Characteristics and radiation effects of MOS capacitors with Al2O3 layers in p-type silicon

Theoretical and experimental studies on MOS capacitors built on p-type Si substrates with different Al2O3 thickness (100–600 Å), have been carried out. The oxide capacitance, (Cmin/Cmax) ratio and conductance are shown to be a function of both the oxide thickness and area. The study also includes the γ-radiation effects with doses up to 1.0 Mrad. Low γ-doses up to 350 krad are shown to improve the (Cmin/Cmax) ratio, for samples with an oxide layer of 600 Å, from their initial value of 0.904 to 0.346. For higher γ-doses, up to 750 krad, the devices lose their main feature as capacitors, where the Cmin/Cmax ratio value of unity is reached. Samples with oxide layers less than 600 Å are shown to lose their characteristics gradually; due to dose increase. The surface depletion region width, at the strong inversion, semicondictor resistance and oxide charge are shown to increase from 22.0 Å, 100 ω and 6.50 × 1012 C/cm2, to 400 Å, 95.0 kω and 10.85 × 1012 C/cm2, respectively, due to γ-doses up to 1.0 Mrad. Finally, oven annealing of the irradiated samples, at 350°C for 30.0 min, recovers most of the initial characteristics.