Design and Characterization of High Breakdown Voltage Field Plated GaN HEMT Device for High Power Applications
Authors: Pattnaik Geeta , Mohapatra Meryleen 
Published: December 2024

Background:
GaN HEMTs with field plates have emerged as a boon for the high power
along with high voltage application domains. The work in this paper is based on developing a
numerical model to study and analyze the device performance of the GaN HEMT device by including
the field plate structure. The study is based on considering both the conventional and the
proposed GaN HEMT device incorporated with a field plate structure and comparing their performances
under various biasing conditions.

Methods:
The study involves initially designing a conventional GaN HEMT device without a
field plate. Next, a GaN HEMT device of the same dimensions but including a field plate is designed.
The field plate length is varied between 0.5 μm and 4 μm to determine the optimal length.
The design and simulations of both devices were performed using the SILVACO ATLAS TCAD
tool. The impact of a field-plate on the device performance is also studied in the work. On the basis
of the DC and RF characteristics, the device performance of both the proposed conventional
and GaN HEMT with a field plate structure was compared. The different S-parameters were also
plotted for the devices, which can be implemented in our future work for impedance matching,
calculating different power-related parameters and stability parameters.

Results:
The increment in the breakdown voltage from 95V (conventional GaN HEMT) to 630V
showcases the beneficial characteristics of the proposed GaN device with a field plate. The Id –
Vgs curve and transconductance curve of both devices were plotted and compared. The drain current
and maximum transconductance exhibited by the conventional HEMT is 838mA/mm at a Vgs
of 2V and 120mS/mm, respectively, while the drain current and maximum transconductance exhibited
by the proposed GaN HEMT, including field-plate, are 814mA/mm at a Vgs of 2V and
118mS/mm respectively. Thus, it can be reported that including the field-plate does not affect the
DC performance of the device. The parasitic capacitances and the frequency parameters were plotted
for both devices. It is observed that the field-plated device exhibits higher parasitic capacitances
in comparison to the conventional GaN HEMT structure. This is further reflected in the frequency
performances as the cut-off frequency and maximum frequency reported for the proposed
field-plated device are 8GHz and 30GHz, respectively while the conventional GaN device reports
a cut-off frequency and maximum frequency of 15GHz and 44GHz, respectively. The delay analysis
reports an intrinsic time delay of 23ps for the field-plated and 19ps for the non-field-plated
GaN HEMT device. Thus, it can be stated that the field plate affected the RF performance of the
device. The S-parameters were also plotted for both the devices.

Conclusion:
The work concludes that including a field-plate structure leads to breakdown voltage
enhancement, which in turn will help achieve high power performance and withstand high voltages.
However, this benefit comes at the cost of compromising the RF performance of the device.
This issue can be minimized to a large extent by proper optimization of the device structure.
Hence based on the requirement and the application area of the device, it should be designed and
optimized accordingly.