Masanobu Mizusaki

Generation mechanism of residual direct current voltage in a liquid crystal display and its evaluation parameters related to liquid crystal and alignment layer materials

The presence of ionic charges in a liquid crystal layer causes the generation of residual direct current (dc) voltage (Vrdc) in a liquid crystal cell. Vrdc is one of the most important factors governing the image quality of liquid crystal displays, because the existence of Vrdc causes the image sticking phenomenon. We studied the generation mechanism of Vrdc based on a model of the adsorption and desorption of the ionic charges at the interface between the liquid crystal and alignment layer. In this paper, we propose three evaluation parameters, (i) saturated residual dc voltage, (ii) time to reach its saturation state, and (iii) relaxation time during the open circuit state after applying the external dc voltage, for effective evaluation of liquid crystal and alignment layer materials from the viewpoint of the improvement of the image sticking.

Behavior of ion affecting image sticking on liquid crystal displays under application of direct current voltage

Image sticking can be observed in some cases and it degrades the image quality of liquid crystal (LC) display. The image sticking is considered to be induced by generation of residual direct current voltage (Vrdc), which would be caused by the presence of ion in a LC cell. We clarified the generation mechanism of Vrdc based on a model of adsorption and desorption of the ion to and from the surface of an alignment layer at various temperatures. The experimental results indicate that these processes can be explained by the Boltzmann distribution. The analysis based on Arrehnius plots shows that the ion adsorbs to the surface of the alignment layer with weak binding such as van der Waals interaction or hydrogen bonding. This finding is effective for development of high image quality LC displays.

Kinetic analysis of image sticking with adsorption and desorption of ions to a surface of an alignment layer

Generation of residual direct current (DC) voltage (VrDC) induces a serious image sticking of liquid crystal (LC) displays. VrDC is generated with the ions in a LC layer adsorbing to a surface of an alignment layer under application of DC offset voltage. We clarified the adsorption and desorption of the ions to and from the surface of the alignment layer with a kinetic model proposed by us. The analysis with using the kinetic model made clear that the processes of the adsorption and desorption occur due to the thermal fluctuation followed by the Boltzmann distribution. The ions adsorb to the surface of the alignment layer by a weak binding, such as the van der Waals interaction.

P‐227L: Late‐News Poster: The Mechanism of Image Sticking on LCD and its Evaluation Parameters Related to LC and Alignment Materials

Residual DC voltage is one of the most important items which govern the image quality of LCD, because the existence of it causes image sticking phenomenon. However, we do not have established evaluation parameters. The generation mechanism of the residual DC voltage was analyzed based on a model of adsorption and desorption of electric charges, ions, at the interface between LC phase and alignment layer. New parameters are proposed for unified evaluation of LC and alignment materials.

Temperature dependence of residual DC voltage and its evaluation parameter related to liquid-crystal and alignment-layer materials

— The temperature dependence of residual DC voltage was studied based on the adsorption and desorption of ions in the liquid-crystal (LC) layer to and from the interface between the LC and alignment layers during the application of an external DC offset voltage. The relaxation process of the adsorbed ions during the open-circuit state was also studied after applying the DC offset voltage. Those processes were found to follow the Arrhenius rule, and a new evaluation parameter related to the temperature is proposed for the design of the LC and alignment-layer materials.