Physical Insights on Negative Capacitance Transistors in Nonhysteresis and Hysteresis Regimes: MFMIS Versus MFIS Structures

We present a comprehensive comparison of the two different types of ferroelectric negative capacitance FET (NCFET) structures: metal-ferroelectric-metal-insulator-semiconductor (MFMIS) and metal-ferroelectric-insulator-semiconductor (MFIS). A new segmentation approach is proposed to simulate MFIS NCFET, which correctly takes care of the nonuniformity in potential and horizontal electric field at the ferroelectric-oxide interface. We show that MFMIS NCFET provides a higher ON-current than MFIS NCFET except for the ferroelectrics with very low remnant polarization (Pr) in the high operating voltage regime. We find that this behavior is caused by a reduction or enhancement of the longitudinal electric field in the channel of MFIS structure depending upon Pr of the ferroelectric and the operating voltage. Moreover, there exists an optimum Pr which provides maximum ON-current for both the devices. We also find that MFIS NCFET is more prone to hysteresis and starts showing a hysteretic behavior at a lower ferroelectric thickness compared with MFMIS NCFET.