1063-7397/04/3306- © 2004 MAIK “Nauka /Interperiodica”
Russian Microelectronics, Vol. 33, No. 6, 2004, pp. 377–380. Translated from Mikroelektronika, Vol. 33, No. 6, 2004, pp. 464–467.
Original Russian Text Copyright © 2004 by Tikhonov.
The dual-collector bipolar magnetotransistor  is a
promising building block of magnetic-ﬁeld sensor
arrays because it can be fabricated concurrently with its
peripheral circuitry, can offer an absolute sensitivity
reaching 7.0 V/T , and can discriminate between dif-
ferent directions of applied magnetic ﬁeld.
Constituent magnetotransistors are formed in indi-
vidual diffused wells so as to prevent cross coupling.
With this design, nonzero differential collector voltages
correspond to negative relative magnetic-ﬁeld sensitiv-
ity of collector current , a phenomenon whose mech-
anism is not identiﬁed in the literature [3–7]. Moreover,
previous workers did not address recombination in the
bulk of the semiconductor, despite the fact that the size
of magnetotransistors is usually comparable with the
Let us try to elucidate the role of bulk recombination
in negative relative sensitivity. We start by investigating
the effect of an applied magnetic ﬁeld on the carrier
density distribution. Figure 1 illustrates this for both
types of semiconductor exposed to a magnetic ﬂux den-
sity normal to the plane of the ﬁgure. The Lorentz force
deﬂects electrons and holes toward the same side if the
two types of carrier move in opposite directions; other-
wise, they are deﬂected toward different sides.
If minority carriers are injected into the bulk (e.g.,
from the emitter), two alternatives exist. If an electric
ﬁeld is present in the region containing both types of
carrier, these drift in opposite directions. If the injected
carriers are transported mainly by diffusion, the major-
ity and minority carriers ﬂow in the same direction so
as to maintain charge neutrality .
The drift and diffusion components of current are
affected differently by an applied magnetic ﬁeld. In the
drift component, electrons and holes are deﬂected
toward the same side. In the diffusion component, they
are deﬂected toward opposite sides.
The electrons and holes are subject to recombina-
tion. The Shockley–Read–Hall model states that
are the respective nonequilib-
rium densities of electrons and holes and
intrinsic carrier density .
With drift transport, magnetic-ﬁeld-induced
increase or decrease in electron density occurs in the
same region as that in hole density. With diffusion
transport, these occur in different regions. An applied
magnetic ﬁeld also increases or decreases the recombi-
nation rate in speciﬁc regions. The magnetic-ﬁeld
effects change the emitter-current transfer efﬁciency.
This mechanism of magnetotransistor sensitivity might
be called the
amounts by which the collector currents are varied
depend on the device geometry.
Figure 2 represents the transport of electrons and
holes in a magnetotransistor fabricated in a diffused
well. The respective distances from the emitter to the
collector and base terminals are set to be large enough
compared with the diffusion length for recombination
in the active and the passive base region to signiﬁcantly
affect the transport of electrons injected from the emit-
ter. It is also assumed that the passive base region is
longer than the active base region, and the doped
regions are formed by diffusion.
Accordingly, injected electrons travel a large dis-
tance along the surface in the passive base region, and
there is an opposing ﬂow of holes. The emitter–base
voltage creates a pulling ﬁeld for both types of carrier.
An applied magnetic ﬁeld deﬂects carriers toward the
surface and thus increases the carrier densities,
enhances the recombination, and reduces the electron
ﬂow in the passive base region. As a result, the current
through the working collector decreases, implying neg-
ative relative sensitivity of the collector current.
In the active base region, there is no external electric
ﬁeld, and injected electrons are involved in the diffu-
sion current component. Being positively charged,
holes are attracted to the electrons and so take part in
the diffusion current to the substrate collector. With an
The Bulk-Recombination Mechanism of Negative Relative
Sensitivity Observed in Bipolar Magnetotransistors
R. D. Tikhonov
Technological Centre, Moscow Institute of Electronic Engineering (Technical University), Moscow, Russia
Received January 5, 2004
—The distribution of recombination rate in a dual-collector lateral bipolar magnetotransistor fabri-
cated from a diffused well is investigated by computer simulation. The signiﬁcance of bulk recombination in
negative relative sensitivity is assessed by analyzing carrier transport at low-level injection.
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