Fig. 1. Roadmap of subthreshold swing (SS) proposed by IRDS^[8].

Fig. 2. The schematic diagram of the classification of dielectrics.

Fig. 3. Ferroelectric hysteresis loop^[41].

Fig. 4. Chemical and crystal structures of the metal-free A(NH₄) X₃ family^[56]: (a) Chemical structures of constituents of the metal-free 3D perovskite ferroelectrics; (b) the packing diagram of MDABCO–NH₄I₃ in the ferroelectric phase at 293 K. The oval to the right contains the space-fill diagram of the organic cation, showing the cationic geometry to be close to a ball; (c) the packing diagram of MDABCO–NH₄I₃ in the paraelectric phase at 463 K.

Fig. 5. The transfer characteristic curve of field effect transistors.

Fig. 6. The schematic diagram of a standard field effect transistors.structure and its eauivalent circuit of capacitance^[73].

Fig. 7. Device structure diagram: (a) Traditional MOSFETs; (b) MFIS; (c) MFMIS.

Fig. 8. (a) Conventional unit cell of an FE perovskite (ABO₃)^[85]; (b) schematic of the dipole fields in the (200) plane^[85].

Fig. 9. The relationship between polarization P and electric field E of ferroelectrics: (a) P vs. E; (b) hysteresis diagram.

Fig. 10. (a) Q_FE vs. V_FE of ferroelectrics; (b) U_FE vs. Q_FE of ferroelectrics.

Fig. 11. Energy landscapes of C_FE, C_DE and their series combination^[90].

Fig. 12. Ferroelectric NC measured by small-signal measurement mode: (a) Equivalent circuit diagram^[91]; (b) schematic diagram of a LAO/BSTO superlattice stack^[90]; (c) capacitance dependence on voltage^[90].

Fig. 13. The schematic of a R-C_FE circuit for studying the transient NC in ferroelectrics^[99].

Fig. 14. The simulation results of transient NC^[99]: (a) Input voltage, output voltage, and free charge on a ferroelectric capacitor as functions of time; (b) polarization and free charge as functions of time; (c) charge density per unit time for free charge and polarization and the difference between them; (d) change in the voltage across a ferroelectric capacitor per unit time as a function of time.

Fig. 15. (a) The effect of the external resistance on transient NC in a R-C_FE circuit; (b)the effect of the viscosity coefficient on transient NC in a R-C_FE circuit^[99].

Fig. 16. The relationship between capacitive charge and voltage of the device: (a) Capacitance model; (b) ; (c) (d) Fe-NCFETs^[91]; (e) Fe-FETs^[91].

Fig. 17. Planar Silicon based HfAlO Fe-NCFETs^[116]: (a) HR TEM cross-section image; (b) polarization as a function of nitrogen content of TaN; (c) schematic band diagram of HfAlO before and after F-passivation; (d) SS as a function of V_DS after different treatments.

Fig. 18. Silicon based NC-FinFET^[123]: (a) TEM cross-sectional image of NC-FinFET with TiN internal gate, HfZrO FE film and TiN gate; (b) the gate amplification coefficient as a function of V_G for NC-FinFET; (c) SS as a function of V_G for conventional FinFET and NC-FinFET.

Fig. 19. (a) TEM cross-sectional image of silicon based NC-p-FinFET^[124]; (b) I_DS as a function of gate length^[124].

Fig. 20. Two-layer stacked silicon nanowire GAA Fe-NCFETs^[126] : (a) TEM cross-sectional image of the device; (b) HRTEM of a portion of the channel; (c) the GIXRD spectrum for the as-deposited HZO layer.

Fig. 21. Germanium based HZO NC-pFET^[129]: (a) Schematic diagram of the device with Ge channel; (b) schematic diagram of the device with Ge-Sn channel; (c) transfer characteristic curve of the device with Ge channel; (d) transfer characteristic curve of the device with Ge-Sn channel.

Fig. 22. Germanium nanowire NC-pFET^[135]: (a) The transfer characteristic curve at different sweep times for ±5 V sweep range; (b) hysteresis versus sweep time for ±5 V sweep range; (c) maximum drain current versus sweep time for different sweep ranges.

Fig. 23. In_0.53Ga_0.47As channel Fe-NCFETs: (a) Schematic diagram^[136] and (c) transfer characteristic curve of planar device^[136]; (b) schematic diagram^[137] and (d) transfer characteristic curve of Fin device^[137].

Fig. 24. Carbon nanotube Fe-NCFETs^[138]: (a) TEM cross-sectional image; (b) P_r vs. E; (c) the transfer characteristic curve; (d) I_GS as a function of V_GS.

Fig. 25. MoS₂ Fe-NCFETs^[145]: (a) Structure of the device; (b)transfer characteristic curve of V_G = ± 7 V; (c)transfer characteristic curve of V_G = ± 10 V.

Fig. 26. WSe₂ Fe-NCFETs^[140]: (a) Structure of MFIS device; (b) structure of MFMIS device; (c) transfer characteristic curve of MFIS device; (d) transfer characteristic curve of MFMIS device.

Fig. 27. Graphene-Hf_xAl_yO₂ transistor^[154]: (a) Hf_xAl_yo₂ films deposited on graphene/SiO₂ substrates; (b) relative dielectric constant of Hf_xAl_yO₂; (c) energy difference among three phases in Hf_xAl_yO₂ with different Al concentrations; (d) transfer characteristic curve.

Fig. 28. Black phosphorus Fe-NCFETs^[155]: (a) Structure of the device; (b) transfer characteristic curve; (c) SS in different I_d.

Fig. 29. SS versus Hysteresis of the reported Fe-NCFETs (2D^{[30,33,108,140,144,146-148,155]}, Si^{[25,116,118,119,121,123-126]}, GeSn^{[129,130,134,156]}, InGaAs^[136,137]).