4.2.2 Magnetic Field

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 $x$ axis, the depth of the channel is along the $y$ axis, and the width of the device is along the $z$ axis. So, the magnetic field strength is set along the $y$ axis.

Figure 4.5: Differential current versus magnetic field at 300 K.

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 $\mu$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 ($x$ axis goes towards the substrate direction and $y$ 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.

Figure 4.6: Current density at 300 K and
a magnetic field of -50 mT.

At 300 K the relative sensitivity is 2.64 % T$^{-1}$ 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$^{-1}$ 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.