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

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 (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k} =32$ </tex-math></inline-formula>) and TiO2 (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k} =80$ </tex-math></inline-formula>) is observed for digital applications, whereas the analog/RF performances are significantly degraded with TiO2 material, highlighting that a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k} =80$ </tex-math></inline-formula> is not suitable for these applications. The Ta2O5 exhibits better dc performance with an improvement in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I} _{\text {on}}$ </tex-math></inline-formula> of ~62.18% and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I} _{\text {on}}$ </tex-math></inline-formula>/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I} _{\text {off}}$ </tex-math></inline-formula> ratio of around four times compared to SiO2 substrates. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${g} _{m}$ </tex-math></inline-formula> is improved by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 5.45\times $ </tex-math></inline-formula> while a marginal improvement in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${A} _{V}$ </tex-math></inline-formula> is noticed as we move from high-k SDM to low-k SDM. An ~44.72% reduction in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f} _{T}$ </tex-math></inline-formula> 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 (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L} _{g}$ </tex-math></inline-formula>) and temperature for all SDMs is analyzed, and it is inferred that downscaling of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L} _{g}$ </tex-math></inline-formula> 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 (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 1.98\times $ </tex-math></inline-formula>) compared to SiO2.