Fringe-Field Switching with a Negative Dielectric Anisotropy Liquid Crystal

Abstract

We report a high performance negative dielectric anisotropy liquid crystal for fringing field switching (n-FFS) display. We compare the electro-optic characteristics of FFS cells using positive and negative LCs. With comparable driving voltage and response time, the n-FFS cell has advantages in higher transmittance, single gamma curve, less cell gap sensitivity and slightly wider viewing angle. LC director deformation distribution is analyzed to explain these performance differences.Index Terms-Fringe field switching, liquid crystal displays (LCD).

High Performance Negative Dielectric Anisotropy Liquid Crystals for Display Applications

“…Under single elastic constant and small angle approximations, Ericksen-Leslie equation can be simplified as [23]: (1) where (Z,t) is the deformed angle of the LC directors, E is the applied electric field, γ 1 is the rotational viscosity of the LC, and K ii is the elastic constant corresponding to the LC alignment. For a negative Δε LC in IPS or FFS cell, the electric field mainly induces twist deformation [14,16]. Thus, K ii can be approximated by K 22 (twist elastic constant) [24].…”

“…To overcome these problems, recently we reported a n-FFS mode using a high performance negative Δε LC [16]. The n-FFS mode has been investigated previously [13,15,17], but mainly by simulations.…”

“…Thus, the required Δn is around 0.12. Previously we reported a high performance n-FFS with UCF-N1 [16], consisting of 60 wt % MLC-6882, 18% lateral difluoro akoxy-biphenyl, 17% lateral difluoro akoxy-cyclohexane-biphenyl [9] and 5% bicyclohexane compounds. The chemical structures are shown in Figure 1.…”

“…A negative Δε LC can be used in homogeneous alignment or vertical alignment (VA), depending on the electric field direction. In an in-plane switching (IPS) cell [13,14] or fringe-field switching (FFS) cell [15][16][17], the electric field is mainly in the lateral direction, while in a VA cell [18,19] or multi-domain VA (MVA) cell [20,21], the field is basically in the longitudinal direction. For mobile displays, IPS or FFS is a favored choice because they are more robust to external pressure, which is crucial for touch panels.…”

“…As a result, FFS mode enables a larger aperture ratio, which translates into higher optical efficiency. Recently, it is found that the FFS mode with a negative Δε LC (n-FFS) exhibits several advantages over its p-FFS (FFS mode using a positive Δε LC) counterpart in higher transmittance, single gamma curve, cell gap insensitivity, and weaker flexoelectric effect [16]. A single-domain VA cell has been employed in liquid-crystal-on-silicon (LCOS) for data projectors because of its unprecedented contrast ratio [22], while MVA is a common choice for wide-view LCD TVs.…”