Ilmenite-hematite (IH) [(1-x)FeTiO 3 ·xFe 2 O 3 ] solid solutions are unique classes of materials showing both magnetic and semiconducting properties, which make them potential candidates for novel applications in microelectronics and spintronics. This paper focuses on their varistor behavior before and after exposure to 40 MeV and 10 MeV proton radiations up to a fluence of 5 ϫ 10 10 p/cm 2 . The IH films are tolerant to these irradiations with little significant change to the nonlinear current-voltage characteristics. The switching voltage of the devices is in the regime of practical applications, and the radiation tolerance makes these materials suitable for aerospace applications.Radiation-induced damage has become an important field of study and continues to gain importance because of the need to protect electronic components, devices, and microelectronic circuits from the potentially catastrophic effects of radiation on their performance. 1 Space systems often require electronics that can operate in a high-radiation environment. This radiation may result from particles trapped in planetary magnetic fields, galactic cosmic rays, or high-energy protons from solar events. Exposure to high energetic particles can degrade device performance and ultimately lead to component failure. The primary effects of natural space radiation on spacecraft electronics are total ionizing dose effects, displacement damage, and single event upsets. 2 Radiation can alter the characteristics of electronic materials and the performance of electronic devices made from these materials by the mechanisms of ionization and atomic displacement. The displacement damage takes place by nuclear interactions and the ionization damage by atomic interactions in which energy deposited by the ionizing radiations creates electron-hole pairs. Semiconductor-based sensors, such as varistors and other current sensitive sensors, have applications in aerospace and other hostile environments for power and other applications. The radiation effects on device performance are important in these applications because the elevated radiation levels associated with these environments can produce both ionization and displacement damage.
We demonstrated the capability of MeV proton irradiation to promote chemical ordering processes in a solid at low temperature. We used the ilmenite–hematite solid solution system which allows estimation of the degree of ordering through measurement of its magnetization. Normally, ordering through diffusion would require high temperature annealing. At high temperatures, however, the equilibrium state would be less ordered and thus the achievable ordering incomplete. High energetic protons continuously transfer energy to the sample through electronic interaction which locally deposits large quantities of energy without a general increase of the sample temperature. This promotes diffusion processes which allow the system to relax towards the ordered equilibrium state.
Zinc oxide is generally considered to be radiation hard, although there are few experimental reports supporting this assertion. In this paper, we present results on the changes in electrical performance of bulk Pt/ZnO Schottky rectifiers exposed to 40-MeV protons at fluences from 5 ϫ 10 9 cm Ϫ2 to 5 ϫ 10 10 cm Ϫ2 . These doses correspond to more than 10 years or 100 years, respectively, in low-earth satellite orbit. The reverse breakdown voltage of the ZnO diodes increased from ϳ3.6 V in unirradiated devices to ϳ4 V after the highest proton dose. The effective barrier height decreased with proton dose, while the diode ideality factor increased from 1.8 to 1.9 for the highest dose. These devices appear promising for both aerospace and terrestrial applications where irradiation hardness is a prerequisite. The main degradation mechanism appears to be creation of recombination centers and traps.
The radiation tolerance of high electron mobility transistors (HEMTs) based on InGaAs/InAlAs lattice matched to InP has been studied. At low fluences of 3 MeV He+ ions, the only effect is a reduction in the leakage currents. At higher fluences, the drain current decreases, the threshold voltage increases toward zero, and the transconductance decreases. These results are consistent with increased trapping in the donor layer and increased scattering in the channel layer. Radiation-induced increases in the threshold voltage occur three to nine times more slowly here than in GaAs/AlGaAs HEMTs, indicating high radiation tolerance.
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