2.4.1.Oxide trapping charge

After the metal oxide semiconductor devices exposed to radiation, Ionizing radiation gradually breaks the bound between the bond of Si-OH, Si-O- Si in the atom of the inside component; therefore, the oxide trapping charge and interface trapping charge is formed. [12] It takes NMOSFET as example, the figure 4 shows the process of trapped charge that the photo of radiation transfer the energy after the exposure of ionizing radiation while the electron and hole is generated in between the gate-source of silicon oxide. [9] The movement is completed, because the mobility of the electron is fast while the electron of silicon oxide will move to gate the source. In contrast, the mobility for hole is significantly slower compared with the electron, so the movement of holes is transport by hopping through the localized state in silicon oxide bulk. This results in a trap in between the movement of holes. The positive trapping charge is formed in the silicon oxide where near between Silicon dioxide and silicon substrate while negative electrons locate in the interface of semiconductors. [13]

Figure 4. The shows the process of the …show more content…
[10] Firstly, trapping charge has a significant impact on the threshold voltage. More exactly, the most common effect is to cause the shift of threshold voltage, the figure 5 illustrates the relationship for C-V characteristic curve. [14] It can clearly see the shift of capacitance-voltage because of trapped charge. In the other word, the total charge of the oxide trapping charge and interface trapping charge find an equivalent negative charge to result in the semiconductor band bending. So it is necessary to add the negative charge between metal and the semiconductor to let it become the flat band. It explains how the trapping charge to affect the threshold voltage illustrated by figure 6.