Deep insight into the voltage amplification effect from ferroelectric negative capacitance

Dear editor, Power dissipation has become one of the most serious problems for nano-electronics. For conventional transistors, the operation voltage cannot be continuously reduced due to the fundamental limitation of subthreshold swing (SS) (60 mV/decade at room temperature) [1, 2]. The voltage amplification (VA) induced by the negative capacitance (NC) effect of ferroelectric (FE) material provides a possible approach for FE-based transistors to achieve sub-60 SS characteristics [3]. However, the physical origin of NC effect in FE-FET are still unclear and controversial. The traditional quasi-static NC theory considers that the NC can be derived from the negative curvature of energycharge relationship of ferroelectric, which is unstable for standalone FE capacitor and can be stabilized by connecting an appropriate positive capacitor to reach a capacitance matching condition for VA [3]. Different with quasi-static NC theory, it has been recently presented that the NC effect can be modeled as a transient phenomenon caused by the FE polarization switching [4, 5]. In [5], we have demonstrated the first direct experimental observation of NC phenomenon in a standalone FE capacitor, verifying its dynamic behavior. It is shown that the time-induced polarization is the origin of NC phenomenon. Nevertheless, further study on the optimization of gate stack in FEFETs for achieving VA is still needed.