Effect of Ferroelectric Damping on Dynamic Characteristics of Negative Capacitance Ferroelectric MOSFET

Static Landau theory has been widely used to confirm negative capacitance ferroelectric MOSFET (FeFET) as a low power switch with sub-60-mV/decade subthreshold swing. However, dynamic switching considering damping effect in ferroelectrics is rarely evaluated. Based on Landau-Khalatnikov theory, dynamic FeFET characteristics are obtained. For experimentally extracted Pb(Zr
_0.2
Ti
_0.8
)O
₃
(PZT) damping constant ξ
_FE
= 75 Ω · m, the amplified gate capacitance induced by negative capacitance occurs when frequency is below a few MHz for large ξ
_FE
. For transient simulation, I
_DS
exhibits a slow response to the rapid change of V
_G
so that the hysteretic I
_DS
-V
_G
curve is generated. Furthermore, inverter prediction with complementary FeFETs shows that the dynamic short circuit switching power is much higher than the static one. These results are attributed to the large PZT response time in comparison with the operation period. For a guidance on ferroelectric selection and improvement, a wide range of damping constants are used to predict the corresponding maximum operation frequency, within which the dynamic and static responses of FeFETs are the same. It indicates that the ferroelectrics with low damping constant are essential to utilize FeFET advantages in high-frequency circuit applications.