4.3.3 Bias Dependence

As it has been shown in Section 4.2, the electro-magnetic interaction shows a complex behavior that can be explained in terms of the drift-diffusion process. At low temperature, some processes are enhanced (or reduced) [2,17] modifying the general behavior of the device.

Figure 4.84 presents the relative sensitivity as a function of the gate voltage for different polarizations at the drains. Surprisingly it shows a complete different behavior as for room temperature (See Figure 4.7). As the drain to source voltage is increased, the relative sensitivity increases too. The carriers in the inversion layer are swept by the lateral electric field [17]. The larger the lateral electric field, the higher the mobility of the electrons in the inversion layer. As explained in Section 4.2, the relative sensitivity is higher at low gate voltages (see Figure 4.7), because the drain currents are comparable with the differential current.

Figure 4.84: Simulated $S_r$ as a function of the gate voltage at 77 K and -50 mT.

Figure 4.85 shows how the differential current increases with respect to the gate voltage for a voltage of 1.0 V at the drains. The differential current at 77 K is almost 20 times higher as for the 300 K (see Figure 4.8), but at the same temperature operation a higher differential current does not mean a higher relative sensitivity, as can be seen from both figures.

Figure 4.85: Simulated $S_r$ and $\Delta$ for a gate swept. $V_{D1}$ and $V_{D2}$ are set to 1.0 V.

The 's' shape of the plots in the room temperature analysis (see Figure 4.7) has been explained by the transition between the diffusion and the drift process. Figure 4.86 shows the relative sensitivity as a function of the drain voltage for different gate voltages. At low temperature, the various minima are not present, explaining that the carriers are swept by the lateral electric field. If this is true, no diffusion process exists at 77 K or it only exist at very low drain to source voltages which are not visible on the plots.

Figure 4.86: Simulated $S_r$ as a function of the drain voltage at 77 K and -50 mT.