TOTAL GAMMA-DOSE CHARACTERISTICS OF CMOS DEVICES IN SOI STRUCTURES BASED ON OXIDIZED POROUS SILICON

The electrical characteristics of complementary metal-oxide-semiconduc tor (CMOS) transistors and ring oscillators fabricated in porous silic on silicon-on-insulator (So) structures are presented before and after gamma irradiation; P-channel SOI/MOS transistors exhibit a front-gate threshold voltage shift of -0.2 and -0.55 V after exposure to doses o f 1 and 10 Mrad(Si), respectively, under floating bias conditions, whi ch are different from worst case conditions. For n-channel transistors the corresponding values are -0.1 and -0.2 V. The additional bottom a nd sidewall Bf ion implants with a dose df 2 x 10(13) cm(-2) are found to be effective to prevent leakage current along the n-channel transi stor bottom and sidewalls. SOI/CMOS ring oscillators present a 40% hig her speed in comparison with the same bulk CMOS devices and continued stable operation under a supply voltage of 3-5.5 V, for gamma irradiat ion up to 10 Mrad(Si), and an operating temperature ranging from 77 to 400 K.