Ionisation induced in semiconductor materials or associated insulators, such as silicon dioxide layers, can lead to charge trapping or the formation of interface states at the semiconductor-insulator boundary, affecting component behaviour or material properties. In MOS devices, the trapped charge can lead to a shift in the gate threshold voltage, and for semiconductors in general, interface states can significantly increase device leakage currents. Materials such as polymers and glasses are also susceptible to total ionising dose (TID) effects and can suffer degradation in mechanical, electrical and optical properties.
The purpose of this clause is to give an overview of total ionising dose (TID) effects and specify the requirements for calculating the TID threat to spacecraft systems in terms of the technologies which are susceptible, and standard methods of calculation.
Radiation dose is the amount of energy per unit mass transferred by particles to a target material, in this case from ionisation and excitation. The International System unit is the gray: 1 Gy = 1 J/kg, but a deprecated unit, the rad (radiation absorbed dose), is still widely used: 1 rad = 1 cGy.
Total ionising dose is included in the overall radiation assessment process.