Positive-to-negative subthreshold swing of a MOSFET tuned by the ferroelectric switching dynamics of BiFeO3

Chuanchuan Liu,Haoyang Sun,Yuewei Yin,Yuchen Wang,Zhen Luo,He Wang,Chao Ma,Xiaoguang Li

doi:10.1038/s41427-021-00345-5

Abstract

Ferroelectricity can reduce the subthreshold swing (SS) of metal-oxide-semiconductor field-effect transistors (MOSFETs) to below the room-temperature Boltzmann limit of ~60 mV/dec and provides an important strategy to achieve a steeper SS. Surprisingly, by carefully tuning the polarization switching dynamics of BiFeO3 ferroelectric capacitors the SS of a commercial power MOSFET can even be tuned to zero or a negative value, i.e., the drain current increases with a constant or decreasing gate voltage. In particular, in addition to the positive SS of lower than 60 mV/dec, the zero and negative SS can be established with a drain current spanning for over seven orders of magnitude. These intriguing phenomena are explained by the ferroelectric polarization switching dynamics, which change the charge redistributions and accordingly affect the voltage drops across the ferroelectric capacitor and MOSFET. This study provides deep insights into understanding the steep SS in ferroelectric MOSFETs, which could be promising for designing advanced MOSFETs with an ultralow and tunable SS.

Highlights

Ferroelectric materials show high potential for use in various applications, such as nonvolatile memories[1,2,3,4], photoelectric detectors[5,6,7,8], and neuromorphic computing[9,10]
It was reported that ferroelectricity can be used to reduce the subthreshold swing (SS) of metal-oxidesemiconductor field-effect transistors (MOSFETs) to below 60 mV/dec at room temperature and break the “Boltzmann Tyranny”, which may be beneficial to lowering power consumption[11,12,13,14]
The atomic force microscopy (AFM) results show that the material has a smooth surface with a small root mean square roughness of ~0.67 nm

Summary

Introduction

Ferroelectric materials show high potential for use in various applications, such as nonvolatile memories[1,2,3,4], photoelectric detectors[5,6,7,8], and neuromorphic computing[9,10]. It was reported that ferroelectricity can be used to reduce the subthreshold swing (SS) of metal-oxidesemiconductor field-effect transistors (MOSFETs) to below 60 mV/dec at room temperature and break the “Boltzmann Tyranny”, which may be beneficial to lowering power consumption[11,12,13,14]. One is based on the concept of a negative capacitance effect, i.e., the ferroelectric material can serve as a negative capacitor[17,18]. This is related to the double-well landscape of the free energy in a ferroelectric material, which inevitably leads to a region of negative capacitance when ferroelectricity switches from one polarization state to the other[19,20,21,22]. In addition to the steep SS, many distinctive phenomena, including a voltage drop across the ferroelectric capacitor with charges flowing, an “S”-shaped relation between polarization (P) and voltage (V), and a stepup conversion of internal voltage, have been reported by using various ferroelectric materials, and these effects

Methods

Results

Conclusion