Insights Into Substrate Dielectric Engineering of Monolayer MoS₂ FET: Digital/Analog/RF Perspective to Circuit Implementation

Abstract

For the first time, we investigate the effects of several substrate dielectric materials (SDMs) using well-calibrated Technology Computer Aided Design (TCAD) physics, ranging from low to high-k, such as SiO2, Si3N4, Al2O3, ZrO2, HfO2, Ta2O5, and TiO2 on both digital and analog/radio frequency (RF) metrics of ML MoS2 MOSFET. Employing the non-equilibrium green’s function (NEGF) approach, self-consistent solutions to the 2-D Poisson’s equation, and density gradient (DG) models we found that employing a high-k SDM beyond Ta2O5 material gives deteriorated performance. A marginal variation in both Ta2O5 ( ${k} =32$ ) and TiO2 ( ${k} =80$ ) is observed for digital applications, whereas the analog/RF performances are significantly degraded with TiO2 material, highlighting that a ${k} =80$ is not suitable for these applications. The Ta2O5 exhibits better dc performance with an improvement in ${I} _{\text {on}}$ of ~62.18% and ${I} _{\text {on}}$ / ${I} _{\text {off}}$ ratio of around four times compared to SiO2 substrates. The ${g} _{m}$ is improved by $\sim 5.45\times $ while a marginal improvement in ${A} _{V}$ is noticed as we move from high-k SDM to low-k SDM. An ~44.72% reduction in ${f} _{T}$ is observed for TiO2 material, whereas only ~8.27% reduction is noticed for Ta2O5 material in comparison with the SiO2 material. Further investigations involving variations in gate length ( ${L} _{g}$ ) and temperature for all SDMs is analyzed, and it is inferred that downscaling of ${L} _{g}$ produces better performance for analog/RF applications, whereas reduction in temperature is suitable for analog applications. The design and evaluation of a CS amplifier further highlight the practical implications of our research, demonstrating a substantial gain enhancement with Ta2O5 ( $\sim 1.98\times $ ) compared to SiO2.