Range in aluminum (mm) Photon Electron Proton Deuton Particule a 0,001 10 100 Energy (MeV) Figure 6. Orders of magnitude of particle range in matter [Adams-91]. 2.6. EXAMPLE AT THE COMPONENT LEVEL: LEO SATELLITES Table 2 illustrates the range of doses in a typical LEO orbit (800 to 900 km). It shows that the required hardness of a given part depends on the position inside the spacecraft. This results in a very broad spectrum from 1 to 16 kilorad(Si)/year. High-level functions are protected by positioning the component deep inside the spacecraft. In Constellation satellites orbiting higher, the dose can be 10 times as much. III-9 Category Function Dose (krad(Si)) per Year Diodes Ultra High Frequency Signal Zener Transistors Bipolar Power MOS Linear Integrated Circuits Amplifiers Regulators Digital Integrated Circuits Bipolar TTL-LS CMOS 4000B HCMOS Microprocessors Memories Table 2. Example of a LEO Satellite [CTTS]. 3. ANALYTICAL MODELING OF TRAPPING EFFECTS IN MOS TRANSISTORS The ionizing dose affects MOS technologies by mainly two different phenomena that lead to the presence of trapped charge. This results in an induced electrical field, which is added to the applied field existing in the functioning component and disturbs this field. As an example, one can take the simplest case of signal (low-power) MOS transistor 2N4351 (N- type) and 3N164 (P-type) irradiated all pins shorted (fig. 7). THRESHOLD VOLTAGE SHIFT COMMERCIAL PARTS DOSE EFFECTS N MOS TRANSISTOR 2N4351-Motorola P MOS TRANSISTOR fabrication date 3N164 4-Siliconix fabrication date 8322 => LOT-TO-LOT VARIATIONS fabrication date 1000 Dose (krod) BIAS DURING IRRADIATION : Vqs=Vds=0 Figure 7. Examples of variations of the threshold voltage for small-signal discrete N and P-MOS transistors (irradiated with Co-60 gamma rays under VGs=VDs=VBS =0 V). III-10 In this figure are summarized certain typical features of total dose effects on MOS devices: linear dependence at low dose sublinear regime at intermediate dose saturation or very slow dependence at high 