Charge effects in dielectric films of MIS structures being under high-field injection of electrons at ionizing radiation

Use of High-Field Electron Injection into Dielectrics to Enhance Functional Capabilities of Radiation MOS Sensors

“…The reducing of the MOS sensor dose range is caused by partial filling of hole traps by positive charge generated by high-field tunnel injection of electrons and by acceleration of degradation processes in the gate dielectric occurring because of high-field injection. The annihilation of a fraction of positive charge and injected electrons, as it has been shown in Andreev et al [27] and Andreev et al [28], can result in rising of amount of surface states at the Si/SiO2 interface, and it can accelerate degradation processes cause by restructuring of the interface and the dielectric film.…”

“…Under the mode, electric fields in the dielectric film significantly increase and these stimulate the accumulation of higher values of positive charge at the same radiation dose. However, when the sensor is under the mode, besides charge effects caused by radiation ionization ( Figure 2) and discussed in detail in Schwank et al [24], Fleetwood et al [25], and Oldham et al [26], it is essential to take into consideration the following charge effects [27,28]: additional generation of positive charge as a result of thermalization of injected electrons (Figure 2, process 11), annihilation of a fraction of positive charge caused by interaction with injected electrons (Figure 2, process 8), generation of additional surface states which takes place because of annihilation of a positive charge fraction and injected electrons ( Figure 2, process 9). In accordance with the model suggested in Andreev et al [27] and Andreev et al [28], we use the following set of equations to describe sensor functioning when it is under concurrent influence of ionizing radiation and high-field injection of electrons:…”

“…Sensors 2020, 20, 2382 4 of 11 -in order to calculate current density initiated by ionization radiation we apply the following equation [24,27,28]:…”

“…Then in Section 2 it has been irradiated by the proton beam with energy of 500 keV and fluence of 10 10 cm −2 . When applying the pulse of constant current with density of J 0 to the MOS structure, we can use the following equation to determine sum of densities of currents flowing through the dielectric film [27]:…”

“…Figure 5 shows experimental data obtained at radiation intensity of 1 rad/s. Figure 5 demonstrates that under the influence of protons and α-particles one observes higher rise of the MOS sensor sensitivity when switching to the high-field injection mode and that probably caused by more noticeable increasing of the charge yield for these sections with respect to the γ-rays irradiation [27]. Thus, in order to obtain high dose sensitivity of the sensor under the γ-rays radiation, it is enough to apply voltage providing creation of electric field which is slightly lower than injection field.…”