A new nonlinear HEMT model for AlGaN/GaN
switch applications
O. Jardel 1, G. Callet 2, C. Charbonniaud 3, J.C. Jacquet 1, N. Sarazin 1,
E. Morvan 1, R. Aubry 1, M.-A. Di Forte Poisson 1, J.-P. Teyssier 2, S. Piotrowicz 1 and R. Que´re´ 2
1Alcatel-Thales 3-5lab
Route de Nozay, 91640 Marcoussis, France
2XLIM - UMR CNRS 6172- Universite´ de Limoges
7, rue Jules Valle`s, 19100 Brive-la-Gaillarde, France
3AMCAD Engineering
ESTER Technopole, 87069 Limoges, France
Abstract—We present here a new set of equations for mod-
eling the I-V characteristics of FETs, particularly optimized
for AlGaN/GaN HEMTs. These equations describe the whole
characteristics from negative to positive breakdown loci, and
reproduce the current saturation at high level. Using this model
allow reducing the modeling procedure duration when a same
transistor topology is used for several applications in a T/R
module. It can even be used for switches design, witch is the
most demanding application in terms of I-V swing. Moreover,
a particular care was taken to model accurately the first third
orders of the current derivatives, which is important for multi-
tone applications. There are 18 parameters for the main current
source (and 6 for both diodes Igs and Igd). This can be compared
to the Tajima’s equations based Model [1] (13 parameters) or to
the Angelov Model (14 parameters) [2], which only fit the I-V
characteristics for positive values of Vds. We will detail here
the model formulation, and show some measurements/modeling
comparisons on both I-V and [S]-parameters obtained for a 8x75
µm GaN HEMT.
I. INTRODUCTION
AlGaN/GaN HEMTs are a promising technology, especially
for T/R Modules including several elements as power ampli-
fiers, LNAs or power switches, and the new trend to improve
the performances, the cost and the size of these modules is
to design all these functions in the same technology and on
the same chip. Thus, the same transistors topologies can be
used in different functions. Designing each of these functions
implies having models with different degrees of accuracies,
and it is very challenging to obtain a valid description of
the nonlinear elements for several applications with the same
model. However, and in order to reduce the modeling process
duration, it is very interesting to re-use, as far as possible, some
parts of a model to design a new one for another application.
The I-V model we will describe here was designed in this
context.
There are different needs concerning the I-V modeling:
- for the design of power amplifiers, the model has to be
capable to predict very accurately the I-V curves at positive
drain-source voltages, the partial derivatives gm and gd, the
knee voltage and the transconductance decrease at high current
(to fit the power saturation and the maximum of PAE).
- for the design of power switches, the model has to be
capable to predict the I-V curves at both positive and negative
drain-source voltages, and particularly the partial derivatives
for the “ON” command voltage, for which the transistor works
most of the time in the linear region. A special care has to
be made on the continuity of the current and its derivatives
in the proximity of Vds=0 V. Most of time, the designers
use splined I-V models for this kind of designs, but their
possible number of derivations is limited to the degree of the
interpolation polynomial, and their high sensitivity to mea-
surements imprecisions in the vicinity of Vds=0 V can induce
some important errors on the partial derivatives. Moreover, it
is important that the model reproduces the breakdown, setting
the power injection limits of the switches.
- for multi-tone application, predicting the third-order inter-
modulation requires to model accurately the third and higher
order derivatives of Ids with respect ot Vgs [3].
We will present here the equations of a new model. The
model is extracted in our case from pulsed I-V measurements,
in order to reduce the thermal effects [4]. The measured
devices can also reveal sensitive to trapping effects. Thermal
and/or trapping sub-circuits can be then added in the same
manner as in [5].
II. EQUATIONS OF THE MODEL
A. Equations of the main current source
The main current source is described by the following
equations:
Id = Idss · dhyp[V dsn + A · V dsn3] · V gsn (1)
with:
V gsn = V gslin ·
[
1 + V p0
vp
]N
(2)
#
olivier.jardel@3-5lab.fr
978-2-87487-012-5  2009 EuMA 28-29 September 2009, Rome, Italy
Proceedings of the 4th European Microwave Integrated Circuits Conference
73