ts reveals the field-collapse effect in the two-dimensional situation of the buried oxide laterally biased the drain voltage. The first set of figures depicts the phenomena under a 4-V drain voltage, all the other electrodes being grounded. The last figure compares the trapped hole charge density for drain bias varying between 0 and 2 V. As it could be anticipated, the charge trapping is not nil at zero-bias, because of built-in fields resulting from doping. But, naturally, the amount of trapped charge is increase with the drain bias. This is why the dose threshold at which the back-gate leakage MOS is triggered is strongly influenced by the drain voltage. III-100 0 krad 90 krad +1e-09 +1e+05 +3e+05 +4e+05 +5e+05 +1e-08 +1e+05 +3e+05 +4e+05 +5e+05 210 krad 300 krad +1e-08 +1e+05 +3e+05 +4e+05 +5e+05 +1e-08 +1e+05 +3e+05 +4e+05 +5e+05 Figure 96. Chart of the electric field in a 0.5 um NMOS/SOI transistor in worst case during irradiation (VDs=+4V) using the self-consistent code A. One clearly sees the strong deformation of the equipotential. At the beginning of the irradiation, we observe the situation of the "drain side-gating" in this thin-film SOI transistor: the electric field lines go directly from the drain to the backside of the transistor. Therefore, holes are directed toward the backside and build-up of the charge begins. In this figure, a 2D field collapse is clearly seen, as expected from [Boes-91] and the modeling in 1D exposed above in chapter 4.4. At the end of the irradiation, the field is nearly horizontal and reinforced, because the space charge has considerably extended. III-101 90 krad 0 krad A/cm2 A/cm2 +2e-12 +9e-08 +4e-03 +2e+02 +1e+07 +2e-12 +9e-08 +4e-03 +2e+02 +1e+07 300 krad 210 krad A/cm2 A/cm2 +2e-12 +9e-08 +4e-03 +2e+02 +1e+07 +2e-12 +9e-08 +4e-03 +2e+02 +1e+07 Figure 97. Apparition of an electron current at the back-side of the MOS between 90 and 210 krads in the back-side of a SOI transistor due to the turn-on of the back parasitic MOS in a N transistor biased in worst case during irr