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 thicknesses (100-600 Angstrom), ha ve been carried out. The oxide capacitance, (C-min/C-max) ratio and co nductance are shown to be a function of both the oxide thickness and a rea. The study also includes the gamma-radiation effects with doses up to 1.0 Mrad. Low gamma-doses up to 350 krad are shown to improve the (C-min/C-max) ratio, for samples with an oxide layer of 600 Angstrom, from their initial value of 0.904 to 0.346. For higher gamma-doses, up to 750 krad, the devices lose their main feature as capacitors, where the C-min/C-max ratio value of unity is reached. Samples with oxide l ayers less than 600 Angstrom are shown to lose their characteristics g radually; due to dose increase. The surface depletion region width, at the strong inversion, semiconductor resistance and oxide charge are s hown to increase from 22.0 Angstrom, 100 Ohm and 6.50 x 10(12) C/cm(2) , to 400 Angstrom, 95.0 k Ohm and 10.85 x 10(12) C/cm(2), respectively , due to gamma-doses up to 1.0 Mrad. Finally, oven annealing of the ir radiated samples, at 350 degrees C for 30.0 min, recovers most of the initial characteristics.