Advantageous voltage-holding ratio characteristics induced by in-plane electric fields, and the optimization concept of liquid crystals for an in-plane switching electro-optical effect

Abstract

In-plane switching (IPS) of liquid crystals showed advantageous voltage-holding ratio (VHR) characteristics so that liquid crystals with low resistivity could provide higher VHRs compared with the twisted nematic effect. This experimental result was obtained when electric fields were applied approximately parallel to the substrate plane using the IPS electro-optical effect. We found that the in-plane electric field generates supplementary capacities which support retention of an externally applied voltage over the liquid crystal layer during non-selected periods of the active matrix driving scheme, because the liquid crystal layer can be connected with an insulating layer, an orientation layer and even a substrate in parallel. Based on these advantageous VHR characteristics, liquid crystal materials suitable for the IPS effect were appropriately optimized. We propose evaluation parameters, derived from the physical switching principles of the liquid crystals, to obtain lower driving voltage and faster response speeds. These parameters are effective in optimizing the physical properties of liquid crystals without variation of the cell gap. We use the proposed evaluation parameters and the advantageous VHR characteristics to demonstrate the optimization approach and we suggest a novel possible use of liquid crystal materials with low resistivity which cannot be implemented conventionally. Finally, we prove that liquid crystals with low resistivity generate the Ir internal potential by the drift of ionic species.