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

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. In ferroelectric MOSFETs, the reduced subthreshold swing (SS) below Boltzmann limit has attracted great attention due to its potential in decreasing power consumption. Here, through tuning the ferroelectric switching dynamics of BiFeO₃ ferroelectric capacitor, the SS of a commercial MOSFET connected with the ferroelectric capacitor is significantly reduced to be zero over seven decades of the drain current. Interestingly, the SS can even be further tuned to be negative, i.e., the drain current increases with decreasing gate voltage. The intriguing strategy to control SS from positive to negative is promising for designing advanced MOSFETs with ultralow and tunable SS. Transistors: A swing in the right direction Ferroelectric materials offer a way to control transistor operation. Metal-oxide-semiconductor field-effect transistors (MOSFETs) use an electric field, created by applying a voltage to one terminal, called the gate, to control the electrical current between two other terminals, the source and the drain. An important operating parameter for MOSFETs is the subthreshold swing, which relates the change in gate voltage to the change in current flow. A lower subthreshold swing means lower power consumption. Xiaoguang Li and Yuewei Yin and their colleagues from the University of Science and Technology of China, Hefei, showed that adding ferroelectric BiFeO₃ to a commercial MOSFET and tuning its dynamics reduced the swing to zero and even made it negative, meaning the drain current increases with decreasing gate voltage. This unexpected result could be promising for designing advanced low-power consumption MOSFETs. [ABSTRACT FROM AUTHOR]