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Efficient Modeling of PIN Diode Switches Employing Time-Domain
Yasser A. Hussein, James E. Spencer, Samir M. El-Ghazaly*, and Stephen M. Goodnick**
Stanford Linear Accelerator Center, Stanford University, Menlo Park, CA 94304, USA
*Department of Electrical and Computer Engineering, University of Knoxville, TN, 37996, USA
**Department of Electrical Engineering, Arizona State University, Tempe, AZ 85281, USA
Abstract-This paper presents an efficient full-wave time-domain
simulator for accurate modeling of PIN diode switches. An
equivalent circuit of the PIN diode is extracted under different
bias conditions using a drift-diffusion physical model. Net
recombination is modeled using a Shockley-Read-Hall process,
while generation is assumed to be dominated by impact
ionization. The device physics is coupled to Maxwell's equations
using extended-FDTD formulism. A complete set of results is
presented for the on and off states of the PIN switch. The results
are validated through comparison with independent
measurements, where good agreement is observed. Using this
modeling approach, it is demonstrated that one can efficiently
optimize PIN switches for better performance.
Index Terms- Device transport physics, global modeling,
Maxwell's equations, PIN diode switches.
Millimeter-wave PIN diode switches are extensively used in
microwave systems, for example, in high resolution radars
(HRR) employed for automotive collision at 77 GHz that
require very high isolation and fast switching speeds .
Another application is in the generation of high-power through
an array of PIN diode microwave switches . Accordingly, it
is indispensable to present analysis of PIN switches based on a
coupled full-wave simulator. The possibility of achieving this
type of modeling is addressed by global circuit modeling as
has been demonstrated in -. Here, we present a fast
electromagnetic (EM) simulator for efficient modeling and
optimization of low-loss and high-isolation mm-wave PIN
diode switches. To our knowledge, this the first time such a
modeling approach has been used for this problem.
II. PROBLEM STATEMENT
The PIN diode model presented in the present work is a
three-dimensional (3-D) full-wave model. The basic model
couples Maxwell's equations for the electric and magnetic
fields with the switch equivalent circuit extracted using a drift-
diffusion model given by:
atq "=G -R (2)
J = -qpypVU -qD Vp.
Where n and p are the electron and hole densities, J~ and Jp
are the electron and hole current densities, q is the electron
charge, G is the extrinsic generation rate, R is the
recombination rate, U is the electrostatic potential, D, and Dp
are the electron and hole diffusion coefficients. The net
recombination rate is modeled using the Shockley-Read-Hall
process, while extrinsic generation is assumed to be
dominated by impact ionization .
Since it is only required to have two different modes of
operation in a PIN diode switch, i.e. the on and off-state, it is
not necessary to model the actual semiconductor physics
during electromagnetic simulation. Thus, the drift-diffusion
physical model can be used to estimate the on-state resistance
RON and the off-state capacitance COFF of the diode switch,
which is the accurate alternative for the analytic formula given
1 W7/,2 I
RON F n + , (5)
ON IFT 4 nu
where Wi is the thickness of the intrinsic region, p, is the
electron mobility, p is the hole mobility, IF is the forward bias
DC current, and T is the effective carrier life-time in the
intrinsic region. In our GaAs PIN diode case, p and pp are
450 and 8000 cm2/Vs. On the other hand, under reverse bias,
another approximation that is used instead of running a drift-
diffusion simulator is to assume a constant depletion
Here e is the dielectric constant of the depletion layer
material. In Fig. (1), Wi and the depletion area are 0.25 pm and
400 (pm)2, respectively. This gives an approximate junction
capacitance of 0.01 pF. The proposed full-wave coupling
approach is carried out using extended FDTD formulism .
For example, for a PIN diode oriented in z-direction, the
electric-field at cell (i,j,k) for the on and off states are given by
Eqs. (7) and (8)
E n+1 _ 2RONEAxAy E n
Ez i,j,k 2 XAY Ez ij,k
1 A Vxz i,J,k (7)
Presented at nternational Microwave Symposium, June 11-17, 2005, Long Beach, CA, USA
Work supported in part by Department of Energy contract DE-AC02-76SF00515
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Hussein, Y.A.; Spencer, J.E.; /SLAC; El-Ghazaly, S.M.; U., /Tennessee; Goodnick, S.M. et al. Efficient Modeling of PIN Diode Switches Employing Time-Domain Electromagnetic-Physics-Based Simulators, article, September 20, 2005; [Menlo Park, California]. (https://digital.library.unt.edu/ark:/67531/metadc879203/m1/1/: accessed April 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.