Electrooptic and viewing angle characteristics of a display device employing a discotic nematic liquid crystal

Abstract

Recently we developed a novel liquid crystal display device employing discotic nematic material. This device exhibits the following improvements over a conventional twisted nematic (TN) display device using a calamitic nematic material. The device (i) is simple to fabricate and (ii) has excellent viewing angle characteristics showing a wide and symmetric viewing angle profile, (iii) has much less difference in the pixel capacitance between the ON and OFF states resulting in reduced cross talk problem. However the response time of the device is slower than conventional TN devices. An obvious solution to this problem is to reduce the viscosity of the material. To achieve this we have doped, in small concentrations, a long chain alkane compound to the parent room-temperature discotic nematic material. Systematic studies show that both the switch ON and switch OFF response times show a significant decrease, i.e., the device switches faster, in the case of the mixtures. It should be mentioned that wide and symmetric viewing angle characteristics remain unaffected by the addition of the dopant material. However both the switch ON and switch OFF response times are still an order of magnitude slower compared to that of conventional TN devices. Considering the fact that these response times are not very different from those for the STN displays, the achievement of symmetric and wide viewing angle characteristics with a simple fabrication process makes this device quite interesting. To make them attractive enough to be considered for commercial applications new materials with faster response have to be developed. Efforts in this direction are underway in our laboratory.