ate on trapped sites: densities up to 1018 cm-3 can be reached. In this course, we will develop as possible the models that link: The Vot threshold voltage shift and the trapped charge Qe and Qh, projected at the silicon interface. The trapped charge Qe and Qh and the charge density profile nt and Pt. The charge profile nt and Pt and the density of traps Ntn and Ntp. The density of traps Ntn and Ntp and the material and process characteristics. POSITIVE AND NEGATIVE TRAPPED CHARGE: PRESENT UNDERSTANDING III-15 The positive and negative charges trapped in the oxide therefore consist of the fraction of the holes and electrons that has not been lost via recombination, and eventually trapped. In the first decade of radiation effects, it was believed that trapped holes only exist, as the trapped charge always revealed as positive. However, evidences of negative charge appeared in metal-implanted oxides [e.g., Wang-75]. Later, it was recognized that trapped charge could be evidenced, even before irradiation, in pure thermal oxides [Shan-83] by combination of Thermally Stimulated Current technique (TSC) and Capacitance-Voltage measurement (C-V). However, the amount of trapped electrons is generally lower as compared to the quantity of trapped holes, which explains the general observation of a net positive trapped charge. Type of oxide Thickness Range of dose Range of the Qe/Qh and method electric field Thermal hard (ATT) 18 nm 5 Mrad +1 to 2 MV/cm Thermal hard (wet) 23 nm 2 Mrad +1 to 2 MV/cm 0.083 Thermal hard (wet) 47 nm 1 Mrad +1 to 2 MV/cm Thermal hard 45 nm 0.1-5 Mrad + 1 MV/cm Thermal hard (wet) 100 nm 0.5 Mrad +1 to 2 MV/cm Thermal hard (dry) 104 nm 0.25 Mrad +1 to 2 MV/cm Thermal hard 98 nm + 2 MV/cm Thermal soft 350 nm 6 krad + 1 MV/cm Thermal soft 348 nm 20 krad +1 to 2 MV/cm SIMOX (SOI oxide) 380 nm 1 Mrad -0.75 MV/cm 1.3 ( Vot bi-ex. fit) Table 3. Ratio of trapped electrons Qe to trapped holes Qh as measured under various circumstances (TSC from [Flee-92], bi-exponential fit (sect. 3.15.2 for SIMOX from [Ler