Ageing of metal/ultra-thin oxide/semiconductor structures under Fowler-Nordheim current injection

In this paper, results of the ageing of metal/ultra-thin oxide/semiconductor structures under Fowler-Nordheim constant current injections are presented. The oxide (silicon dioxide, SiO2) thickness layer of these structures varies from 3 to 12.5 nm for a p-type semiconductor. It is shown that ageing induces trapped charges in the oxide layer (positive and negative near the cathode and positive near the anode) and new interface states at the oxide/semiconductor interface. The positive charge created near the oxide/semiconductor interface, during current injection from the metal (accumulation regime, V-g < 0), cannot be observed on current-voltage (I (V-g)) characteristics in the inversion regime (V-g > 0). It is shown that these charges can trap electrons injected from the semiconductor during acquisition of the I (V-g) characteristics (V-g > 0). This induces a shift in the I (V-g) characteristics as opposed to that what is obtained from capacity-voltage (C(V-g)) characteristics. So, the characteristics (density and centroid) of charges trapped in the oxide layer cannot be obtained, as in the case of thick layers (thickness greater than 20 nm), from the shift obtained from the I (V-g) characteristics in accumulation and inversion regimes. Also, it has been shown that the capture of electrons by the positive charge at the oxide/semiconductor interface promotes the creation of interface states.