Study on the alignment layer properties and alignment mechanisms of a-SiOx:H thin film suitable to the ion beam irradiation process

다국어 초록 (Multilingual Abstract)

Liquid crystal displays are widely used in various information display devices, for example, mobile phone displays, notebook computer monitors, laptop monitors, personal digital assistant (PDA) displays, calculators, and large area TV applications. Liquid crystal molecules are important for liquid crystal display. Uniform alignment of the liquid crystal molecules is essential for liquid crystal display application. For uniform alignment of liquid crystal molecules, liquid crystal alignment layer which is treated by various alignment methods is required to LCD devices. This unidirectional uniform alignment of liquid crystal molecules on treated substrate surfaces is very important in LC science and technology. Rubbing method is the most widely used because it is a very simple method of obtaining uniform liquid crystal alignment, and it ensures high productivity. However, this process has many problems such as the generation of dust and static electricity.To overcome the disadvantages of the mechanical rubbing method, recently, ion beam irradiation method is proposed. This is non-contact alignment method, and it can use inorganic alignment layer instead of polyimide to avoid the heat treatments. In the previous literature, hydrogenated amorphous carbon (a-C:H; diamond-like carbon) is suggested to materials suitable for ion beam irradiation method. However, diamond-like carbon (DLC) has low voltage hold ratio property and low long-term stability property. Therefore, in this study, hydrogenated amorphous silicon oxide (a-SiOx:H) thin films are used as alignment layer. These alignment layers have very uniform alignment property and long-term stability. Also, these alignment layers have pretilt angle which is controlled by various ion beam conditions such as ion beam irradiation energy, ion beam exposure time, and ion beam incident angle. Although the alignment layer does not have physical effect like surface morphology effect, liquid crystal molecules align chemical effect such as Si-H and/or Si-OH bonds.To investigate the alignment mechanism, alignment composition and content of hydrogen is changed by deposition conditions like control of silicon content. When silicon content is increased, incorporated hydrogen content is increased and Si-H bonding is increased. This Si-H bond is very important to factor in alignment layer. Therefore, as the Si-H bonds are increased, alignment property is improved.In addition, carbon-incorporated hydrogenated amorphous silicon oxides (a-SiOxCy:H) are investigated to increase pretilt angle. When carbon is incorporated in hydrogenated amorphous silicon oxide (a-SiOx:H) thin films, difference of electronegativity in alignment layer is decreased, then, total polarity of alignment layer is decreased. Therefore, pretilt angle is increased because surface energy is decreased. Also, incorporated carbon makes form of single and double carbon bonds which are affected uniform alignment of liquid crystal molecules.