Tesis doctoral de Beatriz Cerrolaza Martínez
This thesis is centered on the dynamic characterization and the electro-optics of vertically aligned nematic liquid crystal (vans) devices. A liquid crystal cell is a sandwich consisting of two parallel glass substrates carrying a thin transparent ito (indium-tin-oxide) electrode on their inner surfaces with the liquid crystal in the middle. The first part of this thesis will describe the most important parameters describing a liquid crystal display. This basis is necessary for the understanding of later chapters where models of the liquid crystal display will be discussed and developed. The second chapter includes a description of the van cell materials used and the manufacturing protocols that have been followed as well as the characterization equipment and routines that have been employed. finally the novelties derived from this thesis, two methods for the characterization of van materials, are presented. the van liquid crystal molecules are aligned within the cell with a certain angle, the pretilt, with respect to the substrate normal. This angle determines the electrooptical characteristics of the resulting liquid crystal display. Especially the response time (rt) and the contrast ratio (cr) are directly related to the pretilt angle. The larger the pretilt angle is, the faster the cell responds, but the lower the contrast ratio is. Thus a compromise between response time and contrast ratio must always be made in accordance with the final application of the display. A novelty originating from this work is the employment of two different pretilt angles on the two substrates, generating an asymmetric cell. An asymmetric cell may allow for the optimization of the response time without sacrificing the contrast ratio. A series of transmissive cells has been manufactured and characterized, with very promising results. the importance of the pretilt angle, has made it necessary to develop new accurate measurement techniques. A method for characterizing pretilt angle in transmissive cells has been implemented, and an entirely new method for measuring pretilt in reflective cells has been developed, implemented and validated using experimental data. the pretilt angle affects the response time of the liquid crystal devices, and hence the gray-to-gray (g2g) transition times which in turn determine the final display behavior when showing motion pictures. The blur caused by the finite response time of the display is characterized by the motion picture response time (mprt) parameter. An entirely new method predicting the mprt, based on single pixel gray to gray transition measurements, has been developed.
Datos académicos de la tesis doctoral «Electrooptics and dynamics of vertically aligned liquid crystals«
- Título de la tesis: Electrooptics and dynamics of vertically aligned liquid crystals
- Autor: Beatriz Cerrolaza Martínez
- Universidad: Politécnica de Madrid
- Fecha de lectura de la tesis: 18/10/2010
Dirección y tribunal
- Director de la tesis
- Morten Andreas Geday
- Tribunal
- Presidente del tribunal: manuel Lopez-amo sainz
- roman slawomir Dabrowski (vocal)
- herbert roland l. De smet (vocal)
- José Manuel Sanchez pena (vocal)
