Neutron Radiation Effects on MOS Fets: Theory and Experiment

The effects of a pure neutron environment on Metal-Oxide-Semiconductor Field Effect Transistors (MOS-FET) is studied. A model for neutron-produced ionization in the oxide layer is presented. The energy partition between atomic displacement and electronic ionization processes in the nuclear scattering interaction is calculated and compared to the Lindhard model. It is shown that the neutron ionization causes a positive charge buildup in the oxide similar to a gamma ionization charge buildup. It is also shown that fast neutrons produce significant ionization energy which can become the major cause for ionization damage in a mixed neutron-gamma environment such as a nuclear blast. Specific experimental results are given for commercial and experimental MOS-FETS. The experimental technique used in achieving an almost pure neutron environment is described. Finally, an ionization dose equivalence for fast neutrons in SiO2 is given and compared to experimental values. This relation should prove useful in future studies of ionization damage in SiO2 subjected to a neutron-gamma environment.