A comprehensive model for the I –V characteristics of metal-Ta 2 O 5 /SiO 2 -Si structures

Abstract

The I–V characteristics of metal-Ta2O5/SiO2-Si structures are precisely described with a comprehensive model, for both polarities, in the whole measurement range where there is no noticeable degradation and over seven orders of magnitude of the current. Hopping conduction and tunneling were elucidated to be the dominant conduction mechanisms in the SiO2 layer and Poole–Frenkel internal field-assisted emission in the Ta2O5 layer. Other possible relevant mechanisms were discussed and subsequently discarded, based on their minor contribution. Theoretical calculations are made with fitted values of the defect related constants for hopping conduction of SiO2 and Poole–Frenkel emission of Ta2O5 and the thickness of the SiO2 layer. For gates positively biased, tunneling of electrons from the silicon conduction band through the SiO2 is considered, while for gates negatively biased, tunneling of holes from the silicon valence band. Approximations for practical use are proposed and thus introduced limitations of the model discussed. The model is demonstrated on Al-insulator-Si structures containing thermally grown Ta2O5, previously studied in terms of microstructural, dielectric and electrical properties. The experimental results suggest that at higher current densities (>10 nA/cm2) an effect of compensation of the existing oxide charges by accumulated charges occurs.