Gate leakage currents present a serious challenge for designing modern ultra-scaled metal-oxide-semiconductor (MOS) field effect transistors. While trap-assisted tunneling (TAT) has already been recognized as a major contribution to leakage currents in nanoelectronic devices, the microscopic nature of the traps acting as charge transition centers is still unclear. In this work we utilize a multi-scale modeling approach to link TAT to polaron states, which are acting similar to traps and are intrinsic to the amorphous gate dielectric. We first use density functional theory to study the electronic structure and the charge trapping dynamics of such polarons on an atomistic level in common gate dielectrics like SiO₂ or ZrO₂. From those calculations a nonradiative multiphonon model is derived to describe the charge hopping process between nearby polarons. Finally, the macroscopic gate leakage current is obtained from a Monte-Carlo device simulation, taking into account the stochastic distribution of trapping sites and their varying parameters due to the amorphous host material. By comparing the results of our simulation framework to experimental investigations on gate leakage currents for SiC/SiO2 and TiN/ZrO2 MOSCAPs, we provide compelling evidence that polarons are very likely the root cause for leakage currents in the studied devices. Our simulations further suggest that general features of these polarons, like the comparatively small relaxation energy, make them a universal source for steady-state leakage currents beyond the particular materials studied in this work.

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Dominic Waldhoer, Christian Schleich, Al-Moatasem El-Sayed, and Tibor Grasser, "Polarons as a universal source of leakage currents in amorphous oxides: a multiscale modeling approach," Proc. SPIE 12422, Oxide-based Materials and Devices XIV, 1242203 (Presented at SPIE OPTO: January 31, 2023; Published: 16 March 2023); https://doi.org/10.1117/12.2659249.