© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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current topics in solid state physics
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Phys. Status Solidi C 7, No. 10, 2450–2454 (2010) / DOI 10.1002/pssc.200983877
A scalable EE_HEMT based large
signal model for multi-finger
AlGaN/GaN HEMTs for linear and non-linear circuit design
Valiallah Zomorrodian
*
, Yi Pei, Umesh K. Mishra, and Robert A. York
Electrical and Computer Engineering Department, University of California Santa Barbara, CA 93106, USA
Received 3 September 2009, revised 12 May 2010, accepted 14 May 2010
Published online 12 July 2010
Keywords AlGaN/GaN, MOCVD, HEMTs, power amplifier design
*
Corresponding author: e-mail vzomorro@ece.ucsb.edu, Phone: 805 893 5935, Fax: 805 893 8714
A scalable non-linear large signal model based on the
ADS EE_HEMT model was developed for AlGaN/GaN
HEMTs for use in linear and non-linear circuit design.
Excellent agreement between simulations and measure-
ments was obtained for the DC, small signal and large
signal power and efficiency performance including load-
pull and source-pull contours. Excellent scalability of the
model was also demonstrated.
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1 Introduction
AlGaN/GaN high electron mobility transistor
(HEMT) technology is rapidly emerging as a high-power,
high-frequency device of choice for future wireless applica-
tions. AlGaN/GaN HEMTs have superior power-density
and much higher breakdown voltage compared with other
technologies such as GaAs HEMTs, InP HBTs or Si CMOS
technology. Excellent power performance has been reported
for devices [1-3] as well as for MMIC amplifiers [4].
The ability to successfully implement these devices into
working circuits depends greatly on the accuracy of the
device model available to circuit designer. The modeling
of microwave devices is complicated by the effects of their
intrinsic and extrinsic reactive elements at high frequencies.
For high power applications, such as power amplifiers, the
behavior of the device must be also modeled over a large
swing in the input and output voltage and current, which
requires factors including the non-linearity of the reactive
parasitics such as the input capacitance, and the saturation,
breakdown and soft pinch-off to also be incorporated into
the model. A great deal of work in the past has gone into
developing accurate large signal models for FETs and
HEMTs [5, 6, 11].
In this work, a scalable non-linear large signal model
based on the EE_HEMT model which is available in the
ADS software was constructed for multi-finger Al-
GaN/GaN HEMTs. The EE_HEMT model has been used
successfully in the past in modeling of GaN HEMTs [7]. In
this work, we will show that the model can successfully
predict the bias dependent small signal behavior of the
HEMTs, as well as the large signal load-pull and source-
pull contours. The scalability of the model will also be de-
monstrated.
Figure 1 shows the layout of the HEMTs used in this
work. The fabricated HEMTs had f
t
of about 17–18 GHz,
f
max
of more than 40 GHz, pinch-off voltage of about -2.5
V and gate-drain breakdown voltage of about 60 V. The
model was first extracted for the 0.5mm (4 x 125 μm) de-
vice and its scalability was verified by comparing the per-
formance of the scaled model to the measured data ob-
tained from the 1mm (8 x 125 μm) device.
4 x 125 μm 8 x 125 μm
Figure 1 Layout of HEMTs used for the modeling.
2 HEMT fabrication
The HEMTs were fabricated on a c-plane SiC substrate.
The AlGaN/GaN epitaxial layers were grown by metal or-
ganic chemical vapor deposition (MOCVD). The detailed
epitaxial structure consisted of a semi-insulating Fe-doped