5.4 Geometric Parameters

As in the two-drain MAGFET analysis, the three-drain MAGFET has the same geometric parameters that play an important role in the relative sensitivity. However, extra parameters can be identified. For example, it is quite clear that the distance between the drains can be independently modified but this will lead to an undesirable offset, because the currents at the lateral drains will not be equal.

Figure 5.12 shows simulations results for the relative sensitivity at different drain distances and temperatures. The simulated three-drain MAGFET has a width of 80 $\mu$m and a length of 125 $\mu$m. The drains are set to 1.0 V, the gate to 4.95 V, and the source and substrate to 0.0 V. The magnetic field is set to -50 mT. A maximum relative sensitivity of 4.32 % T$^{-1}$ and 11.10 % T$^{-1}$ can be seen for a distance between drains of 4 $\mu$m at both 300 K and 77 K, where the drains almost share equally the total drain current. As the distance between the drains increases, the total drain current is equally shared by the drains.

Figure 5.12: Simulated $S_r$ for different distances between the drains.

Figure 5.13 shows the simulation results for the relative sensitivity at different lengths and temperatures. The simulated three-drain MAGFET has a width of 80 $\mu$m and a distance between drains of 10 $\mu$m. The drains are set to 1.0 V, the gate to 4.95 V, and the source and substrate to 0.0 V. The magnetic field is set to -50 mT. As predicted by (4.2), the relative sensitivity increases from 2.75 % T$^{-1}$ to 4.08 % T$^{-1}$ at 300 K, and from 6.75 % T$^{-1}$ to 9.18 % T$^{-1}$ at 77 K. However, in absolute terms, this improvement is not as high as in the two-drain MAGFET analysis, even at 77 K.

Figure 5.13: Simulated relative sensitivity
for different lengths.

Figure 5.14 shows the simulation results for the relative sensitivity at different widths. The simulated three-drain MAGFET has a length of 125 $\mu$m and a distance between drains of 10 $\mu$m. The drains are set to 1.0 V, the gate to 4.95 V, and the source and substrate to 0.0 V. The magnetic field is set to -50 mT. As in the two-drain MAGFET analysis, a maximum in the relative sensitivity can be seen at both, 300 K and 77 K. At 300 K, the maximum is of 4.19 % T$^{-1}$ for a device width of 125 $\mu$m, and at 77 K, the maximum is of 11.54 % T$^{-1}$ for a device width of 155 $\mu$m.

Figure 5.14: Simulated relative sensitivity
for different widths.

Figure 5.15 shows the simulations results for the relative sensitivity at different sizes of the central drain. The simulated three-drain MAGFET has a length of 125 $\mu$m, a width of 80 $\mu$m, and a distance between drains of 10 $\mu$m. The drains are set to 1.0 V, the gate to 4.95 V, and the source and substrate to 0.0 V. The magnetic field is set to -50 mT. A tendency cannot be stated unless the magnitude of the drain currents for the zero magnetic field are analyzed. For a central drain size of 12 $\mu$m, a maximum in the relative sensitivity of 4.56 % T$^{-1}$ at 300 K and 13.00 % T$^{-1}$ at 77 K can be observed. The magnitude of the central drain current is almost the half of the lateral drain currents: $I_{D2}=20.86\,\mu$A, $I_{D1,3}=34.60\,\mu$A at 300 K, and $I_{D2}=56.93\,\mu$A, $I_{D1,3}=133.70\,\mu$A at 77 K (See also Figure 5.16).

Figure 5.15: Simulated $S_r$ and $I_{D2}$
for different sizes of Drain 2.

Because the magnitude of the reference current is low, the relative sensitivity is high, according to expression (5.1). However, the magnitude of the central drain current cannot be set as a general rule because the central drain current for the drain size of 8 $\mu$m is high as for the lateral drain currents and it gives a pretty high relative sensitivity at both 300 K and 77 K. A complex relation between lowering the drain current at the Drain 2 or sharing equally the total drain current exists.

Figure 5.16: Simulated $I_{D1,3}/I_{D2}$ ratio
for different sizes of Drain 2.