Radiation resistance of Al2O3MOS devices

Integrated circuits employing MOS devices will play a vital role in tomorrow's civilian and military electronics if their degradation in a radiation environment can be eliminated. One possible approach toward alleviating radiation effects in MOS devices is to use a material with a defect structure that does not allow predominant trapping of either holes or electrons as a gate insulator. This has been done by constructing MOS devices with plasma-grown aluminum oxide. The Al
2
O
3
films are formed by first depositing aluminum on freshly cleaned and properly prepared silicon wafers. Subsequently this aluminum is oxidized in an oxygen plasma and device fabrication is then completed. The devices have excellent characteristics and stability, and their fabrication is not restricted by the conditions of the ultra-clean procedures necessary for SiO
2
-Si devices. Exposure to 1-MeV electron bombardment at various fluence levels and bombardment-bias conditions shows that these structures possess remarkable radiation resistance. Up to a fluence of 1 × 10
¹³
e/cm
²
, under positive or negative bias, no oxide charge buildup or interface state generation is detectable. Above that fluence, only small shifts are observed. This indicates that an order of magnitude improvement in device hardening can be achieved by the use of this material.