Total-dose effects of gamma-ray irradiation on CMOS/SIMOX devices

Radiation-hardened CMOS/SIMOX devices have been developed using a combination of vertical isolation structures obtained by SIMOX technology and newly developed lateral isolation structures. The n-channel MOSFET is vertically isolated by multilayers of highly oxygen-doped polysilicon and buried SiO2, and is laterally isolated by multilayers of thin sidewall SiO2, sidewall polysilicon, and thick field SiO2. The p-channel MOSFET has the same vertical isolation structure as that of the n-channel MOSFET. However, it has no sidewall polysilicon layer but uses a thick field SiO2 layer for lateral isolation. Highly oxygen-doped polysilicon and sidewall polysilicon layers act to shield radiation-induced positive charges trapped in the buried SiO2 and field SiO2 layers, respectively. By utilizing these isolation structures and a thin-gate SiO2 layer, the developed CMOS/SIMOX devices exhibited ample operational characteristics even after exposure to 2 Mrad(Si) of ⁶⁰Co gamma-ray irradiation.