Laterally inhomogeneous charge build-up in CMOS inverters during ionizing irradiation

The build-up of interface states and oxide fixed charges in CMOS inverters during ionizing irradiation (γ-60Co, X-ray, 2.5 MeV electrons) is measured. The interface state spectrum in the inversion region is determined from the transfer characteristics by extending Sabnis' expression. Anomalous behaviour (increase of the transconductance) is found for the p-channel FET, when U/sub GS/(irr) = 0 V. The laterally inhomogeneous field along the gate leads to preferential hole trapping in a small gate oxide region near the drain. This region acts as a short channel FET between the hole-free gate area already in inversion and the drain. This explanation is confirmed by an apparent increase of the mobility and different I/sub D/(U/sub G/; U/sub D/) characteristics when interchanging source and drain. (author)