ISSN 1063-7397, Russian Microelectronics, 2006, Vol. 35, No. 3, pp. 156–161. © Pleiades Publishing, Inc., 2006.
Original Russian Text © A.I. Chumakov, 2006, published in Mikroelektronika, 2006, Vol. 35, No. 3, pp. 184–190.
With pulsed ionizing radiation, identiﬁcation of
major causes and mechanisms of radiation-induced
failures is an important task in the hardness assurance
of integrated circuits (ICs) of whatever complexity. It is
commonly believed today that radiation response can
be predicted by circuit-level computer simulation fol-
lowing well-established techniques, provided that the
parameters are identiﬁed of the semiconductor struc-
tures involved, including parasitic ones [1, 2]. This
approach offers a way to ensure radiation hardness at
the circuit-element level.
However, circuit-level treatment has its limitations
when applied to transient radiation effects. In this case,
all the distinct semiconductor regions in a substrate will
take part in the response to a radiation pulse; further-
more, pulsed irradiation will change their properties to
the extent that charge transfer will follow a pattern
totally different from what may be predicted by equiv-
The global nature of transient radiation response is
most noticeable in power rails. Indeed, their radiation
performance determines the functional failure rate for
many large-scale-integration (LSI) circuits. With pho-
tocurrents reaching a few amperes, the voltage drops
along interconnections and across contact pads and
active substrate regions can lead to a decrease in supply
voltage across inner circuit elements, a phenomenon
known as rail-span collapse [3, 4]. The disturbance can
be strong enough to reduce the supply voltage to below
its lower tolerance limit. In addition, functional failures
can arise from radiation-induced voltage pulses of
opposite polarity acting on the power rails and ground
bus, respectively. Involving all the circuit elements,
rail-span collapse can lead to functional failures of the
circuit as a whole at radiation levels well below ones
causing functional failures of individual elements.
Note also that rail-span collapse impedes the recov-
ery of supply voltage and therefore can signiﬁcantly
lengthen the recovery time of the circuit.
OF RAIL-SPAN COLLAPSE
It has been found that the overall response of power
rails generally takes one of three possible forms as
illustrated by Fig. 1. The linear variation of supply cur-
rent with dose rate implies that only localized radiation
effects occur in the IC, involving both circuit elements
and parasitic structures. This behavior is observed in
charge coupled devices, dynamic random-access mem-
ories, etc. Their radiation-induced functional failures
are linked to malfunction of inner stages; an example is
information loss occurring in memory cells. A linear
current–dose-rate relationship is required of many ICs.
The superlinear growth of supply current with dose
rate is usually associated with a parasitic structure act-
ing as a pnpn device, bipolar transistor, etc. The ﬁrst
effect is known as latchup. Rail-span collapse is negli-
gible in this case as well.
Rail-span collapse is manifested in the saturation of
supply current when the peak photocurrent is limited by
the resistances of inner interconnections and contact
pads. Note also that increasing dose rate affects con-
ductivity, so that the equivalent resistance of the IC
decreases slightly with growing dose rate.
Rail-span collapse may occur in association with
parasitic-structure action, predominating at lower or
higher dose rates (Fig. 2). The former pattern of behav-
ior is related to parasitic pnpn devices, and the latter to
parasitic bipolar transistors. Latchup in this case should
be very sensitive to the supply voltage because this
determines the level to which the peak supply current
tends with increasing dose rate (neglecting the dose-
rate dependence of semiconductor conductivity).
Modeling Rail-Span Collapse in ICs Exposed to a Single
A. I. Chumakov
Specialized Electronic Systems (SPELS), Moscow, Russia
Received July 11, 2005
—The response of IC power rails to pulsed ionizing irradiation is investigated. Rail-span collapse is
shown to be the cause of functional failures in most ICs. A simple analytical model is proposed for calculating
the magnitude of the radiation effect.
AND SIMULATION IN SILICON MICROELECTRONICS