Modelling of the influence of charges trapped in the oxide on the I(Vg) characteristics of metal-ultra-thin oxide-semiconductor structures

This paper deals with the theoretical and experimental influences of the charge trapped in the oxide of metal/ultra-thin oxide/semiconductor structures. It focuses on the two characteristics current-voltage I (V-g) and voltage-charges injected V-g(Q(inj)) (V-g is the voltage applied, Q(inj) is the injected charge) when the conduction is of the Fowler-Nordheim type. The charge is trapped in the thin oxide after injection of a constant current at high field (>12 MV cm(-1)) from the metal (in accumulation regime: V-g < 0). This study considers that, after a given injection, the charge centroid is fixed during the acquisition of the I (V-g) characteristics. A method is proposed to determine the trapped charge characteristics (density and centroid) by analysing the theoretical and experimental I (V-g) and Vg(Q(inj)) characteristics. It is shown that the constant current injection creates a charge trapped in the oxide near the cathode. When the injected charge increases, the trapped charge density increases linearly and the charge centroid position shifts exponentially towards the injecting electrode. These results enable us to draw conclusions on the instability of the trapped charge. Indeed the increase in the charges injected causes the movement of the charge centroid towards the cathode.