Impact of physical parameters of ferroelectric layer on the performance of Negative Capacitance (NC) MOSFETs is experimentally studied in this paper. Electrical behaviors of PZT-based and Si:HfO2-based NC-FETs are investigated and discussed. In a PZT-based p-type NC-FET, a sub-thermal swing down to 20mV/dec is achieved due to the remarkable voltage gain of NC, reaching a maximum value of 10V/V. Nevertheless, the performance improvements with Si:HfO2 NC booster are significantly lower than PZT due to the coexistence of different phases and also high leakage current which can enormously reduce the enhancement by NC.