Page 33 - PEN eBook NOVEMBER 2022

SEMICONDUCTORS : SEMICONDUCTORS

For a specific rated voltage, the thickness of the drift mentioned, GaN is the only viable wide-bandgap
layer is inversely proportional to the critical electric alternative to silicon in low-power applications, as SiC
field. This implies that GaN and SiC devices of a operation is impractical at voltages below 650 V.
particular voltage capability have drift layers that are
10× thinner than those of silicon devices. These factors GALLIUM NITRIDE AND SILICON
drive design changes and have major implications in CARBIDE
semiconductor design. GaN enables a power-factor–correction (PFC)
technology known as “totem-pole bridgeless PFC
Due to their thinner drift layers, SiC devices are topology.” On the other hand, a traditional silicon boost
smaller in size, which decreases their capacitance. solution would have a diode bridge where two of the
These devices can therefore efficiently switch at diodes are constantly on. This would contribute to
frequencies much higher than what is possible with significant losses but is mitigated by GaN due to its
silicon. As a result of the higher switching frequency, essentially zero reverse recovery. 100-V GaN devices are
the size of passive components and magnetic devices also being deployed at data centers, as server racks are
like inductors also decreases. This leads to a significant increasingly moving toward 48 V. Furthermore,
reduction in the overall size of the system, which 650-V GaN devices can also be deployed and run
increases its power density. Furthermore, the large for PFC circuitry. SiC is suitable for higher-power
SiC bandgap and high thermal conductivity allow for applications than what is possible using GaN and is
high temperature operation with simplified cooling available in voltages ranging from 650 V to 3.3 kV,
management, further decreasing system weight and with higher-voltage devices being developed.
volume.
Stephen Russell, subject matter expert for power
None of this is to say that either SiC or GaN is devices at Tech Insights, said during a company
superior or that silicon is obsolete. The choice of webinar, “Gallium nitride has truly found its killer app
semiconductor material to be used will depend on in replacing silicon and USB-C chargers for mobile
the specifications of the application in which they are devices. 2021 [was] a watershed year in market
deployed. Silicon is still a strong contender in devices acceptance, and we only expect this momentum to
rated from 15 V to 650 V while also being much cheaper continue. Gallium nitride’s real advantage, however,
and more reliable, whereas GaN has been gaining is its switching; it is the only viable wide-bandgap
replacement for silicon at voltages less than 600 V.”
popularity in low-power applications like mobile
What Does the Future chargers and similar charging systems. As previously

Hold for WBG Devices?

By Maurizio Di Paolo Emilio, editor-in-chief of Power Electronics News

Silicon carbide and gallium nitride have witnessed increasing amount of EVs that are being introduced
increasing success in the semiconductor device market into the market.
in recent years. GaN is now used in mobile device
chargers and charging systems. Companies like Apple, Their popularity begs the question: What is so special
Samsung, and Xiaomi have chosen GaN-based chargers about these new semiconductor materials, and why are
that provide high power densities while maintaining, they being looked at as alternatives to silicon?
or even decreasing, the weight of these components.
These chargers utilize power GaN high-electron– As explained by Victor Veliadis in his July 28, 2022,
mobility transistor (HEMT) chips offered by companies PSMA webinar, “SiC Power Technology Status and
like GaN Systems and Navitas Semiconductor. Barriers to Overcome,” “SiC and GaN materials have
a critical electric field that is about 10× higher than
On the other hand, SiC devices have primarily been that of silicon, with a bandgap that is 3× higher. In a
used in the field of electric mobility. In 2017, electric- semiconductor system, the drift layer is what holds its
vehicle manufacturers like Tesla chose to use SiC- rated voltage, which makes the thickness and doping
based motor controllers, which boosted the efficiency levels of this layer determine the voltage capability of
of their systems. This has kickstarted a race toward the device.”
developing high volumes of SiC devices to meet the SiC fab infrastructures (Source: Victor Veliadis)

48 NOVEMBER 2022 | www.powerelectronicsnews.com NOVEMBER 2022 | www.powerelectronicsnews.com 49