Polarization-stiffened ferroelectric liquid crystals: A thickness-independent bistable switching voltage with a lower limit of about 2 V and the transition to thresholdless switching

Abstract

Typical ferroelectric Sm-C(*) liquid crystal (FLC) cells exhibit a voltage threshold for switching from one stable state to another despite the FLC's response being inherently continuous and thresholdless (free rotation of the director around the tilt cone). This switching threshold is due to FLC-surface interactions and to the chevron smectic structure commonly formed in cells. It is shown here that the FLC electrostatic energy contribution ∼P(S)(2) responsible for thresholdless switching of high-P(S) FLCs also plays a key role in the bistable switching of lower-P(S) FLCs. Among the consequences are that it can be difficult to lower a cell's threshold below V(TB)∼3.4(B/ɛ(F))(1/2) (B and ɛ(F) are the FLC's elastic and dielectric constants), that a cell's threshold becomes independent of cell thickness once it substantially exceeds the characteristic length ξ(P)=(ɛ(F)B)(1/2)/P(S), and that there are conditions under which alignment layer capacitance can decrease rather than increase the threshold (i.e., transition to thresholdless switching). A model that predicts and explains these behaviors is presented along with threshold measurements of representative FLC cells.

Quenching of Spin Polarization Switching in Organic Multiferroic Tunnel Junctions by Ferroelectric “Ailing-Channel” in Organic Barrier

“…In addition, by extrapolating V C versus t with linear fitting, one can see that a critical V C of 0.2 V is required even when the P(VDF-TrFE) thickness meets zero. This could reflect the polarizationstiffened effect 30 due to the FM/FE-Org interface, where a supplementary energy barrier for ferroelectric polarization switching is created due to the hybridization of the interfacial density of states. 3 To check the homogeneity in ferroelectric polarization switching, the PFM phase maps were recorded on the thin and medium P(VDF-TrFE) surfaces (Figure 4c and d, respectively).…”

Biaxial surface potential effects in polymer-stabilized ferroelectric liquid crystal cells

“…So, we consider the torques N φ =−∂f s / ∂φ and N δ = −∂f s / ∂δ. Equating N φ and N δ to its maxima [13], we obtained the system of coupled equations. Substituting the typical model parameters (Table 1) into the system, it can be numerically solved.…”