Photocontrollable Resistivity Change in Nanoparticle-Doped Liquid Crystal Alignment Layer: Voltage Holding and Discharging Properties of Fringe-Field Switching Liquid Crystal Modes

Abstract

In liquid crystal (LC) displays, deriving an optimum resistance level of an LC alignment polyimide (PI) layer is important because of the trade-off between the voltage holding and surface-discharging properties. In particular, to apply a power-saving low-frequency operation scheme to fringe-field switching (FFS) LC modes with negative dielectric LC (n-LC), delicate material engineering is required to avoid surface-charge-dependent image flickering and sticking problems, which severely degrade with lowering operation frequency. Therefore, this paper proposes a photocontrolled variable-resistivity PI layer in order to systematically investigate the voltage holding and discharging properties of the FFS n-LC modes, according to the PI resistivity (ρ) levels. By doping fullerene into the high-ρ PI as the photoexcited charge-generating nanoparticles, the ρ levels of the PI were continuously controllable with a wide tunable range (0.95 × 1015 Ω∙cm to 5.36 × 1013 Ω∙cm) through Ar laser irradiation under the same LC and LC alignment conditions. The frequency-dependent voltage holding and discharge behaviors were analyzed with photocontrolled ρ variation. Thus, the proposed experimental scheme is a feasible approach in PI engineering for a power-saving low-frequency FFS n-LC mode without the image flickering and image sticking issues.

Preparation and characterization of photo‐decomposable ester‐containing semi‐alicyclic polyimide alignment layers for potential applications in in‐plane switching thin‐film transistor liquid crystal display devices

“…Currently, the most widely used alignment layers for TFT-LCD are semi-aromatic polyimides (PIs) due to the excellent combined properties, including good alignment effects to LC molecules, chemical inertness to LC, good thermal and environment stability, good optical and dielectric properties, and so on. [8][9][10][11] Especially, the semi-alicyclic PIs based on alicyclic dianhydrides and aromatic diamines are often used as the alignment layers for LC molecules, which are mainly due to the prohibited charge transfer (CT) interactions, improved optical transmittance and acceptable molecular weights for the derived PIs.…”