Page 15 - PEN eBook March 2023

SEMICONDUCTORS Semiconductors

smaller device capacitances of GaN HEMTs, compared with silicon and silicon carbide devices
with similar voltage ratings, enable improvements in system efficiency and power density. Hence,
GaN HEMT–based power converters, chargers and adapters have gained widespread adoption in

consumer electronics applications.

GaN HEMTs face several obstacles in their use for automotive, industrial motor drive and
power-grid applications. Voltage scaling for use in 800-V applications and beyond is challenging
from a device area scaling perspective for the lateral device, when compared with the vertical SiC
devices. Another key factor to consider in these applications is the short-circuit (SC) robustness of
the device. SC faults in the load can create conditions in which the device is under high source-
drain voltage (V ) and current (I ). As a result, the device is subject to high temperature, electric
DS DS
fields and mechanical stress. These can be catastrophic and result in system failure.

The short-circuit withstand time (SCWT, or t ) is a metric used to gauge the device’s ability to
sc
withstand this condition. T needs to be long enough for the gate driver to take necessary action
sc
and turn the device off. In Si IGBTs, the t time is typically rated at about 10 µs, while current SiC
sc
MOSFETs are typically in the 3-µs range, with active research activities on expanding this further.
Several studies on GaN power HEMTs have reported much shorter times, especially at voltages
close to the device maximum V ratings, with many reports showing t < 500 ns for V > 400 V.
DS sc DS

An SCWT safe operating region was presented in Reference 1, where the authors also showed that
although the HEMT survived a single SC event (with a t > 300 µs) at a V of 400 V, repeated SC events
sc DS
resulted in a t of only 20 ns. In another study, the SC failure in GaN HEMTs was identified to result
2
sc
from the propagation of high electric fields from the gate to the drain. In this article, we will present
SC performance on
Short-Circuit the vertical Fin-JFET
GaN device from the

Robustness in Vertical work done by a group
at the Center for Power
Electronics Systems at
GaN Fin-JFET Power the Virginia Polytechnic

and
State
Institute
Devices University and NexGen
Power Systems. This
3,4
device is in the process of

By Sonu Daryanani, contributing writer for Power Electronics News being commercialized by
NexGen Power Systems.
Gallium nitride’s superior material properties have driven its usage in power device applications.
The lateral high-electron–mobility transistor (HEMT) device has been commercialized over a wide A simplified cross-section
range of voltage classes, mostly 650 V and below. The high-switching–frequency capability and of the GaN Fin-JFET is
Figure 1: Simplified cross-section schematic of the GaN Fin-JFET 3

34 MARCH 2023 | www.powerelectronicsnews.com MARCH 2023 | www.powerelectronicsnews.com 35