Electron irradiation effects in MOS systems

Flat-band shift measurements were made on p-type MOS devices irradiated with electrons at various gate-bias voltages. A structured reproducible curve of flat-band shift versus gate bias was obtained which could not be readily accounted for with existing models. Experimental data were taken over a wide range of negative and positive gate-bias voltages (consistent with electrical breakdown limits) in order to identify fundamental mechanisms as a basis for formulating a more general model of the entire device. A model is presented based on the known work functions and electron affinities for Al-SiO2-Si devices. It assumes that traps in the Oxide are occupied according to Fermi-Dirac statistics, subject to constraints determined by the interface parameters. A linearized quasi-Fermi level is assumed in the oxide, and the resulting distribution of charged traps is used with Poisson's equation to obtain a self-consistent energy-band structure throughout the entire device.