Effect of Ferroelectric Thickness Variation in Undoped HfO₂-Based Negative-Capacitance Field-Effect Transistor

Negative-capacitance field-effect transistors (NCFETs) are emerging devices which have shown huge potential to replace classical field-effect transistors because of their steep switching characteristic enabled by a ferroelectric stack. The negative capacitance in ferroelectrics results in a voltage step-up action which curtails the subthreshold swing below 60 mV/dec. The ferroelectric thickness is a key design parameter which governs the operation of such devices and resulting circuits. We examine herein for the first time the effect of the ferroelectric thickness of undoped HfO₂-based negative-capacitance field-effect transistors on the device and circuit performance. Increasing the ferroelectric thickness yields higher gain but with increased probability of hysteresis. Also, depending upon the properties of the underlying transistor, at low overdrive voltage, increase in the ferroelectric thickness beyond a certain value may introduce a loss of saturation (negative differential resistance) in the drain characteristic of the NCFET. Also, we design an NCFET-based resistive load inverter and study the effect of thickness variation on the circuit performance. The results of the analysis show that increasing the thickness within a permissible limit increases the noise margin and reduces the power dissipation of the designed circuit.