In-Plane Switching IPS LCDs

The homogeneously aligned nematic liquid crystal mixture does not rotate the plane polarised light generated by the first polariser. Therefore, the light is absorbed by the analyser. Very efficient absorption of light takes place. 

The switch-on time, ton ittd the switch-off time, toff are both proportional to the square of the cell gap, d, as for the TN-LCD,  

Nematic liquid crystals of negative dielectric anisotropy with a low rotational viscosity and a high value of the twist elastic constant k22 are required, see Equations 38-40. Furthermore, a high value for the resistivity and short 

Billard, J. Jacques, M. Leclerq and J. Malthete, Comptes Rendus. Acad. Sci. C Paris, 1971,273,291. 

Blinov, in Handbook of Liquid Crystal Research , Eds. P. J. Codings and J. S. Patel, Oxford University Press, Oxford, 1997, p. 125. 

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Defect-free polymer-stabilized V-shaped switching (PSV)-FLCD is realized by using a smooth PI alignment film [32], for example, the highly smooth PI (RN-1199) of Nissan Chemical Industries that has been widely used for in-plane switching (IPS)-LCD and fringe field switching (FFS)-LCD. 

Thus, the photoalignment of the azo-dye layer on the bottom substrate was perpendicular to that of the upper one, and LC directors on the top and bottom substrates also became perpendicular. The method provides a simple new way of manufacturing photoaligned TN-LCDs. In-plane switching (IPS-LCD) may benefit from the application of photoaUgnment technology for twisted LC config-mations [21]. 

Shortly after the commercial introduction of the first active matrix LCD in 1989 it became clear that cyano-based liquid crystals of the second generation (e.g. 3-6) cannot be used for this application. Even after extensive purification, the voltage holding ratio of this type of material is too low. The stringent reliability requirements could, on the other hand, be easily fulfilled with super-fluorinated materials (SFM), such as those depicted in Scheme 4.11. For this reason - with in-plane switching (IPS) technology as the only exception - only SFM are currently used in AM-LCD. 

In LCDs various LC modes of operation are applied like twisted nematic (TN) [5], super twisted nematic (STN)[6], vertically aligned nematic (VAN) [7,8], optically compensated birefringence (OCB) [9] and in plane switching (IPS) [10-12]. The LC mode used depends on the demands of a specific application, like the viewing angle, power consumption and manufacturing cost. 

Positive Ae LCs have been used in twisted nematic (TN) [31] and in-plane switching (IPS) [32,33] displays, although IPS can also use negative Ae LCs. For thin-fUm-transistor (TFT) based displays, the employed LC material must possess a high resistivity [34]. Fluorinated compounds exhibit a high resistivity and are the natural candidates for TFT LCD applications [35,36]. A typical fluorinated LC structure is shown below ... 

The principle of the IPS (In-Plane Switching) mode is shown in Fig. 4.4.1. In typical LCDs, both substrates have electrodes and the direction of the electric field is perpendicular to the substrates. In the IPS mode, however, only one substrate has electrodes and the electric field runs parallel to the substrates. The molecular long axes of the liquid crystal molecules are thus parallel to the substrates whether an electric field is or is not applied. In other words, the switching of the liquid crystal molecules by the electric field remains within a single plane. 

In-plane switching method, (a) The schematics of the switching principle (b) A 46-inch TFT-IPS-LCD from Samsung Electronics Co., Ltd. 

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