Differential voltage amplification from ferroelectric negative capacitance

Abstract

It is well known that one needs an external source of energy to provide voltage amplification. Because of this, conventional circuit elements such as resistors, inductors or capacitors cannot provide amplification all by themselves. Here, we demonstrate that a ferroelectric can cause a differential amplification without needing such an external energy source. As the ferroelectric switches from one polarization state to the other, a transfer of energy takes place from the ferroelectric to the dielectric, determined by the ratio of their capacitances, which, in turn, leads to the differential amplification. This amplification is very different in nature from conventional inductor-capacitor based circuits where an oscillatory amplification can be observed. The demonstration of differential voltage amplification from completely passive capacitor elements only, has fundamental ramifications for next generation electronics. Free Energy Charge C<0 a Time Source Voltage Ferroelectric Capacitor Voltage Amplification b FIG. 1: Voltage amplification due to ferroelectric negative capacitance: (a) Energy landscape of a ferroelectric capacitor. The capacitance, C, is negative in the region enclosed by the dashed box. (b) The experimental setup.

Modeling of Negative Capacitance in Ferroelectric Thin Films

“…Since the electric field inside the ferroelectric layer of the MIMFM structure is determined by the apparent polarization irrespective of the spatial configuration of the multidomain state, there is theoretically no difference between the NC stabilization method for the single domain state and the multidomain state except that the latter has a L crit limit. Experimentally, while Khan et al recently found a differential voltage amplification by connecting DE capacitors to an epitaxial PZT FE thin film capacitor via a metal wire externally, it was a transient effect with a hysteresis . The experiment showed that the DE layer plays a role nothing but a linear load line for a typical square‐like P − V hysteresis of the ferroelectrics (except that it has a transient V ‐drop at the switching in each direction) in the MIMFM structure.…”

Ferroelectric negative capacitance

“…The question remains whether the negative curvature of the free energy has to be involved in this process 37,39,[46][47][48] . A variant of this direct method to moni tor transient NC is to replace the series resistor with an external series capacitance 105 ; the capacitor then directly controls the charge on the ferroelectric, as originally proposed by Salahuddin and Datta 10 .…”

On the Physical Mechanism of Transient Negative Capacitance Effect in Deep Subthreshold Region

“…This means that finite polarization switching delay is responsible for TNC [17]. In fact, TNC was experimentally demonstrated in an FE-DE series capacitor in [27].…”