ISSN 1063-7397, Russian Microelectronics, 2009, Vol. 38, No. 1, pp. 17–29. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © V.S. Pershenkov, D.V. Savchenkov, A.S. Bakerenkov, A.S. Egorov , 2009, published in Mikroelektronika, 2009, Vol. 38, No.1, pp. 21–33.
The parameters of microelectronic transistor struc-
tures used in integrated circuits of the spaceborne
equipment on aerospace stations experience degrada-
tion under the action of ionizing cosmic radiation. The
entire range of problems emerging in this connection is
described in . However, some problems remain
urgent even now, which follows from the papers of
leading national and international conferences held in
this ﬁeld in recent years. In particular, the so-called
low-intensity effect in bipolar integrated circuits
remains unclear . The essence of this effect is that a
decrease in the intensity of ionizing radiation enhances
the degradation of the ampliﬁcation factor of bipolar
transistors after accumulation of the same absorbed
dose. This enhancement may be stronger than an order
of magnitude. A generally accepted physical model of
the effect has not been developed and, which is most
important, no methods for simulating the effect in lab-
oratory conditions, in which sources with a relatively
high intensity must be used, have been worked out (e.g.,
a radiation source with an intensity of 3–4 orders of
magnitude higher than the cosmic radiation intensity is
required for simulating the ten-year operation of a
microcircuit in the orbit if the duration of the laboratory
experiment is several hours).
Under the action of cosmic radiation, the degrada-
tion of the ampliﬁcation factor of bipolar transistors is
due to an enhancement of surface recombination or an
increase in the surface component of the base current.
Recombination losses increase because of accumula-
tion of positive charge in the bulk of the passivating
oxide and due to embedding of surface states at the
oxide–semiconductor interface. A relation of the sur-
face recombination current with the charge in the oxide
and the density of surface states was derived in .
However, the authors of this publication disregarded
the effect of the charge of surface states on the surface
potential and, hence, on the recombination loss current.
This factor is of fundamental importance since its dis-
regard makes impossible the description of radiation-
induced degradation of NPN and PNP transistors from
a uniﬁed point of view.
This study aims at calculating the surface recombi-
nation current of bipolar transistors as a function of the
charge of surface states, which is determined by the
position of Fermi quasi-levels under direct bias of the
emitted junction. The relations derived here can form
the basis for a physical model of the effect of low inten-
sity in bipolar transistors.
Figures 1 and 2 show the cross section of a bipolar
transistor with a lateral dielectric insulation (SiO
the boundary region of the base under the passivating
oxide. The geometry of the boundary region (see Fig. 2)
forms the basis of further analysis since it is typical of
the most advanced technologies (e.g., ISOPLANAR-S,
ISAC, and SST) used for preparing bipolar large-scale
integration (LSI) devices. The
coordinate is directed
to the bulk of the base from the SiO
oxide–base) interface. Zero value of the
corresponds to the boundary (
) of the space charge
region of the emitter–base junction. The distance to the
wall of the insulating oxide along the
The surface recombination current is calculated
under the following assumptions.
Calculation of Surface Recombination Current in Bipolar
Microelectronic Structures Subjected to Ionizing Radiation
V. S. Pershenkov, D. V. Savchenkov, A. S. Bakerenkov, and A. S. Egorov
Moscow Institute of Engineering Physics (State University), Kashirskoe sh. 31, Moscow, 115409 Russia
Received July 17, 2008
—The surface recombination current of bipolar transistors is calculated as a function of the charge of
surface states, which is determined by the position of Fermi quasi-levels under a direct bias voltage across the
emitter junction. It is shown that the calculation of radiation-induced surface recombination current can be
reduces to the solution of the Shockley equation at the interface between a passivating oxide and the base taking
into account the effect of surface states in the passivating oxide on the charge carrier concentration. A rigorous
expression is derived for the surface recombination current per unit length.
RADIATION-EFFECT MODELING AND ANALYSIS
IN MICROELECTRONICS TECHNOLOGIES