The changes in threshold voltage and DIBL were investigated for changes in remanent polarization P_r and coercive field E_c, which determine the characteristics of the P-E hysteresis curve of ferroelectric in NCFET (negative capacitance FET). The threshold voltage and DIBL (drain-induced barrier lowering) were observed for a junctionless double gate MOSFET using a gate oxide structure of MFMIS (metal-ferroelectric-metal-insulator-semiconductor). To obtain the threshold voltage, seriestype potential distribution and second derivative method were used. As a result, it can be seen that the threshold voltage increases when P_r decreases and E_c increases, and the threshold voltage is also maintained constant when the P_r/E_c is constant. However, as the drain voltage increases, the threshold voltage changes significantly according to P_r/E_c, so the DIBL greatly changes for P_r/E_c. In other words, when P_r/E_c=15 pF/cm, DIBL showed a negative value regardless of the channel length under the conditions of ferroelectric thickness of 10 nm and SiO₂ thickness of 1 nm. The DIBL value was in the negative or positive range for the channel length when the P_r/E_c is 25 pF/cm or more under the same conditions, so the condition of DIBL=0 could be obtained. As such, the optimal condition to reduce short channel effects can be obtained since the threshold voltage and DIBL can be adjusted according to the device dimension of NCFET and the P_r and E_c of ferroelectric.

Ferroelectric Pb(Zr_0.52Ti_0.48)O₃ (PZT) films were deposited on SrTiO₃(100) substrate by using conductive SrRuO₃ films as underlayer and their structural and ferroelectric properties were investigated. PZT films were grown in (00l) orientation on well lattice-matched pseudo-cubic SrRuO₃ films. Thickness dependence of ferroelectric and electrical properties of PZT films was investigated. PZT film with 400 nm thickness showed a remanent polarization (P_r) of 29.0 μC/cm² and coercive field (E_c) of 83 kV/cm, and P_r decreased and E_c increased with thickness reduction. The dielectric constant for PZT films showed gradual decrease with thickness reduction. Breakdown field of PZT films did not show the thickness dependence and displayed as high value as 1 MV/cm.