Investigation of Sub-60 mV/decade switching negative capacitance FET with HfxZr1-xO2/Dielectric thin films

Abstract

Negative capacitance (NC) in ferroelectric HfxZr1-xO2 (HZO) based thin film holds the promise for ultralow-power transistor with subthreshold swing (SS) lower than the Boltzmann limit of 60 mV/decade. Since the negative capacitance region of ferroelectricity is unstable, it is necessary to connect in series with high-k dielectrics to stabilize and maximize the negative capacitance effect. Therefore, the controllability of the ferroelectric is veiled in that negative capacitance field-effect transistor (NCFET) exhibits diverse device characteristics according to some extrinsic factors such as a thickness ratio of ferroelectric/dielectric (FE/DE) heterostructure and gate oxide materials. Here we suggest that optimizing the materials and thickness combinations of FE/DE stack is a key factor to stabilizing and improving NC performance. Thus, we investigated various stack configurations experimentally and analytically to determine the most advantageous properties. The intrinsic ferroelectric contribution to NC was characterized by Landau-Khalatnikov (L-K) parameters, which phenomenologically determine the polarization curve, through model study. These parameters could correlate the ferroelectricity implicitly delivered in polarization to target properties (e.g., subthreshold swing and hysteresis) in the NCFET model. This methodology is meaningful in that it enables rapidly predicting the characteristics of the device with the parameter and this can provide an insight only with the polarization curve.