Fundamental Limits Imposed by Gamma Dose Fluctuations in Scaled MOS Gate Insulators

The statistical methods of Extreme Value Theory [1] are combined with Microdosimetry Theory and applied to the problem of gamma ray ionization fluctuations in the gate insulators of Very Large Scale Integrated (VLSI) MOS circuits, such as memories. It is shown that the fluctuations in dose deposited in scaled gate oxides can be much larger than the nominal dose, as measured by a macroscopic dosimeter, or even by an insulator on a test transistor. Quantitative predictions are made for this effect for a wide range of VLSI circuit dimensions.