How low can the sub-threshold swing be in a negative capacitance classical field effect transistor? Ankit Jain editdelete
Scaling of field effect transistors (FETs) may eventually come to an end due to the non-scalability of sub-threshold swing (S); whose minimum value is thermodynamically limited to 60mV/decade at room temperature. It has been shown in the past that a negative capacitance FET (NCFET) can lower S below 60mV/decade by stabilizing an inherently unstable gate insulator (e.g. Ferroelectric) in its unstable regime. However, the question: What could be the lowest possible sub-threshold swing in an NCFET remains unexplored and unanswered to date. In this presentation, I will use nanoelectromechanical field effect transistor (NEMFET) as an illustrative example of an NCFET to explore the aforementioned question of lowest sub-threshold swing. I will first discuss the physics of unstable regime in NEMFET and demonstrate how simple interaction between mechanical and electrostatic forces leads to the inherent instability in NEMFET. The strategies of stabilization of NEMFET in its unstable regime using series capacitor will be discussed next. Interestingly, the requirement of a unique series capacitor in an NCFET puts a fundamental limit on the maximum voltage amplification and that directly translates to the lowest possible S. These considerations limit the lowest possible sub-threshold swing to 27mV/decade in NEMFET. I will then discuss the generality of the arguments using Ferroelectric-FET. I will finally conclude by introducing the concept of a new class of switches named “Landau switches” having an inherently unstable gate insulator characterized by two well energy landscape.
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