Device simulation of negative-capacitance field-effect transistors with a uniaxial ferroelectric gate insulator

We model the behavior of uniaxial ferroelectrics and simulate planar negative-capacitance (NC) field-effect transistors (FETs) having a gate insulating film made of a uniaxial ferroelectric. The behavior of such NC FETs strongly depends on the direction of the ferroelectric polarization axis. When the direction is away from being parallel to the ferroelectric film to some extent, the ferroelectric polarization becomes larger than the paraelectric polarization and the ferroelectric film begins to act as a negative capacitor. The NC FETs can then be switched on and off more steeply than conventional metal-oxide-semiconductor FETs. This NC effect is maximized at that moment and becomes weaker as the direction approaches perpendicular to the ferroelectric film.