ABSTRACT
Trench Hall and resonant magnetic field sensors, two kinds
of
silicon-based
microsystems for the detection
of
in-chip-plane magnetic fields, are reported on
in this thesis. By arranging such devices in quadrature on a single chip, mono-
lithic 2-D magnetic vector probes can be realized. Contactless angle measure-
mentsystems therefore represent the main application
of
these sensors.
Trench Hall devices (THDs) are presented first. As in the case
of
traditional Hall
plates, the piezo-resistive effect is expected to be one
of
the primary offset
sources
of
THDs. The usual modeling
of
this effect by lumped elements is not
adapted to vertical Hall sensors (VHSs), because
of
the strongly non-rectilinear
current flow inherent to these kinds
of
structures, Therefore, a new method based
on mapping techniques has been developed.
The
insight offered by this
quasi-analytical approach demonstrates that the judicious positioning
of
the
active-area borders may considerably reduce the parasitic offset voltage gener-
ated.
The sensors have been fabricated in-house using a custom-designed process.
Combining dry and wet etching led to the precise release
of
the device active
area, and thus resulted in the desired elimination
of
the bottom pn-junction insu-
lation. Furthermore, the stress on the sensitive structure could be reduced by
removing the polysilicon, which was used to fill the trenches, by means
of
a
mask-less XeF2dry-etching step. The obtained devices exhibit high current- and
voltage-related sensitivities
of
around 1000 V/AT and 0.05 V/VT, respectively,
and a relatively low residual offset typically remaining below 0.5 mT for a bias
of
10pA. A strong field effect generated by the difference
of
potential between the
bulk and the active area was identified.
It
can be decreased by the XeF2polysili-
con etching, but constitutes the largest source
of
electrical non-linearity, which is
closely linked to the sensor residual offset voltage.
A new type
of
resonant magnetic field sensor providing afrequency output is the
focus
of
the second part
of
the thesis. The system consists
of
an electrical har-
monic oscillator, in which the frequency-determining element was replaced by a
resonating cantilever. An electro-thermal bimorph effect performs the actuation
of
the mechanical structure, and a Wheatstone bridge
of
4piezoresistive transis-
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