications for WBG power devices are diverse - ranging from industrial
functions, such as motor drives and power supplies, to automotive and transportation
systems including hybrid and electric vehicles, aircraft, ships, and traction, to
wireless communications, military systems, space programs, and clean energy
generation from solar inverters and wind turbines.
SiC is expected to grow the most in renewable energy applications such as solar power
systems and grid storage. Both SiC and GaN are anticipated to be adopted equally
well in automotive and transportation systems. GaN is forecasted to eclipse SiC in
IT and electronics, as well as more general applications.
Regardless of how the actual applications play out in the future, WBG power devices
will make an impact in power electronics. Overall sales of power discretes (MOSFETs,
IGBTs, BJTs, rectifiers, etc.), power modules, and power ICs are projected to launch
power electronics from the $18 to $20 billion market that it is today to
approximately $65 billion in 2020 – with the share of SiC devices in 2022 expected
to near $1.8 billion, up from around $200M today, while the GaN market is projected
to grow from almost nothing today to over $1 billion in 2022.
Silicon-based RF power transistors are reaching limits of power density, breakdown
voltage, and operating frequency, thus opening up the opportunity for adoption of wide
bandgap (WBG) semiconductors such as gallium nitride (GaN) in RF signal processing
applications. GaN offers key advantages over silicon. The high power density of GaN
leads to smaller devices as well as smaller designs due to reduced input and output
capacitance requirements, an increase in operational bandwidth, and easier impedance
matching. GaN’s high breakdown field allows higher voltage operation and also eases
impedance matching. The broadband capability of GaN devices provides coverage for a
broad frequency range to support both the application’s center frequency as well as the
signal modulation bandwidth. Additional advantages of GaN include lower losses for
higher efficiency, and high-temperature operation (in the case of GaN on bulk-GaN
Available WBG-based RF devices include GaN high-electron-mobility transistors (HEMTs)
and GaN monolithic microwave integrated circuits (MMICs). The HEMT is a field effect
transistor incorporating a junction between two materials with different bandgaps,
enabling it to operate at higher frequencies than ordinary transistors. Applications
where high gain and low noise at high frequencies are desired are suitable for
HEMTs. GaN HEMTs are attractive in RF applications over devices of other materials
due to their high-power performance. The MMIC is an integrated circuit that operates
at microwave frequencies (300 MHz to 300 GHz). These devices typically perform
functions such as high-frequency switching, microwave mixing, power amplification,
and low-noise amplification. GaN enables advanced performance MMICs for high
performance RF applications. Applications for GaN RF devices include broadband
amplifiers, radar, telecom base stations, military communications, and satellite
Though light emitting diodes (LEDs) have been available since the 1960’s, high-brightness
blue LED products only arrived relatively recently - in the early 1990’s, arising from
critical developments with gallium nitride (GaN), a wide bandgap (WBG) semiconductor
material. The color of an LED is determined by the energy bandgap of the semiconductor,
and current blue LEDs are based on GaN and InGaN (indium gallium nitride). When blue
LEDs are mixed with red and green LEDs or coated in yellow phosphor, the more popular
method, the result is high-intensity white light. The availability of LED-based
illumination revolutionized the solid-state (semiconductor based) lighting industry by
providing a much higher efficiency and longer lifetime alternative to filament-based
incandescent lighting, and a mercury-free alternative to compact fluorescent light
bulbs. Energy-saving WBG-based LEDs produce more than 10 times more light per watt, and
last 30 times longer than comparable incandescent bulbs. LED makers today offer products
with lighting efficiency greater than 150 lumens per watt, with lifetimes of around
40,000 hours. Compare this to the 20 lumens per watt lighting output, and 1000-2000
hours rating of incandescent bulbs and it is easy to envision how LED lighting will gain
widespread adoption despite a higher initial purchase cost. Indeed, LED lighting sales
is projected to grow massively over the next few years, overtaking sales of incandescent
bulbs by year 2018.
In addition to efficiency and lifetime improvements in general lighting, LEDs offer
advantages that enable a myriad of applications. LEDs possess directionality,
permitting products to be optimized for directional indoor lighting applications
such as track lighting and spot lights. The robustness and durability of LEDs allows
innovation in areas where incandescent lighting is too fragile. The compact size
makes ever-smaller implementations possible. The high switching speed of LEDs enable
improvements in applications such as television displays, where fast turn-on/off
produces exceptional visual quality. Backlighting for mobile phones, automobile
lighting, aviation lighting, advertising displays, traffic signals, and even
flashlights are just some of the popular uses for LEDs.
Progress in GaN technology has also led to developments in blue, violet, and
ultra-violet (UV) laser diodes. Blue and violet lasers are being used in Blu-ray
players to read the high capacity optical storage discs, for xenon lamp replacement
in projection systems, and in laser printing and medical imaging technologies. UV
lasers are finding applications in watermark inspection for anti-counterfeiting,
medical instrument disinfection and sterilization, and water or air purification.
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