Prospects of Hysteresis-Free Abrupt Switching (0 mV/decade) in Landau Switches

The sub-threshold swing (S) defines the sharpness of ON-OFF switching of a field effect transistor (FET), with S=0 corresponding to abrupt switching characteristics. While thermodynamics dictate S ≥ 60 mV/decade for classical FETs, a new class of switches which we call “Landau switches” e.g., suspended gate FET (SG-FET) and ferroelectric FET (FE-FET) use inherently unstable (negative capacitance) gate insulators to achieve abrupt switching. Unfortunately, S=0 switching in Landau switches is always achieved at the expense of an intrinsic hysteresis, making them unsuitable for low-power applications. The fundamental question therefore is: under what conditions, hysteresis-free abrupt switching can be achieved in a Landau switch? In this paper, we first provide an intuitive classification of all semiconductor FETs in terms of their energy landscapes and identify a two-well energy landscape as the characteristic feature of all Landau switches. We then use the SG-FET as an illustrative example to conclude that a flat energy landscape is essential for hysteresis-free abrupt switching. In contrast, a hysteresis-free smooth switching (S ≤ 60 mV/decade) is less restrictive, and is obtained by stabilizing the unstable gate insulator in its negative capacitance regime. Our conclusions have broad implications for the analysis and design of ultralow power sub-60 mV/decade switches.