Transient Negative Capacitance in Ferroelectric Nematic Liquid Crystals

Negative capacitance (NC) is a novel hysteretic electric field-induced behavior of the magnitude and sign of a solid-state ferroelectric polarization, fixed in direction along a particular crystallographic axis, as it is forced between Landau-like polarization free energy minima. In this work, we showed that negative capacitance can also appear in the recently discovered fluid ferroelectric nematic liquid crystal (FNLC) cells. In this case, the negative capacitance is due to the electric field-induced reorientation of the polarization.  In the FNLC case, the elements being charged are interfacial LC/electrode capacitors, one side of which receives only free charge and the other side of which receives only polarization charge, the latter occurring only if the FNLC polarization rotates appropriately.  In response to applied voltage transients, viscosity retards polarization orientation, leading to apparent negative capacitance.  The properties that make LCs useful in display applications (ambient temperature, low voltage, facile processability, vetting as an industrial and consumer technology) make FNLCs attractive for applications where negative capacitance is desirable in flexible organic electrochemical transistor (OECT) devices.