| Summary: | The radiation response and long term reliability of alternative gate dielectrics will play a critical role in determining the viability of these materials for use in future space applications. The total dose radiation responses of several near and long term alternative gate dielectrics to silicon dioxide are discussed. The midgap voltage shift increases monotonically with dose and depends strongly on both dielectric thickness and processing. The thinnest dielectrics, of most interest to industry, are extremely hard to ionizing irradiation, exhibiting only a few millivolts of shift at a total doses of 1 Mrad(SiO2) or more. Oxygen anneals are found to significantly improve the total dose radiation response and induce a small amount of capacitance-voltage hysteresis. The standard radiation-induced-trapping efficiency equation is adapted for calculating effective trapping efficiencies in alternative gate dielectrics and used to compare the radiation responses of several materials. The alternative gate dielectrics discussed here are shown to have effective trapping efficiencies which are up to 15 to 20 times larger than thermal oxide of comparable electrical thickness. The effects of common reliability screens such as time dependent dielectric breakdown tests, ``burn-in' tests, and bias-stress tests are also discussed. Constant-voltage accelerated life testing has shown these devices have failure distributions with a large population of early extrinsic failures. Baking can degrade some devices by reducing the oxide capacitance and inducing hysteresis. Additionally, large applied voltages inject excess charge into alternative dielectrics with low conduction band offset energies, which can lead to a overestimation of the radiation hardness of these materials. Alternative gate dielectrics have shown encouraging radiation hardness, but there are still several engineering problems that must be addressed before they can be reliably incorporated in future space electronics.
|
|---|
