Radiation Hardening of MOS Transistors for Low Ionizing Dose Levels

The effect on MOS field-effect transistors of moderate doses of ionizing radiation (up to a few tens of kilorads) is a lateral shift in the Id-Vgs characteristic. Experimental results are given here to describe this shift, particularly for low ionizing doses, and from these results a model similar to others recently published is given to describe the mechanisms involved. The experiments are based on measurements of "small-dose radiation sensitivity", defined for the MOSFET as the incremental shift of gate threshold voltage with the application of an increment of radiation, i.e. dVT/d??. Detailed observations of dVT/d?? under a variety of conditions of radiation, bias and temperature, lead to a technique for radiation hardening. Using this technique, the radiation sensitivity can be made negligible for doses up to several thousand rads, at the expense of only minor changes in other device parameters.