Analytical model of subthreshold swing in junctionless gate-all-around (GAA) FET with ferroelectric

Abstract

An analytical SS model is presented to observe the subthreshold swing (SS) of a junctionless gate-all-around (GAA) FET with ferroelectric in this paper. For the gate structure, a multilayer structure of metal-ferroelectric-metal-insulator-semiconductor (MFMIS) was used, and the SS was calculated in $15 \leqslant {P_r} \leqslant 30\,\mu C/c{m^2}$ and $0.8 \leqslant {E_c} \leqslant 1.5\,MV/cm$, which are the ranges of remanent polarization and coercive field suggested in various experiments in the case of HZO as the ferroelectric material. It was found that the SSs from the presented analytical SS model agree well with those derived from the relationship between drain current and gate voltage using a 2D potential distribution in the range of device parameters used for simulation. As a result of analyzing the SS of the junctionless GAA FET with ferroelectric using the analytical SS model presented in this paper, the SS decreased because the voltage across the inner gate decreased when the ferroelectric thickness increased. It was observed that the condition of SS < 60 mV/dec was sufficiently obtained according to changes in device parameters such as channel length, channel radius and ferroelectric thickness, and that the SS maintained a constant value according to the ratio of remanent polarization and coercive field P_r/E_c. As P_r/E_c increases, the SS increases as the ferroelectric capacitance increases. As the channel length becomes smaller, the change in SS according to P_r/E_c is more severe.