IEEE Power Electronics Magazine - June 2022 - 31

technologies included manufacturability,
reliability, system complexity, and
cost (Table 1). But over just the last few
years with numerous advancements, it's
clear that those challenges have been
addressed as 10's of millions of units of
GaNFast power ICs have been shipped
in mass production in applications
from fast mobile chargers to gaming
systems to notebook computer adapters,
and more.
For offline ac/dc, dc/ac, and isolated
GaN power FETs are
replacing silicon power
MOSFETs in applications
from 48 V to 800 V. SiC is
replacing legacy IGBTs in
applications >800 V.
dc/dc power applications where user
safety is paramount, N-channel silicon power MOSFETs
(normally-off power switches that require a positive gate
voltage, relative to source to conduct) have been the most
popular power switch (compared to their P-channel counterpart
that requires a negative gate voltage relative to its
source to conduct). The N-channel devices are easier to
use, easier to interface to controllers, safer and more reliable,
and lower cost to manufacture and design with and
have become ubiquitous in the industry while the P-channel
power switches are more of a niche component for unique
application use cases.
Similarly, GaN power switch technology is now in
production from many vendors, and we see two types
of approaches battling it out for market adoption.
The earliest GaN power devices were depletion-mode
(d-mode, normally " on " devices). 'Normally-on' d-Mode
devices require a negative VGS to turn off - not a practical
solution for off-line or high-voltage applications. This
characteristic was mitigated by
the addition of a second, low
voltage 'cascode' Si FET used
to turn the GaN power device
on and off. This essentially converts
the d-Mode device into an
enhancement-Mode (e-Mode)
device, required to block high
bus voltages when a power converter
is first turned on. The
cascode FET allows for a standard
gate drive signal to be used
(0 V = OFF). However, the Si
FET frequency characteristics are inferior to GaN
and compromise the switching performance of the combined
device. Another cascode variant uses the low voltage
Si FET simply as an on/off switch for the circuit, and
then drives the GaN transistor directly with a negative
voltage drive from an inverting buck-boost controller or
similar, leading to a complex double gate-drive solution
with two supply rails. Cascoding requires at least a twochip
package that presents a variety of other concerns
including complex (multiple and/or stacked die) packaging,
high parasitic inductance, ceramic interposers for
isolation, tendency for oscillation and internal overvoltage
stress due to ac and dc mismatch of the GaN device
and the Si device, as well as additional internal passives
to mitigate these effects. This results in a reduced overall
yield and ultimately a higher cost.
Later, e-Mode (normally " off " devices) GaN discrete
devices came about with more reliable normally off
Table 1. Traditional Challenges of Adoption of GaN in High-Volume Products.
Legacy challenge to practical implementation
of GaN power supplies
Manufacturability and Yields
Status as of February 2022
* GaN power device companies already achieving stable >90%+ yields, leveraging
proven, low-cost GaN-on-Silicon in mature, underutilized 6 " and 8 " wafer Fabs.
* Many GaN power suppliers available today
* Multiple generations of GaN products have been launched and ramped in production
Reliability
* Some GaN companies have already shipped >40 million units individually with zero
failures and >116 billion device hours in the field.
* Devices available with protected gates capable of 2 kV ESD
* 650 V ratings moving even to 700 V continuous VDS ratings with 800 V surge capability
showing strong data and confidence in their guaranteed robustness
System Complexity
(gate drive circuitry, number of components, parasitic
elements, high frequency design, EMI, etc.)
* Easy-to-use GaN building blocks available with integrated gate drive, bias, UVLO, dV/dt,
etc. in low inductance QFN package launches high frequency designs to production
* Continued advancements in integration and features reduces external components
and improves performance still further
* Planar magnetics for AC/DC and HV DC/DC become more widely available and designed
with
Cost
(Device and System-level)
* GaN-based systems approaching cost parity with silicon
* Shipment volumes drive down cost
* Many GaN suppliers available today create competitive cost environment
* Multiple generations of GaN products released to production accelerate cost reductions
June 2022 z IEEE POWER ELECTRONICS MAGAZINE 31
IEEE Power Electronics Magazine - June 2022

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