If a magnetic field is applied perpendicular to the inversion layer, a
differential current will be sensed according to (4.1). Figure
4.5 shows this differential current as a function of the magnetic
field. In the present analysis the two-drain MAGFET is oriented in the
following way (see Figure 4.3): the length of the device is
along the axis, the depth
of the channel is along the
axis, and the width of the device is
along the
axis. So, the magnetic field strength is set along the
axis.
The match between experiments and simulation results is very good. The bias conditions of the two-drain MAGFET are a gate voltage of 4.95 V, a drain voltage of 1.0 V in both drains, and zero volts in the source and substrate. However, the Hall scattering factor for electrons is set to 0.6, a very low value in comparison to those that are found in the literature, specially in [6] and [18], where values between 1.1 and 1.4 are found.
A cut along the device is made again at 90 m from the
source side, as it was made with zero magnetic field. Figure
4.6 shows how the current piles up at one side of the two-drain
MAGFET (
axis goes towards the substrate direction and
axis is the width of the two-drain MAGFET). It is clear that if
the magnetic field is reversed, the current will pile up in the
other drain.
At 300 K the relative sensitivity is 2.64 % T according to
(4.1). This is a very low value for a solid-state magnetic
sensor, where Hall plates and other solid-state sensors are able to render
up to 7 % T
at the same temperature [40].
However, most of the Hall sensors are compared with the current-related
sensitivity, that is, the supply current that the Hall device
needs to generate a higher Hall voltage. This current-related
sensitivity is given in V/A-T units, so a direct comparison
between Hall plates and the two-drain MAGFET is not possible,
because the MAGFET sensor does not give a Hall voltage as output
of the magnetic field sensing as the Hall plates do. The output
of the magnetic field sensing in a two-drain MAGFET is the differential
current between the drains. The higher this value, the higher
the relative sensitivity. This differential current is related to
the carrier deflection as it will be explained in the following section.
Rodrigo Torres 2003-03-26