1063-7397/04/3302- © 2004 MAIK “Nauka /Interperiodica”
Russian Microelectronics, Vol. 33, No. 2, 2004, pp. 64–67. Translated from Mikroelektronika, Vol. 33, No. 2, 2004, pp. 85–90.
Original Russian Text Copyright © 2004 by Agakhanyan.
It is still common practice to rely on experiment
when evaluating the radiation hardness of integrated
circuits (ICs). However, the strategy is costly and, more
importantly, it rarely helps one improve the IC in terms
of hardness. A wealth of experience gained in radiation
testing indicates that the radiation hardness of ICs of
the same design essentially relates to both the way in
which the ICs has been implemented and the purpose
and conﬁguration of the system that uses them [1–6].
The designer should know how the radiation responses
of circuit elements will depend on the IC structure and
functions, the system conﬁguration, and the operating
conditions [5–8]. Thus, it is not sensible to try to
improve radiation hardness by simply summarizing
unrelated ﬁndings obtained in particular cases, as the
traditional approach does [5, 6]. The same appears to be
true of the method whereby the hardness of a system is
estimated by radiation testing of each individual
microassembly employed. Experiments should be com-
plemented by mathematical modeling.
Radiation response has been modeled for almost all
known types of radiation and for building blocks rang-
ing from single transistors to ampliﬁer stages and logic
gates [5, 6, 8–11]. What is needed now is a coherent,
realistic picture of how an IC as a whole will work
BLOCK-MODEL APPROACH: GENERALITIES
One promising approach to hardness assurance is to
identify the blocks in the IC considered that determine
the radiation response of the IC as a whole [5, 6, 12].
This method should be especially helpful with IC sys-
It is wise to model radiation effects in every phase,
from circuit and system design to fabrication and ﬁn-
ished-product testing. Circuit design and fabrication
use electrical models as well as layout ones [5, 6]. An
electrical model can be constructed by solving a basic
system of equations [6, 13, 14]. Aside from well-known
drawbacks , this way may not allow one to identify
circuit elements that will seriously limit the radiation
hardness of the IC. The block-model approach to elec-
trical modeling makes it possible to signiﬁcantly
improve the circuit conﬁguration .
The block-model approach could be very useful in
radiation testing, from certiﬁcation tests to develop-
mental ones . In particular, it helps one to properly
deﬁne key parameters by which to measure radiation
hardness; otherwise, it is easy to grossly miscalculate
the limits of an IC under irradiation. For example, con-
sider the operational ampliﬁer (op amp). Its response to
pulsed irradiation is commonly characterized by the
magnitude of radiation-induced output offset voltage
referred to the input:
is the closed-loop gain of the op amp. The
criterion of failure and the recovery time are deﬁned in
terms of the offset voltage. However, this approach was
found to be inadequate in simulation tests of several
types of op amp from different manufacturers [15, 16].
The issue was resolved by block modeling .
Radiation hardness should be evaluated when
designing an IC or modifying its layout, taking into
account the dose rate and other operational factors .
The evaluation entails modeling with regard to relevant
The block-model approach should be very helpful in
identifying the mechanism of radiation response during
circuit design. It should also be employed in simulation
tests, which reduce the time and cost of full-scale tests
[6, 18, 19]. On the other hand, it is not possible to sim-
ulate any type of radiation impact in quantitative terms.
Simulation can be useful for predicting ionization
effects but not displacement damage [7–11, 20, 21].
Ionization affects circuit parameters by reducing
recombination rate and carrier mobility in the bulk of
the semiconductor, due to a considerable increase in
carrier density. It is responsible for charge buildup in
the insulator bulk and for trap generation at the inter-
faces. Displacement damage causes structural imper-
fections in the bulk and at interfaces. Full-scale testing
Mathematical Modeling of Ionizing-Radiation Effects in ICs:
T. M. Agakhanyan
Specialized Electronic Systems (SPELS), Kashirskoe sh. 31, Moscow, 115409 Russia
Received April 28, 2003
—The block modeling of ICs exposed to ionizing radiation is reviewed. This approach helps one to
predict the radiation response and to improve the radiation hardness of ICs and systems that use them.
RADIATION-EFFECT MODELING AND SIMULATION
IN SILICON MICROELECTRONICS