Abstract: This study presents a comprehensive analysis of the performance of negative capacitance field-effect transistors (NCFETs) based on the metal-ferroelectric-insulator-semiconductor (MFIS) structure, utilizing a Hf_xZr_1−xO₂ (HZO, 0.5≤x≤0.9) thin film. The findings indicate that the NCFETs achieve subthreshold swing (S_S) values consistently below 60 mV/decade, surpassing the theoretical limit for conventional Si-based field-effect transistors (FETs). The ferroelectric HZO composition significantly influences the longitudinal electric field, electron concentration, and hole concentration within the channel, thereby directly affecting the S_S and saturation current. Notably, the MFIS NCFET incorporating an Hf_0.5Zr_0.5O₂ ferroelectric layer exhibited the lowest S_S. By modifying the dielectric material and channel length, variations in the trends of S_S and saturation current were observed. The ZrO₂ dielectric layer, characterized by the highest dielectric constant, demonstrated the lowest S_S of 47.49 mV/decade. Furthermore, the S_S decreased as the channel length increased from 50 nm to 1000 nm. This research provides critical insights into the potential of low-power NCFETs and negative capacitance capacitors.