Influence of the substrate voltage on the random telegraph signal parameters in submicron n-channel metal-oxide-semiconductor field-effect transistors under a constant inversion charge density
In this paper, the impact of the substrate bias UBS on the parameters of a repulsive random telegraph signal in an n-channel metal-oxide-semiconductor field-effect transistor is studied. Particular attention is paid to the variation of the capture time constant τc with the channel current I in linear operation. It is shown that the strong reduction of τc with I can be explained by the Coulomb blockade effect. The corresponding Coulomb energy ΔE of the charged-near-interface oxide trap is shown to be a strong function of the substrate bias. From the analysis of the experimental results considering surface quantization effects follows that the variation of ΔE with UBS is caused by the change in both the inversion layer surface charge density Ns and in the surface electric field Fs that influences the distance between the centroid of the inversion layer and the interface. In fact, it will be demonstrated that ΔE can be expressed in function of a single parameter (NsFs2). Finally, the impact of the substrate bias on the other parameters, i.e., the amplitude ΔI, the emission time constant τe and the distance d of the trap from the interface, will also be addressed.